Patent Application
20240194802
Solar powered water splitting and other photoelectrochemical reactions offer routes to the generation of hydrogen or other high-value chemicals using renewable energy sources. Commercially viable technologies for solar water splitting and fuel generation have been hampered by cost and the tendency of efficient solar absorbing materials to degrade in the presence of water splitting or fuel generation reactions. Metal-insulator-semiconductor (MIS) photoelectrodes for solar water splitting and fuel generation offer a route to addressing the latter issue by covering the semiconductor with a chemically stable protective layer, but these layers are typically electrically insulating and block the flow of photogenerated electrons and/or holes to the surface of the device at which the water splitting or fuel generation reactions take place. Successfully addressing these issues would provide a foundation for the development of a clean, economically viable technology for generation of hydrogen and other high-value chemicals for energy storage, transport, and chemical synthesis applications. The devices, methods, and systems discussed herein address these and other needs.
In accordance with the purposes of the disclosed devices, methods, and systems as embodied and broadly described herein, the disclosed subject matter relates to photoelectrodes, such as metal-insulator-semiconductor photoelectrodes, and methods of making and use thereof.
Additional advantages of the disclosed devices, systems, and methods will be set forth in part in the description which follows, and in part will be obvious from the description. The advantages of the disclosed devices, systems, and methods will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosed systems and methods, as claimed.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
The accompanying figures, which are incorporated in and constitute a part of this specification, illustrate several aspects of the disclosure, and together with the description, serve to explain the principles of the disclosure.
The devices, methods, and systems described herein may be understood more readily by reference to the following detailed description of specific aspects of the disclosed subject matter and the Examples included therein.
Before the present devices, methods, and systems are disclosed and described, it is to be understood that the aspects described below are not limited to specific synthetic methods or specific reagents, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.
Also, throughout this specification, various publications are referenced. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which the disclosed matter pertains. The references disclosed are also individually and specifically incorporated by reference herein for the material contained in them that is discussed in the sentence in which the reference is relied upon.
In this specification and in the claims that follow, reference will be made to a number of terms, which shall be defined to have the following meanings.
Throughout the description and claims of this specification the word “comprise” and other forms of the word, such as “comprising” and “comprises,” means including but not limited to, and is not intended to exclude, for example, other additives, components, integers, or steps.
As used in the description and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a composition” includes mixtures of two or more such compositions, reference to “an agent” includes mixtures of two or more such agents, reference to “the component” includes mixtures of two or more such components, and the like.
“Optional” or “optionally” means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.
Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. By “about” is meant within 5% of the value, e.g., within 4, 3, 2, or 1% of the value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.
“Exemplary” means “an example of” and is not intended to convey an indication of a preferred or ideal embodiment. “Such as” is not used in a restrictive sense, but for explanatory purposes.
It is understood that throughout this specification the identifiers “first” and “second” are used solely to aid in distinguishing the various components and steps of the disclosed subject matter. The identifiers “first” and “second” are not intended to imply any particular order, amount, preference, or importance to the components or steps modified by these terms.
The term “or combinations thereof” as used herein refers to all permutations and combinations of the listed items preceding the term. For example, “A, B, C, or combinations thereof” is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context.
Disclosed herein are photoelectrodes. Referring now to
The light absorbing layer 110 can comprise any material consistent with the methods, devices, and systems disclosed herein. In some examples, the light absorbing layer 110 comprises a semiconductor and/or other light absorber (e.g., molecular absorber, light trapping structure, etc.). For example, the light absorbing layer 110 can comprise silicon, gallium arsenide, AlGaAs, InP, InGaP, InAlP, AlP, InGaAsN, InGaAs, GaN, InGaN, AlInGaN, AlGaN, SiGe, SiC, CdTe, CdSe, ZnO, ZnSe, ZnTe, CdZnTe, SnS2, Zn3P2, ZnP2, Zn3As2, TiO2, hybrid organic-inorganic perovskite compounds, copper oxides, SrTiO3, MoS2, GaSe, SnS, CuInGaSe2, a-Si:H (hydrogenated amorphous silicon), bismuth vanadate (BiVO4), iron oxide (Fe2O3), or a combination thereof. In some examples, the light absorbing layer 110 comprises silicon.
The light absorbing layer 110 has a top surface 112 and a bottom surface 114 opposite and spaced apart from the top surface 112. In some examples, the top surface 112 and the bottom surface 114 of the light absorbing layer 110 are substantially parallel to each other.
The light absorbing layer 110 has an average thickness, the average thickness being the average dimension from the top surface 112 to the bottom surface 114. The average thickness of the light absorbing layer 110 can, for example, be 100 nanometers (nm) or more (e.g., 125 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, 225 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 600 nm or more, 700 nm or more, 800 nm or more, 900 nm or more, 1 micrometer (micron, μm) or more, 2 μm or more, 3 μm or more, 4 μm or more, 5 μm or more, 10 μm or more, 15 μm or more, 20 μm or more, 25 μm or more, 30 μm or more, 40 μm or more, 50 μm or more, 75 μm or more, 100 μm or more, 125 μm or more, 150 μm or more, 175 μm or more, 200 μm or more, 225 μm or more, 250 μm or more, 300 μm or more, 350 μm or more, 400 μm or more, or 450 μm or more). In some examples, the average thickness of the light absorbing layer 110 can be 500 micrometers (micron, μm) or less (e.g., 450 μm or less, 400 μm or less, 350 μm or less, 300 μm or less, 250 μm or less, 225 μm or less, 200 μm or less, 175 μm or less, 150 μm or less, 125 μm or less, 100 μm or less, 75 μm or less, 50 μm or less, 40 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, 10 μm or less, 5 μm or less, 4 μm or less, 3 μm or less, 2 μm or less, 1 μm or less, 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, or 125 nm or less). The average thickness of the light absorbing layer 110 can range from any of the minimum values described above to any of the maximum values described above. For example, the average thickness of the light absorbing layer can be from 100 nm to 500 μm (e.g., from 100 nm to 1 μm, from 1 μm to 10 μm, from 10 μm to 500 μm, from 100 nm to 400 μm, from 150 nm to 500 μm, or from 150 nm to 400 μm).
The top surface 112 and the bottom surface 114 of the light absorbing layer 110 can, independently, be any shape. In some examples, the top surface 112 and the bottom surface 114 of the light absorbing layer 110 can, independently, be substantially circular, ovate, ovoid, elliptic, triangular, rectangular, polygonal, etc. In some examples, the top surface 112 and the bottom surface 114 of the light absorbing layer 110 can be substantially the same shape. In some examples, the top surface 112 and the bottom surface 114 of the light absorbing layer 110 can be substantially rectangular, as shown in
The light absorbing layer 110 has an average lateral dimension (e.g., diameter when the light absorbing layer 110 is circular; diagonal when the light absorbing layer 110 is substantially rectangular, etc.) of 1 micrometer (micron, μm) or more (e.g., 2 μm or more, 3 μm or more, 4 μm or more, 5 μm or more, 10 μm or more, 15 μm or more, 20 μm or more, 25 μm or more, 30 μm or more, 40 μm or more, 50 μm or more, 75 μm or more, 100 μm or more, 125 μm or more, 150 μm or more, 200 μm or more, 250 μm or more, 300 μm or more, 400 μm or more, 500 μm or more, 750 μm or more, 1 millimeter (mm) or more, 1.25 mm or more, 1.5 mm or more, 2 mm or more, 2.5 mm or more, 3 mm or more, 4 mm or more, 5 mm or more, 10 mm or more, 15 mm or more, 20 mm or more, 25 mm or more, 30 mm or more, 40 mm or more, 50 mm or more, 75 mm or more, 100 mm or more, 125 mm or more, 150 mm or more, 200 mm or more, 250 mm or more, 300 mm or more, 400 mm or more, 500 mm or more, 750 mm or more, 1 meter (m) or more, 2 m or more, 3 m or more, 4 m or more, or 5 m or more). In some examples, the average lateral dimension of the light absorbing layer 110 is 10 meters (m) or less (e.g., 9 m or less, 8 m or less, 7 m or less, 6 m or less, 5 m or less, 4 m or less, 3 m or less, 2 m or less, 1 m or less, 750 mm or less, 500 mm or less, 400 mm or less, 300 mm or less, 250 mm or less, 200 mm or less, 150 mm or less, 125 mm or less, 100 mm or less, 75 mm or less, 50 mm or less, 40 mm or less, 30 mm or less, 25 mm or less, 20 mm or less, 15 mm or less, 10 mm or less, 5 mm or less, 4 mm or less, 3 mm or less, 2.5 mm or less, 2 mm or less, 1.5 mm or less, 1.25 mm or less, 1 mm or less, 750 micrometer (μm) or less, 500 μm or less, 400 μm or less, 300 μm or less, 250 μm or less, 200 μm or less, 150 μm or less, 125 μm or less, 100 μm or less, 75 μm or less, 50 μm or less, 40 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, 10 μm or less, 5 μm or less, 4 μm or less, 3 μm or less, or 2 μm or less). The average lateral dimension of the light absorbing layer 110 can range from any of the minimum values described above to any of the maximum values described above. For example, the average lateral dimension of the light absorbing layer 110 can be from 1 μm to 10 m (e.g., from 1 μm to 1 mm, from 1 mm to 10 m, from 1 μm to 100 μm, from 100 μm to 10 mm, from 10 mm to 10 m, from 1 μm to 10 μm, from 10 μm to 100 μm, from 100 μm to 1 mm, from 1 mm to 10 mm, from 10 mm to 100 mm, from 100 mm to 1 m, from 1 m to 10 m, from 1 μm to 1 m, from 1 μm to 100 mm, from 1 μm to 50 mm, from 1 μm to 10 mm, from 10 μm to 300 mm, from 100 μm to 300 mm, from 1 mm to 300 mm, from 25 mm to 300 mm, or from 1 centimeter (cm) to 30 cm).
In some examples, the light absorbing layer 110 can further comprise a doped region, the doped region including a dopant. The dopant can, for example, comprise an n-type dopant or a p-type dopant. For example, the light absorbing layer can comprise a doped region such that the light absorbing layer comprises a buried pn junction.
In some examples, the doped region comprises doped silicon. In some examples the doped region comprises p+ doped silicon. In some examples, the doped region comprises boron doped silicon. In some examples, the light absorbing layer comprises Si with a buried pn junction.
The doped region can, for example, comprise a doped layer. In some examples, the doped layer can have an average thickness of 10 nanometers (nm) or more (e.g., 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 40 nm or more, 50 nm or more, 75 nm or more, 100 nm or more, 125 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, 225 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 600 nm or more, 700 nm or more, 800 nm or more, 900 nm or more, 1 micrometer (micron, μm) or more, 2 μm or more, 3 μm or more, 4 μm or more, 5 μm or more, 10 μm or more, 15 μm or more, 20 μm or more, 25 μm or more, 30 μm or more, 40 μm or more, 50 μm or more, 75 μm or more, 100 μm or more, 125 μm or more, 150 μm or more, 175 μm or more, 200 μm or more, 225 μm or more, 250 μm or more, 300 μm or more, 350 μm or more, 400 μm or more, or 450 μm or more). In some examples, the average thickness of the doped layer can be 500 micrometers (micron, μm) or less (e.g., 450 μm or less, 400 μm or less, 350 μm or less, 300 μm or less, 250 μm or less, 225 μm or less, 200 μm or less, 175 μm or less, 150 μm or less, 125 μm or less, 100 μm or less, 75 μm or less, 50 μm or less, 40 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, 10 μm or less, 5 μm or less, 4 μm or less, 3 μm or less, 2 μm or less, 1 μm or less, 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 125 nm or less, 100 nm or less, 75 nm or less, 50 nm or less, 40 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, or 15 nm or less). The average thickness of the doped layer can range from any of the minimum values described above to any of the maximum values described above. For example, the average thickness of the doped layer can be from 10 nm to 500 μm (e.g., from 10 nm to 1 μm, from 10 μm to 500 μm, from 10 nm to 100 nm, from 100 nm to 1 μm, from 1 μm to 10 μm, from 10 μm to 500 μm, from 10 nm to 400 μm, from 50 nm to 500 μm, or from 50 nm to 400 μm).
The insulator layer 120 can comprise any material consistent with the methods, devices, and systems disclosed herein. For example, the insulator layer 120 can comprise SiO2, TiO2, silicon nitride, silicon oxynitride, aluminum oxide, strontium titanate, tungsten oxide (WO3), aluminum nitride, boron nitride, aluminum gallium nitride, or a combination thereof. In some examples, the insulator layer 120 comprises SiO2.
The insulator layer 120 has a top surface 122 and a bottom surface 124 opposite and spaced apart from the top surface 122. The bottom surface 124 of the insulator layer 120 is disposed on the top surface 112 of the light absorbing layer 110. In some examples, the top surface 122 and the bottom surface 124 of the insulator layer 120 are substantially parallel to each other.
The insulator layer 120 has an average thickness, the average thickness being the average dimension from the top surface 122 to the bottom surface 124. The average thickness of the insulator layer can, for example, be 2 nm or more (e.g., 3 nm or more, 4 nm or more, 5 nm or more, 10 nm or more, 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 55 nm or more, 60 nm or more, 65 nm or more, 70 nm or more, 75 nm or more, 80 nm or more, 85 nm or more, 90 nm or more, 95 nm or more, 100 nm or more, 110 nm or more, 120 nm or more, 130 nm or more, 140 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, 225 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 600 nm or more, 700 nm or more, 800 nm or more, or 900 nm or more). In some examples, the average thickness of the insulator layer can be 1 μm or less (e.g., 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 140 nm or less, 130 nm or less, 120 nm or less, 110 nm or less, 100 nm or less, 95 nm or less, 90 nm or less, 85 nm or less, 80 nm or less, 75 nm or less, 70 nm or less, 65 nm or less, 60 nm or less, 55 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, 15 nm or less, 10 nm or less, or 5 nm or less). The average thickness of the insulator layer can range from any of the minimum values described above to any of the maximum values described above. For examples, the average thickness of the insulator layer can be from 2 nm to 1 μm (e.g., from 2 nm to 20 nm, from 20 nm to 100 nm, from 100 nm to 1 μm, from 2 nm to 900 nm, from 20 nm to 1 μm, or from 20 nm to 900 nm). In some examples, the average thickness of the insulator layer can be 20 nanometers (nm) or more.
The top surface 122 and the bottom surface 124 of the insulator layer 120 can, independently, be any shape. In some examples, the top surface 122 and the bottom surface 124 of the insulator layer 120 can, independently, be substantially circular, ovate, ovoid, elliptic, triangular, rectangular, polygonal, etc. In some examples, the top surface 122 and the bottom surface 124 of the insulator layer 120 can be substantially the same shape. In some examples, the top surface 122 and the bottom surface 124 of the insulator layer 120 can be substantially rectangular, as shown in
The insulator layer 120 has an average lateral dimension (e.g., diameter when the insulator layer 120 is circular; diagonal when the insulator layer 120 is substantially rectangular, etc.) of 1 micrometer (micron, μm) or more (e.g., 2 μm or more, 3 μm or more, 4 μm or more, 5 μm or more, 10 μm or more, 15 μm or more, 20 μm or more, 25 μm or more, 30 μm or more, 40 μm or more, 50 μm or more, 75 μm or more, 100 μm or more, 125 μm or more, 150 μm or more, 200 μm or more, 250 μm or more, 300 μm or more, 400 μm or more, 500 μm or more, 750 μm or more, 1 millimeter (mm) or more, 1.25 mm or more, 1.5 mm or more, 2 mm or more, 2.5 mm or more, 3 mm or more, 4 mm or more, 5 mm or more, 10 mm or more, 15 mm or more, 20 mm or more, 25 mm or more, 30 mm or more, 40 mm or more, 50 mm or more, 75 mm or more, 100 mm or more, 125 mm or more, 150 mm or more, 200 mm or more, 250 mm or more, 300 mm or more, 400 mm or more, 500 mm or more, 750 mm or more, 1 meter (m) or more, 2 m or more, 3 m or more, 4 m or more, or 5 m or more). In some examples, the average lateral dimension of the insulator layer 120 is 10 meters (m) or less (e.g., 9 m or less, 8 m or less, 7 m or less, 6 m or less, 5 m or less, 4 m or less, 3 m or less, 2 m or less, 1 m or less, 750 mm or less, 500 mm or less, 400 mm or less, 300 mm or less, 250 mm or less, 200 mm or less, 150 mm or less, 125 mm or less, 100 mm or less, 75 mm or less, 50 mm or less, 40 mm or less, 30 mm or less, 25 mm or less, 20 mm or less, 15 mm or less, 10 mm or less, 5 mm or less, 4 mm or less, 3 mm or less, 2.5 mm or less, 2 mm or less, 1.5 mm or less, 1.25 mm or less, 1 mm or less, 750 micrometer (μm) or less, 500 μm or less, 400 μm or less, 300 μm or less, 250 μm or less, 200 μm or less, 150 μm or less, 125 μm or less, 100 μm or less, 75 μm or less, 50 μm or less, 40 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, 10 μm or less, 5 μm or less, 4 μm or less, 3 μm or less, or 2 μm or less). The average lateral dimension of the insulator layer 120 can range from any of the minimum values described above to any of the maximum values described above. For example, the average lateral dimension of the insulator layer 120 can be from 1 μm to 10 m (e.g., from 1 μm to 1 mm, from 1 mm to 10 m, from 1 μm to 100 μm, from 100 μm to 10 mm, from 10 mm to 10 m, from 1 μm to 10 μm, from 10 μm to 100 μm, from 100 μm to 1 mm, from 1 mm to 10 mm, from 10 mm to 100 mm, from 100 mm to 1 m, from 1 m to 10 m, from 1 μm to 1 m, from 1 μm to 100 mm, from 1 μm to 50 mm, from 1 μm to 10 mm, from 10 μm to 300 mm, from 100 μm to 300 mm, from 1 mm to 300 mm, from 25 mm to 300 mm, or from 1 centimeter (cm) to 30 cm). In some examples, the insulator layer 120 and the light absorbing layer 110 can have substantially the same average lateral dimension.
The photoelectrodes further comprise a set of protrusions 130, wherein each protrusion 130 penetrates through the insulator layer 120 to the light absorbing layer 110, such that each protrusion 130 is in physical and electrical contact with the light absorbing layer 110. For example, each protrusion 130 can extend from the top surface 122 of the insulator layer 120 to the bottom surface 124 of the insulator layer 120, such that each protrusion 130 is in physical and electrical contact with the top surface 112 of the light absorbing layer 110.
As used herein, “a set of protrusions 130” and “the set of protrusions 130” are meant to include any number of protrusions 130 of any size and in any arrangement. Thus, for example, “a set of protrusions 130” includes one or more protrusions 130 (e.g., 2 or more; 3 or more; 4 or more; 5 or more; 10 or more; 15 or more; 20 or more; 25 or more; 30 or more; 40 or more; 50 or more; 75 or more; 100 or more; 150 or more; 200 or more; 250 or more; 300 or more; 400 or more; 500 or more; 750 or more; 1000 or more; 1500 or more; 2000 or more; 2500 or more; 3000 or more; 4000 or more; 5000 or more; 7500 or more; 1×104 or more; 2.5×104 or more; 5×104 or more; 7.5×104 or more; 1×105 or more; 2.5×105 or more; 5×105 or more; 7.5×105 or more; 1×106 or more; 5×106 or more; 1×107 or more; 5×107 or more; 1×108 or more; 5×108 or more; 1×109 or more; 5×109 or more; 1×1010 or more; 1×1011 or more; 1×1012 or more; 1×1013 or morel 1×1014 or more; 1×1015 or more; 1×1016 or more; 1×1017 or more; 1×1018 or more; 1×1019 or more; or 1×1020 or more). In some examples, the set of protrusions 130 comprises a plurality of protrusions 130. In some examples, the set of protrusions 130 comprises a plurality of protrusions 130 arranged in a random or disordered array. In some examples, the set of protrusions 130 comprises a plurality of protrusions 130 arranged in a an ordered array.
The set of protrusions can be dispersed across the insulator layer laterally such that the areal density of the set of protrusions within the plane of the top surface of the insulator layer can be 104 protrusions per cm2 of the insulator layer or more (e.g., 1×104 protrusions/cm2 or more, 5×104 protrusions/cm2 or more, 1×105 protrusions/cm2 or more, 5×105 protrusions/cm2 or more, 1×106 protrusions/cm2 or more, 5×106 protrusions/cm2 or more, 1×107 protrusions/cm2 or more, 5×107 protrusions/cm2 or more, 1×108 protrusions/cm2 or more, 5×108 protrusions/cm2 or more, 1×109 protrusions/cm2 or more, 5×109 protrusions/cm2 or more, 1×1010 protrusions/cm2 or more, 5×1010 protrusions/cm2 or more, 1×1011 protrusions/cm2 or more, 5×1011 protrusions/cm2 or more, 1×1012 protrusions/cm2 or more, 5×1012 protrusions/cm2 or more, 1×1013 protrusions/cm2 or more, or 5×1013 protrusions/cm2 or more). In some examples, the areal density of the set of protrusions within the plane of the top surface of the insulator layer can be 1013 protrusions/cm2 or less (e.g., 5×1013 protrusions/cm2 or less, 1×1013 protrusions/cm2 or less, 5×1012 protrusions/cm2 or less, 1×1012 protrusions/cm2 or less, 5×1011 protrusions/cm2 or less, 1×1011 protrusions/cm2 or less, 5×1010 protrusions/cm2 or less, 1×1010 protrusions/cm2 or less, 5×109 protrusions/cm2 or less, 1×109 protrusions/cm2 or less, 5×108 protrusions/cm2 or less, 1×108 protrusions/cm2 or less, 5×107 protrusions/cm2 or less, 1×107 protrusions/cm2 or less, 5×106 protrusions/cm2 or less, 1×106 protrusions/cm2 or less, 5×105 protrusions/cm2 or less, 1×105 protrusions/cm2 or less, or 5×104 protrusions/cm2 or less). The areal density of the set of protrusions within the plane of the top surface of the insulator layer can range from any of the minimum values described above to any of the maximum values described above. For example, the areal density of the set of protrusions within the plane of the top surface of the insulator layer can be from 104 to 1013 protrusions/cm2 (e.g., from 1×104 to 1×109 protrusions/cm2, from 1×109 to 1×1013 protrusions/cm2, from 1×104 to 1×106 protrusions/cm2, from 1×106 to 1×108 protrusions/cm2, from 1×108 to 1×1010 protrusions/cm2, from 1×1010 to 1×1013 protrusions/cm2, from 1×104 to 1×1012 protrusions/cm2, from 1×105 to 1×1013 protrusions/cm2, from 1×105 to ×1012 protrusions/cm2, from 1×106 to 1×1010 protrusions/cm2, or from 1×107 to ×109 protrusions/cm2). In some examples, the set of protrusions are dispersed throughout the insulator layer such that the areal density of the set of protrusions within the insulator layer is from 2×108 to 8×108 protrusions per cm2 of the insulator layer.
The set of protrusions 130 can, independently, be any shape, such as a regular shape, an irregular shape, an isotropic shape, or an anisotropic shape. For example, the set of protrusions 130 can, independently, be a polyhedron (e.g., a platonic solid, a prism, a pyramid), a cylinder, a hemicylinder, an elliptical cylinder, a hemi-elliptical cylinder, a cone, a semicone, etc.
In some examples, each of the protrusions 130 can, independently, have a longitudinal axis, a first surface, and a second surface opposite and axially spaced apart from the first surface. In some examples, the longitudinal axis of each of the protrusions 130 can, independently, extend through the insulator layer 120 at an angle of 90° or less relative to the top surface of the insulator layer (e.g., 85° or less, 80° or less, 75° or less, 70° or less, 65° or less, 60° or less, 55° or less, 50° or less, 45° or less, 40° or less, 35° or less, 30° or less, 25° or less, 20° or less, or 15° or less), wherein an angle of 90° means that the longitudinal axis is disposed perpendicular to the top surface of the insulator layer and 0° is parallel to the top surface of the insulator layer. In some examples, the longitudinal axis of each of the protrusions 130 can, independently, extend through the insulator layer 120 at an angle of 10° or more relative to the top surface of the insulator layer (e.g., 15° or more, 20° or more, 25° or more, 30° or more, 35° or more, 40° or more, 45° or more, 50° or more, 55° or more, 60° or more, 65° or more, 70° or more, 75° or more, 80° or more, or 85° or more). The angle at which the longitudinal axis of each of the protrusions 130 independently extends through the insulator layer 120 can range from any of the minimum values described above to any of the maximum values described above. For example, the longitudinal axis of each of the protrusions 130 can, independently, extend through the insulator layer 120 at an angle of from 10° to 90° relative to the top surface of the insulator layer (e.g., from 10° to 45°, from 45° to 90°, from 10° to 30°, from 30 ° to 50°, from 50° to 70°, from 70° to 90°, from 30° to 90°, from 10º to 80°, or from 30° to)80°. In some examples, the longitudinal axis of one or more of the protrusions can be disposed at an angle of 90° relative to the top surface of the insulator layer, such that the longitudinal axis is disposed perpendicular to the top surface of the insulator layer. In some examples, the longitudinal axis of each of the protrusions 130 are substantially parallel to each other.
Each of the protrusions 130 can have a cross-sectional shape in a plane parallel to the top surface of the insulator layer, wherein the cross-sectional shape can be any shape, such as a regular shape, an irregular shape, an isotropic shape, or an anisotropic shape. In some examples, the cross-sectional shape of each of the set of protrusions can be substantially circular, ovate, ovoid, elliptic, triangular, rectangular, polygonal, etc. In some examples, the cross-sectional shape of each of the set of protrusions 130 is substantially the same. In some examples, the cross-sectional shape of the set of protrusions 130 can vary with the thickness of the insulator layer 120.
The set of protrusions 130 can have an average characteristic dimension. The term “characteristic dimension,” as used herein refers to the largest straight line distance spanning the protrusion 130 in a plane parallel to the top surface 122 of the insulator layer 120. “Average characteristic dimension” and “mean characteristic dimension” are used interchangeably herein, and generally refer to the statistical mean characteristic dimension of the protrusions in a population of protrusions. For example, for a cylindrical set of second protrusions, the cross-sectional shape can be substantially circular and the average characteristic dimension can refer to the average diameter. In some examples, the average characteristic dimension of the set of protrusions 130 can be substantially the same for the entire thickness of the insulator layer 120. In some examples, the average characteristic dimension of the set of protrusions 130 can vary with the thickness of the insulator layer 120 (e.g., tapered or stepped).
The set of protrusions can, for example, have an average characteristic dimension of 0.1 nm or more (e.g., 0.2 nm or more, 0.3 nm or more, 0.4 nm or more, 0.5 nm or more, 1 nm or more, 1.5 nm or more, 2 nm or more, 2.5 nm or more, 3 nm or more, 4 nm or more, 5 nm or more, 10 nm or more, 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 55 nm or more, 60 nm or more, 65 nm or more, 70 nm or more, 75 nm or more, 80 nm or more, 85 nm or more, 90 nm or more, 95 nm or more, 100 nm or more, 110 nm or more, 120 nm or more, 130 nm or more, 140 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, 225 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 600 nm or more, 700 nm or more, 800 nm or more, or 900 nm or more). In some examples, the set of protrusions can have an average characteristic dimension of 1 μm or less (e.g., 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 140 nm or less, 130 nm or less, 120 nm or less, 110 nm or less, 100 nm or less, 95 nm or less, 90 nm or less, 85 nm or less, 80 nm or less, 75 nm or less, 70 nm or less, 65 nm or less, 60 nm or less, 55 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, 15 nm or less, 10 nm or less, 5 nm or less, 4 nm or less, 3 nm or less, 2.5 nm or less, 2 nm or less, 1.5 nm or less, 1 nm or less, or 0.5 nm or less). The average characteristic dimension of the set of protrusions can range from any of the minimum values described above to any of the maximum values described above. For examples, the average characteristic dimension of the set of protrusions can be from 0.1 nm to 1 μm (e.g., from 0.1 nm to 1 nm, from 1 nm to 10 nm, from 10 nm to 100 nm, from 100 nm to 1 μm, from 0.1 nm to 900 nm, from 1 nm to 1 μm, or from 1 nm to 900 nm). In some examples, the set of protrusions can have an average characteristic dimension of from 50 nm to 100 nm. The average characteristic dimension of the protrusions can be measured using methods known in the art, such as evaluation by electron microscopy.
In some examples, the set of protrusions 130 can comprise a plurality of protrusions 130, wherein the average characteristic dimension of the plurality of protrusions 130 can be substantially monodisperse. “Monodisperse” and “homogeneous characteristic dimension distribution,” as used herein, and generally describe a population of protrusions where all of the protrusions have the same or nearly the same characteristic dimension. As used herein, a monodisperse distribution refers to distributions in which 80% of the distribution (e.g., 85% of the distribution, 90% of the distribution, or 95% of the distribution) lies within 25% of the mean characteristic dimension (e.g., within 20% of the mean characteristic dimension, within 15% of the mean characteristic dimension, within 10% of the mean characteristic dimension, or within 5% of the mean characteristic dimension).
The photoelectrodes further comprise a plurality of particles 140 on the insulator layer, wherein at least a portion of the plurality of particles 140 are in physical and electrical contact with at least a portion of the set of protrusions. For example, the plurality of particles 140 can be disposed on the top surface 122 of the insulator layer 120.
As used herein, “a plurality of particles” and “the plurality of particles” are meant to include particles of any size and in any arrangement. Thus, for example, “a plurality of particles” includes two or more particles (e.g., 3 or more; 4 or more; 5 or more; 10 or more; 15 or more; 20 or more; 25 or more; 30 or more; 40 or more; 50 or more; 75 or more; 100 or more; 150 or more; 200 or more; 250 or more; 300 or more; 400 or more; 500 or more; 750 or more; 1000 or more; 1500 or more; 2000 or more; 2500 or more; 3000 or more; 4000 or more; 5000 or more; 7500 or more; 1×104 or more; 2.5×104 or more; 5×104 or more; 7.5×104 or more; 1×105 or more; 2.5×105 or more; 5×105 or more; 7.5×105 or more; 1×106 or more; 5×106 or more; 1×107 or more; 5×107 or more; 1×108 or more; 5×108 or more; 1×109 or more; 5×109 or more; 1×1010 or more; 1×1011 or more; 1×1012 or more; 1×1013 or morel 1×1014 or more; 1×1015 or more; 1×1016 or more; 1×1017 or more; 1×1018 or more; 1×10 19 or more; or 1×1020 or more). In some examples, the plurality of particles 140 can be arranged in a random or disordered array. In some examples, the plurality of particles 140 can be arranged in an ordered array.
The plurality of particles 140 can have an average particle size. “Average particle size” and “mean particle size” are used interchangeably herein, and generally refer to the statistical mean particle size of the particles in a population of particles. For example, the average particle size for a plurality of particles with a substantially spherical shape can comprise the average diameter of the plurality of particles. As used herein, the size of a particle can refer to the largest linear distance between two points on the surface of the particle. For an anisotropic particle, the average particle size can refer to, for example, the average maximum dimension of the particle (e.g., the length of a rod shaped particle, the diagonal of a cube shape particle, the bisector of a triangular shaped particle, etc.). Mean particle size can be measured using methods known in the art, such as evaluation by electron microscopy.
The plurality of particles 140 can, for example, have an average particle size of 5 nm or more (e.g., 10 nm or more, 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 55 nm or more, 60 nm or more, 65 nm or more, 70 nm or more, 75 nm or more, 80 nm or more, 85 nm or more, 90 nm or more, 95 nm or more, 100 nm or more, 125 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, 225 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 600 nm or more, 700 nm or more, 800 nm or more, 900 nm or more, 1 micrometer (micron, μm) or more, 2 μm or more, 3 μm or more, 4 μm or more, 5 μm or more, 10 μm or more, 15 μm or more, 20 μm or more, 25 μm or more, 30 μm or more, 35 μm or more, 40 μm or more, or μm or more). In some examples, the plurality of particles 140 can have an average particle size of 50 micrometers (micron, μm) or less (e.g., 45 μm or less, 40 μm or less, 35 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, 10 μm or less, 5 μm or less, 4 μm or less, 3 μm or less, 2 μm or less, 1 μm or less, 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 125 nm or less 95 nm or less, 90 nm or less, 85 nm or less, 80 nm or less, 75 nm or less, 70 nm or less, 65 nm or less, 60 nm or less, 55 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, 15 nm or less, or 10 nm or less). The average particle size of the plurality of particles 140 can range from any of the minimum values described above to any of the maximum values described above. For example, the plurality of particles 140 can have an average particle size of from 5 nm to 50 μm (e.g., from 5 nm to 1 μm, from 1 μm to 50 μm, from 5 nm to 50 nm, from 50 nm to 500 nm, from 500 nm to 5 μm, from 5 μm to 50 μm, from 10 nm to 50 μm, from 5 nm to 40 μm, or from 10 nm to 40 μm). In some examples, the particles 140 can have an average particle size of 0.15 to 1.35 micrometers (μm).
In some examples, the particles 140 can have an average particle size of from 0.25 to 0.85 μm. In some examples, the plurality of particles 140 can be substantially monodisperse. “Monodisperse” and “homogeneous size distribution,” as used herein, and generally describe a population of particles where all of the particles have the same or nearly the same particle size. As used herein, a monodisperse distribution refers to distributions in which 80% of the distribution (e.g., 85% of the distribution, 90% of the distribution, or 95% of the distribution) lies within 25% of the mean particle size (e.g., within 20% of the mean particle size, within 15% of the mean particle size, within 10% of the mean particle size, or within 5% of the mean particle size).
The plurality of particles 140 can, independently, be of any shape, such as a regular shape, an irregular shape, an isotropic shape, or an anisotropic shape (e.g., a sphere, a rod, a quadrilateral, an ellipse, a triangle, a polygon, etc.). In some examples, the plurality of particles 140 can have an isotropic shape. In some examples, the plurality of particles 140 can have an anisotropic shape.
The plurality of particles 140 and optionally the set of protrusions comprise a catalyst material (e.g., the plurality of particles 140 comprise the catalyst material or the plurality of particles 140 and the set of protrusions comprise the catalyst material). The catalyst material can comprise any material consistent with the methods, devices, and systems disclosed herein. For example, the catalyst material can comprise a metal selected from the group consisting of Ni, Pt, Mo, Co, Ru, Ir, or a combination thereof in any spatial arrangement. In some examples, the catalyst material comprises Ni. In some examples, the catalyst material comprises an oxygen evolution reaction catalyst. In some examples, the catalyst material can comprise NiFe, NiFeOx, NiFe-layered double hydroxide, carbon nitrides, certain polymers, NiMo, MoS2, CoP, NiCoOx, RuO2, IrO2, or a combination thereof in any spatial arrangement.
The particles and/or the protrusions can, for example, cover 1% or more of the top surface of the insulator layer (e.g., 2% or more, 3% or more, 4% or more, 5% or more, 10% or more, 15% or more, 20% or more, 25% or more, 30% or more, 35% or more, 40% or more, 45% or more, 50% or more, 55% or more, 60% or more, 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more). In some examples, the particles and/or protrusions can cover 100% or less of the top surface of the insulator layer (e.g., 95% or less, 90% or less, 85% or less, 80% or less, 75% or less, 70% or less, 65% or less, 60% or less, 55% or less, 50% or less, 45% or less, 40% or less, 35% or less, 30% or less, 25% or less, 20% or less, 15% or less, 10% or less, or 5% or less). The amount of coverage of the top surface of the insulator by the particles and/or the protrusions can range from any of the minimum values described above to any of the maximum values described above. For example, the particles and/or the protrusions can cover from 1% to 100% of the top surface of the insulator layer (e.g., from 1% to 50%, from 50% to 100%, from 1% to 20%, from 20% to 40%, from 40% to 60%, from 60% to 80% from 80% to 100%, from 5% to 100%, from 1% to 90%, from 5% to 90%, or from 5% to 80%). In some examples, the particles and/or the protrusions cover 10% or more, 25% or more, 35% or more, 50% or more, or 70% or more of the top surface of the insulator layer. In some examples, the particles and/or the protrusions cover 35% of the top surface of the insulator layer. The coverage of the top surface of the insulator layer by the catalyst material (e.g., by the particles and/or the protrusions) can, for example, be selected to enable a desired balance between available catalyst surface area and transmission of light into the light absorbing material.
In some examples, the catalyst material can comprise a metal, the light absorbing layer can comprise a semiconductor, and the photoelectrodes described herein comprise metal-insulator-semiconductor photoelectrodes.
Also disclosed herein are methods of making photoelectrodes, such as any of the photoelectrodes disclosed herein. For example, disclosed herein are methods of making a photoelectrode, the method comprising: forming the insulator layer on the light absorbing layer; depositing a reactive layer comprising a reactive material on the insulator layer, such that the insulator layer is disposed between the light absorbing layer and the reactive layer, thereby forming a precursor electrode; annealing the precursor electrode such that the reactive material reacts with and diffuses through the insulator layer, thereby forming a set of spikes comprising the reactive material, wherein each of the set of spikes penetrates through the insulator layer to the light absorbing layer, such that each of the set of spikes is in physical and electrical contact with the light absorbing layer, thereby forming a spiked electrode; and subsequently depositing a catalyst material; thereby forming the photoelectrode comprising: the insulator layer disposed on the light absorbing layer, s set of protrusions that penetrates through the insulator layer to the light absorbing layer, such that each of the set of protrusions is in physical and electrical contact with the light absorbing layer; and a plurality of particles disposed on the insulator layer, wherein at least a portion of the plurality of particles are in physical and electrical contact with at least a portion of the set of protrusions; and wherein the plurality of particles and optionally the set of protrusions comprise the catalyst material.
In some examples, the methods can further comprise doping the light absorbing layer to form a doped region prior to forming the insulator layer. Doping the light absorbing layer can, for example, comprise annealing the light absorbing layer in the presence of a dopant source, ion implantation, or other methods such as those known in the art. In some examples, doping the light absorbing layer can comprise annealing the light absorbing layer in the presence of a dopant source. The dopant source can, for example, comprise a dopant, such as an n-type dopant or a p-type dopant. In some examples, the dopant source can comprise a compound or molecule that comprises a dopant atom, such as an n-type dopant or a p-type dopant. In some examples, the dopant source comprises a boron source. In some examples, annealing the light absorbing layer in the presence of a dopant source is performed in an inert atmosphere (e.g., nitrogen, argon, etc.).
In some examples, annealing comprises heating the insulator layer at a temperature of 100° C. or more in the presence of the dopant source for an amount of time (e.g., 150° C. or more, 200° C. or more, 250° C. or more, 300° C. or more, 350° C. or more, 400° C. or more, 450° C. or more, 500° C. or more, 550° C. or more, 600° C. or more, 650° C. or more, 700° C. or more, 750° C. or more, 800° C. or more, 850° C. or more, 900° C. or more, 950° C. or more, 1000° C. or more, 1100° C. or more, 1200° C. or more, 1300° C. or more, 1400° C. or more, 1500° C. or more, 1600° C. or more, or 1700° C. or more). In some examples, annealing comprises heating the insulator layer at a temperature of 1800° C. or less in the presence of the dopant source for an amount of time (e.g., 1700° C. or less, 1600° C. or less, 1500° C. or less, 1400° C. or less, 1300° C. or less, 1200° C. or less, 1100° C. or less, 1000° C. or less, 950° C. or less, 900° C. or less, 850° C. or less, 800° C. or less, 750° C. or less, 700° C. or less, 650° C. or less, 600° C. or less, 550° C. or less, 500° C. or less, 450° C. or less, 400° C. or less, 350° C. or less, 300° C. or less, 250° C. or less, 200° C. or less, or 150° C. or less). The temperature at which the insulator layer is annealed in the presence of the dopant source for an amount of time can range from any of the minimum values described above to any of the maximum values described above. For example, annealing can comprise heating the insulator layer at a temperature of from 100° C. to 1800° C. in the presence of the dopant source for an amount of time (e.g., from 100° C. to 950° C., from 950° C. to 1800° C., from 100° C. to 500° C., from 500° C. to 900° C., from 900° C. to 1300° C., from 1300° C. to 1800° C., from 200° C. to 1800° C., from 100° C. to 1700° C., from 200° C. to 1700° C., or from 900° C. to 1000° C.).
In some examples, annealing comprises heating the insulator layer at a temperature in the presence of the dopant source for an amount of time of 10 seconds or more (e.g., 15 seconds or more, 20 seconds or more, 25 seconds or more, 30 seconds or more, 35 seconds or more, 40 seconds or more, 45 seconds or more, 50 seconds or more, 55 seconds or more, 1 minute or more, 1.5 minutes or more, 2 minutes or more, 2.5 minutes or more, 3 minutes or more, 3.5 minutes or more, 4 minutes or more, 4.5 minutes or more, 5 minutes or more, 6 minutes or more, 7 minutes or more, 8 minutes or more, 9 minutes or more, 10 minutes or more, 15 minutes or more, 20 minutes or more, 25 minutes or more, 30 minutes or more, 35 minutes or more, 40 minutes or more, 45 minutes or more, 50 minutes or more, 55 minutes or more, 1 hour or more, 1.5 hours or more, 2 hours or more, 2.5 hours or more, 3 hours or more, 3.5 hours or more, 4 hours or more, 4.5 hours or more, 5 hours or more, 6 hours or more, 7 hours or more, 8 hours or more, 9 hours or more, 10 hours or more, 12 hours or more, 14 hours or more, 16 hours or more, 18 hours or more, 24 hours or more, 30 hours or more, 36 hours or more, 42 hours or more, 48 hours or more, 60 hours or more, 72 hours or more, 84 hours or more, or 96 hours or more). In some examples, annealing comprises heating the insulator layer at a temperature in the presence of the dopant source for an amount of time of 100 hours or less (e.g., 96 hours or less, 84 hours or less, 72 hours or less, 60 hours or less, 48 hours or less, 42 hours or less, 36 hours or less, 30 hours or less, 24 hours or less, 18 hours or less, 16 hours or less, 14 hours or less, 12 hours or less, 10 hours or less, 9 hours or less, 8 hours or less, 7 hours or less, 6 hours or less, 5 hours or less, 4.5 hours or less, 4 hours or less, 3.5 hours or less, 3 hours or less, 2.5 hours or less, 2 hours or less, 1.5 hours or less, 1 hours or less, 55 minutes or less, 50 minutes or less, 45 minutes or less, 40 minutes or less, 35 minutes or less, 30 minutes or less, 25 minutes or less, 20 minutes or less, 15 minutes or less, 10 minutes or less, 9 minutes or less, 8 minutes or less, 7 minutes or less, 6 minutes or less, 5 minutes or less, 4.5 minutes or less, 4 minutes or less, 3.5 minutes or less, 3 minutes or less, 2.5 minutes or less, 2 minutes or less, 1.5 minutes or less, 1 minute or less, 55 seconds or less, 50 seconds or less, 45 seconds or less, 50 seconds or less, 35 seconds or less, 30 seconds or less, 25 seconds or less, 20 seconds or less, or 15 seconds or less). The amount of time for which the insulator layer is annealed in the presence of the dopant source at a temperature can range from any of the minimum values described above to any of the maximum values described above. For example, annealing comprises heating the insulator layer at a temperature in the presence of the dopant source for an amount of time of from 10 seconds to 100 hours (e.g., from 10 seconds to 1 minute, from 1 minute to 1 hour, from 1 hour to 24 hours, from 24 hours to 100 hours, from 10 seconds to 90 hours, from 1 minute to 100 hours, from 1 minute to 90 hours, or from 60 minutes to 1.5 hours).
Forming the insulator layer can, for example, comprise thermal oxidation, electroplating, lithographic deposition, electron beam deposition, thermal deposition, spin coating, drop-casting, zone casting, dip coating, blade coating, spraying, vacuum filtration, chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), sputtering, pulsed layer deposition, molecular beam epitaxy, evaporation, or combinations thereof.
In some examples, forming the insulator layer comprises thermal oxidation. Thermal oxidation can, for example, comprise heating the light absorbing layer at a temperature of 800° C. or more in the presence of oxygen for an amount of time (e.g., 800° C. or more, 850° C. or more, 900° C. or more, 950° C. or more, 1000° C. or more, 1050° C. or more, 1100° C. or more, or 1150° C. or more). In some examples, forming the insulator layer can comprise heating the light absorbing layer at a temperature of 1200° C. or less in the presence of oxygen for an amount of time (e.g., 1150° C. or less, 1100° C. or less, 1050° C. or less, 1000° C. or less, 950° C. or less, 900° C. or less, or 850° C. or less). The temperature at which the light absorbing layer is heated in the presence of oxygen for an amount of time can range from any of the minimum values described above to any of the maximum values described above. For example, forming the insulator layer can comprise heating the light absorbing layer at a temperature of from 800° C. to 1200° C. in the presence of oxygen for an amount of time (e.g., from 800° C. to 1000° C., from 1000° C. to 1200° C., from 800° C. to 900° C., from 900° C., to 1000° C., from 1000° C. to 1100° C., from 1100° C. to 1200° C., from 850° C. to 1200° C., from 800° C. to 1150° C., or from 850° C. to 1150° C.).
In some examples, forming the insulator layer can comprise heating the light absorbing layer at a temperature in the presence of oxygen for an amount of time of 10 seconds or more (e.g., 15 seconds or more, 20 seconds or more, 25 seconds or more, 30 seconds or more, 35 seconds or more, 40 seconds or more, 45 seconds or more, 50 seconds or more, 55 seconds or more, 1 minute or more, 1.5 minutes or more, 2 minutes or more, 2.5 minutes or more, 3 minutes or more, 3.5 minutes or more, 4 minutes or more, 4.5 minutes or more, 5 minutes or more, 6 minutes or more, 7 minutes or more, 8 minutes or more, 9 minutes or more, 10 minutes or more, 15 minutes or more, 20 minutes or more, 25 minutes or more, 30 minutes or more, 35 minutes or more, 40 minutes or more, 45 minutes or more, 50 minutes or more, 55 minutes or more, 1 hour or more, 1.5 hours or more, 2 hours or more, 2.5 hours or more, 3 hours or more, 3.5 hours or more, 4 hours or more, 4.5 hours or more, 5 hours or more, 6 hours or more, 7 hours or more, 8 hours or more, 9 hours or more, 10 hours or more, 12 hours or more, 14 hours or more, 16 hours or more, 18 hours or more, 20 hours or more, 24 hours or more, 26 hours or more, or 28 hours or more). In some examples, forming the insulator layer can comprise heating the light absorbing layer at a temperature in the presence of oxygen for an amount of time of 30 hours or less (e.g., 28 hours or less, 26 hours or less, 24 hours or less, 20 hours or less, 18 hours or less, 16 hours or less, 14 hours or less, 12 hours or less, 10 hours or less, 9 hours or less, 8 hours or less, 7 hours or less, 6 hours or less, 5 hours or less, 4.5 hours or less, 4 hours or less, 3.5 hours or less, 3 hours or less, 2.5 hours or less, 2 hours or less, 1.5 hours or less, 1 hours or less, 55 minutes or less, 50 minutes or less, 45 minutes or less, 40 minutes or less, 35 minutes or less, 30 minutes or less, 25 minutes or less, 20 minutes or less, 15 minutes or less, 10 minutes or less, 9 minutes or less, 8 minutes or less, 7 minutes or less, 6 minutes or less, 5 minutes or less, 4.5 minutes or less, 4 minutes or less, 3.5 minutes or less, 3 minutes or less, 2.5 minutes or less, 2 minutes or less, 1.5 minutes or less, 1 minute or less, 55 seconds or less, 50 seconds or less, 45 seconds or less, 50 seconds or less, 35 seconds or less, 30 seconds or less, 25 seconds or less, 20 seconds or less, or 15 seconds or less). The amount of time for which the light absorbing layer is heated in the presence of oxygen at a temperature can range from any of the minimum values described above to any of the maximum values described above. For example, forming the insulator layer can comprise heating the light absorbing layer at a temperature in the presence of oxygen for an amount of time of from 10 seconds to 30 hours (e.g., from 10 seconds to 1 minute, from 1 minute to 1 hour, from 1 hour to 30 hours, from 10 seconds to 24 hours, from 1 minute to 30 hours, or from 1 minute to 24 hours, or from 60 minutes to 1.5 hours).
Depositing the reactive layer can, for example, comprise electroplating, lithographic deposition, electron beam deposition, thermal deposition, spin coating, drop-casting, zone casting, dip coating, blade coating, spraying, vacuum filtration, chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), sputtering, pulsed layer deposition, molecular beam epitaxy, evaporation, or combinations thereof. In some examples, depositing the reactive layer comprises sputtering.
The reactive layer can comprise any material consistent with the methods, devices, and systems disclosed herein. For example, the reactive layer can comprise Al.
The reactive layer can, for example, have an average thickness of 1 nm or more (e.g., 1.5 nm or more, 2 nm or more, 2.5 nm or more, 3 nm or more, 4 nm or more, 5 nm or more, 10 nm or more, 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 55 nm or more, 60 nm or more, 65 nm or more, 70 nm or more, 75 nm or more, 80 nm or more, 85 nm or more, 90 nm or more, 95 nm or more, 100 nm or more, 110 nm or more, 120 nm or more, 130 nm or more, 140 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, 225 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 600 nm or more, 700 nm or more, 800 nm or more, 900 nm or more, 1 μm or more, 1.5 μm or more, 2 μm or more, 2.5 μm or more, 3 μm or more, 3.5 μm or more, or 4 μm or more). In some examples, the reactive layer can have an average thickness of 5 μm or less (e.g., 4.5 μm or less, 4 μm or less, 3.5 μm or less, 3 μm or less, 2.5 μm or less, 2 μm or less, 1.5 μm or less, 1 μm or less, 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 140 nm or less, 130 nm or less, 120 nm or less, 110 nm or less, 100 nm or less, 95 nm or less, 90 nm or less, 85 nm or less, 80 nm or less, 75 nm or less, 70 nm or less, 65 nm or less, 60 nm or less, 55 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, 15 nm or less, 10 nm or less, 5 nm or less, 4 nm or less, 3 nm or less, 2.5 nm or less, or 2 nm or less). The average thickness of the reactive layer can range from any of the minimum values described above to any of the maximum values described above. For examples, the average thickness of the reactive layer can be from 1 nm to 5 μm (e.g., from 1 nm to 500 nm, from 500 nm to 5 μm, from 1 nm to 10 nm, from 10 nm to 100 nm, from 100 nm to 1 μm, from 1 μm to 5 μm, from 10 nm to 5 μm, from 1 nm to 1 μm, or from 10 nm to 1 μm).
Annealing the precursor electrode can, for example, comprise heating the precursor electrode at a temperature of 300° C. or more (e.g., 350° C. or more, 400° C. or more, 450° C. or more, 500° C. or more, 550° C. or more, 600° C. or more, 650° C. or more, 700° C. or more, 750° C. or more, 800° C. or more, 850° C. or more, 900° C. or more, 950° C. or more, 1000° C. or more, 1100° C. or more, 1200° C. or more, 1300° C. or more, or 1400° C. or more). In some examples, annealing the precursor electrode can comprise heating the precursor electrode at a temperature of 1500° C. or less (e.g., 1400° C. or less, 1300° C. or less, 1200° C. or less, 1100° C. or less, 1000° C. or less, 950° C. or less, 900° C. or less, 850° C. or less, 800° C. or less, 750° C. or less, 700° C. or less, 650° C. or less, 600° C. or less, 550° C. or less, 500° C. or less, 450° C. or less, 400° C. or less, or 350° C. or less). The temperature at which the precursor electrode is annealed can range from any of the minimum values described above to any of the maximum values described above. For example, annealing the precursor electrode can comprise heating the precursor electrode at a temperature of from 300° C. to 1500° C. (e.g., from 300° C. to 900° C., from 900° C. to 1500° C., from 300° C. to 600° C., from 600° C. to 900° C., from 900° C. to 1200° C., from 1200° C. to 1500° C., from 350° C. to 1500° C., from 300° C. to 1400° C., from 350° C. to 1400° C., or from 300° C. to 800° C.).
In some examples, annealing the precursor electrode can comprise heating the precursor electrode at a temperature for an amount of time of 1 minute or more (e.g., 1.5 minutes or more, 2 minutes or more, 2.5 minutes or more, 3 minutes or more, 3.5 minutes or more, 4 minutes or more, 4.5 minutes or more, 5 minutes or more, 6 minutes or more, 7 minutes or more, 8 minutes or more, 9 minutes or more, 10 minutes or more, 15 minutes or more, 20 minutes or more, 25 minutes or more, 30 minutes or more, 35 minutes or more, 40 minutes or more, 45 minutes or more, 50 minutes or more, 55 minutes or more, 1 hour or more, 1.5 hours or more, 2 hours or more, 2.5 hours or more, 3 hours or more, 3.5 hours or more, 4 hours or more, 4.5 hours or more, 5 hours or more, 6 hours or more, 7 hours or more, 8 hours or more, 9 hours or more, 10 hours or more, 12 hours or more, 14 hours or more, 16 hours or more, 18 hours or more, 24 hours or more, 30 hours or more, 36 hours or more, or 42 hours or more). In some examples, annealing the precursor electrode can comprise heating the precursor electrode at a temperature for an amount of time of 48 hours or less (e.g., 42 hours or less, 36 hours or less, 30 hours or less, 24 hours or less, 18 hours or less, 16 hours or less, 14 hours or less, 12 hours or less, 10 hours or less, 9 hours or less, 8 hours or less, 7 hours or less, 6 hours or less, 5 hours or less, 4.5 hours or less, 4 hours or less, 3.5 hours or less, 3 hours or less, 2.5 hours or less, 2 hours or less, 1.5 hours or less, 1 hours or less, 55 minutes or less, 50 minutes or less, 45 minutes or less, 40 minutes or less, 35 minutes or less, 30 minutes or less, 25 minutes or less, 20 minutes or less, 15 minutes or less, 10 minutes or less, 9 minutes or less, 8 minutes or less, 7 minutes or less, 6 minutes or less, 5 minutes or less, 4.5 minutes or less, 4 minutes or less, 3.5 minutes or less, 3 minutes or less, 2.5 minutes or less, 2 minutes or less, or 1.5 minutes or less). The amount of time for which the precursor electrode is annealed at a temperature can range from any of the minimum values described above to any of the maximum values described above. For example, annealing the precursor electrode can comprise heating the precursor electrode at a temperature for an amount of time of from 1 minute to 48 hours (e.g., from 1 minute to 1 hour, from 1 hour to 48 hours, from 1 minute to 42 hours, from 10 minutes to 48 hours, from 10 minutes to 42 hours, or from 1 hour to 24 hours). For example, annealing the precursor electrode can comprise heating the precursor electrode at a temperature of from 450° C. to 650° C. for an amount of time of from 1 hour to 24 hours.
The precursor electrode can, for example, be annealed in vacuum or an atmosphere comprising nitrogen, argon, forming gas, etc.
In some examples, the methods can further comprise removing the reactive material from the spiked electrode before depositing the catalyst material, thereby forming an intermediate electrode. Removing the reactive material can, for example, comprise etching the reactive material. Etching the reactive material can, for example, comprise contacting the reactive material with an etchant. In some examples, the etchant can comprise H3PO4.
Depositing the catalyst material can, for example, comprise electroplating, lithographic deposition, electron beam deposition, thermal deposition, spin coating, drop-casting, zone casting, dip coating, blade coating, spraying, vacuum filtration, chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), sputtering, pulsed layer deposition, molecular beam epitaxy, evaporation, or combinations thereof. In some examples, depositing the catalyst material comprises electroplating.
Electroplating the catalyst material can, for example, comprise contacting light absorbing layer of the spiked electrode or the intermediate electrode with a plating solution and subsequently applying a voltage for an amount of time. The plating solution can, for example, comprise a salt of the metal. In some examples, the plating solution comprises NiCl2, NiSO4, or a combination thereof. Different plating solutions can, for example, be used sequentially during an electroplating process.
The applied voltage can, for example, be −5 Volts (V) or more vs Ag/AgCl (e.g., −4.5 V or more, −4 V or more, −3.5 V or more, −3 V or more, −2.5 V or more, −2 V or more, −1.5 V or more, −1 V or more, −0.5 V or more, 0 V or more, 0.5 V or more, 1 V or more, 1.5 V or more, 2 V or more, 2.5 V or more, 3 V or more, 3.5 V or more, 4 V or more, or 4.5 V or more). In some examples, the applied voltage can be 5 V or less vs. Ag/AgCl (e.g., 4.5 V or less, 4 V or less, 3.5 V or less, 3 V or less, 2.5 V or less, 2 V or less, 1.5 V or less, 1 V or less, 0.5 V or less, 0 V or less, −0.5 V or less, −1 V or less, −1.5 V or less, −2 V or less, −2.5 V or less, −3 V or less, −3.5 V or less, −4 V or less, or −4.5 V or less). The applied voltage can range from any of the minimum values described above to any of the maximum values described above. For example, the applied voltage can be from −5 V to +5 V (e.g., from −5 V to 0 V, from 0 V to 5 V, from −5 V to −2.5 V, from −2.5 V to 0 V, from 0 V to 2.5 V, from 2.5 V to 5 V, from −5 V to 4 V, from −4 V to 5 V, from −4 V to 4 V, or from −0.5 V to −3.0 V). In some examples, the applied voltage is from −0.5 V to −3.0 V vs. Ag/AgCl.
In some examples, the voltage is applied for an amount of time of 10 seconds or more (e.g., 15 seconds or more, 20 seconds or more, 25 seconds or more, 30 seconds or more, 35 seconds or more, 40 seconds or more, 45 seconds or more, 50 seconds or more, 55 seconds or more, 1 minute or more, 1.5 minutes or more, 2 minutes or more, 2.5 minutes or more, 3 minutes or more, 3.5 minutes or more, 4 minutes or more, 4.5 minutes or more, 5 minutes or more, 6 minutes or more, 7 minutes or more, 8 minutes or more, 9 minutes or more, 10 minutes or more, 15 minutes or more, 20 minutes or more, 25 minutes or more, 30 minutes or more, 35 minutes or more, 40 minutes or more, 45 minutes or more, 50 minutes or more, 55 minutes or more, 1 hour or more, 1.5 hours or more, 2 hours or more, 2.5 hours or more, 3 hours or more, 3.5 hours or more, 4 hours or more, 4.5 hours or more, 5 hours or more, 6 hours or more, 7 hours or more, 8 hours or more, 9 hours or more, or 10 hours or more). In some examples, the voltage is applied for an amount of time of 12 hours or less (e.g., 11 hours or less, 10 hours or less, 9 hours or less, 8 hours or less, 7 hours or less, 6 hours or less, 5 hours or less, 4.5 hours or less, 4 hours or less, 3.5 hours or less, 3 hours or less, 2.5 hours or less, 2 hours or less, 1.5 hours or less, 1 hours or less, 55 minutes or less, 50 minutes or less, 45 minutes or less, 40 minutes or less, 35 minutes or less, 30 minutes or less, 25 minutes or less, 20 minutes or less, 15 minutes or less, 10 minutes or less, 9 minutes or less, 8 minutes or less, 7 minutes or less, 6 minutes or less, 5 minutes or less, 4.5 minutes or less, 4 minutes or less, 3.5 minutes or less, 3 minutes or less, 2.5 minutes or less, 2 minutes or less, 1.5 minutes or less, 1 minute or less, 55 seconds or less, 50 seconds or less, 45 seconds or less, 50 seconds or less, 35 seconds or less, 30 seconds or less, 25 seconds or less, 20 seconds or less, or 15 seconds or less). The amount of time for which the voltage is applied can range from any of the minimum values described above to any of the maximum values described above. For example, the voltage can be applied for an amount of time of from 10 seconds to 12 hours (e.g., from 10 seconds to 2 hours, from 2 hours to 12 hours, from 10 seconds to 1 minute, from 1 minute to 1 hour, from 1 hour to 12 hours, from 1 minute to 12 hours, from 10 seconds to 10 hours, from 1 minute to 10 hours, or from 1 minute to 6 hours). In some examples, voltage is applied for an amount of time of from 1 minute to 120 minutes. In some examples, the morphology and/or composition of the deposited catalyst material can be controlled by varying the applied bias and deposition time for electrodeposition during the electrodeposition process.
Also disclosed herein are devices comprising any of the photoelectrodes described herein and methods of use of any of the photoelectrodes or devices described herein.
For example, also disclosed herein are methods of use of any of the photoelectrodes disclosed herein. The methods can, for example, comprise using the photoelectrode as an electrode in a photoelectrochemical reaction. In some examples, the methods can comprise using the photoelectrode as an electrode in an energy conversion device, a charge storage device, an electronic device, an optoelectronic device, or a combination thereof. In some examples, the methods can comprise using the photoelectrode as an electrode in an energy conversion device, wherein the energy conversion device comprises a solar cell, a fuel cell, a photovoltaic cell, another type of voltage or current source. or a combination thereof
Also disclosed herein are devices comprising any of the photoelectrodes described herein. For example, the device can comprise an energy conversion device, a charge storage device, an electronic device, an optoelectronic device, or a combination thereof. In some examples, the device can comprise an energy conversion device, such as a solar cell, a fuel cell, a photovoltaic cell, another type of voltage or current source, or a combination thereof.
Also disclosed herein are photoelectrochemical cells comprising any of the photoelectrodes described herein and methods of use thereof. For example, also disclosed herein are photoelectrochemical cells comprising: a working electrode in electrochemical contact with a fluid and one or more additional electrodes in electrochemical contact with the fluid, wherein the working electrode can comprise any of the photoelectrodes disclosed herein.
In some examples, the fluid can comprise a fuel precursor. Examples of fuel precursors include, but are not limited to, water, carbon dioxide, and combinations thereof. In some examples, the fuel precursor comprises water in the form of an aqueous solution, such as, for example, contaminated water, nonpurified water, saline water, sea water, etc.
Also disclosed herein are methods of use of any of the photoelectrochemical cells disclosed herein. In some examples, the fluid comprises a fuel precursor and the method can comprise photoelectrochemical fuel generation. The method can, for example, comprise illuminating the photoelectrode in contact with the fuel precursor with electromagnetic radiation that overlaps at least a portion of the photon energy range absorbed by the light absorbing, thereby providing photogenerated electrons or holes in the light absorbing which are transported to the catalyst material at the interface between the photoelectrode and the fuel precursor which participate in the desired electrochemical reaction to thereby convert the fuel precursor to a fuel. In some examples, the methods can further comprise collecting the fuel.
The electromagnetic radiation can, for example, comprise light and the light can be provided by a light source. . The light source can be any type of light source. Examples of suitable light sources include natural light sources (e.g., sunlight) and artificial light sources (e.g., incandescent light bulbs, light emitting diodes, gas discharge lamps, arc lamps, lasers, etc.). In some examples, the electromagnetic radiation comprises sunlight. In some examples, the method comprises solar powered photoelectrochemical fuel production.
In some examples, the fuel precursor comprises water and the method comprises photoelectrochemical water splitting. In some examples, the fuel precursor comprise water, the electromagnetic radiation comprises sunlight, and the method comprises solar water splitting.
In some examples, the fuel comprises H2 and the method comprises photoelectrochemical hydrogen generation.
In some examples, the photoelectrode participates in an oxygen evolution reaction and exhibits an onset potential of 1.5 V or less vs. RHE (e.g., 1.4 V or less, 1.3 V or less, 1.2 V or less, 1.1 V or less, 1.0 V or less, 0.9 V or less, 0.8 V or less, 0.7 V or less, 0.6 V or less, 0.5 V or less, 0.4 V or less, 0.3 V or less, 0.2 V or less, or 0.1 V or less) and a saturation current density of 1 mA/cm2 or more (e.g., 2 mA/cm2 or more, 3 mA/cm2 or more, 4 mA/cm2 or more, 5 mA/cm2 or more, 10 mA/cm2 or more, 15 mA/cm2 or more, 20 mA/cm2 or more, 25 mA/cm2 or more, 30 mA/cm2 or more, 35 mA/cm2 or more, 40 mA/cm2 or more, 45 mA/cm2 or more, or 50 mA/cm2 or more) for AM1.5G solar illumination. In some examples, the onset potential is 1.5 V or less, 1.1 V or less, 1.0 V or less, 0.9 V or less, 0.7 V or less vs. RHE. In some examples, the saturation current density is 1 mA/cm2 or more, 5 mA/cm2 or more, 10 mA/cm2 or more, 15 mA/cm2 or more, 25 mA/cm2 or more, or 30 mA/cm2 or more. In some examples, the onset potential is 0.7 V or less vs. RHE and the saturation current density of 32 mA/cm2 or more.
In some examples, the oxygen evolution reaction produces O2 at the photoelectrode at a rate of 1 micromoles/hour or more (e.g., 2 micromoles/hour or more, 3 micromoles/hour or more, 4 micromoles/hour or more, 5 micromoles/hour or more, 10 micromoles/hour or more, 15 micromoles/hour or more, 20 micromoles/hour or more, 25 micromoles/hour or more, 30 micromoles/hour or more, 35 micromoles/hour or more, 40 micromoles/hour or more, or 45 micromoles/hour or more). In some examples, the oxygen evolution reaction produces O2 at the photoelectrode at a rate of 50 micromoles/hour or less (e.g., 45 micromoles/hour or less, 40 micromoles/hour or less, 35 micromoles/hour or less, 30 micromoles/hour or less, 25 micromoles/hour or less, 20 micromoles/hour or less, 15 micromoles/hour or less, 10 micromoles/hour or less, or 5 micromoles/hour or less). The rate at which the oxygen evolution reaction produces O2 at the photoelectrode can range from any of the minimum values described above to any of the maximum values described above. For example, the oxygen evolution reaction can produce O2 at the photoelectrode at a rate of from 1 micromoles/hour to 50 micromoles/hour (e.g., from 1 micromoles/hour to 25 micromoles/hour, from 25 micromoles/hour to 50 micromoles/hour, from 1 micromoles/hour to 10 micromoles/hour, from 10 micromoles/hour to 20 micromoles/hour, from 20 micromoles/hour to 30 micromoles/hour, from 30 micromoles/hour to 40 micromoles/hour, from 40 micromoles/hour to 50 micromoles/hour, from 5 micromoles/hour to 50 micromoles/hour, from 1 micromoles/hour to 40 micromoles/hour, or from 5 micromoles/hour to 40 micromoles/hour).
In some examples, H2 is produced at another electrode in the photoelectrochemical cell at a rate of 1 micromoles/hour or more (e.g., 2 micromoles/hour or more, 3 micromoles/hour or more, 4 micromoles/hour or more, 5 micromoles/hour or more, 10 micromoles/hour or more, 15 micromoles/hour or more, 20 micromoles/hour or more, 25 micromoles/hour or more, 30 micromoles/hour or more, 35 micromoles/hour or more, 40 micromoles/hour or more, 45 micromoles/hour or more, 50 micromoles/hour or more, 55 micromoles/hour or more, 60 micromoles/hour or more, 65 micromoles/hour or more, 70 micromoles/hour or more, 75 micromoles/hour or more, 80 micromoles/hour or more, 85 micromoles/hour or more, 90 micromoles/hour or more, or 95 micromoles/hour or more). In some examples, H2 is produced at another electrode in the photoelectrochemical cell at a rate of 100 micromoles/hour or less (e.g., 95 micromoles/hour or less, 90 micromoles/hour or less, 85 micromoles/hour or less, 80 micromoles/hour or less, 75 micromoles/hour or less, 70 micromoles/hour or less, 65 micromoles/hour or less, 60 micromoles/hour or less, 55 micromoles/hour or less, 50 micromoles/hour or less, 45 micromoles/hour or less, 40 micromoles/hour or less, 35 micromoles/hour or less, 30 micromoles/hour or less, 25 micromoles/hour or less, 20 micromoles/hour or less, 15 micromoles/hour or less, 10 micromoles/hour or less, or 5 micromoles/hour or less). The rate at which H2 is produced at another electrode in the photoelectrochemical cell can range from any of the minimum values described above to any of the maximum values described above. For example, H2 can be produced at another electrode in the photoelectrochemical cell at a rate of from 1 micromoles/hour to 100 micromoles/hour (e.g., from 1 micromoles/hour to 50 micromoles/hour, from 50 micromoles/hour to 100 micromoles/hour, from 1 micromoles/hour to 20 micromoles/hour, from 20 micromoles/hour to 40 micromoles/hour, from 40 micromoles/hour to 60 micromoles/hour, from 60 micromoles/hour to 80 micromoles/hour, from 80 micromoles/hour to 100 micromoles/hour, from 1 micromoles/hour to 90 micromoles/hour, from 10 micromoles/hour to 100 micromoles/hour, or from 10 micromoles/hour to 90 micromoles/hour).
In some examples, the fuel precursor comprises carbon dioxide and the method comprises photoelectrochemical reduction of CO2.
In some examples, the fluid has a pH of 8 or more and the photoelectrode is stable for 24 hours or more. As used herein, the photoelectrode being “stable” means that the photoelectrode has a photocurrent that is stable, e.g. wherein the photocurrent varies by 10% or less (e.g., 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less, or 1% or less) over the selected time period. In some examples, the fluid has a pH of 14 and the photoelectrode is stable for 48 hours or more (e.g., 72 hour or more, 96 hours or more, 120 hours or more, 144 hours or more, or 168 hours or more).
In some examples, the photoelectrochemical fuel generation has a Faradaic efficiency of 10% or more (e.g., 15% or more, 20% or more, 25% or more, 30% or more, 35% or more, 40% or more, 45% or more, 50% or more, 55% or more, 60% or more, 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, 95% or more, or 99% or more). In some examples, the photoelectrochemical fuel generation has a Faradaic efficiency of 100% or less (e.g., 99% or less, 95% or less, 90% or less, 85% or less, 80% or less, 75% or less, 70% or less, 65% or less, 60% or less, 55% or less, 50% or less, 45% or less, 40% or less, 35% or less, 30% or less, 25% or less, 20% or less, or 15% or less). The Faradaic efficiency of the photoelectrochemical fuel generation can range from any of the minimum values described above to any of the maximum values described above. For example, the photoelectrochemical fuel generation can have a Faradaic efficiency of from 10% to 100% (e.g., from 10% to 55%, from 55% to 100%, from 10% to 40%, from 40% to 70%, from 70% to 100%, from 20% to 100%, from 10% to 95%, from 20% to 95%, from 30% to 100%, from 50% to 100%, or from 80% to 100%).
A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.
The examples below are intended to further illustrate certain aspects of the systems and methods described herein, and are not intended to limit the scope of the claims.
The following examples are set forth below to illustrate the methods and results according to the disclosed subject matter. These examples are not intended to be inclusive of all aspects of the subject matter disclosed herein, but rather to illustrate representative methods and results. These examples are not intended to exclude equivalents and variations of the present invention which are apparent to one skilled in the art.
Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.) but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in ° C. or is at ambient temperature, and pressure is at or near atmospheric. There are numerous variations and combinations of measurement conditions, e.g., component concentrations, temperatures, pressures and other measurement ranges and conditions that can be used to optimize the described process.
Abstract. Metal-insulator-semiconductor (MIS) structures have been widely used in Si-based photoelectrodes to protect the Si absorbing layer from corrosion in aqueous environments. Typically, there is a tradeoff between efficiency and stability when optimizing insulator thickness. Moreover, lithographic patterning is often required for fabricating metal-insulator-semiconductor photoelectrodes. In this study, improved Si-based metal-insulator-semiconductor photoanodes with thick insulating layers are demonstrated. The improved Si-based metal-insulator-semiconductor photoanodes with thick insulating layers are fabricated using thin-film reactions to create localized conduction paths through the insulator and electrodeposition to form metal catalyst islands. This approach yielded metal-insulator-semiconductor photoanodes with low onset potential, high saturation current density, and excellent stability. By combining this approach with a p+n-Si buried junction, further improved oxygen evolution reaction (OER) performance was achieved with an onset potential of 0.7 V versus RHE and saturation current density of 32 mA/cm2.
Introduction. Photoelectrochemical (PEC) water splitting is a promising technology for converting solar energy into clean and storable chemical energy. In photoelectrochemical cells, semiconductors play a key role in absorbing photons from the light source to create mobile charge carriers. Various semiconductor materials have been studied for high performance photoelectrochemical cells, including metal oxides, nitrides, Si, III-V compound semiconductor materials, and others. Among these, Si-based photoelectrodes have attracted substantial interest due to silicon's moderate bandgap (1.12 eV), high charge mobility and diffusion lengths, and well established technological infrastructure. However, Si-based photoanodes for the oxygen evolution reaction (OER) remain challenging to engineer due to the complex four-electron reaction mechanism, which requires a large overpotential, and low chemical stability in alkaline solutions. To improve the oxygen evolution reaction performance of Si-based photoanodes, metal-insulator-semiconductor (MIS) structures have been widely used for Si-based photoanodes due to their high efficiency and good stability (Laskowski F A L et al. Nature Materials 2020, 19, 69-76, Ji L et al Nature Materials 2017, 16, 127-131; Loget G et al. ACS Energy Letters 2017, 2, 569-573; Scheuermann A G et al. ACS Applied Materials & Interfaces 2016, 8, 14596-14603). An efficient metal catalyst at the surface can improve the reaction kinetics of photoanodes, reducing the overpotential for the oxygen evolution reaction. Corrosion of Si in aqueous electrolytes can be prevented in metal-insulator-semiconductor photoelectrode structures by protecting the Si surface with thin layers of insulators such as TiO2 (Chuang C H et al. ACS Applied Energy Materials 2020, 3, 3902-3908; Scheuermann A G et al. ACS Applied Materials & Interfaces 2016, 8, 14596-14603: Liu B et al. Energy & Environmental Science 2020, 13, 221-228), NiOx (Laskowski F A L et al. Nature Materials 2020, 19, 69-76; Loget G et al. ACS Energy Letters 2017, 2, 569-573; Zhao J et al. Nano Research 2018, 11, 3499-3508), SrTiO3 (Ji L et al. Nature Nanotechnology 2015, 10, 84-90), SiNx (Kumar P et al. Communications Chemistry 2019, 2, 4), and SiOx (Laskowski F A L et al. Nature Materials 2020, 19, 69-76; Ji L et al. Nature Materials 2017, 16, 127-131: Loget G et al. ACS Energy Letters 2017, 2, 569-573).
Typically, for a Si-based metal-insulator-semiconductor photoanode, minority carriers are generated under illumination in the semiconductor and extracted to the metal layer by tunneling through the insulator, as shown in
Previous work has demonstrated improvements in effective conductivity of a thick insulating layer in metal-insulator-semiconductor photoelectrodes by electrically inducing localized dielectric breakdown of the insulating region below metal catalyst islands (Ji L et al. Nature Materials 2017, 16, 127-131). Since the breakdown process resulted in formation of localized conductive paths through the thick oxide layer, photogenerated minority carriers are easily transported via the conductive path instead of by tunneling. Using this approach, improved photocurrents were observed with good long-term stability due to the thick insulating layers. Nevertheless, this method requires complex and time-consuming processing techniques for the formation of localized breakdown paths and lithographic patterning of the top metal layer. Recently, the deposition of Ni catalysts for the metal layer of metal-insulator-semiconductor photoanodes using electrodeposition and electroless deposition have been reported (Loget G et al. ACS Energy Letters 2017, 2, 569-573; Zhao J et al. Nano Research 2018, 11, 3499-3508). These methods yielded well defined Ni deposition for the metal-insulator-semiconductor photoanode and enabled efficient oxygen evolution reaction performance without using complex lithographic techniques (Loget G et al. ACS Energy Letters 2017, 2, 569-573; Zhao J et al. Nano Research 2018, 11, 3499-3508). However, there was still a limitation in the long-term stability in high pH aqueous solutions (Loget G et al. ACS Energy Letters 2017, 2, 569-573; Zhao J et al. Nano Research 2018, 11, 3499-3508).
Herein, a low cost and highly scalable method for improving Si-based metal-insulator-semiconductor photoanodes by exploiting a thin-film reaction of Al through an insulating oxide layer followed by Ni-electrodeposition, and not requiring any lithographic patterning is demonstrated. The thin-film reaction of Al with SiO2 or Si, leading to localized penetration of Al “spikes” into the underlying material, has been studied extensively since it can cause an electrical short in silicon pn-junction structures with Al contact metallization. Al spiking can also occur through an insulating SiO2 layer, and has been exploited to form Ohmic contacts through an oxide passivation layer on Si (Bierhals A et al. Journal of Applied Physics 1998, 83, 1371-1378; Ho AWY et al. Progress in Photovoltaics: Research and Applications 2004, 12, 297-308). In a metal-insulator-semiconductor photoelectrode structure with Al as the metal layer, annealing of the Al/SiO2/Si structure above 300° C. causes Al to penetrate the underlying SiO2 and induces formation of localized metal spikes in the metal-insulator-semiconductor structure. As shown in
To optimize the Al thin-film reaction and spiking process, a series of Al/SiO2/Si/SiO2/Al samples was prepared by 90 nm SiO2 growth and 100 nm Al deposition on both sides of Si substrates, and their series resistance from top to bottom (top-bottom resistance) was measured before and after different annealing processes. It has been reported that, in an Al/SiO2/Si structure, Al reduces the underlying SiO2 layer and penetrates to the Si layer during annealing, the phenomenon referred to as Al spiking (Bierhals A et al. Journal of Applied Physics 1998, 83, 1371-1378; Ho A W Y et al. Progress in Photovoltaics: Research and Applications 2004, 12, 297-308; Godfrey R B et al. Applied Physics Letters 1979, 34, 860-861). The formation of Al spikes requires around 2.56 eV of activation energy for the SiO2 reduction process, and can occur at temperature above 300° C. (Godfrey R B et al. Applied Physics Letters 1979, 34, 860-861). The top-bottom resistance changes were measured for annealing temperatures of 450˜600° C. and durations of 0˜24 hours as shown in
For metal-insulator-semiconductor photoanodes, the catalyst on the metal layer is essential in enhancing overall reaction rate, reducing the onset voltage, and increasing the current density. Typically, Ni has been used as the oxygen evolution reaction catalyst due to its good electrical conductivity, efficient catalytic effect, and corrosion resistance at high pH (Loget G et al. ACS Energy Letters 2017, 2, 569-573). In this study, Ni was incorporated as a catalyst for the photoanode using electrodeposition, following the formation of localized voids in the SiO2 protective layer by Al thin-film reaction and etching. Other catalyst materials could readily be employed using this approach. The morphology of Ni deposited on the surface can be controlled by varying the applied bias and deposition time for electrodeposition. When negative bias is applied to the substrate, Ni deposition begins by filling the voids in the SiO2 layer, since the highest electric fields are present at the interface between the aqueous solution and the exposed Si surface. Ni is nucleated at these locations and eventually forms larger islands on the surface.
Photoelectrochemical performance was measured for the spiked Ni/SiO2/Si photoanodes fabricated using various Ni electrodeposition processes in 1 M KOH (pH=14) aqueous solution with a standard three-electrode system under standard AM 1.5 G 1 sun illumination.
The corrosion resistance of the spiked Ni/SiO2/Si photoanodes at high pH was assessed by chronoamperometry (CA). As shown in
The effects of localized contacts in the spiked Ni/SiO2/Si photoanode were also analyzed computationally using a commercial numerical solver, COMSOL Multiphysics, to help explain the favorable onset potentials observed. Three different models were simulated, comprising different Ni/SiO2/Si structures with metal back contacts (
Spiked Ni/SiO2/Si Photoanode With p+n-Si
To further improve the photochemical onset potential, a p+n-Si substrate was used for the spiked Ni/SiO2/Si photoanode. It has been reported that thin p+ doping on the n-Si surface improves the oxygen evolution reaction performance of metal-insulator-semiconductor photoanodes due to the higher hole density at the Si surface (Scheuermann A G et al. Nat. Mater. 2016, 15, 99-105; Green M A et al. Solar Cells 1983, 8, 3-16). The p+ doping on the surface was performed by boron diffusion with an expected junction depth of ˜300 nm, since a junction depth above 1 μm is expected to increase interface recombination (Scheuermann A G et al. Nat. Mater. 2016, 15, 99-105).
The improvement in oxygen evolution reaction performance for the spiked Ni/SiO2/p+n-Si photoanode was analyzed by simulating its band structure for a gaussian acceptor doping profile corresponding to boron diffusion process from the surface with junction depth of 300 nm, referred to as Model 4.
In summary, a general method for low cost, lithography-free, and scalable fabrication of Si-based metal-insulator-semiconductor photoanodes by employing an Al thin-film reaction process combined with Ni electrodeposition was demonstrated. This approach allows a thick SiO2 insulator (90 nm) to be employed, which provides antireflection functionality on Si and high long-term stability in alkaline solutions. Optimization of the Al thin-film reaction process to create a suitable density of openings in the SiO2 layer, and the Ni electrodeposition process to achieve optimal Ni surface coverage, leads to favorable onset potentials and high photocurrent densities. The enhancement in oxygen evolution reaction performance was analyzed by photoelectrochemical measurements and numerical simulations using metal-insulator-semiconductor Schottky contact models. In photoelectrochemical measurements, the optimized Si-based metal-insulator-semiconductor photoanode with a buried p+n-Si junction showed low onset potential and high saturation photocurrent density around 0.7 V versus RHE and 32 mA/cm2, respectively. Furthermore, the high photocurrent density was maintained for a 168 hour stability test in 1 M KOH aqueous solution. These results demonstrate a simple approach for highly efficient photoanodes, without using any complex and costly techniques, which is suitable for large-scale commercial fabrication.
Fabrication of Si-Based Metal-Insulator-Semiconductor Photoanode With Localized spike structure. Four inch n-type (100) c-Si wafers (thickness t˜550 μm and resistivity ρ=0.3-0.5 Ωcm) were used for fabrication of photoanodes. Each wafer was cleaved into 2×2 cm2 samples and cleaned with piranha solution (5:1:1 H2O:H2SO4:H2O2). Cleaned Si substrates were dipped into a 5% HF aqueous solution for 1 min to remove the native oxide. For the back contact, 5 nm Cr and 100 nm Au were deposited on the backside of the Si substrates by e-beam evaporation. High quality SiO2 films were thermally grown on the front side of each Si wafer using an oxidation furnace (MRL 8′ furnace, Sandvik Thermal Process Inc.) at 950° C. in dry O2 ambient. In this work, all photoanodes were fabricated with 90 nm SiO2 layers. Then, the Al layers were deposited onto the SiO2/Si surface by DC magnetron sputtering (UNIVEX 450B) under 1×10−6 Torr of base pressure. The use of Si-doped Al suppresses penetration of the Al metallization into the Si layers. For the formation of localized Al spikes through the SiO2 layer, the Al/SiO2/Si substrate was annealed at 550° C. for 24 hours in a vacuum chamber. To replace the top Al layer with the Ni catalyst, Al was etched using an 10% H3PO4 aqueous solution for 6 hours. After Al etching, the surface was rinsed by DI water and dried under N2 flow. The Ni catalyst was deposited by electrodeposition. The Ni plating solution was prepared by mixing 0.1 M boric acid and 0.1 M NiCl2 aqueous solution. During electrodeposition, only the SiO2/Si surface from which Al was etched was exposed to the Ni plating solution. The working electrode was connected the back contact and both Pt counter electrode and Ag/AgCl (3 M KCI) reference electrode were dipped in the Ni plating solution. The Ni electrodeposition was performed with different applied biases (−0.5, −1.0, and −2.0 V versus Ag/AgCl) with deposition times ranging from 0 to 120 min. The resulting spiked Ni/SiO2/Si metal-insulator-semiconductor photoanode was rinsed in DI water and dried naturally under ambient condition.
Fabrication of Ni/SiO2/p+n-Si photoanode. p+ doping on the surface of 4 inch n-type (100) c-Si wafers was performed by annealing n-Si substrates with boron solid-state source (BoronPlus™) at 950° C. for 70 min with N2 flow rate 3.5 L/min. The p+ doping was maintained until the boron diffusion profile with 300 nm junction depth. The 5 nm Cr/100 nm Au back contact, thermally grown 90 nm SiO2 layer, and 100 nm Al layer were obtained using the same methods with other photoanodes. After the fabrication of Al/SiO2/p+n-Si structure, Al spiking was processed by annealing at 550° C. for 24 hours in a vacuum chamber, followed by Al etching Subsequently, 35% Ni coverage was obtained by electrodeposition at −3.0 V versus Ag/AgCl for 30 min.
Measurements of resistance change after Al spiking. To evaluate the resistance change after Al spiking, dual-sided Al/SiO2/Si/SiO2/Al metal-insulator-semiconductor samples were prepared. At first, 90 nm SiO2 layers were grown on both sides of prepared 2×2 cm2 n-type Si substrates using a thermal oxidation furnace at 950° C. in dry O2 ambient. Then, 100 nm Al films were also deposited on both sides of SiO2/Si/SiO2 substrates using DC magnetron sputtering. To induce localized Al spiking, Al/SiO2/Si/SiO2/Al samples were annealed at 450° C., 500° C., 550° C., and 650° C. for annealing times ranging from 0 to 24 hours. Before and after each annealing process, the top and bottom Al layers were connected to anode and cathode, respectively, and linear sweep voltammetry (LSV) was performed for evaluating the resistance between top and bottom.
Photoelectrochemical measurements. All oxygen evolution reaction performances were measured using a CHI 760E electrochemical workstation (CH Instruments, Austin, United States) with a standard three-electrode electrochemical cell comprising Pt wire as a counter electrode and an Ag/AgCl reference electrode. The alkaline solution (pH=14) for the oxygen evolution reaction characterization comprised a 1 M KOH aqueous solution (semiconductor grade, Sigma-Aldrich, 99.99% trace metal basis). The measured potentials versus Ag/AgCl were converted to potential versus reversible hydrogen electrode (RHE) using the following equation:
E
RHE
=E
Ag/Agcl+0.197V+0.059×pH (1)
The linear sweep voltammetry and chronoamperometry (CA) measurements were carried out for the photoanodes under 100 mW/cm2 light illumination using Xenon arc lamp (66475, Newport) for characterization of oxygen evolution reaction efficiency and long-term stability tests. The H2 and O2 gas evolution were measured by H2 and O2 microsensors connected to a picoammeter (Unisense A/S, Denmark), respectively, in 1 M KOH solution at 1.23 V versus RHE under illumination. The faradaic efficiency (FE) of photoanode was calculated using the following equation (Jiang C et al. Chemical Society Reviews 2017, 46, 4645-4660):
where Jphoto is the current density (A/cm2), A is the illumination area (cm2), T is the measurement time (sec), e is the charge of an electron (1.602×10−19 C), and NA is the Avogadro constant (6.02×1023 mol-1).
Characterization. The surface morphologies of spiked SiO2 and electrodeposited Ni surfaces were characterized using field emission scanning electron microscopy (Zeiss, USA). To evaluate the Ni electrodeposited surface, the diameters and surface coverage of Ni NPs were calculated using the “Image J” platform. The numerical simulations for the photoanodes were performed using the semiconductor module of a commercial numerical finite-element solver (COMSOL Multiphysics).
Si-based photoelectrodes have attracted substantial interest due to their potential for cost-effective conversion of water into clean fuel using solar energy. However, Si-based photoanodes for the oxygen evolution reaction (OER) are still challenging due to the requirements of large overpotential and low stability in alkaline solutions. To achieve high efficiency and long-term stability, metal-insulator-semiconductor (MIS) structures have been widely explored. In Si-based metal-insulator-semiconductor photoanodes, the insulator needs to prevent Si corrosion in alkaline solutions and also transport carriers efficiently. In this work, a series of highly manufacturable processes for fabricating Ni/SiO2/Si metal-insulator-semiconductor photoanodes with SiO2 insulating layers up to 90 nm thick and localized, non-lithographically fabricated Ni catalyst contacts are demonstrated. The resulting photoanode structures show high efficiency and long-term stability in alkaline solutions. Specifically, a Ni/SiO2/n-Si photoanode yielded onset potential and photocurrent density of ˜1.0 V versus RHE and ˜25 mA/cm2, respectively, while a Ni/SiO2/p+n-Si photoanode yielded an onset potential of 0.7 V versus RHE and saturation current density of 32 mA/cm2, all in 1 M KOH alkaline solutions. Moreover, in stability testing in 1 M KOH aqueous solution, a constant photocurrent density of ˜22.0 mA/cm2 was maintained at 1.3 V versus RHE for 168 hours. This approach yields an enhancement in oxygen evolution reaction performance of Si-based metal-insulator-semiconductor photoanodes with highly manufacturable fabrication processes that are amenable to large-scale commercial fabrication.
Described herein are devices , and methods for their fabrication, that can serve as stable, high performance photoelectrodes for electrochemical reactions powered by solar or other illumination sources. In brief, the device structure comprises a semiconductor (e.g., silicon, gallium arsenide, etc.) that serves as an efficient absorber of incident illumination, on top of which is an electrically insulating layer (e.g., silicon dioxide, titanium dioxide, etc.) through which local electrical contacts are created non-lithographically, and a catalyst material (e.g., nickel and nickel oxides, platinum, etc.) that electrically contacts or serves as the electrical contact through the electrically insulating layer and is also in contact with a liquid (typically aqueous) solution in which the electrochemical reaction is occurring. The prototypical application scenario is oxidation or reduction of water molecules to form oxygen or hydrogen, respectively, powered by solar illumination, but other reactions and illumination sources are possible. In this application, the semiconductor layer enables efficient absorption of illumination and conversion to mobile charge carriers (electrons and/or holes). An appropriate electrically insulating layer protects the semiconductor from corrosion or other degradation by the liquid solution in which the desired electrochemical reactions take place. The local electrical contacts through the insulating layer transport charge carriers from the semiconductor to the catalyst. The catalyst increases the rate at which the desired electrochemical reaction occurs.
The process for fabrication of the device structure comprises the following steps. (i) Selection of an appropriate semiconductor substrate material and, if desired, doping of a near-surface layer of the substrate to form a semiconductor pn junction using standard semiconductor doping processes. (ii) Formation of an electrically insulating layer atop the semiconductor by a standard process such as thin-film deposition or thermal oxidation. (iii) Deposition of a reactive material (e.g., aluminum or an aluminum-silicon alloy) as a thin film on top of the electrically insulating layer, and subsequent annealing to enable localized diffusion of the reactive material through the electrically insulating layer. The diffused reactive material creates a local electrical contact to the underlying semiconductor material. This process has been reported previously for formation of ohmic contacts to oxide-passivated silicon surfaces, but has not previously been applied for photoelectrochemical devices. (iv) Creation of the catalyst structure at localized regions either atop or in place of the local electrical contacts formed in step (iii). The catalyst structure can be formed by chemical reaction, electrodeposition, selective-area deposition, or another process. If replacement of the diffused reactive material by catalyst material is desired, e.g., to improve stability under operation, this can be accomplished by initial removal of the diffused reactive species followed by introduction of catalyst material, a chemical reaction in which the catalyst material replaces the diffused reactive material, or another process. Coverage of the device surface by the catalyst material is optimized to enable the optimal balance between available catalyst surface area and transmission of light into the semiconductor material for absorption and carrier generation.
Once fabricated, this device operates as follows. The device is placed with the oxide/catalyst surface in contact with the liquid solution in which the desired electrochemical reaction will occur. The oxide/catalyst surface is illuminated by light with an appropriate wavelength distribution (most commonly from the sun or a solar simulator). This illumination is absorbed in the semiconductor and the resulting photogenerated electrons or holes are transported to the catalyst at the device-liquid interface to participate in the desired electrochemical reaction, e g., generation of H+ ions from H2O for reduction of H2O, or generation of OH− ions from H2O for oxidation of H2O. The complementary reaction then takes place at a counter electrode in the same solution or in an alternate solution, as is standard in electrochemical processes. The product atoms or molecules, e.g., H2 or O2 for water reduction or oxidation, can then be collected as an evolved gas.
The development and demonstration of a device structure and corresponding low-cost, highly scalable fabrication process for creating a stable, high-performance metal-insulator-semiconductor photoelectrode for electrochemical reactions powered by illumination is described herein. In particular, the device structure incorporates a thick insulating layer that provides excellent stability and allows the insulating layer to serve as an antireflective coating. The device and fabrication process are compatible with the use of silicon as the semiconductor, enabling low cost and leveraging the established technological base for silicon electronics. The fabrication process does not require any lithographic or other capital-intensive processes, enabling its implementation at very low cost, and is highly scalable to large manufacturing volumes. The fabrication process also yields a spatial distribution of electrical contacts through the insulating layer that is consistent with typical carrier diffusion and scattering lengths in crystalline semiconductors, and permits adequate transmission of light across the catalyst layer and into the semiconductor.
A fundamental issue plaguing conventional semiconductor photoelectrodes is that semiconductor materials that are efficient absorbers of solar illumination, e.g., silicon, are easily corroded in the liquid environment in which solar-driven photoelectrochemical reactions typically must occur. Incorporation of a wide-bandgap electrically insulating protective layer atop the semiconductor to separate the semiconductor from the solution has been explored quite extensively as an approach to improve stability, resulting in the development of metal-insulator-semiconductor (MIS) photoelectrodes. However, metal-insulator-semiconductor photoelectrodes must contend with the challenge of providing efficient transport of photogenerated carriers across the insulator to the catalyst (typically metal) at the device-liquid interface. The most typical solution is to use an extremely thin (few nanometers or less in thickness) insulating layer to facilitate tunneling by photogenerated carriers, but thin insulating layers are extremely likely to compromise stability, particularly over the long term. The approach reported herein enables the use of thick insulating layers with only localized carrier transport paths across the oxide, and in which those localized transport paths are protected from the solution by the catalyst material atop the transport path. This thick insulating layer provides excellent stability, and is promising for very long term stability.
The devices and methods described herein combine low cost and easily scalable fabrication processes with a high performance device structure that can exhibit excellent stability compared to more conventional metal-insulator-semiconductor photoelectrode structures.
The devices and methods have been have demonstrated for oxidation of water molecules. However, the devices and methods could also be used for realization of photoelectrodes for other electrochemical reactions powered by illumination, e.g., reduction of CO2 to CO, or generation of other fuel molecules from suitable precursors via oxidation or reduction reactions.
The devices described herein can convert solar energy to a clean fuel source (H2). In addition, the devices can enable clean production of hydrogen gas (in contrast to the standard process involving steam reforming of methane) so that it can be used by chemical processing companies.
Solar powered water splitting and other photoelectrochemical reactions offer routes to the generation of hydrogen or other high-value chemicals using renewable energy sources. Commercially viable technologies for solar water splitting have been hampered by cost and the tendency of efficient solar absorbing materials, e.g., silicon or gallium arsenide, to degrade in the presence of water splitting reactions. Metal-insulator-semiconductor (MIS) photoelectrodes for solar water splitting offer a route to addressing the latter issue by covering the semiconductor with a chemically stable protective layer, but these layers are typically electrically insulating and block the flow of photogenerated electrons and/or holes to the surface of the device at which the water splitting reactions take place. The use of low-cost materials, such as silicon, combined with low-cost, scalable processes for photoelectrode fabrication offers a route to addressing the former issue. Successfully addressing these issues would provide a foundation for the development of a clean, economically viable technology for generation of hydrogen and other high-value chemicals for energy storage, transport, and chemical synthesis applications.
Described herein are device designs and fabrication processes that enable the creation of silicon-based metal-insulator-semiconductor photoelectrodes for solar water splitting with thick, extremely stable protective insulating layers, high photocurrent density, and favorable onset voltages using non-lithographic, low cost, highly scalable fabrication processes that are well established in semiconductor manufacturing.
This invention leverages established, low-cost, highly scalable silicon semiconductor process technology for fabrication of low cost, highly stable, high performance metal-insulator-semiconductor photoelectrodes for solar driven water splitting and other photoelectrochemical reactions. Photoanode devices demonstrated experimentally herein are fabricated from standard silicon wafers and incorporate thick (˜90 nm) SiO2 insulator layers and Ni-based catalysts, and with minimal optimization yield, in 1 M KOH aqueous solution under AM 1.5 G illumination from a solar simulator, photocurrent density of over 30 mA/cm2 and onset voltage of 0.7 vs. RHE.
Experimentally demonstrated photoanodes to date yield excellent stability (no discernible degradation for maximum duration tests to date, ˜168 hrs) and high performance (photocurrent density of over 30 mA/cm2 and onset voltage of 0.7 vs. RHE under AM 1.5 G illumination from a solar simulator). Fabrication processes are low cost, based on established semiconductor manufacturing technologies with no need for any lithographic patterning, and easily scalable to high volumes.
Other advantages which are obvious and which are inherent to the invention will be evident to one skilled in the art. It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of the claims. Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.
The methods of the appended claims are not limited in scope by the specific methods described herein, which are intended as illustrations of a few aspects of the claims and any methods that are functionally equivalent are intended to fall within the scope of the claims. Various modifications of the methods in addition to those shown and described herein are intended to fall within the scope of the appended claims. Further, while only certain representative method steps disclosed herein are specifically described, other combinations of the method steps also are intended to fall within the scope of the appended claims, even if not specifically recited. Thus, a combination of steps, elements, components, or constituents may be explicitly mentioned herein or less, however, other combinations of steps, elements, components, and constituents are included, even though not explicitly stated.
This application claims the benefit of priority to U.S. Provisional Application No. 63/176,628, filed Apr. 19, 2021, which is hereby incorporated herein by reference in its entirety.
This invention was made with government support under Grant Nos. CBET1702944, DMR1720595, CBET2109842, and ECCS2025227 awarded by the National Science Foundation. The government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2022/025206 | 4/18/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63176628 | Apr 2021 | US |
