There is great interest in renewable energy generation in order to replace conventional fossil fuels. This includes utilizing solar, wind, and biomass for producing fuels. Solar energy is particularly interesting because it is a fundamental renewable energy source that theoretically can be used to continuously, noiselessly, and passively generate fuels once the infrastructure to produce fuel from solar energy has been developed.
Conventionally, photovoltaic devices have been used to convert solar energy to another form of energy to electrical energy. Photovoltaic devices include one or more semiconductor materials that are capable of capturing photons from solar irradiation and converting at least a portion of their energy into electrical energy. For solar fuel production, the electrical energy generated from the solar energy is used to drive chemical reactions on a catalyst surface, where the catalyst of interest is either placed in a separate electrolyzer device or integrated with the photovoltaic assembly.
In an example, the present disclosure describes a solar fuel production assembly comprising a separation structure including an ion-conducting membrane structurally integrated with one or more solar fuel production units. The one or more solar fuel production units absorb solar energy to drive one or more redox reactions, such as one or more reduction half-reactions occurring on a first side of the separation structure to produce one or more reduction products associated with the reduction half-reaction and one or more associated oxidation half-reactions occurring on a second side of the separation structure opposite from the first side to produce one or more oxidation products associated with the associated oxidation half-reaction. The one or more reduction products are collectable from the first side of the separation structure and the one or more oxidation products are collectable from the second side of the separation structure. The ion-conducting membrane provides facile transport of ions to reduce ion transfer ohmic losses associated with the one or more redox reactions, and also provides for separation of the one or more reduction products from the one or more oxidation products.
In some examples, the one or more solar fuel production units of the solar production assembly each include a multi-junction photosynthetically active heterostructure that includes a continuous sheet-like material forming or supporting a protective structure having a plurality of cavities defining electrically insulating partitions, a plurality of independent light absorbing units, each including one or more types or regions of n-type or p-type semiconductor material, with each independent light absorbing unit being disposed entirely within one of the plurality of cavities of the protective structure such that the protective structure partially covers and protects the semiconductor material of each independent light absorbing unit from corrosion and such that each independent light absorbing unit is separated from and independent of other light absorbing units of the multi-junction photosynthetically active heterostructure, one or more cathodes electrically coupled to the independent light absorbing units, one or more anodes electrically coupled to the independent light absorbing units and electrically isolated from the one or more cathodes so that each independent light absorbing unit is autonomous from other light absorbing units, and a hydrogen permeable layer covering the one or more cathodes, wherein each anode and cathode is capped with an oxidation and reduction electrocatalyst
In order to describe the manner in which the advantages and features of the assemblies and methods described herein can be obtained. A more particular description of the subject matter briefly described above will be rendered by reference to specific embodiments thereof, which are illustrated in the appended drawings. Understanding that these drawings depict only exemplary embodiments and are not therefore to be considered as limiting of the scope of the inventions described herein, the subject matter will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:
Using solar energy to drive the electrolysis of water has become an increased area of research. Electrolysis of water involves the use of electrical energy to split water molecules into hydrogen gas (H2) and oxygen gas (O2), according to overall hydrolysis reaction [1].
2 H2O(l)→2 H2(g)+O2(g) [1]
As will be appreciated by those of skill in the art, the electrolysis of reaction [1] is made up of two half reactions—an oxidation half reaction and a reduction half reaction. The oxidation half reaction occurs at the anode and produces one or more oxidation products, such as oxygen gas (O2) and hydrogen ions (H+). The reduction half reaction occurs at the cathode and produces one or more reduction products, such as hydrogen gas (H2) and hydroxide ions (OH−). The H2 gas can be used as a clean fuel source, while the O2 gas co-product can be collected for further industrial use or simply discarded as a clean byproduct of the reaction. The overall water hydrolysis reaction [1] has a standard potential of −1.23 V, meaning that at standard temperature and pressure, reaction [1] theoretically requires an applied potential difference of 1.23 V to drive the endothermic decomposition for every two water molecules (as in the overall hydrolysis reaction [1]). However, in practical application, water electrolysis requires an additional potential difference, commonly referred to as “overpotential,” to overcome various limitations, such as activation barriers and system inefficiencies.
One common example of such a limitation in solar-powered electrolysis is ohmic losses related to the hindrance of ion diffusion that drives reaction [1] between an anode region and a cathode region of the solar fuel cell. For instance, to maintain reaction [1] in the forward direction toward the H2 and O2 co-products and minimize required overpotentials, oxidation products (i.e., H+ ions) formed at the anode are transported through an electrolyte to the cathode (e.g., where H+ ions can be reduced to form the H2 gas co-product) and/or reduction products (i.e., OH− ions) formed at the cathode are transported through the electrolyte to the anode (e.g., where the OH− ions can be oxidized to form the O2 gas co-product or water). In some instances, limits on ion transport cause a counteracting ion concentration overpotential that limits the effectiveness of the solar fuel cell and of the process that uses the fuel cell to generate H2 fuel.
Another common limitation on solar-powered electrolysis is inefficiency caused by undesirable recombination of oxidation and reduction products, i.e., reaction of H+ ions and OH− ions back into water molecules, reducing the overall efficiency of the process as well as the yield of the solar-derived fuel sought to be produced. In addition, in some examples, the solar-powered fuel cell can produce products or co-products that can produce an undesirable effect. For example, in water splitting applications, the H2 and O2 co-products can form a flammable or even explosive mixture that can pose a safety hazard.
The subject matter present disclosure is not limited to embodiments that solve any disadvantages or that operate only in environments described herein. Rather, the preceding information has been provided to illustrate an exemplary technology area where some of the embodiments and methods described herein can be practiced.
Certain embodiments described herein are directed to effective and efficient solar fuel production units for use in a solar-powered fuel production process. In particular, some embodiments described herein can be particularly effective when used in the electrolysis of water for the efficient generation of H2 fuel. One or more of the embodiments described herein are configured to separate reduction products and oxidation products in order to beneficially enhance fuel production efficiency. One or more of the embodiments described herein are configured to provide for efficient ion transport and for reduced ohmic losses associated with ion transport compared to other known systems and methods for H2 fuel generation via solar-powered electrolysis of water.
In some embodiments, a solar fuel production assembly includes a reduction compartment separated from an oxidation compartment by a planar ion exchange membrane. The ion exchange membrane includes a plurality of embedded solar fuel production units distributed across the ion exchange medium so as to provide a surface area having a mixture of ion exchange functionality and solar radiation capture functionality.
The integrated subassembly 16 is positionable within a housing to form the fuel production assembly 10. In the embodiment shown in
The housing 18 also includes at least one solar face 24A, 24B (collectively referred to as “the solar faces 24” or “the solar face 24”) that is able to transmit, or at least partially transmit, light (such as solar energy) that is irradiated onto the solar fuel production assembly 10 into the main housing chamber 20. Light transmitted through the one or more solar faces 24A, 24B can then irradiate onto the fuel production units 14 so that at least a portion of the photons in the light can be captured by the fuel production units 14 for conversion to fuel (i.e., H2 fuel), as described in more detail below. In the embodiment shown in
In some embodiments, the ion-exchange membrane 12 acts to divide the housing chamber 20 into two sub-chambers 26 and 28 (best seen in
In the embodiment best seen in
The embodiment illustrated in
In an embodiment, shown in
The integrated membrane solar fuel production assembly 10 illustrated in
In addition, the illustrated embodiment of the fuel production assembly 10 is able to achieve this beneficial separation without introducing high ohmic losses. The configuration of the assembly 10, which combines an ion exchange membrane 12 with interspersed solar fuel production units 14, beneficially enables the separate compartments 26, 28 to be functionally separate with respect to the produced co-products 30, 32, yet close in physical proximity with relatively limited ion transport distances. This is in contrast to other solar devices that separate the co-products, which require longer distances for ion transport and therefore higher ohmic losses. In short, the illustrated embodiment of the fuel production assembly 10 is capable of achieving efficient and safe separation of products with minimum loss of efficiencies.
The fuel production assembly 10 also includes one or more liquid inlets 42, 44 for the introduction of water or electrolyte, or both, to the compartments 26, 28. In the embodiment shown in
In some embodiments, the catholyte added to the reduction compartment 26 is substantially the same or even identical to the anolyte added to the oxidation compartment 28. Alternatively, the catholyte and anolyte can be selected as different electrolyte solutions, depending on the specifications for each compartment 26, 28 within the fuel production assembly 10. Exemplary electrolyte sources that may be utilized as catholyte and/or anolyte include, but are not limited to: wastewater (e.g., organic, nitrate, phosphorous, and/or sulfur rich wastewater); seawater or other brines; fresh water; carbonated water; other water source (typically, a low quality or wastewater source), or combinations thereof.
In the example embodiment shown in
In some embodiments, the fastening mechanisms 52 can also act to couple the ion-exchange membrane of the assembly to its housing, rather than only relying on clamping the ion-exchange membrane 12 between the housing sections 18A, 18B. For example, the ion-exchange membrane 58 of the example fuel production assembly 50 of
Other than these modifications to accommodate the fastening mechanisms 52, the housing sections 54A, 54B, the solar faces 56A, 56B, and the ion-exchange membrane 58, can be substantially similar or identical to the housing sections 18A, 18B, the solar faces 24A, 24B, and the ion-exchange membrane 12, respectively, of the assembly 10 described herein with respect to
Although most of the examples described herein describe oxidation and reduction products in the context of electrolysis of water, it will be understood that other reduction and/or oxidation products may additionally or alternatively be generated using one or more of the described embodiments of the assembly 10 or assembly 50, or for any of the other assemblies described herein. In some examples, the one or more solar fuel production units 14 that are integrated with an ion-exchange membrane 12, 58 to form an integrated subassembly 16 may be utilized to generate, as reduction products, ammonia, formic acid, methanol, methane, oxalic acid, metals, sodium hydroxide, formaldehyde, carbon monoxide, ethylene glycol, nitrogen, and phosphorus. In some examples, the one or more integrated membrane solar fuel production units 14 may be utilized to generate, as oxidation products, chlorine, bromine, hydrogen peroxide, oxygen, fluorine, iodine, metal oxides, and sulfides. Those having skill in the art will understand that a variety of combinations of reduction products and oxidation products may be produced according to selected process inputs (e.g., the composition of the reactant or reactants fed to the assembly 10, 50 via the one or more feed inlets 42, 44) and operational configurations.
The plurality of solar fuel production units 14 may be formed as any suitable photosensitizer capable of capturing light energy and transferring electrons to the side of the unit facing the reduction/cathodic compartment 36 so that reduction half reactions can occur. In some embodiments, the solar fuel production units 14 also include one or more suitable electrocatalysts and/or protective layers. Examples of protective layer may include, for example, any suitable electrically insulating material, including, but not limited to A1203, SiO2, ZrO, AlF3, and TiF2, ZnO, TiO2, or combinations thereof.
In some examples, an electrocatalyst layer on the side of the fuel production units 14 that act as the cathode side (i.e., that are exposed to the reduction compartment 36) may include, for example, conductors including, but not limited to: noble metals, including platinum group metals such as platinum (Pt) or precious metals including gold (Au); transition metals; transition metal oxides (e.g. NiO); metal carbides (e.g., WC); metal sulfides (e.g. MoS2); electrically-conducting carbon containing materials, such as graphite, graphene, and carbon nanotubes; or combinations thereof. In some examples, an electrocatalyst layer on the side of the fuel production units 14 that act as the anode (i.e., that are exposed to the oxidation compartment 28) may include, for example, conductors including, but not limited to: metals; metal oxides; and mixtures of, metals including Ru, Ag, V, W, Fe, Ni, Pt, Pd, Ir, Cr, Mn, Cu, Ti, and metal sulfides (e.g., MoS2); electrical conducting carbon containing materials such as graphite, graphene, and carbon nanotubes; and combinations thereof
A semiconductor absorber portion of each of the solar fuel production units 14 can include one or more types of semiconductor materials (e.g., p-type and/or n-type) to form one or more p-n junctions or one or more Schottky junctions, as is known in the art of photovoltaic devices.
Examples of suitable p-type semiconductor materials include at least one of, but are not limited to, intrinsic or p-doped SnS, ZnS, CdS, CdSe, CdTe, Cu2S, WS2, CuxO, Cu2ZnSnS4, CuInxGa1-xSe2, GaN, InP, SiC, and others selected from the classes of doped (p-type) or undoped i) elemental semiconductors including Si, and Ge, or ii) compound semiconductors including, but not limited to: metal sulfides; selenides; arsenides; nitrides; antinomides; phosphides; oxides; tellurides; and their mixtures containing respectively, sulfur (S), selenium (Se), arsenic (As), antimony (Sb), nitrogen (N), oxygen (O), tellurium (Te), and/or phosphorus (P) as one or more electronegative element(s) (designated as “A”), and one or more metals (designated as “M”) of the form MnAx where M is one or a combination of elements including but not limited to Cu, Ga, Ge, Si, Zn, Sn, W, In, Ni, Fe, Mo, Bi, Sb, Mg.
Examples of suitable n-type semiconductor materials include at least one of, but are not limited to, intrinsic or n-doped InS, CdTe, CdS, CdSe, CdTe, Cu2S, WS2, CuxO, Cu2ZnSnS4, CuInxGa1-xSe2, GaN, InP, SiC, and others selected from the classes of doped (n-type) or undoped i) elemental semiconductors including Si, and Ge, or ii) compound semiconductors including, metal sulfides, selenides, arsenides, nitrides, antinomides, phosphides, oxides, tellurides, and their mixtures containing respectively, sulfur (S), selenium (Se), arsenic (As), antimony (Sb), nitrogen (N), oxygen (O), tellurium (Te), and/or phosphorus (P) as one or more electronegative element(s) (“A”), and one or more metals (“M”), of the form MnAx where M is one or a combination of elements including but not limited to Cu, Ga, Ge, Si, Zn, Sn, W, In, Ni, Fe, Mo, Bi, Sb, Mg.
The ion-exchange membranes described herein, such as the membrane 12 or membrane 58, may be formed, for example, at least partly from one or more of the following: polyethylene oxide, polyacrylonitrile, fluorinated polymers functionalized with sulphonic acid moieties (such as Nafion™), polyethylene oxide, polyacrylonitrile, poly(ethylene-co-tetrafluoroethylene), poly(hexafluoropropylene-co-tetrafluoroethylene), poly(epichlorhydrinally glycidyl ether), poly(ether imide), poly(ethersulfone) cardo, poly(2,6-dimethyl-1,4-phenylene oxide), polysulfone, or polyethersulfone, associated with a plurality of cationic species (e.g., quaternary ammonium groups, phosphonium groups, etc.), ceramic membranes coated with appropriate functional groups, and combinations thereof. However, the ion-transport membranes described herein for use in solar fuel production assemblies are not limited to only these materials, but rather any material currently known or yet to be discovered that can provide desired transport properties for one or more specified ions and/or desired barrier properties with respect to one or more other reactants or products in the assembly 10, 50 can be used to form the membrane 12, 58.
In some examples, smaller individual fuel production units or devices may be structurally integrated within or on a corresponding larger ion-exchange membrane, as is the case with the fuel production units 14 in the membrane 12 in
The assembled housing (i.e., comprised of the assembled and coupled together housing sections 102A, 102B) defines a housing chamber 106 within the housing 102A, 102B. A subassembly 108 is at least partially housed within the housing chamber 106, wherein the subassembly 108 comprises a relatively large sheet-like solar fuel production structure 110 (referred to hereinafter as “the solar fuel production sheet 110” or simply “the fuel production sheet 110”) and a plurality of ion-exchange membranes 112 that are integrated into the fuel production sheet 110. In the examples shown in
The fuel production sheet 110 and the membranes 112 divide the housing chamber 106 into a pair of compartments 116, 118. Similar to the compartments 26 and 28 described above with respect to the fuel production assembly 10, the compartments 116 and 118 can act as a reduction compartment 116 where a reduction half-reaction occurs (i.e., where H+ ions are reduced to form an H2 fuel gas) and as an oxidation compartment 118 where an oxidation half-reaction occurs (i.e., where water molecules are oxidized to produce H+ ions and an O2 co-product gas). As is also described above, gas products (such as the H2 fuel gas and the O2 co-product gas) can be withdrawn from the compartments 116, 118 via gas outlets 120, 122, such as a reduction outlet 120 for reduction product gases (such as H2 fuel gas) and an oxidation outlet 120 for oxidation product gases (such as O2 co-product gas). the half reactions that occur in the compartments 116, 118 can be carried out in one or more electrolyte solutions (i.e., an anolyte and a catholyte), which in turn can be fed to the compartments 116, 118 via one or more inlets 124, 126, such as a catholyte inlet 124 for feeding catholyte to the reduction compartment 116 and an anolyte inlet 126 for feeding anolyte to the oxidation compartment 118.
In an example, the fuel production sheet 110 is a specialized structure that has found to be particular advantageous in electrolytically splitting water molecules via the conversion of solar energy. In these examples, the specialized structure comprises a plurality of multi-junction photosynthetically active heterostructure (PAH) units 130 (shown in the magnified inset of
In an example, the PAH fuel production sheet 110 is formed from a continuous sheet-like material that provides a support structure for the light-absorbing and fuel producing structures of the PAH units 130. In some examples, the sheet-like material of the fuel production sheet 110 forms or supports a protective structure that is porous with a plurality of small-scale pores or cavities 132 (which are, in some example micro-scale or even nano-scale cavities). The pores or cavities 132 are defined by a plurality of partitions 134, as shown in the magnified inset of
In the example shown, a PAH unit 130 is formed in each of the cavities 132 formed in the PAH sheet 110. As summarized below, the PAH units 130 are small-scale devices (and in some examples micro-scale devices or even nano-scale devices) that are configured to absorb photons from light radiation (and particularly from solar radiation) and to convert at least a portion of the energy from the absorbed photons to a form that can drive the electrolysis of water molecules in the compartments 116 and 118. In an example, at least a portion of each partition 134 acts to electrically insulate each cavity 132 from adjacent cavities 132, which in turn acts to electrically insulate the PAH unit 130 formed in each cavity from adjacent PAH units 130. In this way, each light-absorbing PAH unit 130 is separated from and independent of the other light absorbing PAH units 130 in the PAH sheet 110.
In some embodiments, each PAH unit 130 is made from a plurality of vertically stacked nanostructured semiconductors (n-type or p-type) of the same or different materials with the same or different thicknesses. In some embodiments, the PAH units 130 are electrically isolated from each other and are capped with appropriate oxidation and reduction electrocatalyst, described in more detail below. In an example, each of the PAH units 130 include one or more types or regions of n-type or p-type semiconductor material, or both, which in turn provides for the light-absorbing and converting functionality of the PAH unit 130. In the example shown, each PAH unit 130 includes a p-type semiconductor region 136 and an n-type semiconductor region 138, which are also referred to as the “p-type region 136” and the “n-type region 138” or simply as “the p-region 136 and “the n-region 138,” respectively. A non-limiting list of examples of n-type semiconductor materials and p-type semiconductor materials that can be used to form the p-type region 136 and the n-type region 138, respectively, is provided above. When the p-type region 136 and the n-type region 138 are in electrical contact without one another, they form a p-n junction 140. As will be appreciated by those of skill in the art, a p-n junction (such as the junction 140) can allow for the conversion of at least a portion of the energy from photons that are irradiated onto the semiconductor structures 136, 138 to electrical energy, which in turn can drive the electrolysis half reactions in compartments 116 and 118, described above.
In the example shown, the p-type region 136 is positioned so that it is closer to the reduction compartment 116 while the n-type region 138 is positioned so that is closer to the oxidation compartment 118. In examples of water electrolysis, those of skill in the art will appreciate that the p-type region 136 is associated with the cathode side of the reduction and oxidation half reactions such that the p-type region 136 is associated with the reduction half reaction that produces H2 gas in the reduction compartment 116. Similarly, those of skill in the art will appreciate that the n-type region 138 is associated with the anode side such that the n-type region 138 is associated with the oxidation half reaction that produces O2 gas in the oxidation compartment 118.
In the example shown in
The relative sizes of the structures of the PAH sheet 110 and the membrane 112 (i.e., of the small-scale light-absorbing and converting units 130 formed in the cavities 116) are not necessarily drawn to scale in
In some examples, each PAH unit 130 is disposed entirely or substantially entirely within one of the cavities 132 so that the supporting structure of the PAH sheet 110 at least partially covers and protects the semiconductor material (
Additional details of PAH units such as the PAH units 130 and the overall sheet-like structure in which they are incorporated, such as in the PAH sheet 110, are described in: U.S. patent application Ser. No. 13/676,901, filed on Nov. 14, 2012, which published as U.S. Patent Application Publication No. 2017/0141258 A1 on May 18, 2017, and issued as U.S. Pat. No. 9,593,053 B1 on Mar. 14, 2017; U.S. patent application Ser. No. 14/426,594, filed on Sep. 3, 2013, which published as U.S. Patent Application Publication No. 2015/0303540 A1 on Oct. 22, 2015; and U.S. patent application Ser. No. 14/659,243, filed on Mar. 16, 2015, which published as U.S. Patent Application Publication No. 2016/0076154 A1 on Mar. 17, 2016, the disclosures of which are incorporated herein by reference in their entireties. Additional examples of materials and components that may be utilized to form one or more structures or components of the solar fuel production assemblies and solar fuel production units described herein may be found in: U.S. patent application Ser. No. 10/454,009, filed on Jun. 3, 2003, which published as U.S. Patent Application Publication No. 2003/0233940 A1 on Dec. 25, 2003 and issued as U.S. Pat. No. 7,144,444 B2 on Dec. 5, 2006; U.S. patent application Ser. No. 14/111,673, filed on Apr. 12, 2012, which published as U.S. Patent Application Publication No. 2014/0127093 A1 on May 8, 2014 and issued as U.S. Pat. No. 9,186,621 B2 on Nov. 17, 2015; and U.S. patent application Ser. No. 12/576,066, filed on Oct. 8, 2009, which published as U.S. Patent Application Publication No. 2010/0133111 A1 on Jun. 3, 2010, the disclosures of which are incorporated by reference herein in their entireties.
In order to provide those of skill in the art with a better understanding of the subject matter of the present disclosure, the following non-limiting example is provided. This EXAMPLE demonstrates the improvement of ion transport in the integrated membrane solar fuel production assembly that can be achieved using the systems and methods described in the present disclosure.
A solar fuel production assembly with triple junction monolithic silicon solar cell structure with perforations (such as the example solar fuel production structure 74 with holes 76 for an ion-exchange membrane 72, as shown in
Light simulating solar light was illuminated onto both the perforated solar cell structure and the solid, non-perforated solar cell structure using a solar lamp. An O2 evolution reaction was observed on the anode side and a H2 evolution reaction was observed on the cathode side for both solar cell structures. Ohmic losses across both solar cell structures was measured using electrochemical impedance spectroscopy (Multi-channel multi-potentiostat/galvanostat/frequency response analyzer, Bio-Logic, VSP-300) and H2 product analysis (Gas Chromatograph, SRI 8610c).
The present invention may be embodied in other forms, without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.
This application claims the benefit of priority to U.S. Provisional Application Ser. No. 62/399,747, filed on Sep. 26, 2016, entitled “INTEGRATED MEMBRANE SOLAR FUEL PRODUCTION ASSEMBLY,” which application is incorporated by reference herein in its entirety.
Filing Document | Filing Date | Country | Kind |
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PCT/US2017/053408 | 9/26/2017 | WO | 00 |
Number | Date | Country | |
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62399747 | Sep 2016 | US |