Patent Application
20230132969
The present disclosure relates to ternary and quaternary iridium oxide catalyst materials for membrane electrode assemblies (MEA) for hydrogen-generating devices, a method of identifying the same, and a method of producing the same.
Hydrogen-producing devices such as fuel cells and electrolyzers are becoming increasingly popular due to their ability to produce clean energy. But cost of their individual components has remained to be a hurdle to large scale production. Due to the harsh environment of the fuel cells and electrolyzers, only a limited number of materials has been identified as suitable for production of their components such as electrodes and reaction catalysts. Most of the traditional materials include rare elements which are cost prohibitive.
In an embodiment, a catalyst for a membrane electron assembly (MEA) is disclosed. The catalyst includes a ternary oxide material having at least one composition of formula (I):
IrxM1-xO2 (I),
where
x is any number between about 0.25 and 0.75, and
the material being configured to catalyze an oxygen evolution reaction (OER) and to increase stability, activity, or both of the catalyst. The MEA may be a polymer-electron membrane (PEM) MEA. The MEA may be a fuel cell MEA. The catalyst may include a first composition and a second composition of the formula (I), the first and second compositions having different M, x values, or both. M may be Bi. x may be about 0.25 to 0.5. The catalyst may further include at most about 50 wt. % of Ir, Ru, IrO2, RuO2, or a combination thereof, based on the total weight of the catalyst. The ternary oxide material may form a nanoparticle layer on an anode of the MEA.
In another embodiment, a catalyst of a membrane electron assembly (MEA) is disclosed. The catalyst may include a quaternary oxide material having at least one composition of formula (II):
IrxBiyMzO2 (II),
where
x, y, z is each individually and independently any number between about 0.25 and 0.75, x+y+z=1, and
the material being configured to catalyze an oxygen evolution reaction (OER) and increase stability, activity, or both of the catalyst. The MEA may be a polymer-electron membrane (PEM) MEA. The MEA may be a MEA in a fuel cell stack. M may be Ce, Sb, Se, or Sn. The quaternary oxide material may include at least two different compositions of the formula (II). Each of the at least two compositions may have different constituents, but the same values of numeric subscripts. The catalyst may further include Ir, Ru, IrO2, RuO2, or a combination thereof.
In a yet another embodiment, a membrane electron assembly (MEA) is disclosed. The MEA may include an OER catalyst material having a first material including
(a) a ternary oxide material having at least one composition of formula (I):
IrxM1-xO2 (I),
where
x is any number between about 0.25 and 0.75; and
(b) a quaternary oxide material having at least one composition of formula (II):
IrxBiyMzO2 (II)
where
x, y, z is each individually and independently any number between about 0.25 and 0.75, x+y+z=1, and
the material of the formulas (I) and (II) being configured to catalyze oxygen evolution reaction (OER) and increase stability, activity, or both of the catalyst. The MEA may be a polymer-electron membrane (PEM) MEA. The MEA may be a fuel cell MEA. M in the formula (II) may be Se, Sn, Sb, or Ce. M in the formula (I) may be Bi.
Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments may take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present embodiments. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures may be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations.
Except in the examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word “about” in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred. Also, unless expressly stated to the contrary: percent, “parts of,” and ratio values are by weight; the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description, and does not necessarily preclude chemical interactions among the constituents of a mixture once mixed.
The first definition of an acronym or other abbreviation applies to all subsequent uses herein of the same abbreviation and applies mutatis mutandis to normal grammatical variations of the initially defined abbreviation. Unless expressly stated to the contrary, measurement of a property is determined by the same technique as previously or later referenced for the same property.
It must also be noted that, as used in the specification and the appended claims, the singular form “a,” “an,” and “the” comprise plural referents unless the context clearly indicates otherwise. For example, reference to a component in the singular is intended to comprise a plurality of components.
As used herein, the term “substantially,” “generally,” or “about” means that the amount or value in question may be the specific value designated or some other value in its neighborhood. Generally, the term “about” denoting a certain value is intended to denote a range within +/−5% of the value. As one example, the phrase “about 100” denotes a range of 100+/−5, i.e. the range from 95 to 105. Generally, when the term “about” is used, it can be expected that similar results or effects according to the invention can be obtained within a range of +/−5% of the indicated value. The term “substantially” may modify a value or relative characteristic disclosed or claimed in the present disclosure. In such instances, “substantially” may signify that the value or relative characteristic it modifies is within ±0%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5% or 10% of the value or relative characteristic.
It should also be appreciated that integer ranges explicitly include all intervening integers. For example, the integer range 1-10 explicitly includes 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. Similarly, the range 1 to 100 includes 1, 2, 3, 4, . . . 97, 98, 99, 100. Similarly, when any range is called for, intervening numbers that are increments of the difference between the upper limit and the lower limit divided by 10 can be taken as alternative upper or lower limits. For example, if the range is 1.1. to 2.1 the following numbers 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, and 2.0 can be selected as lower or upper limits.
In the examples set forth herein, concentrations, temperature, and reaction conditions (e.g., pressure, pH, flow rates, etc.) can be practiced with plus or minus 50 percent of the values indicated rounded to or truncated to two significant figures of the value provided in the examples. In a refinement, concentrations, temperature, and reaction conditions (e.g., pressure, pH, flow rates, etc.) can be practiced with plus or minus 30 percent of the values indicated rounded to or truncated to two significant figures of the value provided in the examples. In another refinement, concentrations, temperature, and reaction conditions (e.g., pressure, pH, flow rates, etc.) can be practiced with plus or minus 10 percent of the values indicated rounded to or truncated to two significant figures of the value provided in the examples.
For all compounds expressed as an empirical chemical formula with a plurality of letters and numeric subscripts (e.g., CH2O), values of the subscripts can be plus or minus 50 percent of the values indicated rounded to or truncated to two significant figures. For example, if CH2O is indicated, a compound of formula C(0.8-1.2)H(1.6-2.4)O(0.8-1.2). In a refinement, values of the subscripts can be plus or minus 30 percent of the values indicated rounded to or truncated to two significant figures. In still another refinement, values of the subscripts can be plus or minus 20 percent of the values indicated rounded to or truncated to two significant figures.
As used herein, the term “and/or” means that either all or only one of the elements of said group may be present. For example, “A and/or B” means “only A, or only B, or both A and B”. In the case of “only A”, the term also covers the possibility that B is absent, i.e. “only A, but not B”.
It is also to be understood that this invention is not limited to the specific embodiments and methods described below, as specific components and/or conditions may, of course, vary. Furthermore, the terminology used herein is used only for the purpose of describing particular embodiments of the present invention and is not intended to be limiting in any way.
The term “comprising” is synonymous with “including,” “having,” “containing,” or “characterized by.” These terms are inclusive and open-ended and do not exclude additional, unrecited elements or method steps.
The phrase “consisting of” excludes any element, step, or ingredient not specified in the claim. When this phrase appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole.
The phrase “consisting essentially of” limits the scope of a claim to the specified materials or steps, plus those that do not materially affect the basic and novel characteristic(s) of the claimed subject matter.
With respect to the terms “comprising,” “consisting of,” and “consisting essentially of,” where one of these three terms is used herein, the presently disclosed and claimed subject matter can include the use of either of the other two terms.
The term “one or more” means “at least one” and the term “at least one” means “one or more.” The terms “one or more” and “at least one” include “plurality” as a subset.
The description of a group or class of materials as suitable for a given purpose in connection with one or more embodiments implies that mixtures of any two or more of the members of the group or class are suitable. Description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description, and does not necessarily preclude chemical interactions among constituents of the mixture once mixed. First definition of an acronym or other abbreviation applies to all subsequent uses herein of the same abbreviation and applies mutatis mutandis to normal grammatical variations of the initially defined abbreviation. Unless expressly stated to the contrary, measurement of a property is determined by the same technique as previously or later referenced for the same property.
Fuel cells, or electrochemical cells, that convert chemical energy of a fuel (e.g. H2) and an oxidizing agent into electricity through a pair of electrochemical half (redox) reactions, have become an increasingly popular hydrogen-fuel-generating technology. Fuel cells are now a promising alternative transportation technology capable of operating without emissions of either toxins or green-house gases. One of the current limitations of wide-spread adoption of this clean and sustainable technology is related to clean production of H2 fuel.
A proton-exchange membrane fuel cell (PEMFC) represents an environment friendly alternative to internal combustion engines for a variety of vehicles such as cars and buses. A PEMFC typically features a relatively high efficiency and power density. A very attractive feature of the PEMFC engine are no carbon emissions, provided that the hydrogen fuel has been gained in an environmentally friendly manner. Besides being a green engine, the PEMFC may be used in other applications such as stationary and portable power sources.
The PEMFC technology; however, presents a number of challenges connected to its maintenance, sustainable performance over time, longevity, and production cost. For example, the PEMFC has a highly corrosive environment requiring materials capable of withstanding the challenging conditions. While focus is on the overall performance of the fuel cells, incremental improvements of individual components of the PEMFC are needed.
A non-limiting example of a PEMFC is depicted in
Different types of MEA may be incorporated, for example a proton-exchange membrane (PEM) electrolyzer stack. A PEM electrolyzer is an electrochemical device designed to convert electricity and water into hydrogen and oxygen, which may be in turn used to store energy. The PEM electrolyzer utilizes electrolysis for hydrogen production. Besides fuel cells, the PEM electrolyzer may be utilized in other applications including industrial, residential, and military applications and technologies focused on energy storage such as electrical grid stabilization from dynamic electrical sources including wind turbines, solar cells, or localized hydrogen production.
A depiction of the electrolysis principal, utilized by a PEM electrolyzer, with relevant reactions is depicted in
Different materials are used to produce the PEM electrolyzer 30. An example of the anode PTL layer material may be titanium (Ti) and the cathode PTL layer may be carbon-based materials such as carbon paper, carbon fleece, etc. The PEM 32, anode 34, and cathode 36 may be surrounded by bipolar or separator plates which may be made, for example, from Ti, or gold- or platinum-coated Ti metals.
Catalysts are typically used on the anode 34 and the cathode 36 to assist with the half-reaction processes. The typical catalyst material on the cathode 36 is platinum (Pt) while the typical catalyst used on the anode 34 is ruthenium (Ru), iridium (Ir), Ir—Ru, ruthenium oxide (RuO2), iridium oxide (IrO2), or iridium-ruthenium oxide (Ir—Ru—O) due to a combination of a relatively high activity and durability. But large-scale use and production of PEM electrolyzes, and fuel cells utilizing PEM electrolyzes, requires substantial amount of the catalyst materials, which poses a problem for the industry. Out of all PEM electrolyzer components, the anode catalyst is the most expensive constituent due to use of the rare metals Ir and/or Ru, and lack of opportunity to reduce its cost through economies-of-scale effects.
At the anode 34, Ir typically catalyzes the EOR (H2O→2H++½O2+2e−); and, at the cathode 36, Pt typically catalyzes the HER (2H++2e−→H2). The cell temperature typically ranges from 50 to 80° C. The cell voltage in the electrolyzer 30 is rather high compared to a fuel cell (greater than 1.23 V), typically ranging from 1.8 to 2.2 V vs. SHE at full load. Due to high operating voltage, the electrolyzer 30 materials may undergo further catalyst degradation (e.g., metal dissolution that can lead to the loss in electrochemically active surface area), which may affect the entire electrolyzer 30 stack system throughout its lifetime.
There are typically two important design factors for selecting the PEM electrolyzer anode 34 catalyst: 1) catalytic activity and 2) catalyst stability or durability during high voltage operation. While noble metals such as Ir, Ru, or Pt are known to be “immune” against corrosion, high voltage operation that oxidizes the surface of the metal may still trigger dissolution. For example, IrO2 is actively used for PEM electrolyzer applications which can add value in terms of catalyst stability. Adding Ru (or another transition metal like Nb) to IrO2 may increase the catalytic activity for the OER, when compared to pure IrO2 catalyst. But Ru and the transition metal may leach out in the acidic environment with elevated voltage operation. This may lead to reduced electrochemical surface area (ECSA) loss and PEM electrolyzer degradation. Due to the dissolution of these expensive catalyst materials and high cost associated with their acquirement, a large-scale production is unsustainable, costly, and impracticable.
Additionally, the same electrolysis principles described above with respect to the PME electrolyzer 30 apply to the PEMFC anode. When the fuel cell is operated under harsh operating conditions such as rapid load change or subzero start-up, fuel starvation may occur. Upon the fuel starvation at the anode, hydrogen is no longer sufficient to provide the needed protons and electrons so water electrolysis reaction and carbon corrosion may occur. The corrosion may deteriorate and compromise the anode materials. To prevent the degradation, an OER catalyst may be added to the anode to promote water electrolysis reaction over carbon corrosion.
Thus, there is a need to identify alternative materials with high activity, good stability, and strong acid tolerance at high oxidation potentials which may fully or at least partially replace Ir and Ru as catalysts at the electrolyzer anode 34 and/or at the PEMFC anode.
In one or more embodiments, a material is disclosed. The material may be a binary oxide. The material may be an OER catalyst material. The material may be a first, second, and/or third material. The material may include, comprise, consist essentially of, or consist of one or more compositions of formula (I):
IrxM1-xO2 (I),
where
x is any number between about 0.1 and 0.99, and
M is an element from the Period 4, 5, or 6 of the Periodic Table of Elements.
In formula (I), x may be any number between about 0.1 and 0.99. x may be about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, or a range including any two of the disclosed numerals. A non-limiting example of the range may be about 0.25-0.50, 0.50-0.75, or 0.25-0.75. Another non-limiting example of the range may be about 0.10-0.90, 0.20-0.80, or 0.30-0.70.
In formula (I), at least the following condition may apply: x+(1−x)=1.
In formula (I), M may be an element from Period 4 of the Periodic Table of Elements and may include Ca, Ti, Ge; Period 5 of the Periodic Table of Elements and may include Y, Zr, Nb, Mo, Rh, Pd, Ag, Sn, Sb; or Period 6 of the Periodic Table of Elements and may include Ba, La, Ce, Pr, Nd, Sm, Eu, Hf, Ta, W, Re, Os, Pt, Au, Tl, or Bi. In formula (I), M may be from Group IIA, IIIA, IVA, VA, VIA, IB, IIB, IIIB, IVB, VB, VIB, VIIB, or VIIIB. In formula (I), M may be an alkaline earth metal, coinage metal, volatile metal, icoasagen, tetrel, pentel, chalcogen, transition metal, port-transition metal, metalloid, nonmetal, or lanthanoid.
In formula (I), M may be an element selected from the group consisting of Ca, Ti, Ge, Y, Zr, Nb, Mo, Rh, Pd, Ag, Sn, Sb, Ba, La, Ce, Pr, Nd, Sm, Eu, Hf, Ta, W, Re, Os, Pt, Au, Tl, and Bi. In formula (I), M may be an element selected from the group consisting of Ag, Au, Ba, Bi, Ca, Ce, Eu, Ge, Hf, La, Nd, Os, Pd, Pr, Re, Rh, Sb, Se, Sm, Sn, Tl, and W. In formula (I), M may be an element selected from the group consisting of Bi, Ce, Sb, Se, and Sn.
Non-limiting examples of binary oxides of formula (I) may include IrxCax-1O2, IrxTix-1O2, IrxGex-1O2, IrxYx-1O2, IrxZrx-1O2, IrxNbx-1O2, IrxMox-1O2, IrxRhx-1O2, IrxPdx-1O2, IrxAgx-1O2, IrxSnx-1O2, IrxSbx-1O2, IrxBax-1O2, IrxLax-1O2, IrxCex-1O2, IrxPrx-1O2, IrxNdx-1O2, IrxSmx-1O2, IrxEux-1O2, IrxHfx-1O2, IrxTax-1O2, IrxWx-1O2, IrxRex-1O2, IrxOsx-1O2, IrxPtx-1O2, IrxAux-1O2, IrxTlx-1O2, or IrxBix-1O2,
Further non-limiting examples of binary oxides of formula (I) may include Ir0.25Ag0.75O2, Ir0.5Ag0.5O2, Ir0.75Ag0.25O2, Ir0.25Au0.75O2, Ir0.5Au0.5O2, Ir0.75Au0.25O2, Ir0.25Ba0.75O2, Ir0.5Ba0.5O2, Ir0.75Ba0.25O2, Ir0.25Bi0.75O2, Ir0.5Bi0.5O2, Ir0.75Bi0.25O2, Ir0.25Ca0.75O2, Ir0.5Ca0.5O2, Ir0.75Ca0.25O2, Ir0.25Ce0.75O2, Ir0.5Ce0.5O2, Ir0.75Ce0.25O2, Ir0.25Eu0.75O2, Ir0.5Eu0.5O2, Ir0.75Eu0.25O2, Ir0.25Ge0.75O2, Ir0.5Ge0.5O2, Ir0.75Ge0.25O2, Ir0.25Hf0.75O2, Ir0.5Hf0.5O2, Ir0.75Hf0.25O2, Ir0.25La0.75O2, Ir0.5La0.5O2, Ir0.75La0.25O2, Ir0.25Nd0.75O2, Ir0.5Nd0.5O2, Ir0.75Nd0.25O2, Ir0.25Os0.75O2, Ir0.5OS0.5O2, Ir0.75Os0.25O2, Ir0.25Pd0.75O2, Ir0.5Pd0.5O2, Ir0.75Pd0.25O2, Ir0.25Pr0.75O2, Ir0.5Pr0.5O2, Ir0.75Pr0.25O2, Ir0.25Re0.75O2, Ir0.5Re0.5O2, Ir0.75Re0.25O2, Ir0.25Rh0.75O2, Ir0.5Rh0.5O2, Ir0.75Rh0.25O2, Ir0.25Sb0.75O2, Ir0.5Sb0.52, Ir0.75Sb0.25O2, Ir0.25Se0.75O2, Ir0.5Se0.5O2, Ir0.75Se0.25O2, Ir0.25Sm0.75O2, Ir0.5Sm0.5O2, Ir0.75Sm0.25O2, Ir0.25Sn0.75O2, Ir0.5Sn0.5O2, Ir0.75Sn0.25O2, Ir0.25Tl0.75O2, Ir0.5Tl0.5O2, Ir0.75Tl0.25O2, Ir0.25W0.75O2, Ir0.5W0.5O2, or Ir0.75W0.25O2.
In one or more embodiments, another or second material may be disclosed. The material may be a ternary oxide. The material may be an OER catalyst material. The material may be a first, second, and/or third material. The material may include, comprise, consist essentially of, or consist of one or more compositions of formula (II):
IrxBiyMzO2 (II),
where
x, y, z is each individually and independently any number between about 0.1 and 0.98, x+y+z=1, and
M is an element from the Period 4, 5, or 6 of the Periodic Table of Elements.
In formula (II), x, y, and z may be each individually and independently about 0.1 and 0.99. x, y, and/or z may be about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.5, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, or a range including any two of the disclosed numerals. A non-limiting example of the range for x, y, and/or z may be about 0.10-0.90, 0.20-0.80, or 0.30-0.70. Another non-limiting example of the range for x, y, and/or z may be about 0.25-0.5, 0.5-0.75, or 0.25-0.75.
In formula (II), at least the following condition may apply: x+y+z=1.
In formula (II), M may be an element from Period 4 of the Periodic Table of Elements and may include Ca, Ti, Ge; Period 5 of the Periodic Table of Elements and may include Y Zr, Nb, Mo, Rh, Pd, Ag, Sn, Sb; or Period 6 of the Periodic Table of Elements and may include Ba, La, Ce, Pr, Nd, Sm, Eu, Hf, Ta, W, Re, Os, Pt, Au, Tl, or Bi. In formula (I), M may be from Group IIA, IIIA, IVA, VA, VIA, IB, IIB, IIIB, IVB, VB, VIB, VIIB, or VIIIB. In formula (I), M may be an alkaline earth metal, coinage metal, volatile metal, icoasagen, tetrel, pentel, chalcogen, transition metal, port-transition metal, metalloid, nonmetal, or lanthanoid.
In formula (II), M may be an element from the Period 4 of the Periodic Table of Elements and may include Se, Period 4 of the Periodic Table of Elements and may include Sb, or Period 6 of the Periodic Table of Elements and may include Ce. In formula (II), M may be an element from Group VA, VIA, or IIIB. In formula (II), M may be a chalcanoid, metalloid, metal, lanthanoid, or nonmetal.
In formula (I), M may be an element selected from the group consisting of Ca, Ti, Ge, Y, Zr, Nb, Mo, Rh, Pd, Ag, Sn, Sb, Ba, La, Ce, Pr, Nd, Sm, Eu, Hf, Ta, W, Re, Os, Pt, Au, T, and Bi. In formula (II), M may be Se, Sb, or Ce. In formula (II), M may be selected from the group consisting of Se, Sb, and Ce.
Non-limiting example ternary oxides of formula (II) may include Ir0.33Bi0.33Se0.33O2, Ir0.33Bi0.33Sn0.33O2, Ir0.33Bi0.33Sb0.33O2, Ir0.33Bi0.33Ce0.33O2, Ir0.25Bi0.25Se0.5O2, Ir0.25Bi0.5Se0.25O2, Ir0.5Bi0.25Se0.25O2, Ir0.25Bi0.25Sn0.5O2, Ir0.25Bi0.5Sn0.25O2, Ir0.5Bi0.25Sn0.25O2, Ir0.25Bi0.25Sb0.5O2, Ir0.25Bi0.5Sb0.25O2, Ir0.5Bi0.25Sb0.25O2, Ir0.25Bi0.25Ce0.5O2, Ir0.25Bi0.5Ce0.25O2, or Ir0.5Bi0.25Ce0.25O2.
In one or more embodiments, the material of formula (I) may be combined with the material of formula (II). In one or more embodiments, a MEA may include one composition, at least one composition, or more than one composition of the material of formula (I) and one composition, at least one composition, or more than one composition of the material of formula (II).
One or more oxides of the formulas (I), (II), or both may form a protective, stabilizing, and/or active layer. The material of the formulas (I), (II), or both may form an internal layer, external layer, or both with respect to adjoining, adjacent, or integral bulk region. The bulk region may be an electrode. The electrode may be an anode, cathode, or both of a MEA, PEM electrolyzer, or PEMFC. The material and/or the layer including the material may form a catalyst or be part of a catalyst. The catalyst may be a part of a MEA, PEM electrolyzer, or PEMFC electrode. The material of the formula (I), (II), or both may be used as an OER catalyst in a MEA (e.g. MEA of a PEMFC or an electrolyzer MEA), an anode OER catalyst in a PEM electrolyzer, or as an additive or OER catalyst in a PEMFC anode. Alternatively, the material of formula (I), (II), or both may be used on a PEMFC cathode.
The material may be in a form of nanoparticles. The nanoparticles may have the same or different size, diameter, dimensions, orientation, structure, facets content, composition in each layer. The loading of the oxides of the formulas (I), (II), or both may be different or the same within the layer(s). It is contemplated that more than one layer including the oxides of the formulas (I), (II), or both may be formed. The layers may have the same or different architecture, loading of individual oxides, types of oxides, size of the oxide nanoparticles, the like, or a combination thereof.
Furthermore, variation of catalyst loading levels (e.g., gradient) may be used to lead to different OER activities and current density within the catalyst material/catalyst layer/electrode/cell/stack/MEA/electrolyzer/PEMFC. In other words, homogenization of the current density may be realized by tailoring the catalyst material/catalyst layer/electrode/cell/stack/MEA/electrolyzer/PEMFC by redistributing the catalyst loading.
The material of formula (I), (II), or both may be used in addition to traditional electrolyzer catalyst material(s) such as Ir, Ru, Ir—Ru, IrO2, RuO2, Ir—Ru—O. The material of the formula (I), (II), or both may replace a portion of the traditional electrolyzer catalyst material, especially toward the bulk region of the nanoparticles. For example, about 5 to 99, 10 to 80, or 20 to 70 wt. % of the traditional electrolyzer catalyst material may be replaced with the material of the formula (I), (II), or both. For example, about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 99, 100 wt. % of the traditional electrolyzer catalyst material may be replaced with the material of the formula (I), (II), or both. In a non-limiting specific example, an OER catalyst includes about 20 to 40 wt. % of Ir, Ru, Ir—Ru, IrO2, RuO2, Ir—Ru—O, or a combination thereof, and the remainder such as about 60 to 80 wt. % of the material of the formula (I), (II), or both.
The material of choice for the OER catalyst may be tailored to a specific application. For example, a more stable oxide of the formula (I), (II), or both may be placed within the MEA stack, electrolyzer stack, or PEMFC stack in the location requiring higher stability. Alternatively, or in addition, a more active oxide of the formula (I), (II), or both may be placed within the MEA stack, electrolyzer stack, or PEMFC stack in the location requiring higher activity. The MEA, electrolyzer, or PEMFC stack may thus be designed to maximize activity and stability by using different oxides of the formula (I), (II), or both in different locations.
For example, it was discovered that Bi-containing oxide of the formula (I), (II), or both is more stable than IrO2. It was also discovered that Se-, Sb-, and Ce-containing oxides of the formula (I), (II), or both have increased activity in comparison to IrO2. Thus, an electrolyzer or PEMFC cell and/or stack may include a first material including Bi-containing oxide of the formula (I), (II), or both to increase stability and/or a second material including Se-, Sb-, and Ce-containing oxides of the formula (I), (II), or both to increase activity. The first and second material may be used to partially or entirely replace a traditional MEA material/electrolyzer material/PEMFC electrode material, the third material, or be included together with the third material.
In the MEA, electrolyzer, and/or PEMFC region(s) that experience the least degradation, the performance and cost may be optimized by selecting the material of formula (I), (II), or both, structured to deliver the highest catalytic activity. In the non-limiting example, the region(s), cell(s), layer(s), catalyst(s), or a combination thereof may incorporate the material of formula (I), (II), or both including Se, Sn, Sb, Ce, Ti, Zr, Ta, W, Nb, Mo, Re, Ru, Os, or a combination thereof.
Similarly, the material of formula (I), (II), or both that are more stable may be utilized in the MEA, electrolyzer, and/or PEMFC region(s) that lead to a fast degradation. In a non-limiting example, the region(s), cell(s), layer(s), catalyst(s), may incorporate the material of formula (I), (II), or both including Bi, Y, La, Pr, Nd, Sm, Eu, Ag, Hf; Ba, Rh, Pd, Pt, Au, Tl, or a combination thereof.
Table 1 shows oxides of formulas (I) and (II) having higher stability, higher activity, and equal activity and stability with respect to IrO2.
The material may be further arranged such that different MEA within a single stack include different disclosed species at various locations, depending on susceptibility to corrosion and desired performance (activity, stability). For example, a MEA stack may include a first material with one or more species of the material of formula (I), (II), or both in a number of first cell(s). A number of second cell(s), adjacent to the first cell(s), may include the disclosed material of formula (I), (II), or both with at least partially or completely different species/elements/M. A number of third cell(s) adjacent to the second cell(s) on the opposite side than the first cell(s) may include the material of formula (I), (II), or both with yet different species than the first and second cell(s). Alternatively, the second cell(s) may be adjacent to the first cell(s) on both sides. It is contemplated that various arrangements may be made within the MEA, PEM electrolyzer, PEMFC stack(s).
In a non-limiting example, shown in
The material of the formulas (I), (II), or both may be synthesized in the following manner. Metal containing precursors of the disclosed species may be annealed with desired stoichiometric amount in oxidizing (air or O2) or reducing heat treatment condition using N2, Ar, or H2 mixture gas. The heat treatment temperature may range from about 150 to 1500° C. to yield a desired ternary oxides or doped composition. The heat treatment time may vary from about 30 seconds to 48 hrs. The metal precursors may be prepared by solid-state synthesis route (e.g., ball milling process), co-precipitation process (e.g., solution-based process), sol-gel process, hydrothermal process, or the like. The oxide specie(s) may be deposited on to a designated support materials (carbon, metal, ceramic, etc.) during the synthesis process or as a post-treatment step. Deposition techniques may include, but are not limited to, physical vapor deposition, chemical vapor deposition, atomic layer deposition, or solution-based approach, etc.
The electrode fabrication may include the following process. The oxide or the oxide on a support (see above) may be deposited on a membrane, a decal material, or a PTL with an ink containing additional ionomer and solvent(s) using typical deposition technique, followed by drying and/or annealing steps.
To reveal the structural and morphological details of the herein-disclosed oxide materials, X-ray diffraction (XRD) technique may be used to identify crystal structure. Different crystal structures may be found: e.g., cubic, tetragonal, trigonal, orthorhombic, monoclinic, etc. It may be possible to find other XRD peaks due to impurity and/or phase decomposition. For more accurate size distribution, high-resolution transmission electron microscope (HR-TEM) imaging technique may be used.
The above-mentioned material of the formulas (I) and (II) was identified using database-driven materials screening. While typically, a surface-based slab DFT model may be used to understand thermodynamic stability, metal mixing, element segregation toward surface or bulk, OER activity, and durability, both human and CPU times are quite expensive to build DFT slab models, carry out atomistic simulation, and analyze the results. Additionally, while the DFT slab models are ideal for a simple metal or a binary oxide system such as pure Ir, Ru, IrO2, and RuO2, even modeling binary metallic catalyst such as IrxR1-x becomes very complicated due to the increased degree of freedoms in structural generation. Instead, a different approach was adopted to identify suitable material to replace the traditional electrolyzer and PEMFC electrode materials. The approach is described below in the Experimental section.
Experimental Section
In the first step, RuO2, IrO2, and PtO2 were examined against corrosive species H, H3O, OH, OOH, O, and CO. Analysis of various reaction enthalpy Erxn(eV/atom) values of the studied species in reducing and oxidizing reactions revealed tendencies of Ru and Ir compositions to lean more towards either higher activity or higher stability. For example, RuO2 typically shows enhanced OER performance—i.e., more activity than IrO2—but leads to poor stability due to corrosion from the strong acidity at the perfluorosulfonic membrane and high anodic potential at OER. On the other hand, IrO2 is a more resistive material to OER in the acidic environment, but IrO2 exhibits lower performance than RuO2. Other Ir and Ru compositions were studied. Specific reaction parameters which reveal tendencies of materials to be more active (like RuO2) or more stable (like IrO2) were identified. The relevant reaction parameters were then studied with respect to 56 elements of the Periodic Table: Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Ni, Co, Cu, Zn, Ga, Ge, Se, Rb, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Sb, Te, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Pt, Au, Tl, and Bi.
The “interface reactions” module kit, publicly available from materialsproject.org was used. The decomposition products of Ir0.75M0.25O2, where M represented each element named above, was conducted. The loading of Ir was chosen to be higher than loading of M. Because PEM electrolyzer operates in acidic conditions, the decomposition products of the studied material should be “acid stable.” Decomposition products of each studied element were identified, and stable compositions determined. The Ir0.75M0.25O2 compositions with stable decomposition products included M=Ca, Ti, Ge, Se, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, Ba, La, Ce, Pr, Nd, Sm, Eu, Hf, Ta, W, Re, Os, Pt, Au, Tl, and Bi.
Next, the thermodynamic decomposition of Ir0.75Mo25O2 at its given chemical space was studied. For example, Ir0.75Ru0.25O0.2 tends to thermodynamically decompose to 0.75 IrO2 and 0.25 RuO2, where both oxides belong to a tetragonal crystal system (P42/mnm). But Ir0.75Pt0.25O2 thermodynamically decomposes to 0.75 IrO2 and 0.25 PtO2. PtO2 belongs to orthorhombic crystal system (Pnnm). Each phase mixture was examined to evaluate whether the decomposition products are tetragonal or non-tetragonal structures. Percentage of non-tetragonal phase in all phase mixtures was determined, and penalty points (PP) based on this value were assigned to non-tetragonal structures. Table 2 summarizes the thermodynamic decomposition reactions for Ir0.75M0.25O0.2 and their assigned penalty points (PPdcmp).
Generally, noble metals are immune in the acidic region, and there are metals that passivate (e.g., TiO2) which are also stable in the acidic regions. Some metals that are known to be not stable in the acid (e.g., Ca) when decomposition product is not a pure metal or a binary oxide but forms a ternary oxide (e.g., CaIrO3) were included.
Further analysis included testing of chemical reactivity of each oxide system in oxidizing conditions (against OH, OOH, 0), reducing conditions (against H and H3O), and CO poisoning or carbon corrosion at high potential: CO+H2O→H2+CO2.
For studying these reactions, each ternary oxide was tested during the most thermodynamically stable reaction pathway (i.e., at its minimum reaction enthalpy in 2D phase space between ternary oxide catalyst phase and H, H3O, OH, OOH, O, and CO). IrO2 catalyst was chosen as a reference material to evaluate each Ir0.75M0.25O2 phase. A phase diagram between H3O (representative oxidizing agent: H2O+H) and IrO2 PEM electrolyzer catalyst was generated. The phase diagram is shown in
The most thermodynamically stable reaction (at minimum Erxn) for each studied Ir0.75M0.25O2 ternary oxide catalyst phase was determined and compared to IrO2. Evaluating such reactions against H, H3O, OH, OOH, O, and CO (also called the PEM electrolyzer species) accounts for situations, where both PEM electrolyzer species and potential catalyst materials are abundantly present, where decomposition reactions may proceed at the minimum reaction enthalpy (i.e., the most favorable condition). By evaluating these reactions, the following information was obtained: (1) the amount of species (H, H3O, OH, OOH, O, and CO) each ternary oxide catalyst is capable of consuming at its thermodynamic equilibrium and (2) how favorable is the most stable decomposition reaction (i.e., what is the magnitude of Erxn,min).
Tables 3 and 4 summarize the H and H3O reactions respectively for Ir0.75M0.25O2. For Tables 3 and 4, when molar ratio is different between H/oxide, normalization to H/oxide of IrO2, which is 2, was made. For example, Ba0.25Ir0.75O2 in Table 3 shows lower H/oxide value (1.75) when compared to IrO2. Normalization of H/oxide=2 for Ba0.25Ir0.75O2 further increases the Erxn to a higher value. A higher H or H3O/oxide ratio indicates that an OER catalyst can take more PEM electrolyzer species per mol. It was discovered that in the reducing conditions, a lower H or H3O/oxide ratio and increased Erxn,H values indicate more active OER catalyst (RuO2-like) and a higher H or H3O/oxide ratio and lower Erxn,H values indicate more stable OER catalyst (IrO2-like).
Tables 5, 6, and 7 summarize Ir-M-O chemical reactivity with OH, OOH, and O at its most stable thermodynamic reaction between the OER catalyst and the PEM electrolyzer species. In Tables 5, 6, and 7, when molar ratio is different between the oxidizing agent and the catalyst, normalization to 2 was made. For example, the ratio between OH and IrO2 in Table 5 is 2—i.e., 0.667 OH (or, 0.333 H2O2) per 0.333 IrO2. Ir0.75NB0.25O2 in Table 5 shows lower OH/oxide value (1.75) when compared to IrO2. Normalization of OH/oxide to 2 for Ir0.75Nb0.25O2 increases the Erxn to become a higher value. A higher OH, OOH, or O/oxide ratio indicates that an OER catalyst can take more PEM electrolyzer species per mol. In the oxidizing conditions, the goal was to identify a higher amount of OH, OOH, or O per oxide, meaning, the OER catalyst is capable of absorbing more PEM electrolyzer species per mol. It was discovered that in the oxidizing conditions, a higher OH, OOH, or O/oxide ratio and lower Erxn,H values indicate more active OER catalyst (RuO2-like) and a lower OH, OOH, or O/oxide ratio and higher Erxn,H values indicate more stable OER catalyst (IrO2-like).
To study the CO poisoning or corrosion, chemical reactivity was studied against CO. CO reactions follow the same trend as reducing conditions i.e., H and H3O reactions above.
The results of the (a) thermodynamic decomposition analysis (i.e., tetragonal vs. non-tetragonal phase decomposition) and (b) data from the Tables 3-8 (chemical reactions against H, H3O, OH, OOH, O, and CO) are shown in
Similar screening process and analysis were repeated for an increased concentration of M and reduced amount of Ir for the S-tier 1, S-tier 2, A-tier 1, and C-tier 1 species from Tables 9-11: Ir0.5M0.5O2 and Ir0.25M0.75O2, respectively.
From thermodynamic decomposition analysis, it was found that Ca and Y formed CaO and Y2O3 unstable in the acidic condition. In addition, Eu was eliminated from further screening due to O2 gas release during thermodynamic decomposition.
The described research revealed the overall capabilities of the following studied species, captured in Table 13.
Based on the findings summarized in Table 13, various compositions of Ir—Bi-M-O material, where M=Se, Sn, Sb, and Ce were analyzed. The quaternary system may supply the stability-increasing Bi in combination with an activity-enhancing element and cost savings due to the use of less expensive elements than Ir. Comparison of Ir0.33Bi0.33M0.33O2 composition with Ir0.25Bi0.25M0.5O2 shows that as concentration of Se, Sn, Sb, and Ce increases, the material becomes more active. When the amount of Bi increases in Ir0.33Bi0.33M0.33O2 to Ir0.25Bi0.5M0.25O2, the corresponding material is predicted to become more stable. The results are summarized in Table 14 below.
In the plot of
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes can include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, to the extent any embodiments are described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics, these embodiments are not outside the scope of the disclosure and can be desirable for particular applications.
