Patent Application
20220407086
The present disclosure relates to anode catalyst materials for electrochemical cells, for example, anode catalyst materials for fuel cells or electrolyzers.
An electrochemical cell is a device capable of either generating electrical energy from chemical reactions (e.g. fuel cells) or using electrical energy to conduct chemical reactions (e.g. electrolyzers). Fuel cells have shown promise as an alternative power source for vehicles and other transportation applications. Fuel cells operate with a renewable energy carrier, such as hydrogen. Fuel cells also operate without toxic emissions or greenhouse gases. One of the current limitations of widespread adoption and use of this clean and sustainable technology is the relatively expensive cost of the fuel cell. A catalyst material (e.g. platinum catalyst) is included in both the anode and cathode catalyst layers of a fuel cell. The catalyst material is one of the most expensive components in the fuel cell.
Electrolyzers undergo an electrolysis process to split water into hydrogen and oxygen, providing a promising method for hydrogen generation from renewable resources. An electrolyzer, like a fuel cell, includes an anode and cathode catalyst layers separated by an electrolyte membrane. The electrolyte membrane may be a polymer, an alkaline solution, or a solid ceramic material. A catalyst material is included in the anode and cathode catalyst layers of the electrolyzer.
According to one embodiment, an anode catalyst layer of an electrochemical cell is disclosed. The anode catalyst layer of the electrochemical cell may include an anode catalyst material. The anode catalyst material may be a Pt-based alloy. The Pt-based alloy may be a binary Pt-M alloy, where M may be Ge, Se, Ag, Sb, Os, or Tl.
According to another embodiment, an anode catalyst layer of an electrochemical cell is disclosed. The anode catalyst layer of the electrochemical cell may include an anode catalyst material. The anode catalyst material may be a Pt-based alloy. The Pt-based alloy may be a ternary Pt-MI-MII alloy, where MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd.
According to yet another embodiment, an electrochemical cell is disclosed. The electrochemical cell may include an anode catalyst layer having an anode catalyst material. The anode catalyst material may be a Pt-based alloy. The Pt-based alloy may be a binary Pt-M alloy, where M is Ge, Se, Ag, Sb, Os or Tl. The Pt-based alloy may be a ternary Pt-MI-MII alloy, where MI is Ru, Ge, or Mo, and MII is Ir, Os, Tl, Au, Bi, Se, or Pd. The electrochemical cell may further include a cathode catalyst layer. The electrochemical cell may also include an electrolyte membrane situated between the anode and cathode catalyst layers.
Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of 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 embodiments. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can 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 applications or implementations.
This present disclosure 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 embodiments of the present disclosure and is not intended to be limiting in any way.
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.
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.
Except where expressly indicated, all numerical quantities in this description indicating dimensions or material properties are to be understood as modified by the word “about” in describing the broadest scope of the present disclosure.
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.
The term “substantially” may be used herein to describe disclosed or claimed embodiments. The term “substantially” may modify any value or relative characteristic disclosed or claimed in the present disclosure. “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.
Reference is being made in detail to compositions, embodiments, and methods of embodiments known to the inventors. However, disclosed embodiments are merely exemplary of the present disclosure which may be embodied in various and alternative forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, rather merely as representative bases for teaching one skilled in the art to variously employ the present disclosure.
Electrochemical cells show great potential as an alternative solution for energy production and consumption. For instance, fuel cells are being developed as electrical power sources for automobile applications, and electrolyzers are being used for hydrogen production from renewal resources (e.g. water). However, widespread adoption of the electrochemical cells requires further research into lifetime and cost reduction for components used in the electrochemical cells. These components include an electrolyte membrane and catalyst layers separated by the electrolyte membrane.
A typical single polymer electrolyte membrane (PEM) fuel cell is composed of a PEM, an anode layer, a cathode layer, and gas diffusion layers (GDLs). These components form a membrane electrode assembly (MEA), which is surrounded by two flow field plates. A catalyst material, such as platinum (Pt) catalysts, is included in the anode and cathode layers of the PEM fuel cell. At the anode layer, Pt catalysts catalyze a hydrogen oxidation reaction (HOR, H2→2H++2e−), where H2 is oxidized to generate electrons and protons (H+). At the cathode layer, Pt catalysts catalyze an oxygen reduction reaction (ORR, ½O2+2H++2e−→H2O), where O2 reacts with H+ and is reduced to form water.
Due to dynamic changes of operational conditions in the PEM fuel cell, Pt catalysts may be subject to various degradations, including dissolution, migration, and re-deposition. In addition, because the kinetics of an ORR is significantly slower than that of an HOR, a higher loading of Pt catalysts is required at the cathode layer than the anode layer. Further, the sizes of Pt catalysts may grow during a normal operation of the PEM fuel cell. The growth of the Pt catalysts may cause a loss of an electrochemical surface area (ECSA), which adversely affects the HOR and/or ORR and leads to the degradation of the PEM fuel cell.
Global H2 fuel starvation may occur, especially at the anode layer of the PEM fuel cell. The occurrence of H2 fuel starvation may substantially impact the performance of the PEM fuel cell. Specifically, due to a lack of H2 fuel, an oxygen evolution reaction (OER, 2H2O→O2+4H++4e), i.e., water electrolysis, may occur at 1.23 V vs. standard hydrogen electrode (SHE) at the anode layer. A carbon oxidation reaction (COR, C+2H2O→CO2+4 H++4e−) may also take place at 0.21 V vs. SHE at the anode layer. For a normal fuel cell operation, i.e., when there is no H2 fuel starvation, a cathode voltage at the cathode layer is normally higher than the anode voltage at the anode layer, as the HOR takes place at 0.00 V vs. SHE. A cell terminal voltage between the cathode and anode voltages is normally above 0.00 V. However, when H2 fuel starvation occurs, the OER and/or COR increases the anode voltage at the anode layer, causing the cell terminal voltage to decrease, i.e., causing cell voltage reversal. For example, the cell terminal voltage may drop below −2.00 V. In addition, the COR may lead to carbon corrosion at the anode layer. The occurrence of cell voltage reversal may also generate a significant amount of waste heat, which further damages the MEA and accelerates the degradation of the PEM fuel cell.
To alleviate or prevent cell voltage reversal due to H2 fuel starvation, metal elements such as ruthenium (Ru) or iridium (Ir), as well as their metal oxides such as RuO2 or IrO2, may be added to the anode layer of the PEM fuel cell. The incorporation of Ru and/or Ir element may help reduce carbon corrosion at the anode layer during H2 fuel starvation. For instance, a voltage of about 0.6 to 0.7 V is typically required to fully recover Pt surfaces from catalyst poisoning (i.e., to oxidize CO to CO2 gas). However, due to the presence of Ru, about 0.35 V is required to fully recover Pt—Ru surfaces from catalyst poisoning. Furthermore, some Ir-based intermetallic compounds, such as IrRu4Y0.5 or IrRu4, may also be added to the anode layer to prevent carbon corrosion and/or water hydrolysis during H2 fuel starvation. However, because these metals and metal oxides are relatively expensive, using them in the anode layer undesirably increase the total cost of the PEM fuel cell.
Therefore, there is a need for an electrochemical cell anode catalyst material that is not only relatively low-cost but comparatively effective as adding Ru and/or Ir element to the anode layer to prevent cell voltage reversal during H2 fuel starvation. Aspects of the present disclosure are directed to anode catalyst materials for electrochemical cells, for example, anode catalyst materials for fuel cells or electrolyzers. The anode catalyst material may be a Pt-based alloy. In one embodiment, the Pt-based alloy may be a binary Pt-M alloy, where M may be Ge, Se, Ag, Sb, Os, or Tl. In another embodiment, the Pt-based alloy may be a ternary Pt-MI-MII alloy, where MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd.
In addition, a first side 24 of the MEA 22 is bound by an anode flow field plate 28, and the second side 26 of the MEA 22 is bounded by a cathode flow field plate 30. The anode flow field plate 28 includes an anode flow field 32 configured to distribute H2 to the MEA 22. The cathode flow field plate 30 includes a cathode flow field 34 configured to distribute O2 to the MEA 22.
The processor 52 may be configured to read into memory and execute computer-executable instructions residing in a DFT software module 58 of the non-volatile storage 56 and embodying DFT slab model algorithms, calculations and/or methodologies of one or more embodiments. The DFT software module 58 may include operating systems and applications. The DFT software module 58 may be compiled or interpreted from computer programs created using a variety of programming languages and/or technologies, including, without limitation, and either alone or in combination, Java, C, C++, C#, Objective C, Fortran, Pascal, Java Script, Python, Perl, and PL/SQL.
Upon execution by the processor 52, the computer-executable instructions of the DFT software module 58 may cause the computing platform 50 to implement one or more of the DFT algorithms and/or methodologies disclosed herein. The non-volatile storage 56 may also include DFT data 60 supporting the functions, features, calculations, and processes of the one or more embodiments described herein.
The program code embodying the algorithms and/or methodologies described herein is capable of being individually or collectively distributed as a program product in a variety of different forms. The program code may be distributed using a computer readable storage medium having computer readable program instructions thereon for causing a processor to carry out aspects of one or more embodiments. The computer readable storage medium, which is inherently non-transitory, may include volatile and non-volatile, and removable and non-removable tangible media implemented in any method or technology for storage of information, such as computer-readable instructions, data structures, program modules, or other data. The computer readable storage media may further include RAM, ROM, erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other solid state memory technology, portable compact disc read-only memory (CD-ROM), or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and which can be read by a computer. Computer readable program instructions may be downloaded to a computer, another type of programmable data processing apparatus, or another device from a computer readable storage medium or to an external computer or external storage device via a network.
Computer readable program instructions stored in the computer readable medium may be used to direct a computer, other types of programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions that implement the functions, acts, and/or operations specified in the flowcharts or diagrams. In certain alternative embodiments, the functions, acts, and/or operations specified in the flowcharts and diagrams may be re-ordered, processed serially, and/or processed concurrently consistent with one or more embodiments. Moreover, any of the flowcharts and/or diagrams may include more or fewer nodes or blocks than those illustrated consistent with one or more embodiments.
Referring to
Table 1 depicts information of reactions between Pt and O2, H2O2, or OOH, respectively, under similar reaction conditions. Table 1 provides a reaction equation and a reaction enthalpy (E, eV/atom) for each reaction.
Table 2 depicts information of reactions between Ir and O2, H2O2, or OOH, respectively, under similar reaction conditions. Table 2 provides a reaction equation and a reaction enthalpy (E, eV/atom) for each reaction.
Table 3 depicts information of reactions between Ru and O2, H2O2, or OOH, respectively, under similar reaction conditions. Table 3 provides a reaction equation and a reaction enthalpy (E, eV/atom) for each reaction.
In view of Tables 1 to 3, the reactions between Ir and O2, H2O2, or OOH appear to be more favorable than the reactions between Pt and O2, H2O2, or OOH, respectively. Further, the reactions between Ru and O2, H2O2, or OOH appear to be more favorable than the reactions between Ir and O2, H2O2, or OOH, respectively, and thus more favorable than the reactions between Pt and O2, H2O2, or OOH, respectively. This indicates that when using either Ir or Ru alone as an anode catalyst in the anode layer of an electrochemical cell, the anode catalyst may be less stable than using Pt alone as the anode catalyst. Using either Ir or Ru alone as the anode catalyst in the anode layer may not help prevent cell voltage reversal during H2 fuel starvation.
Table 4 depicts information of reactions between Pt0.75Ir0.25 and O2, H2O2, or OOH, respectively, under similar reaction conditions. Table 4 provides a reaction equation and a reaction enthalpy (E, eV/atom) for each reaction.
Table 5 depicts information of reactions between Pt0.75Ru0.25 and O2, H2O2, or OOH, respectively, under similar reaction conditions. Table 5 provides a reaction equation and a reaction enthalpy (E, eV/atom) for each reaction.
In view of Tables 2 and 4, the reactions between Pt0.75Ir0.25 and O2, H2O2, or OOH appears to be less favorable than the reactions between Ir and O2, H2O2, or OOH, respectively. This suggests that adding Ir to Pt, thereby forming a Pt—Ir alloy, may help increase the stability of the anode catalyst as compared to using Ir alone as the anode catalyst in the anode layer of the electrochemical cell.
Similarly, in view of Tables 3 and 5, the reactions between Pt0.75Ru0.25 and O2, H2O2, or OOH appear to be less favorable than the reactions between Ru and O2, H2O2, or OOH, respectively. Adding Ru to Pt, thereby forming a Pt—Ru alloy, may also help increase the stability of the anode catalyst as compared to using Ru alone as the anode catalyst in the anode layer of the PEM fuel cell.
Further, when comparing the chemical reactivities of Pt0.75Ir0.25 and Pt0.75Ru0.25 in Tables 4 and 5, Pt0.75Ir0.25 appears to be less chemically reactive against O2, H2O2, or OOH than Pt0.75Ru0.25. This further indicates that Pt0.75Ir0.25 may be more suitable than Pt0.75Ru0.25 to be used as an electrochemical cell anode catalyst material to prevent cell voltage reversal during H2 fuel starvation.
Apart from Pt—Ir and Pt—Ru alloys, other metal elements M, such as palladium (Pd) or cerium (Ce), may be mixed with Pt to form Pt-M alloys. Table 6 depicts information of reactions between Pt0.75Pd0.25 and O2, H2O2, or OOH, respectively, under similar reaction conditions. Table 6 provides a reaction equation and a reaction enthalpy (E, eV/atom) for each reaction.
Table 7 depicts information of reactions between Pt0.75Ce0.25 and O2, H2O2, or OOH, respectively, under similar reaction conditions. Table 7 provides a reaction equation and a reaction enthalpy (E, eV/atom) for each reaction.
In view of Tables 6 and 7, the reactions between Pt0.75Pd0.25 and O2, H2O2, or OOH appear to be less favorable than the reactions between Pt0.75Ce0.25 and O2, H2O2, or OOH, respectively. This indicates that Pt0.75Pd0.25 may be more stable than Pt0.75Ce0.25 in an oxidizing environment. In other words, adding Pd to Pt, thereby forming a Pt—Pd alloy, may help increase the stability of the anode catalyst as compared to adding the same amount of Ce to Pt to form a Pt—Ce alloy.
Further, when comparing the chemical reactivities of Pt0.75Pd0.25 and Pt0.75Ir0.25 in Tables 4 and 6, Pt0.75Pd0.25 appears to be less chemically reactive against O2, H2O2, or OOH than Pt0.75Ir0.25. This further indicates that Pt0.75Pd0.25 may be more suitable than Pt0.75Ir0.25 to be used as a fuel cell anode catalyst material to prevent cell voltage reversal during H2 fuel starvation.
To further examine the chemical reactivity of a Pt-M alloy against O2, H2O2, or OOH, the data-driven materials screening method may be utilized to identify other Pt-M alloys that are suitable to be used as electrochemical cell anode catalyst materials to prevent cell voltage reversal during H2 fuel starvation. In addition to Ru, Ir, Pd, and Ce, M may also be, for example, titanium (Ti), germanium (Ge), selenium (Se), zirconium (Zr), niobium (Nb), molybdenum (Mo), rhodium (Rh), silver (Ag), tin (Sn), antimony (Sb), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), gold (Au), thallium (Tl), or bismuth (Bi).
Table 8 depicts information of thermodynamic decomposition products of a Pt-M alloy, where M may be Ti, Ge, Se, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, Ce, Hf, Ta, W, Re, Os, Ir, Au, Tl, or Bi. Each Pt-M alloy in Table 8 shows a ratio of Pt to M as 2, i.e., Pt0.67M0.33. Pt0.67M0.33 may also be represented as PtxMy, where x=2y, x>0, and M may be Ti, Ge, Se, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, Ce, Hf, Ta, W, Re, Os, Ir, Au, Tl, or Bi. Noted that Pt-M alloys having ratios of Pt to M other than 2 may similarly be evaluated using the method described herein. For instance, in some other embodiments, the data-driven materials screening method may be utilized to evaluate Pt-M alloys, such as Pt0.95M0.05 or Pt0.5M0.5, where M may be Ti, Ge, Se, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, Ce, Hf, Ta, W, Re, Os, Ir, Au, Tl, or Bi, to identify those suitable to be used as electrochemical cell anode catalyst materials to prevent cell voltage reversal during H2 fuel starvation.
Table 8 provides a thermodynamic decomposition reaction of each Pt-M alloy. The thermodynamic decomposition products of each reaction are obtained using “interface reactions” module kit available on materialsproject.org. Among the thermodynamic decomposition products of each reaction, some are cubic phases, and some are non-cubic phases. A percentage of the non-cubic phases of the thermodynamic decomposition products for each reaction may be calculated. For example, the thermodynamic decomposition products of Pt0.67Ru0.33 may be 0.67 Pt and 0.33 Ru, where Pt belongs to a cubic crystal system (Fm-3m), and Ru belongs to a hexagonal crystal system (P63/mmc). Therefore, the percentage of the non-cubic phases of the thermodynamic decomposition products for Pt0.67Ru0.33 is calculated as 0.33/(0.67+0.33), which is about 0.33. Table 8 further provides a penalty point (PP1) to indicate the percentage of the non-cubic phases of the thermodynamic decomposition products for each reaction. For easy comparison, a PP1 of 0 is assigned to the scenario where 100% of the thermodynamic decomposition products are cubic phases. As such, the PP1 for Pt0.67Ru0.33 is 0.330.
To determine the percentage of cubic or non-cubic phases in the thermodynamic decomposition products of an alloy, such as a Pt-based alloy, X-ray diffraction (XRD) techniques may be employed. Particularly, an XRD pattern of a cubic phase may show strong signature peaks at (111), (110), and/or (100), representing face-centered cubic (fcc) characters. On the other hand, an XRD pattern of a non-cubic phase may show small impurity peaks, which can be differentiated from the signature peaks for cubic phases. In addition, the XRD techniques may be used to determine an average crystallite size of a Pt-based alloy nanoparticle. A size distribution of the Pt-based alloy nanoparticles may be determined using high-resolution transmission electron microscope (HR-TEM) imaging techniques. An average size of a Pt-based alloy nanoparticle may be in a range of 1 and 20 nm, or alternatively, between 3 and 10 nm.
In addition to the composition of the Pt-based alloy, the properties of the Pt-based alloy may also vary depending on its microstructure, morphology, and/or crystallinity. A lattice mismatch between the thermodynamic decomposition products of the Pt-based alloy may impact a local structure and/or electronic structure of the alloy. When the Pt-based alloy nanoparticles are de-alloyed near a surface, a lattice constant in a bulk region may decrease, thereby leading to a compressive strain at an outer Pt surface. In general, such an effect may increase the catalyst activity. Further, introducing tensile strain and/or increasing lattice constants may enhance the durability of the Pt-based alloy.
0.509OOH+0.491Ru0.33Pt0.67→0.11Pt3O4+0.162RuO2+0.254H2O (1)
According to Reaction (1), after reacting with 0.509 OOH, Pt0.67Ru0.33 is turned into 0.11 Pt3O4 and 0.162 RuO2.
Using the same evaluation method as described in
Table 9 also provides a reaction enthalpy (E, eV/atom) of the most stable decomposition reaction between each Pt0.67M0.33 and OOH. Table 9 further provides a penalty point (e.g. PP3) regarding the reaction enthalpy, where PP3 of 1.000 is assigned to the reference reaction between OOH and Pt0.67Ru0.33 (i.e. −0.672 eV/atom). PP3 is calculated by dividing the reaction enthalpy between OOH and each Pt0.67M0.33 of each reaction by that between OOH and Pt0.67Ru0.33. For example, since the reaction enthalpy of the reaction between OOH and Pt0.67Ti0.33 is −1.107 eV/atom, PP3 thus equals −1.107/−0.672, which is about 1.647.
If both the molar fraction between OOH and Pt0.67M0.33, and the reaction enthalpy of the reaction between OOH and Pt0.67M0.33 are greater than those for Pt0.67Ru0.33, it may indicate that the Pt0.67M0.33 is more stable than Pt0.67Ru0.33, and thus, more suitable to be used as an electrochemical cell anode catalyst material to prevent cell voltage reversal during H2 fuel starvation. For example, because the molar fraction between OOH and Pt0.67Pd0.33 (i.e. 1.114) and the reaction enthalpy of the most stable decomposition reaction between OOH and Pt0.67Pd0.33 (i.e., −0.548 eV/atom) are both greater than those for Pt0.67Ru0.33, Pt0.67Pd0.33 may therefore be more stable than Pt0.67Ru0.33, consistent with the observation in Tables 5 and 6. For another example, because the molar fraction between OOH and Pt0.67Ce0.33 (i.e. 0.441) and the reaction enthalpy of the most stable decomposition reaction between OOH and Pt0.67Ce0.33 (i.e., −1.241 eV/atom) are both less than those for Pt0.67Ru0.33, Pt0.67Ce0.33 may therefore be less stable than Pt0.67Ru0.33, consistent with the observation in Tables 6 and 7.
Table 10 depicts information of the most stable decomposition reaction between each Pt0.67M0.33 and H2O2. Particularly, Table 10 provides a reaction equation of the most stable decomposition reaction between each Pt0.67M0.33 and H2O2. Table 10 also provides a molar fraction between H2O2 and each Pt0.67M0.33 for each reaction. Information of the most stable decomposition reaction between Pt0.67Ru0.33 and H2O2 is used as a reference for comparison. Table 10 further provides a penalty point (e.g. PP4) regarding the molar fraction, where PP4 of 1.000 is assigned to the reference reaction between H2O2 and Pt0.67Ru0.33 (i.e. the molar fraction is 1.320). PP4 is calculated by dividing the molar fraction between H2O2 and Pt0.67Ru0.33 by the molar fraction between H2O2 and each Pt0.67M0.33 of each reaction. For example, since the molar fraction between H2O2 and Pt0.67Ti0.33 is 1.320, PP4 thus equals 1.320/1.320, which is about 1.000.
Table 10 also provides a reaction enthalpy (E, eV/atom) of the most stable decomposition reaction between each Pt0.67M0.33 and H2O2. Table 10 further provides a penalty point (e.g. PP5) regarding the reaction enthalpy, where PP5 of 1.000 is assigned to the reference reaction between H2O2 and Pt0.67Ru0.33 (i.e. −0.459 eV/atom). PP5 is calculated by dividing the reaction enthalpy between H2O2 and each Pt0.67M0.33 of each reaction by that between H2O2 and Pt0.67Ru0.33. For example, since the reaction enthalpy of the reaction between H2O2 and Pt0.67Ti0.33 is −0.765 eV/atom, PP5 thus equals −0.765/−0.459, which is about 1.667.
If both the molar fraction between H2O2 and Pt0.67M0.33, and the reaction enthalpy of the reaction between H2O2 and Pt0.67M0.33 are greater than those for Pt0.67Ru0.33, it may indicate that the Pt0.67M0.33 is more stable than Pt0.67Ru0.33. Otherwise, Pt0.67M0.33 may be less stable than Pt0.67Ru0.33.
Table 11 depicts information of the most stable decomposition reaction between each Pt0.67M0.33 and O2. Table 11 provides a reaction equation of the most stable decomposition reaction between each Pt0.67M0.33 and O2. Table 11 also provides a molar fraction between O2 and each Pt0.67M0.33 for each reaction. Information of the most stable decomposition reaction between Pt0.67Ru0.33 and O2 is used as a reference for comparison. Table 11 further provides a penalty point (e.g. PP6) regarding the molar fraction, where PP6 of 1.000 is assigned to the reference reaction between O2 and Pt0.67Ru0.33 (i.e. the molar fraction is 1.000). PP6 is calculated by dividing the molar fraction between O2 and Pt0.67Ru0.33 by the molar fraction between O2 and each Pt0.67M0.33 of each reaction. For example, since the molar fraction between O2 and Pt0.67Ti0.33 is 0.331, PP6 thus equals 1.000/0.331, which is about 3.030.
Table 11 also provides a reaction enthalpy (E, eV/atom) of the most stable decomposition reaction between each Pt0.67M0.33 and O2. Table 11 further provides a penalty point (e.g. PP7) regarding the reaction enthalpy, where PP7 of 1.000 is assigned to the reference reaction between O2 and Pt0.67Ru0.33 (i.e. −1.112 eV/atom). PP7 is calculated by dividing the reaction enthalpy between O2 and each Pt0.67M0.33 of each reaction by that between O2 and Pt0.67Ru0.33. For example, since the reaction enthalpy of the reaction between O2 and Pt0.67Ti0.33 is −1.584 eV/atom, PP7 thus equals −1.584/−1.112, which is about 1.392.
If both the molar fraction between O2 and Pt0.67M0.33, and the reaction enthalpy of the reaction between O2 and Pt0.67M0.33 are greater than those for Pt0.67Ru0.33, it may indicate that the Pt0.67M0.33 may be more stable than Pt0.67Ru0.33. Otherwise, Pt0.67M0.33 may be less stable than Pt0.67Ru0.33.
Based on the information provided in Tables 8 to 11, a sum of the penalty points (ΣPP) is calculated for each Pt0.67M0.33, i.e., ΣPP=PP1+PP2+PP3+PP4+PP5+PP6+PP7. The sum of the penalty points for Pt0.67Ru0.33 is 6.330, i.e. ΣPP (Pt0.67Ru0.33)=6.330. Table 12 provides a summary of the information in relation to each Pt0.67M0.33. Particularly, Table 12 provides a sum of the penalty points (ΣPP) for each Pt0.67M0.33. Table 12 further provides the molecular weight (MW) of each Pt0.67M0.33, a sum of penalty points of each Pt0.67M0.33 per MW (ΣPP per MW), and a percentage (%) of improvement of each Pt0.67M0.33 when compared to Pt0.67Ru0.33 based on the ΣPP per MW. It is noted that 1PP (Pt0.67Ru0.33) per MW is about 38.585. To calculate the percentage of improvement of each Pt0.67Ru0.33 when compared to Pt0.67Ru0.33 based on the ΣPP per MW, ΣPP (Pt0.67Ru0.33) per MW is divided by the ΣPP per MW of each Pt0.67M0.33. For example, since 1PP (Pt0.67Ti0.33) per MW 82.505, the percentage of improvement of Pt0.67Ti0.33 when compared to Pt0.67Ru0.33 thus equals 38.585/82.505, which is about 46.8%.
Referring to
Noted that Pt-M alloys having ratios of Pt to M other than 2 may similarly be evaluated using the method described herein. For instance, in some other embodiments, the data-driven materials screening method may be utilized to evaluate Pt-M alloys, such as Pt0.95M0.05 or Pt0.5M0.5, where M may be Ti, Ge, Se, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, Ce, Hf, Ta, W, Re, Os, Ir, Au, Tl, or Bi, to identify those suitable to be used as electrochemical cell anode catalyst materials to prevent cell voltage reversal during H2 fuel starvation.
Apart from binary Pt-based alloys, the data-driven materials screening method may further be used to screen ternary Pt-based alloys, i.e. Pt-MI-M11, to identify those that are suitable to be used as electrochemical cell anode catalyst materials to prevent cell voltage reversal during H2 fuel starvation. MI is a metal element other than Pt, and MII is also a metal element other than Pt. In some embodiments, the ternary Pt-based alloys may be PtxMIyMIIz, where x=2y=6z, x>0, MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd. For example, the ternary Pt-based alloys are Pt0.6MI0.3MII0.1, where MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd. In some other embodiments, the ternary Pt-based alloys may be PtxMIyMIIz, where x=6y=2z, x>0, MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd. For example, the ternary Pt-based alloys are Pt0.6MI0.1MII0.3, where MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd. In yet some other embodiments, the ternary Pt-based alloys may be PtxMIyMIIz, where x+y+z=1, 0<x<0.5, 0<y<0.5, 0<z<0.5, MI is Ru, Ge, or Mo, and MII is Ir, Os, Ti, Au, Bi, Se, or Pd.
Table 13 provides a summary of information of some exemplary Pt-MI-MII. Table 13 provides a sum of penalty points (ΣPP′) for each Pt-MI-M11. Table 13 further provides the molecular weight (MW) of each Pt-MI-MII, a sum of penalty points of each Pt-MI-MII per MW (ΣPP′ per MW), and a percentage (%) of improvement of each Pt-MI-MII when compared to Pt0.67Ru0.33 based on the ΣPP′ per MW. It is noted that 1PP (Pt0.67Ru0.33) per MW is about 38.585. To calculate the percentage of improvement of each Pt-MI-MII when compared to Pt0.67Ru0.33 based on the ΣPP′ per MW, ΣPP (Pt0.67Ru0.33) per MW is divided by the ΣPP′ per MW of each Pt-MI-M11. For example, since 1PP′ (Pt0.6Ru0.3Ir0.1) per MW 35.841, the percentage of improvement of Pt0.6Ru0.3Ir0.1 when compared to Pt0.67Ru0.33 thus equals 38.585/35.841, which is about 107.7%.
In view of the foregoing, Pt-based alloys that are comparatively effective as Pt—Ru to be used as electrochemical cell anode catalyst materials may be a binary Pt-M alloy, where M may be Ge, Se, Mo, Rh, Pd, Ag, Sn, Sb, W, Re, Os, Ir, Au, Tl or Bi. In some embodiments, the binary Pt-M alloy may be PtxMy, where x=2y, x>0, and M may be Ge, Se, Mo, Rh, Pd, Ag, Sn, Sb, W, Re, Os, Ir, Au, Tl or Bi. For example, the binary Pt-M alloy is Pt0.67M0.33, where M may be Ge, Se, Mo, Rh, Pd, Ag, Sn, Sb, W, Re, Os, Ir, Au, Ti or Bi. In some other embodiments, the binary Pt-M alloy may be Pt0.95M0.05, where M may be Ge, Se, Mo, Rh, Pd, Ag, Sn, Sb, W, Re, Os, Ir, Au, Ti or Bi. In yet some other embodiments, the binary Pt-M alloy may be Pt0.5M0.5, where M may be Ge, Se, Mo, Rh, Pd, Ag, Sn, Sb, W, Re, Os, Ir, Au, Ti or Bi.
The Pt-based alloys may also be a ternary Pt-MI-MII alloy, where MI is a metal element other than Pt, and MII is also a metal element other than Pt. In some embodiments, the ternary Pt-MI-MII alloy may be PtxMIyMIIz, where x=2y=6z, x>0, MI may be Ru, Ge, or Mo, and Mu may be Ir, Os, Tl, Au, Bi, Se, or Pd. For example, the ternary Pt-MI-MII alloy is Pt0.6MI0.3MII0.1, where MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd. In some other embodiments, the ternary Pt-MI-MII alloy may be PtxMIyMIIz, where x=6y=2z, x>0, MI may be Ru, Ge, or Mo, and M may be Ir, Os, Tl, Au, Bi, Se, or Pd. For example, the ternary Pt-MI-MII alloy is Pt0.6MI0.1MII0.3, where MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd. In yet some other embodiments, the ternary Pt-based alloys may be PtxMIyMIIz, where x+y+z=1, 0<x<0.5, 0<y<0.5, 0<z<0.5, MI is Ru, Ge, or Mo, and MII is Ir, Os, Tl, Au, Bi, Se, or Pd.
Either the binary or ternary Pt-based alloys may further be mixed with Ir, Ru and/or an Ir—Ru alloy. Either the binary or ternary Pt-based alloys may also be mixed with Ir- or Ru-containing oxides, such as IrO2, RuO2, and/or Ir—Ru—O. Ir—Ru—O is a metal oxide of Ir and Ru.
To synthesize a Pt-based alloy catalyst, Pt may be annealed with stoichiometric amounts of other metal element precursors under a reducing heat treatment condition (e.g. under a nitrogen (N2), argon (Ar), or H2 gas atmosphere). Depending on the alloy, a heat treatment temperature may be in a range of 150 and 1,000° C., and a heat treatment time may be in a range of 30 seconds and 24 hours.
The loss of ECSA of a Pt-based alloy catalyst may be determined using a potentiostat with either a triangular or square wave having a voltage up to 0.9 V. In some embodiments, to understand catalyst degradation induced by carbon corrosion, the voltage may be further up to 1.5 V. When determining the loss of ECSA, H2 may be used to measure an amount of the adsorbed or desorbed gas. For a more accurate determination of the loss of ECSA, a carbon monoxide stripping method may be utilized. In addition, mass activity measurements of the Pt-based alloy catalyst may be performed in a rotating disk electrode (RDE) or using a full membrane-electrode-assembly (MEA) setup under H2 or O2 atmosphere.
Referring back to
The Pt-based alloy may also be a ternary Pt-MI-MII alloy, where MI is a metal element other than Pt, and MII is also a metal element other than Pt. In some embodiments, the ternary Pt-MI-MII alloy may be PtxMIyMIIz, where x=2y=6z, x>0, MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd. For example, the ternary Pt-MI-MII alloy is Pt0.6MI0.3MII0.1, where MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd. In some other embodiments, the ternary Pt-MI-MII alloy may be PtxMIyMIIz, where x=6y=2z, x>0, MI may be Ru, Ge, or Mo, and M may be Ir, Os, Tl, Au, Bi, Se, or Pd. For example, the ternary Pt-MI-MII alloy is Pt0.6MI0.1MII0.3, where MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd. In yet some other embodiments, the ternary Pt-based alloys may be PtxMIyMIIz, where x+y+z=1, 0<x<0.5, 0<y<0.5, 0<z<0.5, MI is Ru, Ge, or Mo, and MII is Ir, Os, Tl, Au, Bi, Se, or Pd.
Either the binary or ternary Pt-based alloys may also be mixed with Ir- or Ru-containing oxides, such as IrO2, RuO2, and/or Ir—Ru—O. Ir—Ru—O is a metal oxide of Ir and Ru. Either the binary or ternary Pt-based alloys may be nanoparticles having an average size in a range of 1 and 20 nm.
Continuing referring to
Individual PEM fuel cells may be assembled into a fuel cell stack. Each fuel cell in the stack is sandwiched between two flow field plates which separate each fuel cell from neighboring fuel cells. In a fuel cell stack, cell voltages of individual fuel cells may be different depending on the location of each fuel cell in the fuel cell stack. Different cell voltages may induce different degradations upon the catalyst performance in each fuel cell. For example, fuel cells that are positioned near a reactant inlet of the fuel cell stack may degrade faster than the ones positioned in a middle area of the fuel cell stack. Therefore, to improve the performance and durability of a fuel cell stack, catalyst materials of a PEM fuel cell may be varied based on its location in the fuel cell stack.
Referring to
At least one fuel cell, for example, fuel cell X, in the first region 80 may include an MEA with a first anode catalyst material on an anode layer of the fuel cell X. Similarly, at least one fuel cell, for example, fuel cell Z, in the second region 90 may include an MEA with a second anode catalyst material on an anode layer of the fuel cell Z. Likewise, at least one fuel cell, for example, fuel cell Y, in the third region 100 may include an MEA with a third anode catalyst material on an anode layer of the fuel cell Y. According to the locations of fuel cells X, Y and Z in the fuel cell stack 70, at least one of the first, second, and third anode catalyst materials are different.
To prevent cell voltage reversal during H2 fuel starvation, the first anode catalyst material in fuel cell X may include a first Pt-based alloy. The first Pt-based alloy may be a binary Pt-M alloy, where M may be Ge, Se, Mo, Rh, Pd, Ag, Sn, Sb, W, Re, Os, Ir, Au, Tl or Bi. In some embodiments, the binary Pt-M alloy may be PtxMy, where x=2y, x>0, and M may be Ge, Se, Mo, Rh, Pd, Ag, Sn, Sb, W, Re, Os, Ir, Au, Tl or Bi. For example, the binary Pt-M alloy is Pt0.67M0.33, where M may be Ge, Se, Mo, Rh, Pd, Ag, Sn, Sb, W, Re, Os, Ir, Au, Tl or Bi. In some other embodiments, the binary Pt-M alloy may be Pt0.95M0.05, where M may be Ge, Se, Mo, Rh, Pd, Ag, Sn, Sb, W, Re, Os, Ir, Au, Tl or Bi. In yet some other embodiments, the binary Pt-M alloy may be Pt0.5M0.5, where M may be Ge, Se, Mo, Rh, Pd, Ag, Sn, Sb, W, Re, Os, Ir, Au, Tl or Bi. The first Pt-based alloy may also be a ternary Pt-MI-MII alloy. In some embodiments, the ternary Pt-MI-MII alloy may be PtxMIyMIIz, where x=2y=6z, x>0, MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd. For example, the ternary Pt-MI-MII alloy is Pt0.6MI0.3MII0.1, where MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd. In some other embodiments, the ternary Pt-MI-MII alloy may be PtxMIyMIIz, where x=6y=2z, x>0, MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd. For example, the ternary Pt-MI-MII alloy is Pt0.6MI0.1MII0.3, where MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd. In yet some other embodiments, the ternary Pt-based alloys may be PtxMIyMIIz, where x+y+z=1, 0<x<0.5, 0<y<0.5, 0<z<0.5, MI is Ru, Ge, or Mo, and MII is Ir, Os, Tl, Au, Bi, Se, or Pd. The first Pt-based alloy may further be mixed with Ir, Ru and/or an Ir—Ru alloy. The first Pt-based alloy may also be mixed with Ir- or Ru-containing oxides, such as IrO2, RuO2, and/or Ir—Ru—O. Ir—Ru—O is a metal oxide of Ir and Ru. The first Pt-based alloy may be a nanoparticle having an average size in a range of 1 and 20 nm.
The second anode catalyst material in fuel cell Z may include a second Pt-based alloy. The second Pt-based alloy may be a binary Pt-M alloy, where M may be Ge, Se, Mo, Rh, Pd, Ag, Sn, Sb, W, Re, Os, Ir, Au, Ti or Bi. In some embodiments, the binary Pt-M alloy may be PtxMy, where x=2y, x>0, and M may be Ge, Se, Mo, Rh, Pd, Ag, Sn, Sb, W, Re, Os, Ir, Au, Ti or Bi. For example, the binary Pt-M alloy is Pt0.67M0.33, where M may be Ge, Se, Mo, Rh, Pd, Ag, Sn, Sb, W, Re, Os, Ir, Au, Ti or Bi. In some other embodiments, the binary Pt-M alloy may be Pt0.95M0.05, where M may be Ge, Se, Mo, Rh, Pd, Ag, Sn, Sb, W, Re, Os, Ir, Au, Ti or Bi. In yet some other embodiments, the binary Pt-M alloy may be Pt0.5M0.5, where M may be Ge, Se, Mo, Rh, Pd, Ag, Sn, Sb, W, Re, Os, Ir, Au, Ti or Bi. The second Pt-based alloy may also be a ternary Pt-MI-MII alloy. In some embodiments, the ternary Pt-MI-MII alloy may be PtxMIyMIIz, where x=2y=6z, x>0, MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd. For example, the ternary Pt-MI-MII alloy is Pt0.6MI0.3MII0.1, where MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd. In some other embodiments, the ternary Pt-MI-MII alloy may be PtxMIyMIIz, where x=6y=2z, x>0, MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd. For example, the ternary Pt-MI-MII alloy is Pt0.6MI0.1MII0.3, where MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd. In yet some other embodiments, the ternary Pt-based alloys may be PtxMIyMIIz, where x+y+z=1, 0<x<0.5, 0<y<0.5, 0<z<0.5, MI is Ru, Ge, or Mo, and MII is Ir, Os, Ti, Au, Bi, Se, or Pd. The second Pt-based alloy may further be mixed with Ir, Ru and/or an Ir—Ru alloy. The second Pt-based alloy may also be mixed with Ir- or Ru-containing oxides, such as IrO2, RuO2, and/or Ir—Ru—O. Ir—Ru—O is a metal oxide of Ir and Ru. The second Pt-based alloy may be a nanoparticle having an average size in a range of 1 and 20 nm.
The third anode catalyst material in fuel cell Y may include a third Pt-based alloy. The third Pt-based alloy may be a binary Pt-M alloy, where M may be Ge, Se, Mo, Rh, Pd, Ag, Sn, Sb, W, Re, Os, Ir, Au, Ti or Bi. In some embodiments, the binary Pt-M alloy may be PtxMy, where x=2y, x>0, and M may be Ge, Se, Mo, Rh, Pd, Ag, Sn, Sb, W, Re, Os, Ir, Au, Ti or Bi. For example, the binary Pt-M alloy is Pt0.67M0.33, where M may be Ge, Se, Mo, Rh, Pd, Ag, Sn, Sb, W, Re, Os, Ir, Au, Ti or Bi. In some other embodiments, the binary Pt-M alloy may be Pt0.95M0.05, where M may be Ge, Se, Mo, Rh, Pd, Ag, Sn, Sb, W, Re, Os, Ir, Au, Ti or Bi. In yet some other embodiments, the binary Pt-M alloy may be Pt0.5M0.5, where M may be Ge, Se, Mo, Rh, Pd, Ag, Sn, Sb, W, Re, Os, Ir, Au, Ti or Bi. The third Pt-based alloy may also be a ternary Pt-MI-MII alloy. In some embodiments, the ternary Pt-MI-MII alloy may be PtxMIyMIIz, where x=2y=6z, x>0, MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd. For example, the ternary Pt-MI-MII alloy is Pt0.6MI0.3MII0.1, where MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd. In some other embodiments, the ternary Pt-MI-MII alloy may be PtxMIyMIIz, where x=6y=2z, x>0, MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd. For example, the ternary Pt-alloy is Pt0.6MI0.1MII0.3, where MI may be Ru, Ge, or Mo, and MII may be Ir, Os, Tl, Au, Bi, Se, or Pd. In yet some other embodiments, the ternary Pt-based alloys may be PtxMIyMIIz, where x+y+z=1, 0<x<0.5, 0<y<0.5, 0<z<0.5, MI is Ru, Ge, or Mo, and MII is Ir, Os, Tl, Au, Bi, Se, or Pd. The third Pt-based alloy may further be mixed with Ir, Ru and/or an Ir—Ru alloy. The third Pt-based alloy may also be mixed with Ir- or Ru-containing oxides, such as IrO2, RuO2, and/or Ir—Ru—O. Ir—Ru—O is a metal oxide of Ir and Ru. The third Pt-based alloy may be a nanoparticle having an average size in a range of 1 and 20 nm.
Continuing referring to
In addition to catalyst materials, catalyst loadings may also influence catalytic activities of a fuel cell stack. High catalyst loadings may extend a lifetime of the fuel cell stack and consequently boost the fuel cell stack performance. On the other hand, low catalyst loadings may accelerate catalyst consumption and affect fuel cell performance. Therefore, besides varying the anode catalyst materials according to the locations of the fuel cells in the fuel cell stack, dynamically allocating catalyst loadings in the fuel cells according to the locations of the fuel cells in the fuel cell stack may further improve the performance and durability of the fuel cell stack.
Apart from catalyst materials and catalyst loadings, other factors may also influence the performance and durability of the fuel cell stack. Some of these factors may include ionomers used in the MEAS of the fuel cells in the fuel cell stack. Therefore, varying the ionomers in the fuel cells based on the locations of the fuel cells in the fuel cell stack may also improve the performance and durability of the fuel cell stack.
Noted that a catalyst support, such as an anode catalyst support, may not be required for some types of electrochemical cells, such as electrolyzers.
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 present disclosure 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.
