Grafted catalyst

Abstract

Catalysts with ionomer-like polymer chains grafted onto them are disclosed. The ionomer-like chains provide a reactant bridge between the catalyst and the ionomer, as in a fuel cell, particularly when deposited in deep pores or cracks. In an improvement, the polymer chains are deposited on less active facets of the catalyst.

Description

Field of expertise

[0001] The present disclosure relates to a catalyst for electrochemical cells. In particular, grafting onto the catalyst in less active regions can be particularly effective in increasing catalyst efficiency and / or longevity. background

[0002] Electrochemical cells are crucial to achieving a greener future with less dependence on fossil fuels. However, significant improvements in electrochemical cells are needed before effective and viable alternatives to the overwhelming dependence on fossil fuels can be realized. Electrochemical cells may include a catalyst, which is often one of the most expensive yet crucial components. Accordingly, improving the efficiency of the catalyst is essential to achieving more practical electrochemical cells. Brief description

[0003] An electrochemical cell comprising a pair of electrodes (e.g., cathode and electrode) and a plurality of catalyst particles deposited on a catalyst support, each catalyst having a plurality of polymer chains grafted thereto, is disclosed. The plurality of polymer chains are grafted onto a less active portion or facet of the catalyst particles. The polymer chains act as a reactant bridge between the catalyst and the ionomer.

[0004] A catalyst layer comprising a porous catalyst support, a catalyst deposited on the catalyst support, and a plurality of polymer chains grafted onto the catalyst is disclosed, wherein the plurality of polymer chains comprise groups having acid functionality.

[0005] A method for preparing a catalyst layer is disclosed, comprising providing a catalyst supported by a catalyst support and grafting polymer chains onto the catalyst. The polymer chains comprise ionic functional groups and are grafted onto the catalyst at undercoordinated facets or atoms. Short description of the drawings Fig. 1 is a schematic view of one embodiment of an electrochemical cell. Fig. Figure 2 is a schematic view of one embodiment of a catalyst composite / layer. Fig. Figure 3 is a perspective view of one embodiment of a grafted catalyst particle. Fig. 4A is a view of a catalyst particle and Fig. Figure 4B is an enlarged partial view of one embodiment of a catalyst particle. Fig. 5A-C are perspective views of embodiments of a catalyst with radical scavengers grafted thereon. Fig. Figure 6A is a schematic plan view of one embodiment of a catalyst with polymer grafting for steric hindrance. Fig. Figure 6B is a schematic side view of a catalyst without polymer grafting and steric hindrance. Fig. Figure 6C is a schematic side view of the embodiment of Fig. 6A. Fig. 7 is a method for producing a catalyst. Detailed description

[0006] Embodiments of the present disclosure are described herein. It should 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 may be exaggerated or reduced to show details of particular components. Accordingly, the 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 embodiments of the present invention.It will be apparent to one of ordinary skill in the art that various features illustrated and described with reference to any of the figures may be combined with features illustrated in one or more other figures to produce embodiments not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desirable for specific applications or implementations.

[0007] Except in the examples, or where expressly stated otherwise, all numerical values ​​in this specification indicating amounts of material or conditions of reaction and / or use are to be understood as modified by the word "about" to describe the widest scope of the invention. Reaction within the recited numerical limits is generally preferred. In addition, unless expressly stated to the contrary, percent, "parts of," and ratios are by weight. The term "polymer" includes "oligomer," "copolymer," "terpolymer," and the like. The description of a group or class of materials as suitable or preferred for a particular purpose in connection with the invention implies that mixtures of any two or more members of the group or class are equally suitable or preferred.Molecular weight information provided for any polymers refers to the number average molecular weight. The description of components in chemical terms refers to the components at the time of addition to any combination recited in the description and does not necessarily preclude chemical interactions between the components of a mixture once mixed; the first definition of an acronym or other abbreviation applies to all subsequent uses of the same abbreviation herein and applies mutatis mutandis to normal grammatical variations of the originally defined abbreviation; and, unless expressly stated to the contrary, the measurement of a property is made by the same technique previously or later recited with respect to the same property.

[0008] The present invention is not limited to the specific embodiments and methods described below, as specific components and / or conditions may vary. Furthermore, the terminology used herein is used only to describe particular embodiments of the present invention and is not intended to be limiting in any way.

[0009] The term "substantially," "generally," or "about" may be used herein to describe disclosed or claimed embodiments. The terms "substantially," "generally," or "about" may modify a value or relative characteristic disclosed or claimed in the present disclosure to indicate that it is within manufacturing tolerances and / or within ± 0%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or 10% of the value or relative characteristic.

[0010] With respect to the terms "comprising," "consisting of," and "consisting essentially of," where any of these three terms is used in the context of the present invention, the subject matter disclosed and claimed herein may include the use of any of the other two terms.

[0011] Note that integer ranges explicitly include all intermediate 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, if an arbitrary range is required, intermediate numbers that are increments of the difference between the upper and lower bounds divided by 10 can be used as alternative upper or lower bounds. 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 bounds.

[0012] In relation to Fig. 1, the electrochemical cell 100 (e.g., a fuel cell, flow battery, and / or electrolysis cell) comprises a plurality of electrodes (e.g., a first electrode 102 and a second electrode 106) and an electrolyte 104 disposed therebetween. Electrochemical cells generally elicit desired chemical reactions with the aid of a catalyst. For example, in a fuel cell, redox reactions are used to generate electricity—often with hydrogen and oxygen. In various embodiments, for example, the first electrode 102 may be a cathode and the second electrode 106 may be an anode. In an improvement, the electrodes may be or include catalyst layers or composites. In some embodiments, the electrode may have a thickness of 0.5 to 500 µm, or more preferably 1 to 250 µm, or most preferably 2 to 200 µm.For example, a fuel cell electrode may be 2-10 µm thick, an electrolysis electrode may be 2 to 10 µm thick, and a battery electrode may be 50-200 µm thick. In one or more embodiments, an electrochemical stack (not shown) may include a plurality of electrochemical cells. In various embodiments of the stack, the electrochemical cells may be arranged adjacent to one another and in electrical communication. Each electrochemical cell or stack may further include one or more gas diffusion layers, one or more current collectors, one or more bipolar plates, and / or a separator.

[0013] In relation to Fig. 2, the catalyst layer or composite 200 may be adjacent to, for example, an electrolyte or ion-conducting membrane 210 and gas diffusion layer 220 by being sandwiched therebetween or disposed therebetween. The catalyst layer or composite 200 may comprise a catalyst 202 supported by, deposited on, and / or embedded within a catalyst support 204. The catalyst 202 and catalyst support 204 may be in contact with, dispersed within, or adjacent to an ionomer 206. In one or more embodiments, the catalyst 202 is any suitable catalyst, such as a metal (e.g., transition metal), alloy, oxide, or ceramic thereof (e.g., platinum, ruthenium, palladium, iron-nitrogen, etc.). Traditionally, catalyst efficiency is improved merely by increasing the surface area to volume ratio.For example, in a fuel cell, the electrochemically active surface area (ECSA) indicates a cell's performance. Electrochemically active surfaces are in electrical communication with the current collector, for example, through the catalyst support, but must also be accessible to the chemical reactants (e.g., hydrogen, oxygen, protons, and / or water). This support-catalyst-reactant interface can be a highly dynamic and chemically aggressive environment, creating challenges, such as longevity, for many components.

[0014] In various embodiments, catalyst nanoparticles (i.e., less than 100 nm) with a higher surface-to-volume ratio can be used. For example, platinum nanoparticles can be used. Traditionally, the efficiency of such catalyst nanoparticles has focused on their arrangement on and / or within a catalyst support.

[0015] In one or more embodiments, the catalyst support 204 is carbonaceous or a metal oxide. For example, the catalyst support 204 may be carbon black. Such supports may have catalyst embedded therein. For example, the catalyst support is often porous with deep cracks. The surface of such pores and cracks often comprises catalyst, which may be difficult to reach, rendering the catalyst and cell ineffective. This may be particularly true for catalyst support particles with a greater porosity or a larger surface area, such as at least 400 m 2 / g or at least 1,000 m 2 / g or at least 1,600 m 2 / g (e.g., a larger surface area to volume ratio and / or a higher anchor point density), which can accommodate deeper pores and cracks. For example, carbon with medium (e.g., 400 to 1000 m 2 / g) or larger (e.g. 800 m 2 / g or more) surface area may be associated with such problems to a much greater extent than carbon with a low surface area (e.g. less than 400 m 2 / g). This situation is further exacerbated under dry conditions (e.g., an inlet relative humidity of 50% or less and / or a nominal relative humidity of 70% or less) where a polar or ionic solvent such as water is scarce, since solvents such as water promote reactant transport and / or conductivity.

[0016] In various embodiments, the ionomer 206 provides ionic conductivity. For example, the ionomer 206 may be an ion-conducting polymer matrix. In one or more embodiments, the ionomer 206 comprises ionic functional groups such as acids (e.g., carboxylic acid and / or sulfonic acid). For example, the equivalent weight with respect to the ionic functional groups such as sulfonic acid may be 500 to 2,000 g / mol, or more preferably 600 to 1,500 g / mol, or most preferably 650 to 1,200 g / mol). In one variation, the ionomer 206 may have a thickness of 0.1 to 10 nm, or more preferably 0.5 to 7 nm, or most preferably 1 to 5 nm. In some embodiments, the ionomer 206 is an ionic fluoropolymer such as Nafion® (e.g., a sulfonated tetrafluoroethylene-based fluoropolymer copolymer).Given the length and size of conventional ionomer polymer chains, the ionomer may be sterically hindered or otherwise have difficulty reaching the entire catalyst, particularly, for example, in deep pores and cracks.

[0017] In numerous embodiments, one or more polymer grafts (i.e., polymer branches or chains) 302 may be grafted onto the catalyst or catalyst support. For example, with reference to Fig. 3, the polymeric graft units 302 may be grafted directly onto the catalyst particle 304 or agglomerates 306. In one or more embodiments, the catalyst particle / agglomerate 304 / 306 may have areas (e.g., facets) with greater activity and areas (e.g., facets, edges, and / or corners) with lower activity. For example, different facets of different crystalline structures may have different activities (e.g., facet FCC 111 may have greater activity than other facets such as FCC 100 and / or FCC 110). In an improvement, the polymer graft 302 may not be grafted to the FCC 111 facet (e.g., having a coordination number of 9) or may be grafted to facets other than the FCC 111 facet, such as FCC 100 (having a coordination number of 8) and / or FCC 110.In other words, the polymer units 302 may be grafted onto the areas of lower activity and / or regions / sections with undercoordination (e.g., undercoordinated atoms). In an improvement, the polymer units 302 may be grafted onto sites having a coordination number of at most 8, or more preferably at most 7, or even more preferably at most 6. In other words, the polymer units 302 may not be grafted onto areas having a coordination number of at least 7, or more preferably at least 8, or even more preferably at least 9. For example, the polymer units may be grafted onto the corner (e.g., coordination number of 5-6) and / or edges (e.g., coordination number of 7) of the catalyst particle / agglomeration 304 / 306. These regions, such as corners and edges, may also, in many cases, exhibit less steric hindrance.

[0018] Numerous polymers may be grafted onto the catalyst 304 / 306 to provide specific effects or enhancements. In various embodiments, the polymer 302 has a specific functionality correlated with its structure. For example, a polymer chain 302 may comprise more or fewer double bonds to reduce or enhance strength and / or stiffness, or may comprise certain functional groups (e.g., ionic groups) to provide specific properties. The grafted polymer 302 may have 10 to 500 repeat units, or more preferably 15 to 300 repeat units, or most preferably 20 to 100 repeat units. The catalyst particle may have a graft density of 2 to 20 polymer chains per catalyst particle 306, or more preferably 5 to 18 chains per catalyst particle 306, or most preferably 10 to 17 chains per catalyst particle 306.

[0019] In one or more embodiments, one or more ionic polymer units 406 (e.g., a plurality of ionic polymer units), as in Fig. 4A-B, may be grafted onto the catalyst 402 or catalyst support 404 to enhance the (ionic / electrical) conductivity (i.e., a reactant, ion, and / or conductive bridge between the catalyst and the ionomer), for example, under dry conditions. In some embodiments, polymer units with radical scavenging properties 504 may be grafted onto the catalyst 502, as shown in Fig. 5A-5B to locate radical scavengers 506, 506', 506" where they are most needed and most effective (i.e., eliminate or reduce scavenger migration). In yet another example, polymer units 604 may be grafted onto the catalyst 602 to prevent catalyst poisoning, for example, by providing steric hindrance, as in Fig. 6A and Fig. 6C.

[0020] The chemical reactions that drive electrochemical cells generally occur at the catalyst interface. For example, in a fuel cell, redox reactions (e.g., reduction at the cathode and oxidation at the anode) occur at the catalyst-ionomer interface because the ionomer 406 provides ionic conductivity (e.g., via protons). Water 412 and a humid environment can further facilitate ionic conductivity and reactant transport, particularly in the absence of ionomer 406 or when small gaps exist between the catalyst 402 and the ionomer 406. For example, the ionomer 406, which contains long polymer chains (e.g., 10 4 there or more, 10 5 there or more or even 10 6or more), have difficulty reaching the catalyst active sites, for example in pores and cracks 408 due to, for example, steric hindrance, as in Fig. 4A-4B.

[0021] However, under humid conditions, these pores 408 can also be filled with water 412, thus maintaining ionic conductivity. However, the amount of water available in a cell can vary considerably based on numerous factors, including the environment, temperature, nominal relative humidity, cell age, cell use, cell location, and numerous other factors. Under dry conditions, the absence of water 412 can render certain catalyst sites less active or even inactive due to reduced ionic conductivity and reduced reactant transport.During humid conditions, these small gaps may be occupied by water 412 and exhibit greater ionic conductivity, but during drier conditions, water 412 migrates from these regions, so changes in humidity can affect the efficiency and operation of the electrochemical cell. However, grafting polymers with ionic functionality 410 onto the catalyst 402 or catalyst support 404 (particularly when grafted directly onto the catalyst 402) can serve as a bridge to maintain reactions at the catalyst active sites despite reduced water content or even in the absence of water 412. In variations, the grafted polymer units 410 can be much smaller than conventional ionomer chains 406 such as Nafion®. For example, oligomers or smaller polymer chains can be used (e.g., 10,000 da or less, or more preferably 5,000 da or less, or most preferably 1.000 da or less). In an improvement, the grafted polymer unit 410 may have a molecular weight of 50,000 da or less, or more preferably 25,000 da or less, or most preferably 20,000 da or less. In a variation, the polymeric graft units 410 may have a size (e.g., molecular weight or length) that is 75% or less of that of the ionomer chains 406 or side chains, or more preferably 50% or less, or most preferably 25% or less.

[0022] In various embodiments, the polymeric graft unit or bridge 410 may comprise ionic functional groups such as acids (e.g., carboxylic acid and / or sulfonic acid groups). In an improvement, the equivalent weight with respect to the ionic functional groups such as sulfonic acid may be 500 to 2,000 g / mol, or more preferably 600 to 1,500 g / mol, or most preferably 650 to 1,200 g / mol. In a variation, the grafted polymer units 410 may be more hydrophilic than the corresponding ionomer 406 (e.g., have a larger equivalent weight such as 800 g / mol, or more preferably 1,000 g / mol, or most preferably 1,200 g / mol). In some embodiments, the polymeric graft unit or bridge 410 may comprise a fluoropolymer backbone or backbone of non-fluorinated polymer, such as a hydrocarbon backbone. For example, the grafted polymer units can be 410 ionomer-like or Nafion®-like, but smaller (iesmaller molecular weights and / or chain length) - shorter ionomer chains. In other words, ionomer-like or Nafion®-like can refer to the use of polymer chains with the same or a similar chemical composition, but smaller in terms of, for example, molecular weight, chain length, or repeating units. For an ionomer-like, the chain can be at least 50% smaller in terms of weight, length, or units, or more preferably at least 60% smaller, or most preferably at least 75% smaller. For example, the grafted polymer units 410 can have 10 to 500 repeating units, or more preferably 15 to 300 repeating units, or most preferably 20 to 100 repeating units. In other words, the polymeric graft units 410 can be sulfonated, tetrafluoroethylene-based fluoropolymer copolymer.

[0023] Different grafting densities may be used. For example, grafting densities may be used to achieve a desired hydrophobicity or hydrophilic nature around the catalyst sites. For example, larger grafting densities may be desirable to provide a more hydrophilic environment around the catalyst, which attracts water 412 and facilitates reactant movement / delivery to the catalyst sites (e.g., enhances proton and / or oxygen diffusion). More hydrophilic environments may also coordinate better with water 412 to flood or fill such pathways during wetter conditions to further improve efficiency. For example, a grafting density of 2 to 20 chains per catalyst particle 306, or more preferably 5 to 18 chains per catalyst particle 306, or most preferably 10 to 17 chains per catalyst particle 306 may be used.

[0024] The dynamic and aggressive nature of the various chemical reactions occurring at the catalyst-ionomer interface is rich in radical precursors and leads to free radicals (e.g., ▪ OH), which can be destructive if left unabated. For example, free radicals can compromise or reduce the stability of the ionomer. Traditionally, mobile radical scavengers such as cerium ions (e.g., Ce 3+) by adding / dispersing cerium oxide, such as cerium oxide nanoparticles, into the ionomer phase and / or proton exchange membrane (i.e., away from the catalyst). In other words, radical scavengers are provided by a primary source of free radicals (i.e., the catalyst-reactant interface) and thus protect less effectively against free radicals. Furthermore, due to their mobility, even when sufficiently dispersed in the early stages of a cell's life, radical scavengers tend to migrate and accumulate in more polar regions, such as wetter sections / regions of the cells—again, away from a primary source of free radicals. For example, radical scavengers, such as cerium ions, often drift with the water flow toward the proton exchange membrane and / or accumulate near the outlet, which is minimally affected by free radicals, so that once migration occurs, such scavengers offer little or no benefit.These inhomogeneities in terms of density and capture power are undesirable and inefficient.

[0025] In yet another embodiment, the radical scavengers 506, 506', 506" may be localized by the polymer unit 504 grafted onto the catalyst support or, more preferably, the catalyst 502, as in Fig. 5A-C. In this way, the radical scavengers 506, 506', 506" are located near or close to a primary source of free radicals for the most productive and efficient neutralization or stabilization of the free radicals. In various embodiments, a polymeric graft moiety 504 may be grafted onto the catalyst 502, for example, in a less active area / facet (e.g., corner or edge). The polymeric graft moiety 504 may include one or more radical scavenging functional groups or may localize such radical scavengers 506. For example, radical scavengers 506 may be ionically bound or form crosslinks 506, such as weak crosslinks, across the polymer chains 504. In yet another example, radical scavenging nanoparticles 506' may be bound to a terminal end of the polymer chains 504 opposite the catalyst 502, for example, through covalent bonds.In yet another embodiment, the radical scavengers 506" may form part of a complex, a coordination compound, and / or a metal-organic framework 506".

[0026] The polymeric backbone or scavenger chain is not particularly limited and may be any suitable polymer. Polymeric units described herein, such as fluoropolymer and / or ethylene (e.g., a sulfonated tetrafluoroethylene-based fluoropolymer copolymer), may be particularly useful. In one variation, the polymeric graft unit 506" may be modified and / or capable of containing Ce 3+ -cluster or a coordination compound such as a metal-organic framework containing Ce 3+ , i.e. the polymer graft units 504 comprise coordinate / complexate radical scavengers.

[0027] In various embodiments, molecules, ions, compounds, or atoms capable of scavenging free radicals may serve as weak crosslinks 506, as in Fig. 5A. In some variations, small clusters or single atoms, such as cerium ion clusters or cerium ions, can weakly bind to ionic groups, such as sulfonate groups, of the grafted polymer units 504. The weak crosslinks 506 will detach or break away to trap free radicals. This technique reduces or delays migration while still providing the benefits of a mobile radical scavenger.

[0028] In one or more embodiments, one or more cerium particles 506', such as cerium nanoparticles, may be disposed on the polymer chain 504, such as near the terminal end of the grafted polymer unit 504 opposite the catalyst 502, as in Fig. 5B. In an improvement, the cerium particle can form a bond (e.g., strong adsorption bond, electrostatic bond, hydrogen bond, chelate bond, etc.) that can sever during operation of the electrochemical cell, releasing the cerium nanoparticle. This immobilizes the radical scavengers, at least temporarily, preventing them from migrating and localizing them near the catalyst. When the cerium is directly bound to the polymer plugs, it ensures a minimal concentration of radical scavengers near the catalyst active sites.

[0029] In still other embodiments, the grafted polymer unit 504 may be or comprise a complex coordination compound and / or a metal-organic framework (MOF) 506. In variations, the MOF 506 may comprise radical scavengers such as cerium. The MOF 506 may provide the correct oxidation for radical scavengers such as cerium(III) ions (e.g., Ce 3+) and provide more effective radical scavenging. Furthermore, this strategy can also provide the minimum concentration of cerium.

[0030] In various embodiments, one or more of the above strategies can be combined, each offering unique advantages for localization and radical capture.

[0031] In yet another embodiment, grafted polymer units 604 can serve to protect the catalyst 602 from, for example, degradation or damage. For example, catalyst poisoning is widespread, for example, by common ionomers such as Nafion®. Nafion® includes sulfonic acid groups capable of binding to the catalyst facets or surface, thus reducing or blocking the desired catalytic activity, which is often referred to as catalyst poisoning. As discussed above, the ionomer and catalyst must often be in close proximity to facilitate the desired catalyst-reactant interface and provide adequate reactant transport to the catalyst. However, this presents problems because, over time, the ionomer responsible for transporting such reactants can attack the catalyst, reducing its efficiency.

[0032] In one or more embodiments, polymer chains 604, 604' may be grafted onto the catalyst 602 to protect it from such reactions with the ionomer 606 or harmful functional groups thereof, such as sulfonic acid groups thereon, as in Fig. 6A and Fig. 6C. In various embodiments, the grafted polymer chains 604, 604' can shield the catalyst 602 from the harmful functional groups, such as through steric hindrance. For example, short and / or stiff polymer chains 604' can prevent the ionomer chains 606 from coming into direct contact with the catalyst 602, as shown in Fig. 6C, while without such steric hindrance, such ionomer branches 606 can freely come into contact with the catalyst surface, so that the sulfonic acid groups can bind to the catalyst surface, as in Fig.6B. In an improvement, these polymer chains 604 may be stiff to provide better steric hindrance. In variations, the polymer chains 604 may resist folding upon themselves, for example, by comprising a plurality of double bonds, including bulky functional groups such as cyclic rings (e.g., benzene rings), and / or forming semicrystalline structures or crystalline domains within themselves or with adjacent chains. In an improvement, the polymer chains may have a flexural stiffness (k b ) of at least 3, or more preferably at least 10, or most preferably at least 25, or most preferably at least 50. In yet another example, the grafted polymer chains 604' may have a persistence length (L p) of at least 4.5 angstroms, or more preferably at least 5.0 angstroms, or most preferably at least 6.0 angstroms, or especially preferably at least 7.0 angstroms, or a Kuhn length of at least 8.0 angstroms, or more preferably at least 8.5 angstroms, or most preferably at least 9.0 angstroms. In a variation, the use of polymer chains 604 with bulky functional groups such as cyclic rings (e.g., benzene rings) can provide suitable steric hindrance while reducing the overall graft density, thus reducing catalyst poisoning without significantly reducing catalytic activity. For example, polyethylene terephthalate and / or styrene polymer chains can be grafted onto the catalyst 602.

[0033] In one or more embodiments, a method 700 for preparing a catalyst and / or catalyst layer, for example, for an electrochemical cell is disclosed. The method includes providing a catalyst (i.e., step 702), providing a catalyst support (i.e., step 704), providing a monomer, oligomer, and / or polymer (i.e., step 710), depositing the catalyst on a catalyst support (i.e., step 708), and forming or grafting polymer units onto the catalyst (i.e., step 712). In one or more embodiments, the catalyst and catalyst support may be dissolved and / or dispersed in a solvent to form a dispersion or ink. The mixture may further comprise a binder, such as an ionomer binder. The solvent may be water and / or an organic solvent (e.g., an alcohol).In various embodiments, the mixture may be dried and shaped to form a composite or catalyst layer.

[0034] The catalyst may comprise platinum, platinum alloys, ruthenium, palladium, iron-nitrogen. In an improvement, catalyst nanoparticles may be used. In one or more embodiments, the catalyst nanoparticles are added to a catalyst ink or slurry (i.e., step 706) and precipitated onto the catalyst support. In still other embodiments, catalyst precursors may be used. For example, H 2 PtCl 6 , K 2 PtCl 4 , K 2 PtCl 6 , Pt(NO 3 ) 4or other platinum salts such as organic platinum precursor salts. In various embodiments, other precious metal precursor materials may be used, for example, by adding them to the grafting process to form platinum alloy catalyst. For example, platinum (II) (i.e., Pt 2+ ) or platinum (IV) (ie Pt 4+ ) can be used. The catalyst support can be carbonaceous, such as carbon black or a metal oxide. In still other embodiments, commercially available catalyst-catalyst support products such as platinum-carbon can be used.

[0035] The polymer units can be grafted onto the catalyst before deposition on the support or after deposition on the support. In still other embodiments, the polymer units can be formed or grown in solution and / or grafted simultaneously with deposition, for example, in the ink / slurry. Depending on the polymer units used, further steps may be necessary. For example, if a scavenger is incorporated into the polymer graft units, for example in the form of a coordination compound, a complex, or weak crosslinks, a metal oxide powder such as cerium oxide can be added to the ink or added after the catalyst has been deposited and the polymer units have been grafted. In yet another embodiment, the cerium oxide can be added to the ionomer so that when the catalyst layer and the ionomer are brought together, the cerium ions (Ce 3+) are attracted to the catalyst and interact with the polymer chains to keep the cerium ion scavengers localized around the catalyst.

[0036] While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms included in the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the scope of the disclosure. As described above, the features of several embodiments may be combined to form further embodiments of the invention that may not have been explicitly described or illustrated.While several embodiments may have been described as advantageous and preferred over other prior art embodiments or implementations with respect to one or more desired characteristics, one of ordinary skill in the art will appreciate that one or more features or characteristics may be compromised to achieve desired overall system attributes depending on the particular application and implementation. These attributes may include, but are not limited to, cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, usability, weight, manufacturability, ease of assembly, etc.Therefore, embodiments that have been described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for certain applications.

Claims

An electrochemical cell comprising:a pair of electrodes; anda plurality of catalyst particles deposited on a catalyst support, each catalyst particle having portions of greater activity, portions of lesser activity, and polymer chains grafted onto the portions of lesser activity, the polymer chains acting as a reactant bridge between the catalyst and an ionomer. The electrochemical cell of claim 1, wherein the electrochemical cell is a fuel cell. Electrochemical cell according to claim 1, wherein the catalyst particles are nanoparticles. Electrochemical cell according to claim 1, wherein the catalyst particles have a grafting density of at least 2 to 20 chains per catalyst particle. Electrochemical cell according to claim 1, wherein the electrochemical cell is an electrolytic cell. Electrochemical cell according to claim 1, wherein the lower activity portions comprise corners and / or edges of the catalyst particles. Electrochemical cell according to claim 1, wherein the polymer chains comprise groups with acid functionality. Electrochemical cell according to claim 1, wherein the polymer chains comprise sulfonic acid groups. A catalyst layer comprising:a porous catalyst support;a catalyst deposited on the porous catalyst support; anda plurality of polymer chains grafted onto the catalyst, wherein the plurality of polymer chains comprise groups having acid functionality. The catalyst layer of claim 9, wherein the catalyst comprises a plurality of less active facets and the plurality of polymer chains are grafted onto the plurality of less active facets. A catalyst layer according to claim 9, wherein the catalyst comprises platinum. Catalyst layer according to claim 9, wherein the porous catalyst support is carbon black having a surface area of ​​at least 400 m2 / g. Catalyst layer according to claim 9, wherein the porous catalyst support has a surface area of ​​at least 800 m2 / g. The catalyst layer of claim 9, wherein the plurality of polymer chains are sulfonated. The catalyst layer of claim 9, wherein the plurality of polymer chains comprises sulfonated tetrafluoroethylene-based fluoropolymer. The catalyst layer of claim 9, wherein the plurality of polymer chains comprise ionic functional groups. A method for producing a catalyst layer, comprising:providing a catalyst supported by a catalyst support; andgrafting polymer chains having ionic functional groups onto undercoordinated facets of the catalyst. A process according to claim 17, wherein the polymer chains are grafted onto the catalyst before it is deposited on the catalyst support. The process of claim 17, wherein the polymer chains are grafted onto the catalyst after it has been deposited on the catalyst support. The process of claim 17, wherein the catalyst is deposited on the catalyst support and simultaneously grafted with polymer chains.

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