Graft catalyst

Abstract

The invention relates to a graft catalyst. Catalysts grafted with polymer chains are disclosed. The polymer chains provide steric hindrance to eliminate or reduce ionomer induced catalyst poisoning in fuel cells. In one variant, a short and rigid polymer chain can be grafted to the catalyst to provide sufficient steric hindrance. In one improvement, polymer chains are deposited on facets where the activity of the catalyst is lower.

Description

Technical Field

[0001] The present disclosure relates to catalysts for use in electrochemical cells. More particularly, grafting to less active regions of the catalyst can be particularly effective in increasing catalyst efficiency and / or lifetime. Background Art

[0002] Electrochemical cells are essential to achieving a green future that is less dependent on fossil fuels. However, before it is possible to replace over-dependence on fossil fuels with effective and viable alternatives, significant improvements in electrochemical cells are necessary. Electrochemical cells may contain catalysts, which are often one of the most expensive but critical components. Therefore, improving the efficiency of catalysts is essential to achieving more viable electrochemical cells. Summary of the invention

[0003] An electrochemical cell is provided, comprising a pair of electrodes (e.g., a cathode and an anode) and a plurality of catalyst particles deposited on a catalyst support, wherein each catalyst has polymer chains grafted thereto. The polymer chains are grafted to the less active portions or facets of the catalyst. The polymer chains provide steric hindrance near the catalyst to reduce catalyst poisoning.

[0004] A catalyst layer is disclosed, which comprises a catalyst support, a catalyst deposited on a catalyst support, and a plurality of polymer chains grafted onto the catalyst, wherein the plurality of polymer chains provide steric hindrance to reduce catalyst poisoning.

[0005] A method for preparing a catalyst layer is disclosed, which includes providing a catalyst supported by a catalyst carrier and grafting a plurality of polymer chains onto the catalyst. The polymer chains are grafted onto less active regions or facets of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is a schematic diagram of one embodiment of an electrochemical cell.

[0008] Figure 2 is a schematic diagram of one embodiment of a catalyst composite / layer.

[0009] Figure 3 is a perspective view of one embodiment of a grafted catalyst particle.

[0010] Figure 4A is a view of the catalyst particles, Figure 4B is an enlarged partial view of one embodiment of a catalyst particle.

[0011] Figure 5A -C is a perspective view of one embodiment of a catalyst having a free radical scavenger grafted thereon.

[0012] Fig. 6A is a top view of one embodiment of a catalyst with polymer grafting for steric hindrance.

[0013] Figure 6B Schematic side view of the catalyst without polymer grafting and steric hindrance.

[0014] Figure 6C yes Fig. 6A A side schematic diagram of an implementation scheme of .

[0015] Figure 7 A method for preparing a catalyst. DETAILED DESCRIPTION

[0016] Embodiments of the present disclosure are described herein. However, it should be understood that the disclosed embodiments are merely examples, and other embodiments may take various alternative forms. The drawings are not necessarily drawn to scale. Some features may be exaggerated or minimized to show the details of a particular component. Therefore, the specific structural and functional details disclosed herein should not be interpreted as restrictive, but merely as a representative basis for teaching those skilled in the art to adopt the embodiments of the present invention in various ways. As will be understood by those of ordinary skill in the art, the various features shown and described with reference to any one of the figures may be combined with the features shown in one or more other figures to produce an embodiment that is not explicitly shown or described. The combination of features shown provides representative embodiments for typical applications. However, various combinations and modifications of features consistent with the teachings of the present disclosure may be required for specific applications or implementations.

[0017] Except in the examples or otherwise explicitly stated, all numerical values ​​in this specification indicating the amount of material or reaction conditions and / or conditions of use should be understood as modified by the word "about" to describe the widest scope of the present invention. It is usually preferred to practice within the numerical limits. In addition, unless otherwise explicitly stated: percentages, "parts" and ratio values ​​are all by weight. The term "polymer" includes "oligomers", "copolymers", "terpolymers", etc. Describing a group or class of materials as suitable or preferred for a given purpose associated with the present invention means that a mixture of any two or more members of the group or class is also suitable or preferred. The molecular weight provided for any polymer refers to the number-average molecular weight. The description of the ingredients in the chemical terms refers to the ingredients when added to any combination specified in the specification, and does not necessarily exclude chemical interactions between the ingredients of the mixture after mixing; the first definition of an acronym or other abbreviation applies to all subsequent uses of the same abbreviation in this article, and is applicable to the normal grammatical changes of the initially defined abbreviation; and, unless otherwise explicitly stated, the measurement of the performance should be determined by the same technology as previously or later cited for the same performance.

[0018] 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 only used to describe specific embodiments of the present invention and is not intended to limit the present invention in any way.

[0019] The terms "substantially," "generally," or "about" may be used to describe the disclosed or claimed embodiments. The terms "substantially," "generally," or "about" may modify a numerical value or relative property disclosed or claimed in the present disclosure to mean within manufacturing tolerances and / or within ±0%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or 10% of a numerical value or relative property.

[0020] With respect to the terms "comprising," "consisting of," and "consisting essentially of," when one of these three terms is used herein, the presently disclosed and claimed subject matter may include the use of either of the other two terms.

[0021] It should also be understood 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, when any range is required, the intermediate numbers that are the difference between the upper and lower limits divided by the increment of 10 can be used 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.

[0022] See also Figure 1, an electrochemical cell 100 (e.g., a fuel cell, a flow battery, and / or an electrolysis cell) includes a plurality of electrodes (e.g., a first electrode 102 and a second electrode 106) and an electrolyte 104 located therebetween. Electrochemical cells typically initiate the desired chemical reaction with the help of a catalyst. For example, in a fuel cell, a redox reaction is used to generate electrical energy - typically using hydrogen and oxygen. In various embodiments, the first electrode 102 may be, for example, a cathode, and the second electrode 106 may be an anode. In one refinement, the electrode may be or include a catalyst layer or a composite material. In some embodiments, the thickness of the electrode may be 0.5 to 500 μm, or more preferably 1 to 250 μm, or even more preferably 2 to 200 μm. For example, a fuel cell electrode may be 2-10 μm, an electrolysis electrode may be 2 to 10 μm, and a battery electrode may be 50-200 μm. 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 each other and electrically connected. Each electrochemical cell or stack may also include one or more gas diffusion layers, one or more current collectors, one or more bipolar plates, and / or separators.

[0023] See also Figure 2 , the catalyst layer or composite material 200 can be adjacent to the electrolyte or ion conductive membrane 210 and the gas diffusion layer 220, such as sandwiched between them or placed between them. The catalyst layer or composite material 200 can include a catalyst 202, which is supported by a catalyst support 204, deposited on the catalyst support 204 and / or embedded in the catalyst support 204. The catalyst 202 and the catalyst support 204 can be in contact with and / or dispersed in or adjacent to the ionomer 206. In one or more embodiments, the catalyst 202 is any suitable catalyst, such as a metal (e.g., a transition metal), an alloy thereof, an oxide or a ceramic (e.g., platinum, ruthenium, palladium, iron nitrogen, etc.). Traditionally, catalyst efficiency is improved only by increasing the ratio of surface area to volume. For example, in a fuel cell, the electrochemically active surface area (ECSA) indicates the performance of the cell. The electrochemically active surface is electrically connected to the current collector, such as through the catalyst support, but must also be able to contact chemical reactants (e.g., hydrogen, oxygen, protons and / or water). This support-catalyst-reactant interface can be a highly dynamic and chemically aggressive environment, which poses challenges to the lifetime of many components.

[0024] In various embodiments, catalyst nanoparticles having a high ratio of surface area to volume (i.e., less than 100 nm) may be used. For example, platinum nanoparticles may be used. Traditionally, the efficiency of such catalyst nanoparticles has focused on their arrangement on and / or within a catalyst support.

[0025] In one or more embodiments, the catalyst support 204 is carbonaceous or a metal oxide. For example, the catalyst support 204 can be carbon black. Such a support can have a catalyst embedded therein. For example, the catalyst support is typically porous and has deep cracks. The surfaces of such pores and cracks typically contain catalysts that are difficult to access, resulting in lower catalyst and cell efficiency. For catalysts with larger porosity or larger surface area (e.g., at least 400 m 2 / g, or at least 1000m 2 / g or at least 1600m 2 / g (e.g., a larger surface area to volume ratio and / or a higher anchor point density) of catalyst support particles (which can accommodate deeper pores and cracks). For example, medium (e.g., 400 to 1000 m 2 / g) or high (e.g. 800m 2 / g or higher surface area carbon may be higher than low surface area carbon (e.g. less than 400m 2 This problem is significantly more severe in dry conditions (e.g., inlet relative humidity of 50% or less and / or nominal relative humidity of 70% or less) where polar or ionic solvents such as water are scarce, as solvents such as water may promote reactant transport and / or conductivity.

[0026] In various embodiments, the ionomer 206 provides ionic conductivity. For example, the ionomer 206 can be an ionically conductive polymer matrix. In one or more embodiments, the ionomer 206 includes ionic functional groups, such as acids (e.g., carboxylic acids and / or sulfonic acids). For example, the equivalent weight relative to the ionic functional groups (e.g., sulfonic acids) can be 500 to 2000 g / mol, or more preferably 600 to 1500 g / mol, or even more preferably 650 to 1200 g / mol). In one variation, the thickness of the ionomer 206 can be 0.1 to 10 nm, or more preferably 0.5 to 7 nm, or even more preferably 1 to 5 nm. In some embodiments, the ionomer 206 is an ionic fluoropolymer, such as (eg, sulfonated tetrafluoroethylene-based fluoropolymer-copolymers.) However, given the length and size of the polymer chains of conventional ionomers, the ionomers may be sterically hindered or otherwise have difficulty reaching all of the catalyst, particularly in deep pores and crevices.

[0027] In various embodiments, one or more polymer grafts (ie, polymer branches or chains) 302 may be grafted onto the catalyst or catalyst support. For example, see Figure 3, the polymer graft unit 302 can be directly grafted onto the catalyst particles 304 or agglomerates 306. In one or more embodiments, the catalyst particles / agglomerates 304 / 306 can have regions with higher activity (e.g., facets) and regions with lower activity (e.g., facets, edges, and / or corners). For example, various facets of different crystal structures have different activities (e.g., the FCC 111 facet may have higher activity than other facets (e.g., FCC 100 and / or FCC 110)). In one refinement, the polymer graft 302 may not be grafted onto the FCC 111 facet (e.g., having a coordination number of 9) or may be grafted onto 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 unit 302 can be grafted onto regions with lower activity and / or regions / portions with insufficient coordination (e.g., insufficiently coordinated atoms). In one refinement, the polymer units 302 may be grafted to sites having a coordination number no greater than 8, or even more preferably no greater than 7, or even more preferably no greater than 6. In other words, the polymer units 302 may not be grafted to regions having a coordination number of at least 7, or even more preferably at least 8, or even more preferably at least 9. For example, the polymer units may be grafted to corners (e.g., coordination numbers 5-6) and / or edges (e.g., coordination number 7) of the catalyst particles / agglomerates 304 / 306. In many cases, these regions (e.g., corners and edges) may also have less steric hindrance.

[0028] Multiple polymers can be grafted onto catalyst 304 / 306 to provide specific effects or enhancements. In various embodiments, polymer 302 has a specific function related to its structure. For example, polymer chain 302 can include more or less double bonds to reduce or enhance strength and / or rigidity, or can include specific functional groups (such as ionic groups) to provide specific properties. Grafted polymer 302 can have 10 to 500 repeating units, or more preferably 15 to 300 repeating units, or even more preferably 20 to 100 repeating units. The grafting density of catalyst particles can be 2 to 20 polymer chains per catalyst particle 306, or more preferably 5 to 18 chains per catalyst particle 306, or even more preferably 10 to 17 chains per catalyst particle 306.

[0029] In one or more embodiments, Figure 4A As shown in Figure 4B, one or more ionomer units 406 (e.g., a plurality of ionomer units) may be grafted onto the catalyst 402 or catalyst support 404 to enhance (ionic / electrical) conductivity (i.e., reactants, ions, and / or conductive bridges between the catalyst and the ionomer), for example, under dry conditions. Figure 5A-5BAs shown, a polymer unit 504 having free radical scavenging ability can be grafted onto a catalyst 502 to position free radical scavengers 506, 506', 506" where they are most needed and most effective (i.e., to eliminate or reduce scavenger migration). In yet another embodiment, as Fig. 6A and 6C As shown, polymer units 604 may be grafted onto catalyst 602 to prevent catalyst poisoning, such as by providing steric hindrance.

[0030] The chemical reactions that drive electrochemical cells often 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., through protons). Water 412 and a humid environment can further promote ionic conductivity and reactant transport, especially in the absence of ionomer 406 or when there is a small gap between the catalyst 402 and the ionomer 406. For example, it is possible to have long polymer chains (e.g., 10 4 da or more, 10 5 da or more, or even 10 6 The ionomer 406 of 200 Å or more may have difficulty in reaching the catalyst active sites, such as pores and cracks 408, due to, for example, steric hindrance. Figures 4A-4B shown.

[0031] However, under humid conditions, these pores 408 may also be filled with water 412, thereby maintaining ionic conductivity. However, the amount of water available in the battery can fluctuate greatly due to a variety of factors, including the environment, temperature, nominal relative humidity, battery age, how the battery is used, where the battery is used, and many other factors. Under dry conditions, the absence of water 412 may cause certain catalyst sites to be less active or even deactivated due to reduced ionic conductivity and reactant transport. Under humid conditions, these small gaps may be occupied by water 412 and have greater ionic conductivity, but under drier conditions, water 412 migrates from these areas, so humidity changes may affect the efficiency and operation of the electrochemical cell. However, grafting a polymer 410 with ionic functional groups onto the catalyst 402 or catalyst support 404 (especially when directly grafted onto the catalyst 402) can act as a bridge to maintain the reaction at the catalyst active site in the presence of reduced water content or even the absence of water 412. In a variant, the polymer grafted unit 410 may be larger than a conventional ionomer chain 406 (e.g. ) is much smaller. For example, oligomers or smaller polymer chains (e.g., 10,000 Da or less, or more preferably 5,000 Da or less, or even more preferably 1,000 Da or less) may be used. In one refinement, the polymer grafting unit 410 may have a molecular weight of 50,000 Da or less, or more preferably 25,000 Da or less, or even more preferably 20,000 Da or less. In one variation, the size (e.g., molecular weight or length) of the polymer grafting unit 410 may be 75% or less, or more preferably 50% or less, or even more preferably 25% or less of the size of the ionomer chain 406 or side chain.

[0032] In various embodiments, the polymer graft unit or bridge 410 may include an ionic functional group, such as an acid (e.g., a carboxylic acid and / or a sulfonic acid group). In one refinement, the equivalent weight relative to the ionic functional group (e.g., a sulfonic acid) may be 500 to 2000 g / mol, or more preferably 600 to 1500 g / mol, or even more preferably 650 to 1200 g / mol. In one variation, the grafted polymer unit 410 may be more hydrophilic than the corresponding ionomer 406 (e.g., having a greater equivalent weight, such as 800 g / mol, or more preferably 1000 g / mol, or even more preferably 1200 g / mol). In some embodiments, the polymer graft unit or bridge 410 may have a fluorinated polymer backbone or a non-fluorinated polymer backbone, such as a hydrocarbon backbone. For example, the grafted polymer unit 410 may be an ionomer-like or ionomer-like, but smaller (i.e., smaller molecular weight and / or chain length)—shorter ionomer chains. In other words, ionomer-like or The ionomer-like chain may refer to the use of a polymer chain having the same or similar chemical composition but smaller in molecular weight, chain length or repeating units. For an ionomer-like chain, the weight, length or unit may be at least 50% smaller, or more preferably at least 60% smaller, or even more preferably at least 75% smaller. For example, the grafted polymer unit 410 may have 10 to 500 repeating units, or more preferably 15 to 300 repeating units, or even more preferably 20 to 100 repeating units. In other words, the polymer grafted unit 410 may be a sulfonated tetrafluoroethylene-based fluoropolymer copolymer.

[0033] Various grafting densities can be used.For example, grafting density can be used to realize the required hydrophobicity or hydrophilicity around the catalyst site.For example, a larger grafting density may be needed to provide a more hydrophilic environment around the catalyst, to attract water 412 and promote reactants to advance / be transported to the catalyst site (for example, to enhance proton and / or oxygen diffusion). A more hydrophilic environment can also be better coordinated with water 412 to flood or fill such channels under more humid conditions, thereby further improving efficiency.For example, a grafting density of 2 to 20 chains can be used per catalyst particle 306, or more preferably per catalyst particle 306 has 5 to 18 chains, or even more preferably per catalyst particle 306 has 10 to 17 chains.

[0034] The dynamic and aggressive nature of the various chemical reactions occurring at the catalyst-ionomer interface are rich in free radical precursors and generate free radicals (e.g. OH) that can cause damage if not suppressed. For example, free radicals can compromise or degrade the stability of the ionomer. Traditionally, mobile free radical scavengers (e.g., cerium ions (e.g., Ce 3+ )) is used by adding / dispersing cerium oxide (e.g., cerium oxide nanoparticles) into the ionomer phase and / or proton exchange membrane (i.e., not near the catalyst). In other words, the free radical scavenger is far away from the main source of free radicals (i.e., the catalyst-reactant interface) and therefore provides less effective protection against free radicals. Moreover, even if well dispersed during the initial stages of the battery life, due to its mobility, the free radical scavenger tends to migrate and accumulate in more polar areas, such as the more humid parts / areas of the battery - again away from the main source of free radicals. For example, free radical scavengers such as cerium ions will often drift with the water flow to the proton exchange membrane and / or accumulate near the outlet, which is least affected by the free radicals, so once migration occurs, such scavengers will provide little benefit. These non-uniformities in density and scavenging ability are undesirable and inefficient.

[0035] In yet another embodiment, the free radical scavenger 506, 506', 506" may be positioned by a polymer unit 504 grafted to a catalyst support or more preferably a catalyst 502, such as Figure 5A-C. In this way, the radical scavengers 506, 506', 506" are close to or near the main source of free radicals to achieve the most efficient and effective neutralization or stabilization of free radicals. In various embodiments, the polymer grafting unit 504 can be grafted onto, for example, a less active area / facet (such as a corner or edge) of the catalyst 502. The polymer grafting unit 504 can include one or more radical scavenging functional groups or position such radical scavengers 506. For example, the radical scavenger 506 can ionically bond or form crosslinks 506, such as weak crosslinks throughout the polymer chain 504. In another embodiment, the radical scavenging nanoparticle 506' can be bonded to the end of the polymer chain 504 opposite the catalyst 502, such as by a covalent bond. In yet another embodiment, the radical scavenger 506" can form a part of a complex, coordination compound and / or metal organic framework 506".

[0036] The polymer backbone or scavenger backbone chain is not particularly limited and can be any suitable polymer. However, the polymer units described herein, such as fluoropolymers and / or ethylene (e.g., sulfonated tetrafluoroethylene-based fluoropolymer-copolymers) may be particularly useful. In one variation, the polymer grafting unit 506" may be modified and / or capable of complexing Ce 3+ Clusters or coordination compounds, such as Ce 3+ The metal organic framework, ie, the polymer grafted unit 504 comprises a coordinated / complexed free radical scavenger.

[0037] In various embodiments, molecules, ions, compounds, or atoms capable of scavenging free radicals can act as weak crosslinks 506, such as Figure 5A As shown. In some variations, small clusters or single atoms (e.g., cerium ion clusters or cerium ions) may weakly bind to ionic groups (e.g., sulfonate groups of grafted polymer units 504). Weak crosslinks 506 will separate or break to scavenge free radicals. This technique mitigates or slows migration while still providing the benefits of mobile free radical scavengers.

[0038] In one or more embodiments, one or more cerium particles 506' (eg, cerium nanoparticles) can be disposed on the polymer chain 504, for example, near the end of the grafted polymer unit 504 opposite the catalyst 502, such as Figure 5B As shown. In one refinement, the cerium particles can form bonds (e.g., strong adsorption bonds, electrostatic bonds, hydrogen bridges, chelate bonds, etc.) that can be broken during operation of the electrochemical cell, thereby releasing the cerium nanoparticles. This at least temporarily fixes the free radical scavengers so that they cannot migrate and are located near the catalyst. When cerium is directly bound to the polymer graft, it ensures a minimum concentration of free radical scavenging amounts close to the catalyst active sites.

[0039] In yet another embodiment, the grafted polymer unit 504 may be or include a complex coordination compound and / or a metal organic framework (MOF) 506". In a variation, the MOF 506" may include a free radical scavenger, such as cerium. The MOF 506" may be a free radical scavenger, such as cerium (III) ions (e.g., Ce 3+ ) provides the correct oxidation and more effectively provides free radical scavenging. In addition, this strategy can also provide a minimum concentration of cerium.

[0040] In various embodiments, one or more of the above strategies, each of which provides unique benefits for localization and free radical scavenging, can be combined.

[0041] In yet another embodiment, the grafted polymer units 604 can be used to protect the catalyst 602, for example, to prevent it from being degraded or damaged. For example, catalyst poisoning (e.g., from, for example, This is common with common ionomers such as The inclusion of sulfonic acid groups that are capable of binding to catalyst facets or surfaces, thereby reducing or preventing the desired catalytic activity, is often referred to as catalyst poisoning. As noted above, the ionomer and catalyst must generally be in close proximity to promote the desired catalyst-reactant interface and provide adequate reactant transport to the catalyst. However, this can be problematic because over time, the ionomer responsible for transporting such reactants may attack the catalyst, thereby reducing its efficiency.

[0042] In one or more embodiments, polymer chains 604, 604' may be grafted onto catalyst 602 to protect it from such reactions with ionomer 606 or harmful functional groups thereon (eg, sulfonic acid groups), such as Fig. 6A and 6C In various embodiments, the grafted polymer chains 604, 604' can protect the catalyst 602 from harmful functional groups (e.g., steric hindrance). For example, short and / or rigid polymer chains 604' can prevent the ionomer chains 606 from directly contacting the catalyst 602 (e.g., Figure 6C Without such steric hindrance, such ionomer branches 606 can freely contact the catalyst surface so that the sulfonic acid groups can be bound to the catalyst surface (such as Figure 6B In one refinement, these polymer chains 604 can be rigid to provide better steric hindrance. In a variant, the polymer chain 604 can resist self-folding, for example, include multiple double bonds, include large functional groups, such as cyclic rings (e.g., benzene rings) and / or form semi-crystalline structures or crystalline domains within itself or with adjacent chains. In one refinement, the polymer chain can have a bending stiffness (k of at least 3, or more preferably at least 10, or even more preferably at least 25, or even more preferably at least 50. bIn yet another embodiment, the grafted polymer chain 604' may have a persistence length (L) of at least 4.5 angstroms, or more preferably at least 5.0 angstroms, or even more preferably at least 6.0 angstroms, or even more preferably at least 7.0 angstroms. p ) or at least 8.0 angstroms, or more preferably at least 8.5 angstroms, or even more preferably at least 9.0 angstroms. In one variation, the use of polymer chains 604 with large functional groups, such as cyclic rings (e.g., benzene rings), can provide suitable steric hindrance while reducing the overall grafting density, thereby reducing catalyst poisoning without significantly reducing catalytic activity. For example, polyethylene terephthalate and / or styrene polymer chains can be grafted onto catalyst 602.

[0043] 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 carrier (i.e., step 704), providing a monomer, oligomer, and / or polymer (i.e., step 710), depositing the catalyst on the catalyst carrier (i.e., step 708), and forming or grafting polymer units on the catalyst (i.e., step 712). In one or more embodiments, the catalyst and the catalyst carrier can be dissolved and / or dispersed in a solvent to form a dispersion or ink. The mixture can also include an adhesive, such as an ionomer adhesive. The solvent can be water and / or an organic solvent (e.g., alcohol). In various embodiments, the mixture can be dried and formed to form a composite material or a catalyst layer.

[0044] The catalyst may include platinum, platinum alloys, ruthenium, palladium, iron nitrogen. In one refinement, catalyst nanoparticles may be used. In one or more embodiments, the catalyst nanoparticles are added to the catalyst ink or slurry (i.e., step 706) and precipitated onto the catalyst support. In yet another embodiment, a catalyst precursor may be used. For example, H 2 PtCl 6 , K 2 PtCl 4 , K 2 PtCl 6 、Pt(NO 3 ) 4 or other platinum salts, such as organic platinum precursor salts. In various embodiments, other noble metal precursor materials may be used for grafting, such as by adding them to the grafting process to form a platinum alloy catalyst. For example, platinum (II) (i.e., Pt 2+ ) or platinum (IV) (Pt 4+ ). The catalyst support may be carbonaceous, such as carbon black or a metal oxide. In yet other embodiments, commercial catalyst-catalyst support products, such as platinum on carbon, may be used.

[0045] The polymer units can be grafted onto the catalyst before or after the catalyst is deposited onto the support. In yet another embodiment, the polymer units can be formed or grown in solution and / or grafted simultaneously with deposition, such as in an ink / slurry. Depending on the polymer units used, further steps may be required. For example, if a scavenger such as a coordination compound, complex or weakly crosslinked form is introduced into the polymer grafted unit, a metal oxide powder such as cerium oxide can be added to the ink or added after the catalyst is deposited and the polymer units are grafted. In yet another embodiment, cerium oxide can be added to the ionomer so that when the catalyst layer and ionomer are assembled, the cerium ions (Ce 3 + ) are attracted to the catalyst and interact with the polymer chains to keep the cerium ion scavenger positioned around the catalyst.

[0046] Although exemplary embodiments are described above, these embodiments are not intended to describe all possible forms covered by the claims. The words used in the specification are descriptive rather than restrictive words, and it should be understood that various changes can be made without departing from the scope of the present disclosure. As previously mentioned, the features of each embodiment can be combined to form further embodiments of the present invention that may not be clearly described or illustrated. Although each embodiment may be described as providing advantages or being superior to other embodiments or prior art embodiments in terms of one or more desired characteristics, it will be recognized by those of ordinary skill in the art that one or more features or characteristics can be sacrificed to achieve the desired overall system properties, depending on the specific application and implementation. These properties may include, but are not limited to, cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, applicability, weight, manufacturability, ease of assembly, etc. Therefore, if any embodiment is described as being less ideal than other embodiments or prior art embodiments in terms of one or more characteristics, these embodiments are not outside the scope of the present disclosure and may be ideal for a specific application.

Claims

1. An electrochemical cell comprising: a pair of electrodes; and A plurality of catalyst particles are deposited on a catalyst support, each catalyst particle having a more active portion, a less active portion, and a polymer chain grafted onto the less active portion, wherein the polymer chain provides steric hindrance near the catalyst to reduce catalyst poisoning.

2. The electrochemical cell of claim 1, wherein the electrochemical cell is a fuel cell.

3. The electrochemical cell of claim 1, further comprising an ionomer adjacent to the catalyst particles and having acid functional groups. The electrochemical cell of claim 3 , wherein the ionomer comprises sulfonic acid groups.

5. A catalyst layer comprising: Catalyst carrier; a catalyst deposited on a catalyst support; and A plurality of polymer chains are grafted onto the catalyst, the plurality of polymer chains providing steric hindrance to reduce catalyst poisoning.

6. The catalyst layer according to claim 5, wherein the polymer chains have a bending stiffness (k b ).

7. The catalyst layer according to claim 6, wherein the bending stiffness (k b ) is at least 25.

8. The catalyst layer of claim 5, wherein the polymer chains have a persistence length of at least 5.0 angstroms.

9. The catalyst layer of claim 8, wherein the polymer chains have a persistence length of at least 6.0 angstroms.

10. The catalyst layer of claim 5, wherein the polymer chains have a Coulomb length of at least 8.0 angstroms. The catalyst layer of claim 10 , wherein the polymer chains have a Coulomb length of at least 8.5 angstroms.

12. The catalyst layer of claim 5, wherein the polymer chains contain double bonds.

13. The catalyst layer of claim 6, wherein the polymer chains are cyclic. The catalyst layer of claim 13 , wherein the polymer chain comprises a benzene ring.

15. The catalyst layer of claim 5, wherein the catalyst has a grafting density of at least 2 to 20 chains per catalyst particle.

16. A method for preparing a catalyst layer, comprising: providing a catalyst supported by a catalyst carrier; as well as The polymer chains are grafted onto the less active facets of the catalyst.

17. The method of claim 16, wherein the polymer chains have a bending stiffness (k b ).

18. The method of claim 16, wherein the polymer chains have a persistence length of at least 4.

5.

19. The method of claim 16, wherein the polymer chain has a Cohn length of at least 8.0 angstroms.

20. The method of claim 16, wherein the polymer chain comprises double bonds.

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