Hdv-enabled electrochemical electrode with novel composition, structure and manufacturing method

Abstract

To provide a novel catalyst layer (CL) composition and a structure that provide excellent durability and sustained catalyst performance for contemplated large vehicle applications.SOLUTION: A CL composition and a structure include: an internal composition composed of binder-coated nanoparticles, binder-free catalyst nanoparticles, and regular electrical, ionic, gas, and liquid pathways; a multilayer structure with different packing densities between multiple sub-layers; and an external pattern of an outer surface of the CL. An improvement in CL durability and catalyst performance is achieved, and by using the CL of the present invention, a novel solid electrolytic plating process is demonstrated and a novel thin film coating catalyst product is obtained. The binder-coated nanoparticles function as interconnecting substrates or sites to which nanoparticles that are not coated on their binder-coated surface are adhesively attached, and achieve a regular structure in which the binder-free catalyst nanoparticles are consistently interspersed between the binder-coated nanoparticles and their aggregates.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates generally to electrochemical electrodes such as those used in hydrogen fuel cells and electrolyzers, and energy storage devices, and more particularly to electrochemical electrodes suitable for use in fuel cells in heavy duty vehicle (HDV) applications. [Background technology]

[0002] The composition and fabrication technology of catalyst coated membranes (CCMs) are core building blocks of electrochemical products. Several factors prevent competitors from achieving the best performance products at a cost that can meet the long-term clean energy market demand. Ballard Power is one of the leading companies developing high performance CCM products and owning the commercial manufacturing process technology. A CCM is an electrode containing two catalyst layers coated on a solid electrolyte membrane. A membrane electrode assembly (MEA) is an assembly of CCMs with one gas diffusion layer on each side. Current state-of-the-art MEAs have a Pt / cm2 concentration of approximately 0.300 mg Pt / cm2. 2They can generate power densities ranging from 0.78 to 1.2 watts per square centimeter. However, throughout the past several decades of development, the commercial target for such small, portable generators has been passenger vehicles. Since 2015, the electrochemical vehicle market has shifted to the commercial taxi market due to limitations in hydrogen fuel cell (HFC) vehicles' hydrogen fueling stations. Since 2019, due to severe air pollution in China, the Chinese government has been committed to pursuing clean energy power generation for transportation vehicles, including public transportation, ships, and trucks. With market demand shifting to commercial applications, most technology development has prioritized cost, durability, and performance over all other factors, including the strong zero-emission capabilities of all HFC-powered products. Furthermore, the world as a whole is refocusing its product demands on the same trends for light-duty vehicle (LDV), medium-duty vehicle (MDV), and heavy-duty vehicle (HDV) markets. Since these sectors are a greater source of greenhouse gases compared to passenger vehicles, it is clear that in order to reduce greenhouse gas (GHG) emissions, these commercial sectors must first adopt zero-emission technologies such as those mentioned above.

[0003] For the HFC market, durability and cost have become key economic factors for meeting all commercial HDV applications. The migration of passenger car HFC powertrains to HDV applications is not a long-term, sustainable solution. Therefore, the development of durable, cost-effective HFC products is highly desirable. For an electrochemical stack to reach more than 25,000 hours under normal operating conditions at high power density, compared to 5,000 hours for passenger cars, the CCM or its MEA, the core component of a fuel cell (FC) stack, must reach or exceed such durability. Prior to this application, no such technology or product capable of meeting current market needs in terms of cost and performance sustainability has been disclosed in the public domain.

[0004] In a 2019 publication of the Electrochemical Society (ECS), Schuler et al. [Reference 16] stated that catalyst layer (CL) structure is crucial for enabling durable and highly catalytic electrodes. In this paper, Schuler et al. theorized various components that affect power density within CL structures fabricated using known methods. They further measured and identified various sub-resistances of the CL components. Notably, their results indicated that Knudsen and ionomer transport resistances were the dominant CL resistances, followed by interfacial resistance. Through their systematic study, Schuler et al. concluded that the CL design and fabrication process significantly impacted the through-plane CL resistance, even for the same CL thickness. Therefore, fabricating durable and catalytically active CLs has proven to be an enormous challenge in science and engineering.

[0005] As MEA is a core component of hydrogen-based electrochemical stacks, its CL degradation has become a significant challenge to the expansion and upswing of the market.

[0006] Hu et al. [Reference 9] summarized three key durability degradation mechanisms for polymer electrolyte membrane fuel cells (PEMFCs) that shorten their lifetime under typical operating conditions: (1) degradation of durability under start-up and shutdown conditions; (2) durability under dynamic load cycling; and (3) durability of PEMFCs under idle and high load cycling. In the first mechanism, the high reversal potential of 1.6 V generated at the interface from unprotected start-up causes corrosion of the catalyst support, leading to the aggregation and growth of Pt-based catalyst particles. This process directly results in the loss of electrochemical surface area (ECSA) of the catalyst during CL, which is a key factor in durability degradation. In the second mechanism, the degradation of Pt / C anode materials was found to be responsible for the majority of PEMFC performance degradation under accelerated stress test (AST) cycling [Reference 18]. Various publications have observed the growth and agglomeration of Pt nanoparticles. Furthermore, membrane thinning and catalyst layer decay were the two main factors behind the persistent performance degradation under this accelerated aging test [Reference 5]. In the publication [Reference 5], it was found that after 370 hours of testing, the uniformity of the Pt-based catalyst changed, with some of it migrating into the membrane. More cracks and gaps were observed in the CL. The microstructural change was concluded based on the correlation between the loss of ECSA and the increase in membrane resistance and charge transfer resistance. Furthermore, regarding the third mechanism, many scholars have demonstrated that fuel cell performance deteriorates more rapidly when electrochemically operated at high power. Jian Xie [Reference 1] reported that when the current density was 0.8 A / cm 2demonstrated that degradation of FC output voltage is significantly accelerated above 0.25 V. Hu's findings in 2018 [Reference 10] were largely consistent with those summarized by Bruijn in 2008 in Section 4.2, Electrode Degradation Mechanisms [Reference 3]. De Bruijn [Reference 8] summarized that key factors include loss of ECSA, supported carbon corrosion, oxygen evolution due to reverse potential, and other degradation factors including ionomer, gas diffusion layer (GDL), and macroporous layer (MPL).

[0007] De Bruijn further concluded that the primary cause of steady-state degradation under constant load conditions was a decrease in the drainage capacity of the GDL. Other contributing factors included (1) membrane degradation, which led to a short lifespan, and (2) Pt particle growth, which led to a steady decline in cell potential. However, Bruijn also showed that degradation rates could increase by orders of magnitude under AST or vehicle load cycles, start-stop, low humidification, and fuel starvation. Through years of research and development, these challenges have been at least partially overcome by energy management, utilizing system controls such as air purging to remove residual hydrogen. However, no clear method or CL composition or structure has been shown to overcome these existing challenges and deliver high power output and excellent long-term durability for the much more desirable HDV application. The HDV AST protocol was published by the U.S. Department of Energy (DOE) in November 2019.

[0008] In his 2020 paper, Rodney Burrup [5], titled "Recent Developments in Catalyst-Related PEMFC Electrochemical Durability," pointed out that catalyst particle growth and loss, as well as support corrosion, are important factors in MEA degradation. The morphology of the electrode layer was also found to play a key role in fuel cell performance and durability. Finally, Burrup concluded that degradation of Pt and Pt alloy catalyst nanoparticles and cathode electrode structures remains a major concern hindering the commercialization of PEMFCs for transportation applications. Furthermore, catalyst and support ASTs continue to provide useful information on the relative stability of materials and benchmarking for catalyst-based solutions that do not require system mitigation strategies to achieve sufficient lifetimes.

[0009] Schuler

[16] identified various sub-resistance components in CL. However, Schuler did not provide a solution to the problem, instead stating that further research was needed.

[0010] One objective of the present application is to overcome the identified sub-resistance contributors and improve performance and durability by providing novel CL compositions, novel CL structures, and / or combinations thereof.

[0011] Another object is to provide novel, durable catalyst products that minimize or reduce the dissolution and / or growth.

[0012] In another area, the use of durable and cost-effective supported catalysts in electrochemical reactions has been the subject of extensive research and development over the past few decades. The driving force behind this is the reduction in the cost of long-life clean energy products. Many innovative structures and geometries of active catalysts, either on supports or alone, have been developed and tested. However, most of them are only available in the range of 25-50 cm. 2The lifespans of MEA tests with a surface area of ​​1000 nm were significantly shorter. Many of them could not even be fabricated into good MEAs because homogenization of such catalysts or supported catalysts is extremely difficult. Some highly active catalysts deteriorated rapidly due to unstable structures, including cage structures and dealloyed framework structures. Such structures cannot provide stable activity due to rapid changes in their initial structure. It is an indisputable scientific fact that electrochemical catalytic reactions in fuel cell applications involve powerful catalytic reactions.

[0013] Ruan presented plate-shaped nanocatalysts on supports in 2011, and these nanocatalysts showed exceptional durability compared to other commercially available catalysts in the same category. However, activity declined due to the loss of ECSA, albeit at a much slower rate.

[0014] Therefore, another object of the present application is to address the loss and resulting degradation of ECSAs found in the prior art.

[0015] Thin films of platinum on bulk supports are well known to be highly durable in fuel cell electrochemical processes. However, due to the limited surface area on bulk supports, the required amount of platinum is not feasible for commercial applications. This was the primary reason for the increased adoption of hydrogen fuel cell technology after the development and testing of supported nanocatalysts. Platinum and its alloys or composites have been extensively researched and developed due to the dramatic reduction in the loading of platinum, the most stable and active material. However, it is not possible to utilize currently known processes (including chemical vapor deposition (CVD), physical vapor deposition, metal-organic CVD, impregnation, photochemical methods, etc.) to fabricate thin-film coated nanoparticle supports. One major obstacle is the lack of known means to manipulate individual nanoparticles to achieve the required orientation or to fix nanoparticles in the proper position to produce a uniform thin-film coating on them. In any wet chemistry, spherical catalyst nanoparticles are formed by thermodynamic conditions.

[0016] Therefore, another object of the present application is to provide supported nanoparticles coated with thin films (nanometer or angstrom thick) for much desired improvement in electrochemical or other catalytic applications.

[0017] As demonstrated by the past 20 years of research, development, and road testing, the technical challenges of achieving high power density with exceptional endurance remain.

[0018] In response to this demonstrated need for novel solutions, applicants have developed several superior techniques, the details of which are disclosed below. Summary of the Invention

[0019] In no particular order, certain inventive aspects of the present application are summarized below, other aspects of which will become apparent from reading the following detailed description of the preferred embodiments.

[0020] According to a first aspect of the present invention, there is provided a supported catalyst product coated with a thin film of catalytic material, the supported catalyst product comprising: a) nano-sized conductive solid nanoparticles; and b) a thin film of catalytic material deposited on the surface of the conductive solid nanoparticles.

[0021] According to a second aspect of the present invention, there is provided a catalyst layer composition comprising: Binder-coated nanoparticles coated with a binder as a binding substrate; Binder-free catalyst nanoparticles attached to at least binder-coated nanoparticles by their binder matrix; regular electrical, ionic, gas, and liquid pathways within the layer that are defined at least in part by the interconnections of binder-coated nanoparticles and binder-free catalytic nanoparticles; A catalyst layer composition is provided comprising:

[0022] According to a third aspect of the present invention there is provided a method of preparing a catalyst layer ink mixture comprising the steps of: a) in any order or simultaneously, i. preparing a binder-coated nanoparticle ink solution consisting of solid nanoparticles homogenized in a first selected solvent solution and then homogenously mixed with a solution of a binder that coats the solid nanoparticles; ii. preparing a binderless catalyst nanoparticle ink solution consisting of binderless catalyst nanoparticles homogenized in a second selected solvent solution without the addition of a binder; b) slowly adding the binder-coated nanoparticle ink solution from step (a)(ii) to the binder-free catalyst solution from step (a)(i) to attach the binder-free catalyst nanoparticles to the binder-coated solid nanoparticles in the resulting mixed ink solution; A method is provided which includes:

[0023] According to a fourth aspect of the present invention, there is provided a method for manufacturing a laminated laminate comprising: a) an innermost layer characterized by a first material packing density; b) an outermost layer opposite the innermost layer and characterized by a second material packing density; one or more intermediate layers present between the innermost layer and the outermost layer, each characterized by a respective material packing density different from the first material packing density or the second material packing density; A catalyst layer structure is provided having a multi-layer catalyst layer comprising a plurality of sub-layers including:

[0024] According to a fifth aspect of the present invention, there is provided a method for producing a catalyst layer structure from the fourth aspect of the present invention, comprising the steps of: a) preparing or obtaining a catalyst layer ink comprising a mixture having at least catalyst nanoparticles and a binder in a solvent system; b) depositing a first layer of catalytic material on the solid substrate at a first packing density by coating the solid substrate with uniform aggregates from the catalytic layer ink by controlling a set of process parameters, thereby forming an innermost layer; c) depositing at least one additional layer having a different respective packing density of catalyst material onto the innermost layer by coating the innermost layer with different sized aggregates from the catalyst layer ink through controlled adjustment of one or more of the process parameters, thereby forming one or more intermediate layers. d) immediately depositing a final layer with a different packing density of catalyst material onto the one or more intermediate layers by coating the one or more intermediate layers with more catalyst layer ink under controlled adjustment of at least one of the process parameters, thereby forming an outermost layer of the catalyst layer structure; e) subjecting the catalyst layer structure to a heat drying process to remove any residual solvent; A method is provided which includes:

[0025] According to a sixth aspect of the present invention, there is provided an outer patterned catalyst layer composed of the catalyst layer composition of the second aspect of the present invention, an exterior surface having an exterior pattern formed thereon, the pattern comprising: a) a raised area on the outer surface of the catalyst layer; b) a compressed region on an outer surface of the catalyst layer, the compressed region being in a recessed relationship with the raised region; is further characterized by the raised regions and compressed regions are staggered on the outer surface of the catalyst layer; An outer patterned catalyst layer is provided.

[0026] According to a seventh aspect of the present invention, there is provided a method of forming an externally patterned catalyst layer from the seventh aspect of the present invention, the method comprising starting with an already fabricated catalyst layer having a catalyst layer composition from the second aspect of the present invention, followed by imparting an external pattern to the already fabricated catalyst layer.

[0027] According to an eighth aspect of the present invention, there is provided a solid electroplating method for producing a supported catalyst product coated with a thin film of the catalytic material according to the first aspect of the present invention, the method comprising using an electrode having a catalytic layer comprising the electrocatalyst layer composition from the second aspect of the present invention and the electrocatalyst layer structure from the fourth aspect of the present invention, and subjecting the electrode to an electrochemical reaction during which the catalytic nanoparticles in the catalytic layer are redistributed to form a thin film of the catalytic material on the nano-sized conductive solid nanoparticles.

[0028] Key factors affecting the durability of PEMFCs are largely related to the catalyst materials, their supports, and the cathode electrode structure. Disclosed embodiments of the present invention optimize these factors to achieve improved performance and extended durability of the resulting MEAs of the present invention, providing a unique solution for meeting or exceeding benchmarks for laser diode, membrane diode, and high-voltage vehicle (HDV) applications. More specifically, embodiments of the present disclosure include novel catalyst products having durable thin-film coatings of catalyst materials, high-performance, durable electrochemical electrode compositions and inventive multilayer structures for producing and maintaining such high performance, and external patterning that localizes the catalyst particle dissolution and redeposition process, providing excellent redistribution of Pt nanoparticles, imparting superior durability to the fabricated electrodes. Embodiments of the present disclosure also disclose novel methods for fabricating the highly durable and high-performance catalyst-coated membranes (CCMs) of the present invention.

[0029] Additionally, the invention disclosed herein is suitable for other catalytic processes, including advanced oxidation processes for water treatment, industrial fixed-bed reactors, and high-temperature solid oxide fuel cells, all of which may benefit from the significant improvements of the inventive composition of the catalyst layer.

[0030] In this application, the term catalytic nanoparticles encompasses both catalytic nanoparticles themselves and catalytic nanoparticles disposed on support nanoparticles. The support nanoparticles may be conductive or non-conductive nanoparticles. As used herein, nanoparticles primarily refer to particles ranging in size from 1 nanometer to 999 nanometers. [Brief explanation of the drawings]

[0031] Preferred embodiments of the present invention will now be described in conjunction with the accompanying drawings. [Figure 1] FIG. 1 is a schematic diagram of ionomer-coated catalyst particle clusters in a prior art catalyst layer of a hydrogen fuel cell. [Figure 2] 1 is a schematic diagram of clustered ionomer-coated catalyst particles and ionomer-free catalyst particles in the novel catalyst layer of the present invention. FIG. [Figure 3] FIG. 1 is a schematic diagram of a membrane electrode assembly of the present invention in which the catalyst layer is composed of multiple sublayers, each of varying density. [Figure 4] 4 is a chart showing power density measurements of tested membrane electrode assemblies of the type shown in FIG. 3. [Figure 5] FIG. 2 is a schematic diagram illustrating an external patterned catalyst layer of the present invention. [Figure 6] FIG. 10 is a schematic diagram illustrating compressing a membrane electrode assembly (MEA) between two flow field plates to form external patterning on the catalyst layer of the MEA. [Figure 7] 1 is a scanning electron microscope (SEM) image of an externally patterned catalyst coating film of the present invention. [Figure 8] FIG. 8 is an end-of-life (EOL) cross-sectional view of the externally patterned catalyst coating film shown in FIG. 7. [Figure 9] 10 is an SEM image of a CL of the present invention with a densely packed outer layer showing a smooth surface finish before testing. [Figure 10] 10 is an SEM image showing a cross-sectional image of a CL of the present invention after testing, showing catalytically enriched bands on the PEM side of the CL. [Figure 11] 1 is a scanning electron microscope image of three different regions of a CL of the present invention, where the content of those regions was measured. Detailed Description of the Invention

[0032] In most current CL ink compositions, the composition contains catalytic nanoparticles, an ionomer used as a binder, and some conductive nanoparticles. However, the compositions are often homogenized together before coating the CL. The key to such ink formulation relies on the selection of highly active catalytic nanoparticles, the type and ratio of ionomers, the selected solvent system, and the homogenization method and procedure. The resulting CL must be primarily one homogenous composition layer with similar or identical content throughout the layer. The resulting CL also required highly complex activation processes and steps to achieve optimal performance and the required lifespan. These remaining challenges have been fully explained above.

[0033] This application discloses a completely novel design of CL composition and layer structure. A first portion of nanoparticles is mixed with a binder, such as one or more ionomers. Either conductive or non-conductive nanoparticles can be used in this process. It is preferable to utilize conductive nanoparticles to reduce or minimize their additional contribution to electrode resistance, which is critical for high power density applications. When non-conductive or semi-conductive nanoparticles are used, it is preferable to use more binder and minimize the amount of non-conductive or semi-conductive nanoparticles to achieve the same goal of minimal additional layer resistance.

[0034] It is even more preferable to use catalyst nanoparticles with high electrical conductivity, which are well known for fuel cell or electrolyzer applications. Therefore, to achieve the desired performance and durability of the fabricated CL, the correct ionomer-to-catalyst ratio, which is easily determined by those skilled in the art, is important. The simple reason for this requirement is that most ionomers are both electrically insulating and ionically conductive. Too much ionomer leads to high resistance. Using too little ionomer results in too low proton conductivity to achieve the desired power density.

[0035] More importantly, this portion of the solid nanoparticles after homogenization and mixing, generally referred to herein as binder-coated nanoparticles, acts as intentionally binding nanoparticles for binding with binder-free catalyst nanoparticles. The use of binder-free catalyst nanoparticles bound to the coating surface of binder-coated nanoparticles is innovative, as such a new interconnected structure significantly reduces ionomer resistance, since the binder-free catalyst nanoparticles are free to react with adsorbed gas molecules while the underlying or adjacent ionomer layer on the binder-coated nanoparticles provides the necessary protons in the case of fuel cell CLs. This composition, in which binder-free nanoparticles adhere to binder-coated nanoparticles and form an ordered interconnected structure with the binder-free nanoparticles, is disclosed for the first time herein.

[0036] Furthermore, applicants have discovered that when binder-coated nanoparticles alone are unable to provide the catalyst particles with the electrons necessary for the desired electrochemical reaction, the addition of binder-free conductive nanoparticles provides more benefit by adding more conductive paths to the binder-free catalyst nanoparticles.

[0037] In previous publications, conductive carbon supports were used in some electrode inks to reduce layer cracking in thin catalyst layers (less than 5 microns) and provide additional conductivity. In most commercial processes, most anode CLs were decal-transferred onto the membrane (CCM). Adding carbon to the ink mixed with the catalyst can provide a smooth CL layer for better decal transfer. The addition of the same or similar carbon support to the cathode of a PEMFC has not been utilized in the prior art because inactive supports could degrade catalytic performance and the additional layer thickness could reduce mass activity due to increased water penetration in thicker layers. There are conflicting priorities regarding CL cracking: smoothing cracks in cathode CLs is less of a significant issue than cracks in anode CLs, which can cause incomplete CL transfer to the membrane. As disclosed below, the present invention encompasses a unique composition of CLs that utilizes bare conductive supports in CLs in a manner that is significantly more beneficial than the potential adverse effects of the prior art.

[0038] In most commercial and research publications, catalyst inks were prepared by simultaneously adding and mixing all solids to form a homogeneous solution before coating. The bonding between nanoparticles was random and arbitrary. In the present invention, we utilize some nanoparticles as bonding centers to which more catalytically active catalyst nanoparticles are bonded. Our design allows for the following additional advantageous properties: (1) By spreading the catalyst nanoparticles within the gas or liquid-entering spaces or channels, this expansion of the catalyst nanoparticles into the reaction space can enhance the catalytic reaction. (2) This structure minimizes ionomer resistance because the proton-conducting ionomer is coated onto the binder-coated nanoparticles, allowing the majority of the binder-free catalyst particles to react with the incoming fuel molecules and generate electricity. (3) The attachment of interconnected binder-free catalyst nanoparticles to binder-coated nanoparticles can enable the formation of more gas and / or liquid channels between the binder-free nanoparticles or their aggregates, as shown in Figure 2, which is highly beneficial for the desired electrochemical reaction.

[0039] As will be appreciated by those skilled in the art, the CL compositions of the present invention disclosed herein below can work with any catalyst binder, examples of which include cationic ionomers, anionic ionomers, or even PTFE, in a variety of ink formulations for a variety of applications.

[0040] 1) Addition of binder-free catalyst to the catalyst layer In their publication (2012) entitled "Influence of ink composition on the electrochemical properties of Pt / C," Kocha et al. reported that RDE experiments showed that in the absence of Nafion® (a cationic ionomer that acts as a proton conductor as well as a binder for catalyst particles), Nafion-free Pt / C particles exhibited higher oxygen reduction reaction (ORR) ratios and mass activities than Pt / C electrodes incorporating approximately 1.8 times more Nafion in a 0.1 M HClO4 electrolyte. However, in one example, 50 cm3 electrodes with an average thickness of over 10 microns were used. 2 For electrodes with semi-industrial-sized CCMs, such as those described above, the absence of ionomer as a binder in the catalyst layer leads to rapid disintegration and uneven redistribution of the catalyst at the vertical position. Even without ionomer, CLs with thicknesses of 5 to 10 microns can conduct protons well under operating conditions. Numerous scientific experiments have shown that without the correct amount of ionomer for CLs in PEMFCs, catalyst-coated membranes perform poorly. In contrast, the present applicant discloses compositions containing several ionomer-free catalysts in electrodes fabricated with CLs that are capable of producing high power output and have excellent durability. Embodiments of the present disclosure include blending an ionomer-coated catalyst with an ionomer-free catalyst to fabricate CLs using any bare conductive support, in addition to the same or different catalyst materials. Such inventive compositions have been found to significantly alleviate several known issues related to electrode performance and durability, including sub-resistance of various components such as the ionomer, electronic insulating layers of the ionomer, and inaccessible gas pathways. The hypothesized mechanism of such a new composition in CLs is shown in Figure 2.

[0041] Figure 1, taken from reference 16, shows a conventional CL in which all catalyst particles are ionomer-coated particles, e -The light dashed lines marked with a dot indicate the restricted electron conduction pathway. The voids (pores) surrounded by the ionomer are inactive unless reactant gas molecules diffuse through the ionomer layer to the surface of the ionomer-coated catalyst particle. In the enlarged portion on the right side of Figure 1, more than approximately 60% of the particle is within the inactive region. Thus, many catalyst particles are rendered inactive by the ionomer coating. However, Figure 2 shows a particle structure within a CL of the present invention that contains both ionomer-coated and ionomer-free catalyst particles, of which the ionomer-coated catalyst particles are visually distinguishable in the enlarged portion on the left side by surrounding these coated particles with a visually contrasting outer ring that indicates the ionomer coating on the particle's periphery. The ionomer-free catalyst particles are directly exposed to the incoming gas molecules, while the ionomer-coated catalyst particles interconnect to form the necessary proton conductors. The amount of ionomer used in the first ionomer-containing portion of the overall catalyst content of the CL is selected to provide sufficient proton conduction pathways as well as partially exposed carbon-supported surfaces to allow the ionomer-coated catalyst particles to electrically connect to each other or to other particles to maximize the desired electrochemical reaction.

[0042] On the unmagnified right side of Figure 2, the large black circles and ovals represent agglomerated catalyst particles that have been premixed with a binder, e.g., a cationic ionomer, and are therefore shown surrounded by a visually contrasting outer ring. On the magnified left side of Figure 2, the black circles lacking the contrasting outer ring represent supported, ionomer-free catalysts that lack their own ionomer coating but are attached to the outer ionomer layer of the agglomerates. As shown on the unmagnified right side of Figure 2, an appropriate mixing ratio is selected to connect the agglomerates to each other. The smaller, darker dots represent additional conductive support material (e.g., bare carbon) that provides better electron paths between the faces to enhance catalytic activity. e s -The lighter pathway lines labeled O represent electron pathways, and the darker pathway lines labeled O represent gas molecule pathways. The diagram shows the labeling for oxygen gas, but hydrogen gas or other gas molecules could be used as well.

[0043] As Schuler shows on the left side of Figure 1, the ionomer does not need to cover all interconnected catalyst particles. The secondary pores in Figure 1 allow more gas molecules to migrate and reach the catalyst nanoparticles, while the primary pores allow gas to permeate through the ionomer layer to reach the catalyst nanoparticles. Because of the large number of secondary pores in our CLs, the enclosed spaces between particles in the enlarged inset of Figure 2 of our CLs can contain a certain amount of water, which is also a proton-conducting material. High-temperature fuel cells use water as a proton conductor in CLs and polytetrafluoroethylene (PTFE) as a high-temperature binder. Therefore, our novel CL compositions can take advantage of this advantage and use less ionomer for better catalytic performance. Less ionomer in well-constructed CLs reduces the ionomer-induced resistance in the CLs, which is in good agreement with Schuler's conclusion.

[0044] In addition, catalyst solutions with lower catalyst particle loadings, or even non-catalyst loaded solutions containing bare conductive support nanoparticles, can be used in the first binder- or ionomer-containing portion of the ink formulation of the present invention. This is because, as reported by Schuler, the subresistance of ionomer-coated catalyst particles is greater. Because binder- or ionomer-free catalyst particles are more readily free to interact with reactants, higher-loading catalyst solutions containing higher amounts of catalyst particles can be used in the second binder- or ionomer-free catalyst portion of the ink formulation of the present invention. Selecting the appropriate amount of binder or ionomer to achieve optimal performance and durability of the CL of the present invention is within the skill of those skilled in the art.

[0045] The binder- or ionomer-coated surfaces of the binder- or ionomer-coated catalyst can be connected to each other in the first portion of the ink, or the interconnections can be achieved during mixing of the binder- or ionomer-coated catalyst solution with the binder- or ionomer-free catalyst solution, or during further mixing with additional ionomer-free (bare) conductive support to achieve the final ink solution, achieving the necessary interconnections between all of the ionomer-coated catalyst, ionomer-free catalyst, and bare conductive support. Alternatively, the interconnections can be achieved during a separate process after ink preparation, such as during coating of the ink onto the substrate to form the catalyst layer, and / or during a solvent evaporation step performed after coating, where interconnections between binder-coated and binder-free nanoparticles can occur as the particles deposit on each other.

[0046] This interconnection is in the form of binder-free catalytic nanoparticles attached onto binder-coated nanoparticles, or binder-free conductive nanoparticles attached to binder-coated catalytic nanoparticles, or binder-free conductive nanoparticles attached to binder-free catalytic nanoparticles, or binder-coated nanoparticles attached to binder-coated nanoparticles.

[0047] In the catalyst layer of the present invention, such nanoparticles and / or their aggregates pack onto one another during the fabrication process, allowing for the formation of an ordered layer composition instead of an arbitrary composition produced from a homogenized ink solution. As shown in Figure 2, binder-coated nanoparticles function as interconnection substrates or sites to which at least some of the other nanoparticles are at least partially attached by adhesive-like connections to the binder of the binder-coated nanoparticles. When a sufficient amount of binder-free catalyst nanoparticles are attached to the interconnected binder-coated nanoparticles, an ordered structure of nanoparticles is produced in the resulting catalyst layer, with the binder-free catalyst nanoparticles interspersed among the binder-coated nanoparticles and / or their aggregates, forming smaller catalytic bridges between them. Similarly, as described in Section 2 below, when binder-free conductive support nanoparticles are included in the composition, they intersperse among the binder-coated nanoparticles and / or their aggregates, forming additional highly conductive bridges between them.

[0048] The ordered structure includes binder-free catalyst nanoparticles that adhere directly to binder-coated nanoparticles in an adhesive-like manner at least at the binder-coated surface of the binder-coated nanoparticles, thereby interconnecting with any other contained binder-coated nanoparticles or their aggregates to achieve much better electrical, ionic, and liquid and gas pathways. More specifically, when conductive support nanoparticles are used, as long as less than the entire surface of the support nanoparticles is covered with an ionomer that is an electrical insulator, the conductive support nanoparticles act as conductors that allow electrons generated from electrochemical reactions to pass or conduct to surrounding or adsorbed molecules or ions. When binder-free catalyst nanoparticles come into contact with the at least partially uncoated surfaces of the conductive support nanoparticles, these conductive catalyst and support nanoparticles pass electrons to each other for the intended reaction. In addition, in the present invention, binder-coated nanoparticles adhere binder-free catalyst nanoparticles together to form aggregates, and when such aggregates are packed, an ordered structure of interconnected binder-coated and binder-free catalyst nanoparticles is formed. This differs from prior art homogenized catalyst particle compositions in which the layering of homogenized catalyst particles and binder in the catalyst layer is random or arbitrary, with no discernible interconnections between individual particles or their aggregates. In the present invention, binder-coated nanoparticles connect to each other to form a connected network, while binder-free catalyst nanoparticles and / or binder-free support nanoparticles are distributed around and in contact with such binder-coated nanoparticles and their aggregates, thereby forming a regular structure of particle interconnections. Contact between binder-free nanoparticles can significantly enhance electrical pathways. Meanwhile, the layering or contact between binder-free nanoparticles creates many necessary interconnected pores or voids whose interconnections form pathways for gases or liquids to pass through. The connected binder-coated nanoparticles within the packed aggregates of the catalyst layer form ionic pathways, directing protons to the attached binder-free catalyst nanoparticles.To maximize electrochemical reactions, a well-connected binder layer is ensured on the binder-coated nanoparticles in such aggregates. These ionic pathways are random and randomly distributed, unlike those produced by a single homogenized ink of catalyst nanoparticles. Thus, novel construction of ordered electrical, ionic, gas, and liquid pathways is achieved by the catalyst layer composition of the present invention, as disclosed and enabled herein.

[0049] To the best of the applicant's knowledge, the use of binder- or ionomer-free catalysts in the CL of commercial CCMs, or high catalytic performance (average 0.7-1.2 w / cm) has not been reported. 2 Previous publications have not disclosed a mixture of binder- or ionomer-coated nanoparticles and binder- or ionomer-free nanoparticles that not only maintains a high thermal conductivity (>25,000 h equivalent) but also exhibits excellent durability (reaching 25,000 h equivalent) to meet HDV applications. This paper is the first to disclose the use of binder- or ionomer-coated nanoparticles as a binding substrate in a CL structure, and the addition of highly active binder- or ionomer-free catalyst particles, with or without a support, together with a versatile bare conductive support in the CL composition of the present invention. This novel CL composition offers a better solution to many of the existing challenges related to catalyst performance and durability for PEMFC applications.

[0050] In all of the exemplary catalyst ink formulations or processes disclosed herein, for the intended electrocatalytic layer coating, all inks may be made from the same catalyst, different catalysts, or a mixture of different catalysts, the same or different mixtures of catalysts in the inks. A selected binder or ionomer is mixed in a selected ratio relative to the carbon in the ink. Such inks are then cast, die coated, spray coated, or brushed onto the membrane to form the catalyst layer.

[0051] One additional benefit from CL's novel composition is that such significantly enhanced conductive pathways of interconnected binder-free catalyst nanoparticles and / or binder-free conductive nanoparticles result in the production of novel supported catalyst products during electrochemical processes, which are ideal for highly desirable electrochemical reactions, including those in fuel cells and electrolyzers, or battery applications. The novelty of the resulting supported catalyst products is that a thin film of catalytic material, e.g., Pt, is coated onto the conductive support nanoparticles.

[0052] 2) Catalyst layer composition containing an additional conductive support In some embodiments, the novel CL compositions of the present invention utilize catalyst particles deposited on some conductive support. To prevent corrosion of the support, e.g., carbon corrosion, enhance the electronic conductivity of the through-layer, and promote better electrochemical reactions, highly graphitized conductive supports are preferred for the following intended reasons:

[0053] 2.1) Acts as a new catalyst support The dissolution and redeposition of catalyst particles, such as Pt or Pt-containing nanoparticles (NPs), on carbon-supported particles is well known and has been investigated by various scientists and engineers in the prior art. However, the use of additional carbon-supported nanoparticles added to a solution of existing carbon-supported catalyst particles, such that the additional conductive support nanoparticles act as a new, additional support for further deposition of reduced Pt-NPs, is believed to be novel and is disclosed herein for the first time. This novel supported catalyst has been found to provide additional ECSA that can maintain the required performance.

[0054] 2.2) Act as a further electron conduction path Additional conductive supports or similar (e.g., semiconductive) support particles provide better electrical conductivity within catalyst layers formed with the compositions of the present disclosure. In all commercially available CCM products, ionomers are used in the ink mixture without exception. Ionomers are electronic insulators. Electrons are lost when they cannot move from the generation site or to the reactive active site. Adding a conductive support that does not contain additional ionomer (i.e., bare, uncoated) enhances and increases the electronic conduction pathways for better desired electrochemical reactions. This is believed to be novel and disclosed for the first time herein.

[0055] 2.3) Improve hydrophobicity The addition of a bare carbon support or similar conductive support that does not contain ionomer provides better hydrophobicity to the catalyst layer, which is also important to allow the produced water or any condensed water to be easily pushed out of the CL.

[0056] 2.4) Acts as a sacrificial corrosion support It has been demonstrated that catalyst particles deposited on a carbon support result in a slightly higher carbon corrosion rate than the same support without catalyst particles deposited on it [Reference 2]. The more corrosion-prone support selected as the additional support (bare carbon lacking pre-deposited catalyst when added to the ink composition) acts as a sacrificial support to mitigate corrosion of the catalyst support. This is disclosed for the first time in this application.

[0057] Furthermore, the additional bare support utilized in selected embodiments of the novel CL compositions of the present invention improves the durability of the catalyst product, as indirectly supported by the conclusions of a recent review by Burup [Reference 5]. As noted there, the large size of catalyst particles (the Ostwald ripening effect) led to performance degradation due to the loss of ECSA. Redeposition of reduced Pt onto the bare support creates newer ECSA for the Pt nanoparticles, thereby mitigating the loss of ECSA. Compared to the redeposition of Pt on neighboring Pt NPs on the support, such Ostwald ripening is one of the key factors behind ECSA loss.

[0058] Furthermore, the migration of dissolved Pt ions from the CL to the GDL or membrane caused irreversible loss of Pt ECSA. Platinum bands in the membrane close to the CL are often observed due to migration effects. Catalytic particles such as Pt have also been observed on the GDL mesoporous layer. In the present invention, such migration is minimized and reduced by providing a nearby localized bare support for the deposition of reduced Pt.

[0059] Further disclosed herein is the inventive multilayer internal structure of the CL, which restricts the migration of dissolved Pt ions and redeposits them within the catalytic layer. The image in Figure 8, obtained by high-resolution scanning electron microscopy, clearly shows that a uniform layer was observed within the cathode CL, with a band of more catalytic nanoparticles concentrated near the PEM side. This was first reported and is quite different from the migration or irregular redistribution of metal catalyst particles [Reference 1]. Second, no metal particles were observed deposited within the PEM. This was a direct indication of the development of a dense layer of CL on the PEM side, which provided protection against further migration of dissolved Pt into the PEM, as observed by various researchers.

[0060] Additionally, no prior art has disclosed that plate-shaped catalyst nanoparticles [Reference 19] maintain their plate-like structure as they grow larger, nor has it been stated that such particles remain on the support for better performance and durability. The present invention has disclosed that by utilizing plate-shaped catalyst particles, migration, aggregation, and agglomeration of growing nanoparticles can be further minimized, thereby maintaining their catalytic performance. The shape, size, and composition of such plate-shaped catalyst particles are disclosed in more detail in applicant's previous U.S. Patent No. 9,761,885, the entire contents of which are incorporated herein by reference.

[0061] Furthermore, the plate-shaped structure of the catalyst particles on the support exhibited a 0.90 w / cm at 0.585 V at the end of life. 2 The gradual growth of catalyst particle size on the support has been shown to be a factor in promoting uniform distribution of catalyst particles on the support surface for over 150,000 cycles. Previous publications have not disclosed that the gradual growth of catalyst particle size on the support provides such expected performance and durability, but rather the opposite. The gradual size growth of plate-shaped catalyst particles was evident in the development of the present invention.

[0062] Furthermore, uniform size growth was observed during durability testing, and it is hypothesized that, absent at least one or more of the additional novel features detailed below, aggregation and agglomeration of large Pt-based catalyst particles would be further suppressed. Additionally, these particles would migrate in the vertical mounting direction from the top of the MEA to the bottom of the MEA.

[0063] 3) Solid-state electroplating process for thin film coating of nanoparticles In our research, we found that fuel cell cathodes with the CL layer of the present invention constructed according to the present invention, due to the use of platinum-supported catalysts, exhibited a thin Pt film coating on top of many nanoparticles or nanoparticle aggregates after a period of use. Some of these coated individual or aggregated nanoparticles were found to contain no catalytic nanoparticles on the support. Others were found to contain some catalytic nanoparticles located underneath the thin Pt film. As is known in the public domain, a continuous thin Pt film exhibits negligible degradation of catalytic activity. With this in mind, this novel solid-state electroplating process can be utilized and further developed to produce such novel catalysts of the present invention.

[0064] In Figure 10, white nanoparticles were observed throughout the layer thickness, more abundant at the interface between the film and the CL. These white spots were analyzed by electron diffraction and X-ray spectroscopy and found to be Pt-rich particles.

[0065] The observation of such Pt thin film-coated particles across the CL indicated the availability of well-connected electrical and proton-conducting pathways. Optimized compositions can lead to further advances in this novel solid-state electroplating process. Continuing with FIG. 10, it was also observed that such thin films were coated on agglomerated particles, and that such thin films were also coated on some pre-existing catalyst nanoparticles on the surface of the support.

[0066] Existing scientific knowledge in the field of liquid-state electroplating allows most transition metals to be electroplated onto some conductive substrates, provided that known ionic complexes are available. Solid-state electroplating utilizes the same mechanism by reducing nearby metal ions onto the surface of the cathode material without immersion in a liquid process phase. Therefore, many metals, including chromium, iron, copper, nickel, cobalt, yttrium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, indium, tin, barium, hafnium, tantalum, rhenium, osmium, iridium, platinum, gold, lead, bismuth, lanthanum, and samarium, can be used in this process to produce thin-film catalytic material-coated nanoparticles.

[0067] Some key differences between existing electroplating methods and the solid electroplating of the present invention disclosed herein include: (a) Solid-state electroplating does not involve plating metal ion compounds in a liquid electrolyte or electrolyte; (b) solid-state electroplating coats nanoparticles instead of bulk objects; (c) solid-state electroplating occurs within the cathode, where dissolution of the plating metal and reduction of the plating metal ions occur simultaneously, which differs from most commercial electroplating in that the metal migrates from the anode to the cathode or from the solution to the cathode; (d) Solid state electroplating does not produce waste or toxic exhaust gases or solutions.

[0068] In one embodiment of the solid-state electroplating process of the present invention, an electrode of the present invention was fabricated having the composition described above and the layered structure described below. This CCM was combined with a GDL and mounted in a battery fixture. The battery was subjected to cyclic voltammetry cycles from 0.6 V to 0.95 V under humidified conditions and elevated temperatures of 60 to 85°C, using hydrogen as the anode and nitrogen as the cathode. This duty cycle was continued while monitoring the change in ECSA of the CCM. The solid-state electroplating process was considered complete when the ECSA reached a stable value. Due to the nature of the nanoparticles, in some experiments, some plated nanoparticles were observed early, for example, after approximately 65,000 cycles, before "completion" indicated by stabilization of the ECSA. Electron microscopy revealed many metal-plated nanoparticles.

[0069] The solid-state electroplating process of this invention can easily produce such novel Pt thin-film-coated nanoparticles or other similar catalytic material-coated nanoparticles. As far as the inventors understand, if the cycling potential is increased to 100 mV / sec or even 200 mV / sec, the deposition process is expected to be significantly faster. Therefore, it is expected that such novel Pt thin-film-coated nanoparticles can be produced in large quantities.

[0070] This solid electrolytic plating for thin film coatings can be extended to other applications by utilizing the catalyst layer composition of the present invention in those applications. The advantages of this novel process are described in the following non-exhaustive list: a) It allows the production of many other metal thin-film coated nanoparticles for various applications. For example, it is highly desirable to produce iridium thin-film coated supported catalysts. Since iridium is the most expensive catalyst in water electrolysis devices for green hydrogen production, reducing the Ir loading is highly beneficial. b) The process of the present invention achieves what was previously thought to be impossible: coating nanoparticles with a thin layer on their outer surface that can range in thickness from a few angstroms to a few nanometers. If the process is well developed and controlled, the thickness of such a coating can be controlled and defined. As with previous developments in liquid phase electroplating, the new process holds great promise for the development and manufacture of many new and novel materials. c) One of the notable advantages of this solid-state electroplating process is also its zero-emission status, and the fact that it produces much less or negligible waste and / or hazardous chemicals compared to current liquid electroplating, where waste and / or hazardous chemicals are unavoidable. d) This novel solid-state electroplating process can be easily amplified based on existing scientific and engineering knowledge. The large-scale and rapid charging process makes the production of thin-film coated nanoparticles as new support materials readily feasible. e) In the present invention, a thin film of catalytic material was formed on the supported nanoparticles by a fuel cell reaction process. However, this can also be done using an electrolytic cell, in which case the plating material can be placed on the anode side. The catalytic material involved in the oxygen reduction process undergoes a dissolution and redeposition process. By utilizing the layer composition of the present invention, the catalytic metal ions can migrate to the conductive support surface and be reduced when electrons appear.

[0071] The catalytic metal was found to have a much higher content in the innermost layer than in the other sublayers. However, the exact mechanism of such migration was unknown at this stage. A possible reason may be that within the compact packing density of the innermost layer, the contact between the conductive nanoparticles and the nanocatalyst was greater than in the more loosely packed intermediate layer. Under steady-state operation, the concentration gradient of metal ions within the catalyst layer during the process may be the main force driving more metal ions into the depletion region, where they are reduced more quickly in the innermost layer than in the intermediate layer.

[0072] Combined with the known knowledge of electrolytic plating under electrolytic processes, the solid electrolytic plating of the present invention can be carried out under forced current conditions to make the process more efficient.

[0073] Separation of thin-coated nanoparticles from uncoated or partially coated nanoparticles can be achieved by utilizing capping ligands to remove non-thin-coated nanoparticles, or vice versa, by washing, centrifugation, etc.

[0074] The catalysts of the present invention, including those coated with binders or ionomers, those without binders or ionomers, and even those with bare (binder- or ionomer-free) conductive supports, provide more electron pathways, gas fuel pathways, and accessible catalyst particle pathways. This significant enhancement in pathways provides enhanced catalytic activity and dramatically reduces all of the subresistances identified by Schuler. It is also predictable by those skilled in the art that such reduction of CLs, which would equally reduce the loading of catalyst particles such as platinum, is easily achievable. At the same time, reducing the catalyst particles in the CL also reduces the thickness of the CL, which is favorable for better mass activity because it alleviates the problem of flooding.

[0075] 4) Multilayer catalyst layer structure Another object of the present invention is to reduce the migration of dissolved catalyst ions. In conventional CL fabrication processes, there is no intentionally obtained structure that is particularly useful for reducing catalyst particle ions. In conventional fabrication of bilayer CLs for cathodes, the packing densities between the two sublayers of the CL are similar to each other. In the present invention, different sublayers with different sublayer packing densities are used instead. In certain embodiments of the present invention, at least three sublayers with different packing densities are constructed in the CLs of the present invention.

[0076] As used herein, material packing density is defined as the number of solid particles, including individual particles and agglomerates, in a given volume. Thus, the smaller the particle size, the higher the material packing density compared to larger particles in a given volume of material.

[0077] In one embodiment, the multilayer CL structure of the present invention consists of three sublayers: (1) an innermost layer located on top of the membrane and having a compact layer structure of nanoparticles or their aggregates with a high packing density; (2) a middle layer fabricated on top of the innermost layer and having a loosely packed structure of large nanoparticle aggregates with a low packing density; and (3) an outermost layer fabricated directly on top of the middle layer, which utilizes smaller aggregates of nanoparticles to create a compact layer with a smooth surface (see Figure 7).

[0078] The purpose of the innermost layer, with a high packing density, is twofold: (1) to create an intact interface to prevent delamination of the CL from the substrate, e.g., PEM. This can be problematic because it contains binderless conductive nanoparticles and / or binderless catalytic nanoparticles (large aggregates can create pores between the membrane and the sublayer, and these air pockets increase localized flooding and interfacial resistance, making them undesirable); and (2) to create a buffer zone for the high concentration of protons that migrate through the membrane. The purpose of this buffer zone is to create a concentration gradient, allowing the high concentration of protons to remain in this zone longer for the intended electrochemical reduction reaction in the CL.

[0079] The purpose of the intermediate layer is to fully utilize the binderless catalyst nanoparticles to improve the highly desirable reduction reaction, especially when the CL is the cathode of a fuel cell. Therefore, for high current density applications, it is preferable to make this layer thick.

[0080] The purpose or benefit of the outermost layer is twofold: (1) because this outermost layer is in direct contact with the GDL, it smooths the rough surface of the more loosely packed middle layer. Furthermore, since air pockets, gaps, or depressions impair the performance of the CL, a smooth top surface provides better interfacial conductivity. (2) It creates a compact layer to prevent the binderless nanoparticles from being lost or washed away by the water generated under high-current operation. In some embodiments, the nanoparticle size of the innermost and outermost layers is much smaller than that of the middle layer. In one specific, non-limiting example, the former has an average nanoparticle size of 150 nm or less, while the average nanoparticle size of the middle layer is in the range of 100–500 nm. The small average size of nanoparticles in the innermost layer of the CL was engineered by controlling different coating process parameters, while the larger size in the middle layer was achieved in a controlled manner by varying some of those process parameters.

[0081] In one example, a densely packed first sublayer of CL solids was prepared on a membrane, which could be a proton exchange membrane (PEM), anion exchange membrane (AEM), or hydrocarbon membrane (HCM), or on a mesoporous layer of GDL. A loosely packed second sublayer of larger solid particles was then deposited. This second sublayer was followed by a smooth outermost layer of smaller solid particles to form a smooth outermost layer. The reason the compact sublayer is at the bottom of the CL (i.e., closer to the membrane) is to provide a layer intentionally structured to slow the migration of catalyst particle ions and further deposit these catalyst particle ions onto small agglomerates, including binderless catalyst particles. When Pt is used as the catalyst particle, Pt nanoparticles are an excellent reducing agent for Pt(2+) ions. With partial or minimal crossover hydrogen, the soluble Pt(2+) ions can be completely reduced in the dense layer either on the surface of the existing catalyst nanoparticles or on the surface of the bare conductive support.

[0082] The clear observation of several fully Pt-coated nanoparticles at the boundary between the CL and the membrane and within the CL in Figure 10 provides strong evidence of the unique results from this multilayer structure of our CL. The white particles are individual particles (30–80 nm in size) and agglomerates fully coated with platinum in this imaged sample. The uniform brightness of the catalyst particles under SEM imaging indicates that their surfaces are completely coated with platinum. Some pre-existing nanoparticles were present beneath the thin coating. This is undoubtedly the first time that such catalyst particles fully coated with a thin platinum film have been fabricated and disclosed in this invention. These novel catalyst particles were not only generated at the interface but also within the innermost layer of our CL (vertically in the image of Figure 10, which shows a cross-section of our CL after over 100,000 cycles of the HDV MEA protocol published by the U.S. Department of Energy).

[0083] Electron diffraction X-ray spectra detected a uniformly high content of catalyst particles in the innermost layer of the CL (Figure 8). The catalyst particle content in this innermost layer was nearly three times that of the adjacent sublayer. These data demonstrate that the multilayer structure of the present invention successfully reduced platinum ion migration within the innovatively constructed CL. Since Pt(2+) ions were reduced every time an electron appeared, a well-connected electron pathway was evidenced by the deposition of fully coated platinum catalyst nanoparticles and aggregates within the CL. In catalysts coated with binders or ionomers, Pt(2+) ions migrated into the membrane and were reduced within the membrane, causing permanent loss of ECSA. Crossover hydrogen was another source of reduction for the migrating Pt(2+). Hydrogen crossover in PEMs has also been described in the literature.

[0084] This inventive multi-sublayer CL structure also prevents the detachment of unbound catalyst particles from the catalyst layer electrode, which can cause significant CL structure changes and catalyst delamination during operation, and a carefully designed sandwich structure consisting of multiple layers of varying material densities has been invented and is disclosed herein as follows: In this inventive multi-sublayer CL structure, two compact sublayers are created at the top (i.e., outermost region farthest from the membrane) and bottom (i.e., innermost region closest to the membrane) of the catalyst layer, and the middle sublayer located between the top and bottom sublayers is filled with large aggregates of nanoparticles and therefore has a lower material density than the top and bottom sublayers.

[0085] The dense or compact sublayers at the top or bottom of the CL were created by utilizing smaller particles in the solids of the catalyst ink to form a compact layer. The layer thickness could be varied based on the layer structure design. The middle layer was formed with larger aggregated particles that created more pores, resulting in a more loosely packed sublayer structure than the top or bottom sublayers.

[0086] Referring to Figure 3, LE1, LE2, and LE3 are the outermost, middle, and innermost layers, respectively, of the left electrode of the novel MEA of the present invention. Meanwhile, RE1, RE2, and RE3 are the outermost, middle, and innermost layers of the right electrode of the MEA, with the two electrodes separated by a membrane. The outermost and innermost layers, LE1 and LE3, of the left electrode are dense layers with higher material density, while the middle layer, LE2, is a more loosely packed sublayer with lower material density than LE1 and LE3. Similarly, the outermost and innermost layers, RE1 and RE3, of the right electrode are dense layers with higher material density, while the middle layer, RE2, is a more loosely packed sublayer with lower material density than RE1 and RE3.

[0087] Experimental results show that at end-of-life (EOL), the CL thickness still remains within an average of 90+% of the original CL thickness. This persistent structure is important for high performance and the required lifetime. Applicant believes that one of the important contributing factors is this inventive multilayer structure design, especially when combined with the inventive CL composition composed of binder-coated catalyst particles, binder-free catalyst particles, and an additional bare (ionomer-free) conductive support.

[0088] DOE HDV AST (2019.11) [Reference 18] The higher catalytic performance over the test period was clear evidence of the success of this structure [see Figure 4]. The improved sustained high power density demonstrates that this inventive electrode layer structure technology is of great value for practical industrial applications.

[0089] Furthermore, within the CL, a larger number of sublayers with different packing densities, formed of the same or different catalysts, can be utilized, e.g., replacing the illustrated scenario of a single intermediate layer, such as LE2 or RE2, with two or more intermediate layers. For example, the middle portion of the CL can be constructed with two different loosely packed catalyst sublayers, with one catalyst layer being more durable and the other being a more catalytically active layer. Such a structure can provide improved catalyst performance and much longer durability, since the compositions of the present invention provide the same functionality for retaining catalyst particles during their dissolution and redeposition processes.

[0090] Ballard Power has disclosed multilayer electrodes to enhance catalytic performance. Essentially, they developed a two-layer structure for cathode CLs. One layer consisted of a Pt-only supported catalyst for the necessary durability. The other consisted of a Pt alloy-supported catalyst to provide high catalytic performance. However, these layers did not incorporate free carbon or ionomer-free supported catalysts. They also did not disclose the use of artificial patterning of the fabricated catalyst layer. They also did not disclose the ink formulation and associated catalyst structure sublayers of the present invention to provide sustained durability. Reference 20 discloses the addition of black carbon particles to the anode layer to minimize cracking due to its thinness. However, they do not disclose the addition of an ionomer-free catalyst in a separate step, nor the use of a sandwich / sublayer structure for CLs. Based on known science, platinum thin films have been shown to exhibit minimal degradation over 10 years in satellite fuel cell applications. These platinum film-coated catalyst particles of the present invention can achieve similar durability and performance.

[0091] When the catalyst particle composition of the present disclosure is used to form the correct interconnections between all catalyst particles, stable catalyst performance can be obtained, as supported by known science, which also supports that minimizing the loss of catalytically active surface area can lead to maintaining catalyst performance over time. When the condensation catalyst particle layer is optimized, stable catalyst performance can be achieved based on the formation of connected catalyst particles. This is fully supported by known science that shows minimal to negligible performance decay over time for platinum continuous films.

[0092] As evidence of the usefulness of the present invention, a 50 cm 2 MEAs with active area sizes of 1000 sq. m were fabricated by coating, activated, and tested under the U.S. DOE HDV AST protocol published in November 2019 (Reference 18).

[0093] In other applications, such as advanced oxidation processes for water treatment, the catalyst layer composition disclosed above can be coated onto any absorbent substrate, such as activated carbon. The surface layer structure formed by this composition allows active catalyst nanoparticles, such as Fe3O4, to spread throughout the water stream and capture more pollutants, such as phenol complexes. Such compositions not only conserve the loading of active catalyst nanoparticles, but also allow for a rapid reactivation process by reacting with select oxidizing agents, such as hydrogen peroxide, to cleave contaminants adsorbed on the surface or adjacent sites of the catalyst nanoparticles. A distinct difference between the compositions of the present invention and catalyst particles deposited directly on the surface of the same activated carbon substrate is that the compositions allow significant capture of pollutants through their extended network structure on surfaces with the same or even fewer active nanoparticles.

[0094] In particular, given this foresight into the various potential applications of the inventive subject matter disclosed herein, those skilled in the art will appreciate that the catalyst layer compositions of the present invention may be utilized not only in electrocatalyst layers but also in other catalytic reaction-oriented processes.

[0095] 5) Post-fabrication of patterned catalyst layers Also disclosed herein is a post-fabrication of the catalyst layer of the present invention to further mitigate several degradation factors known in the scientific public domain, including migration of dissolved Pt ions into the membrane, migration into the GDL, and redeposition on the catalyst, forming larger catalyst particles that form a depletion zone from top to bottom along the vertical position due to the vertical assembly of most MEA products, and allowing the produced water to easily drain away. This artificial patterning changed the dissolution-redeposition pathway of the catalyst particles throughout the CL region.

[0096] Burup et al. (Reference 5) found that one important factor affecting the degradation of MEA performance and durability is the cathode electrode structure and electrode layer characteristics, including the composition of the materials in the ink and the formed layer structure itself.

[0097] Byron Gates

[17] disclosed patterning CLs to improve performance. However, patterning the CCL (cathode catalyst layer) or ACL (anode catalyst layer) did not demonstrate exceptional performance, as the current density was 1.5 A / cm^2 at 0.6 V under hydrogen and oxygen gases, nearly 1.5 times lower than that of unpatterned normal CLs under the same test conditions. It should be noted that catalytic activity under hydrogen and oxygen conditions can provide up to 2–3 times better performance than that tested under hydrogen and air conditions. Simply put, the oxygen content in air is low, about 21%, so pure oxygen gas is close to 100% oxygen. Durability data was not reported. Furthermore, Gates utilized nanolithography techniques, which are expensive and difficult to scale up for commercial use. In the public domain, most Pt / C unpatterned CCLs can reach over 2.0 A / cm^2, or even over 2.5 A / cm^2 at the same or better voltage under hydrogen and air conditions.

[0098] A drawback of such design and fabrication is the large number of small pocket holes that can cause localized water flooding during moderate or high current densities, which can lead to performance degradation. Such patterning across the entire electrode area means that much of the pattern is under the lands, so this patterning does not effectively mitigate known degradation factors due to water accumulation. Furthermore, their experimental results did not provide any indication of the extent of this degradation. However, based on their fabrication process, they were fundamentally different from the disclosed artificial patterning of the CLs of the present invention. Furthermore, those processes are very expensive and not suitable for commercial production. However, the artificial patterning of the present disclosure can be performed by simple mechanical assembly means, making it extremely cost-effective.

[0099] Since migration of dissolved Pt(2+) ions and uncontrolled Pt redeposition are known to occur in the lower portions of current commercial MEAs, localized restriction of such migration and / or locally controlled redeposition pathways could provide superior mitigation effects and reduce MEA degradation. Experimental results from the inventive post-patterning of the disclosed CLs strongly support this theory.

[0100] In the present invention, the external patterning structure of the CL is not created during fabrication of the CL to prevent discontinuities in the catalytic reaction in the CL, but is instead imparted after the CL has already been fabricated using an external means to create the external patterning of the CL. Referring to Figure 5, this pattern comprises an alternating layout of raised / uncompressed areas RUA and recessed / compressed areas RCA across the outer surface of the CL (i.e., its surface opposite the membrane). This external patterning was devised with the intention of localizing the catalyst particle dissolution and redeposition process, which mitigates catalyst particle migration and agglomeration, thereby reducing or significantly smoothing the reduction of the electrochemical area of ​​the catalyst particles.

[0101] More specifically, referring to Figure 6, which shows an MEA with two electrode CLs on opposite sides of the membrane in combination with two flow field plates on opposite sides of the MEA, facing the two electrode CLs, the raised / uncompressed areas RUA of each CL are located within the gas flow field channels FFC of the respective flow field plate, and the recessed / compressed areas RCA of each CL are aligned with the raised ribs RR of the respective flow field plate that separate the flow field channels FFC from each other. The raised / uncompressed areas RUA have more catalyst particles available to react with diffusing gas reactants, resulting in greater catalytic activity. Even when the recess depth measures only about 10-15% of the total thickness of the CL layer, this external patterning has been shown to achieve significant improvements in catalytic performance, along with significant durability improvements. The improved durability can be explained by the fact that the CL patterning of the present invention localizes the dissolution and redeposition of catalyst particles in the repeating pattern areas. When the same amount of catalyst particles was in the recessed / compressed region CA and the raised / uncompressed region CA, the localization of those regions to allow for the dissolution and redeposition process resulted in a uniform catalyst density during operation instead of a graded catalyst density across the CL.

[0102] Unlike other conventional assemblies, in the absence of such post-patterning of the CL, dissolution and redeposition of catalyst particles throughout the CL created a gradient of Pt concentration across the CL in a manner from a thin top (fewer particles) to a thick bottom (more catalyst particles). While it is not possible to stop this dissolution and redeposition effect, utilizing such inventive patterning of the CL, their degrading effects were significantly mitigated and reduced.

[0103] This distinct feature is highly beneficial for high-performance, long-term power generation. Consequently, such patterning during MEA assembly resulted in a uniform Pt-enriched band near the RIM side, rather than a gradient. The formation of such a uniform layer of higher Pt concentration can be attributed to the following factors: 1) the local Pt dissolution and redeposition effect described above; 2) the incorporation of additional free carbon particles. The bare carbon particles can serve as additional support for the reduced Pt redeposition. This feature significantly reduced the growth of catalyst particles on the newly reduced and deposited Pt nanoparticles. This may also fully explain the significant slowdown in ECSA decay due to the newly formed supported catalyst.

[0104] Second, the recessed / compressed regions RCA located under the raised ribs RR of the flow field plate allow electrons to access more adjacent catalyst particles within the sidewalls of the CLs that transition between the recessed / compressed regions RCA and the raised / uncompressed regions RUA, or allow electrons to be rapidly released to or from the conductive flow field plate. This is because, unlike conventional surface contact between the raised ribs RR and the conductive CLs, the patterned CL structure of the present invention allows electrons to be released from the flow field channel walls of the flow field plate to the adjacent sidewalls of the CLs. In the case of ORR, this increased electron access enhances the ORR reaction rate and also improves the utilization of oxygen as a reactant. Precise compression is also beneficial for reducing contact resistance. In the case of heterogeneous multiphase reactions, this feature provides better reaction paths to maintain and enhance power generation performance.

[0105] In the post-fabricated non-limiting example shown in Figure 5, the normalized overall CL thickness was 0.95 and the compression depth of the recessed / compressed area REA was 0.15. Beneath the floor of the recessed / compressed area REA, the material density of the CL layer is more compressed than beneath the raised / uncompressed area RUA, and the material density of the CL is more loosely packed.

[0106] These patterns were observed in our CLs, shown in Figure 8, where the CL thickness at the RCA compressed under the lands of the flow field plate was seen to transition from a relative thickness of 9.2 microns to a larger thickness of 10 microns, typical of target cathode CLs, moving outward toward the adjacent RUA. It should be noted that SEM imaging was performed after the external pressure was removed. Due to the image field size constraints of the SEM instrument, it was not possible to observe a sufficiently small thickness difference (e.g., 0.8-1.5 microns) within an area large enough (e.g., 2000 x 1000 microns) to encompass the complete RCA / RUA transition. Therefore, the selected imaged area shown in Figure 8 represents only a partial percentage of the transition region between the RCA and the adjacent RUA. The visible CL thickness difference between the extremes of the imaged area was approximately 8% of the maximum visible thickness (10 microns for the thickest visible region and 9.2 microns for the thinnest visible region). Assuming the overall slope transition after pressure release was 0.1-0.2 mm long, the estimated difference in thickness between the RCA and RUA was 2-4 microns, which indicates an RUA / RCA thickness difference of approximately 15%-30% of the overall CL thickness for an estimated overall CL thickness of 13 microns at the RUA. Therefore, given that the thickness difference could be smaller if less pressure were applied in the patterning process, the RUA / RCA thickness difference could vary within a larger range of 10%-30% of the overall CL thickness.

[0107] An appropriate pattern profile is selected to avoid further cracking or pockets in the CL, which could cause localized flooding under high current density operation. Flooding is a common low-mass activity problem. Furthermore, the novel CL composition disclosed above, and the internal sublayer structure also described above, offer significant advantages for creating such desired external patterns over CLs from other conventional manufacturing processes. Adding post-fabrication formation of this patterned structure to several existing commercially available CCM fabrication processes for CLs is hypothesized to also benefit their durability due to the same underlying scientific and engineering principles discussed above.

[0108] Referring to FIG. 6, application of external CL patterning to a prefabricated MEA can be performed in a known manner by matching the layout to the flow field channel / rib pattern of the flow field plate of that MEA, which may be a bipolar flow field plate. In our testing, the external pattern in the two CLs of the MEA was created by utilizing a slightly higher torque pressure on the bipolar flow field plate to compress the MEA between them, using corresponding regions of the flow field plate (flow field channels FFC and raised ribs RR) to create raised / uncompressed regions RUA and recessed / compressed regions RCA of the CL. This mechanical pressing of the MEA between two flow field plates to create the external CL patterning is shown schematically in FIG. 6 by the pressing force arrows PF, which indicate uniform pressure application across the MEA.

[0109] Post-patterning of continuous CLs to create compressed and uncompressed regions on the CL has been found to contribute to the production and maintenance of superior high power density with excellent durability. The notable differences between this post-patterning and micropatterning or other similar methods are their characteristics, which are listed below. 1) They were fabricated by in vivo cell assembly, a process that did not require additional expensive and precise control systems to generate patterns such as those used in micropatterning. 2) The process of creating such patterns did not result in potential pinholes or delamination of nearby CL or CL material as disclosed in other publications such as Byron's group, which can be attributed at least in part to the catalyst ink composition of the present invention and the process technique for CL fabrication. 3) Furthermore, the raised / uncompressed regions RUA of the external CL pattern within the gas flow channel promote better catalytic performance due to the larger CL thickness at these raised / uncompressed regions RUA. This improves catalytic performance because a persistent layer pattern with a controlled porous structure promotes catalytic reactions. Furthermore, many prior publications have shown that the CL under the flow field channel is more reactive than the CL under the flow field ribs. By utilizing properly embedded lands in the CL by the method of the present invention, more electrons are provided to the CL region under the channel. Conductive particles also enhance this requirement. 4) Furthermore, the localized, highly catalytic layer pattern prevents or dramatically reduces the migration of dissolved catalytic metal ions, further limiting their redeposition within the limited post-fabrication pattern area. This was evident from the fact that at the end of life, the catalytic particles were still large and uniformly distributed on the support. The size growth of the catalytic particles is mitigated by this pattern structure and assembly technique. Scientifically, the retention of catalytic particles on the support within the active area is one of the key factors that can promote durability. 5) To avoid localized flooding that also floods adjacent areas, the recessed / compressed regions of the MEA under the raised ribs of the flow field plates (RCA) must be empty or cannot be emptied without a catalyst layer. Another aspect is to avoid cracks between the RCE and RUA, which are not ideal for high-performance electrochemical applications.

[0110] 6) Further protection of the solid electrolyte membrane Solid electrolyte membranes are the key raw materials for CCMs. Most commercially available reinforced membranes (RIMs) do not last long under high-power density operation. Several factors cause RIM degradation. The dominant products on the market are Gore Select RIM products. However, they are very expensive and still suffer from constant degradation during operation. In most cases, RIM thickness thins over time due to fluorine leaching, ionomer loss, hydroxyl radical attack, thermal stress, or operating gas pressure. As a result, RIM bursts, terminating the lifespan of the CCL and stack.

[0111] Testing of the present invention has shown that the CL structure of the present invention coated on the RIM significantly reduced the shrinkage or thinning of the commercially available RIM. 2 The high power density at the end of the test, exceeding 150,000 cycles, was solid evidence of this additional protection of the RIM. The high power density indirectly indicated the superior proton conductivity of the RIM at the end of the life of the tested CCM.

[0112] High-resolution images taken by scanning electron microscopy of the CCM of the present invention after testing [Figure 10] showed less than 8% thickness loss, averaging 12 microns (±1 micron) compared to the CCM at BOL and 11 microns (±1 micron) at EOL.

[0113] A cross section of the CCM at EOL is shown in Figure 8. The dense layer (Pt-enriched band) on the PEM side is shown to have a thickness of 3.2 (±1.0) microns. The average thickness of the catalyst layer was approximately 9.6 microns. The thickness of the commercial PEM used was 15.0 microns, which closely matches the thickness of the product before coating. The top / outermost layer of CL was not clearly observed, as it was intended not to produce a dense packing of significant thickness, but rather to smooth the rough surface of the more loosely packed middle / intermediate layer, thus preventing delamination of the catalyst or bare support particles.

[0114] Such results show a good potential to reduce CCM costs by not utilizing special RIM for the same application.

[0115] <Example> Example 1: Ink Formulation of the Present Invention A platinum-containing catalyst was selected based on its ECSA and catalyst size distribution. For example, a carbon-supported catalyst with a platinum content of 20% to 50% or more could be selected as the first catalyst portion. This catalyst was homogenized in a solvent solution by known methods, including overnight jar milling. For example, 1.0 gram of Pt- / C catalyst was used in a solution mixed with alcohol and water, and a homogenous solution was formed by jar milling. The volume of the solvent system was determined by the coating process based on the required viscosity or solids content. For example, for the above amount of catalyst, the volume of the alcohol solution was 40 to 70 ml. However, microfluidization or sonication can also be used instead. This homogenized catalyst ink solution 1 was mixed with the desired amount of binder, in this case Nafion ionomer, to form the ionomer-coated catalyst ink solution (Catink 1). The amount of ionomer used can vary, for example, between 20% and 90% of the amount of conductive support of the catalyst. The amount of binder selected may depend on the type of catalyst layer and its intended application. In this example, a ratio of 70% ionomer to conductive catalyst support was used.

[0116] A second portion of catalyst, which may have the same or different catalyst-to-support content ratio as the first portion, was measured and homogenized in an alcohol solution to obtain a binder-free catalyst ink solution (Catink 2). In this particular example, an equal amount of selected catalyst nanoparticles was used as in Catink 1.

[0117] Catink1 was then slowly added to Catink2 with vigorous stirring, thereby obtaining a catalyst ink mixture (Catink3), which was continuously stirred before use. A portion of Catink3 was used directly to prepare the catalyst layer of the present invention.

[0118] Next, a binderless support ink (Supink 1) was prepared containing bare conductive supports, such as carbon-supported nanoparticles, in a solvent solution and homogenized by sonication before use. The amount of bare support particles was calculated based on the total catalyst product used in one catalyst ink (Catink 1, Catink 2). A support-to-catalyst ratio of less than 1 is preferred, with less than 0.5 being even more preferred. For the above sample, 0.80 grams of conductive carbon in 50 ml of alcohol solution was used in Supink 1. Supink 1 was further homogenized in the same solvent system by sonication for a period of time, e.g., up to 1 hour, and then slowly added to Catink 3 with vigorous stirring. After mixing, the resulting final catalyst layer ink mixture was stirred for at least 1 hour before use.

[0119] The use of a high-power fluidizer can significantly reduce the Catink 1 mixing time. The same applies to the homogenization of the catalyst with the selected solvent solution using a high-power fluidizer.

[0120] Example 2: Alternative Inventive Ink Formulations In Example 1, if the catalyst used in Catink 1 and Catink 2 is the same, most of the same catalyst can be used in the first ink solution preparation. After homogenization, the ink solution was divided into two portions. A small amount of the desired amount of ionomer solution was added to form Catink 1. The remaining ink without ionomer formed Catink 2. After stirring overnight, Catink 1 was slowly added to Catink 2 to form Catink 3. Supink 1 was prepared in the same manner as described in Example 1. After sonication of Supink 1, it was slowly added to Catink 2 to form the final ink solution, which was stirred for at least 1 hour before use.

[0121] Example 3: Inventive preparation of a CCM product of the invention The ink of Example 1 prepared above was transferred to a coating machine. A multilayer CCM structure of the present invention was fabricated by the following process using an ultrasonic spray coater. However, this process can alternatively be carried out using known process techniques, including slot die coating, other doctor blade coating, or screening printing techniques, or any multilayer coating process.

[0122] The material packing densities of the different sublayers are designated as MPD1 for the innermost layer and MPD2 for the outermost layer. The labeling format MPD-I# is used for the intermediate layers, where # is a numeric identifier for the different sublayers within the intermediate layer. For example, MPD-i1 and MPD-i2 indicate the respective packing densities of two different intermediate layers. For general purposes, the values ​​of MPD1 and MPD2 are typically larger than the value of MPD-i#.

[0123] Step 1) To reduce membrane swelling during coating, a clean membrane, such as a Nafion membrane or other reinforced proton exchange membrane, was placed on a hotplate set at a temperature lower than the membrane's gasification temperature. A thin layer of ink solids was fabricated on the membrane by controlling coating parameters, including the ultrasonic spray coater's flow rate, forming air pressure, hotplate temperature, and sonication frequency and power. Because ultrasonic spray coating is a well-known coating process, appropriate optimization of process parameters to achieve the desired results described herein will be apparent to those skilled in the art. By controlling the set of coating parameters for each layer, it is possible to produce atomized droplets of various sizes. Preferably, such control is used to obtain semi-dry or dry solid particles with the desired MPD1. In this ink sample, the size of such deposited particles ranged from 50 to 150 nm. This first layer was fabricated using approximately 10 to 30% of the total ink volume of the catalyst layer. In this example, the ink solution disclosed above was used to fabricate the innermost layer, approximately 30% thick of the total catalyst layer. This creates a dense bottom / innermost layer, the thickness of which can vary depending on the ink solids content and CL design.

[0124] Step 2) A second layer was immediately coated on top of the first layer using an increased flow rate and related adjustments of other coating process parameters to achieve the desired droplet size and wettability. The flow rate was increased above the initial flow rate to generate large agglomerated particles in the CL, creating an intermediate layer with a lower material packing density than the previous sublayer. The dried solid particles ranged in size from approximately 80 nm to approximately 500 nm. Uniformly large agglomerated particles are preferred. This intermediate layer contains approximately 50-70% of the total ink volume of the desired CL in selected embodiments. In this example, the thickness of the intermediate layer was approximately 5-6 microns. Furthermore, significant swelling of the film by the solvent during the coating process was known to be less than ideal for high-performance CCMs. Most droplets were controlled to reach a semi-wet state before film deposition. Those skilled in the art can easily achieve this requirement through manipulation of coating parameters.

[0125] Step 3) A third layer was created on top of the second layer. The flow rate was changed to a lower value to create a compact, dense top / outermost layer with a smooth surface. Other coating process parameters were adjusted to create the required top layer with uniform coverage and thickness.

[0126] Step 4) Once one catalyst layer with three layers was completed on the first side of the membrane, the catalyst-coated membrane was turned over and the same coating process from steps 1) to 3) was repeated to prepare another CL on the other side of the membrane.

[0127] By implementing this novel combination of processing steps, a CCM of the present invention having a CL composition of the present invention was prepared for subsequent testing. Figure 9 shows a top-view SEM image of a CCM showing a uniform and smooth top-surface morphology. Such a top / outermost layer is ideal because no cracks were observed and no loose islands or large packed aggregates were exposed. The uniform pores throughout the coated electrode also provided ideal pathways for gas diffusion and liquid (e.g., water) leakage.

[0128] Example 4: Fabrication of membrane electrode assembly The following steps will allow you to create a 50cm active area: 2 A membrane electrode assembly (width 50.0 mm, length 100.0 mm) was fabricated.

[0129] A piece of the CCM of the present invention prepared above was cut to the desired size to be sandwiched between two gas diffusion layers. Typically, the CCM is cut to a width of 70 mm and a length of 120.0 mm. Two pieces of rectangular GDL were cut to dimensions of 58 x 108 mm. This set of electrodes was laminated between two pieces of adhesive-backed plastic film with an open area of ​​50 mm x 100 mm, precisely aligned and centered on the cut CCM. The final MEA product was then hot-pressed at 115°C for 3 to 8 minutes under sufficient pressure to provide a leak-tight seal for the MEA.

[0130] After assembling the MEAs into a mono-cell stack, a leak test was performed. 5 PSI of compressed air was applied to each gas inlet of the stack, and the switch valves at each outlet were closed. The cell was immersed in a water container and observed for air bubbles emerging from the center. The MEA leak test was performed by pressurizing only one side of the MEA at 5 PSI and checking for gas escaping from the other side of the MEA gas channel, i.e., the outlet.

[0131] Example 5: Fabrication of external patterns on a CCM The external pattern of the catalyst-coated membrane was simultaneously created by compressing the MEA between two flow field plates on either side with sufficient pressure. For example, the MEA prepared above was placed between two graphite flow field plates and compressed to achieve the compression zone depth described above.

[0132] After removing the GDL, lands (RUA) and valleys (RCA) can be seen on the top of the CCM. Figure 7 shows a top-view SEM image of such a CCM fabricated by the above method. The lengths of lines 1, 2, 3, and 4 are 1.00 mm, 0.92 mm, 1.06 mm, and 0.90 mm, respectively. Lines 1 and 3 are measurement lines spanning the RCA, while lines 2 and 4 are measurement lines spanning the RUA. These are in good agreement with those of a flow field with a channel width of 1.0 mm and a land width of 0.90 mm. The width expansion may be caused by elastic compression of the GDL between the flow field and the CCM.

[0133] <Test of MEA using CCM of the present invention> The completed MEA was subjected to an activation process in a fuel cell test station at 100% RH using hydrogen as fuel and air as oxidant at 80° C. After the activation process, the MEA was subjected to a polarization test according to a test program.

[0134] The MEAs were then subjected to the HDV DOE MEA testing protocol published in November 2019. Essentially, the MEAs were subjected to CV cycling from 0.6 to 0.95 V at 50 mV / s at 85°C, 100% relative humidity, and less than 1 bar per side for a total of 150,000 cycles. ECSA measurements were performed and recorded at the 1,000th or 3,000th cycle, respectively. At the 5,000th cycle, polarization curves were measured under hydrogen and air at 85°C and 100% relative humidity, respectively. The cells were then thoroughly purged with nitrogen on the cathode, and durability testing continued until 150,000 cycles were reached.

[0135] 1.0A / cm 2 and 1.5A / cm 2 The cell voltage at different cycle numbers is summarized in Figure 4. Results showed that the cells were cycled for over 150,000 cycles under the DOE HDV MEA test protocol published in November 2019. 2 The voltage change at power density is 5.0%, which is half the benchmark MEA performance requirement for HDV applications.

[0136] Example 6: Preparation of Pt thin film coated supported catalyst When CLs of the present invention were prepared and tested under CV cycling conditions with hydrogen gas supplied to the anode side and nitrogen supplied to the cathode side at 60°C to 80°C and selected relative humidity levels of 80% to 100%, the ECSA of the CLs decreased by approximately 20% over a sufficient number of cycles, e.g., over 50,000 cycles at 50 mV / s. Cycling the MEA for 100,000 cycles reduced the ECSA by approximately 28% of its initial value. Cycling the MEA for 150 kJ / s also reduced the ECSA by approximately 40% of its initial value. It appears that the Pt thin-film-coated supported catalyst of the present invention was gradually formed during this period. The presence of Pt thin-film-coated nanoparticles and aggregates of various sizes within the CL support strongly supports the progression of formation over time. The high Pt content in the innermost region (close to the membrane) of the CL and the very low Pt content in the adjacent region are other strong evidence of the gradual formation of Pt thin-film-coated nanoparticles.

[0137] The resulting Pt coated nanoparticles are observable as bright dots in the image in Figure 10. Similar bright particles are also observable within the intermediate layer, although in lower amounts and concentrations.

[0138] Referring to Figure 11, the Pt content of different regions analyzed by electron dispersive X-ray spectroscopy was obtained as follows: in handwritten region 1, the Pt content was 39.0%; in handwritten region 2, the Pt content was 34.9%; and in handwritten region 3, the Pt content was 14.9%. Except for this analyzed Pt content, the remaining mass was mainly carbon.

[0139] Because the invention as hereinabove described is susceptible to various modifications and to many obviously widely differing embodiments, it is intended that all matter contained in the appended specification be interpreted as illustrative only and not in a limiting sense.

[0140] References 1. Jian Xie, Journal of The Electrochemical Society, 151(11), A1841-46, 2004 2. Jung, W. S., Study on durability of Pt supported on graphitized carbon under simulated start-up / shut-down conditions for polymer electrolyte membrane fuel cells, Journal of Energy Chemistry (2017) 3. Natalia Macauley et all 2018, J. Electrochem. Soc. 165 F3148, “Carbon corrosion in PEM fuel cells and the development of Accelerated stress Tests” 4. Elliot Adgett et al 2019 J. Electrochem. Soc. 166 F198, “Mitigation of PEM Electrochemical catalyst degradation with Porus Carbon Supports 5. Borup, R et al 2020 Current Opinion in Electrochemistry, “Recent developments in catalyst-related PEM electrochemical durability” 6. DeBruijn, F. A., et al 2008, Fuel Cells, 08, No. 1, Page 3 -22 7. Wang, Y., et al, Applied Energy, 2011, Page 981-1007, “A review of polymer electrolyte membrane fuel cells: Technology, application, and needs on fundamental research” 8. Wang, H. J., et al, Journal of Power Sources, 2011, 196, 9107-9116, “A review of polymer electrolyte membrane electrochemical durability rest protocols” 9. Hu, X., Song, K., NIU, W., and Zhang, T., “Powertrain System Durability in Proton Exchange Membrane Electrochemical Electric Vehicles: A Review,” SAE Technical Paper 2018-01-1303, 2018 10. Mohammed J. et al, international journal of engineering science and advanced Technology, 2017, V7, Issue 1, 100-107 11. Qin, C. W., et al Catalysts, 2016, 6, 197, “Proton Exchange Membrane Electrochemical reversal: A review 12. Ascarekku P., et al, Journal of Applied Physics 91, 4556 (2002); doi: 10.1063 / 1.1453495,” Formation process of nanocrystalline materials from x-ray diffraction profile analysis: Application to platinum catalysts 13. Z. Siroma et al. / Electrochemistry Communications 7 (2005) 1153-1156, “Imaging of highly oriented pyrolytic graphite corrosion accelerated by Pt particles. 14. Willisau, J, Heitbaum, J. Electroanal. Chem., 161 (1984)93-101, “The Influence of Pt activation on the corrosion of carbon in gas diffusion electrodes-a DEMS study” 15. Chong et al., Science 362, 1276-1281 (2018), “Ultralow loading Platinum-cobalt fuel ell catalysts derived from imidazolate frameworks. 16. Schuler, T., Journal f The Electrochemical Society, 166 (7), F3020-3031 (2019) 17. Gates, 2020, ACS Journal of applied energy materials, 202, 3,1,478-486 18. Accelerate Stress Testing protocol for HDV MEA by Department of Energy of the United States.

Claims

1. 1. A supported catalyst product coated with a thin film of catalytic material, comprising: a) nanosized conductive solid nanoparticles; b) a thin film of catalytic material deposited on the surface of said conductive solid nanoparticles; 1. A supported catalyst product comprising:

2. 10. The product of claim 1, wherein the solid nanoparticles have pre-existing catalyst nanoparticles deposited on at least a portion of the surface, at least a portion of the pre-existing catalyst nanoparticles being at least partially coated with a thin film of the catalytic material.

3. 10. The product of claim 1, wherein the solid nanoparticles comprise catalyst-free solid nanoparticles having no catalyst particles thereon, and at least some of the solid catalyst-free solid nanoparticles are at least partially coated with a thin film of the catalytic material.

4. 10. The product of claim 1, wherein the conductive solid nanoparticles comprise agglomerated conductive nanoparticles.

5. 5. The article of manufacture of claim 4, wherein at least some of the aggregated conductive nanoparticles have pre-existing catalytic nanoparticles thereon, and at least some of the pre-existing catalytic nanoparticles are at least partially coated with a thin film of the catalytic material.

6. 10. The product of claim 1, wherein the catalytic material is an electrically reducible metal or metalloid.

7. 7. The product of claim 6, wherein the catalytic material is selected from the group consisting of chromium, iron, copper, nickel, cobalt, yttrium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, indium, tin, barium, hafnium, tantalum, rhenium, osmium, iridium, platinum, gold, lead, bismuth, lanthanum, samarium, and combinations or alloys thereof.

8. 1. A solid electroplating method for producing a supported catalyst product coated with a thin film of catalytic material, the method comprising: nano-sized conductive solid nanoparticles; and a thin film of catalytic material deposited on the surface of the conductive solid nanoparticles, the method comprising: An electrode catalyst layer composition, Binder-coated nanoparticles coated with a binder as a binding substrate; Binder-free catalyst nanoparticles attached to at least said binder-coated nanoparticles by their binder matrix; regular electrical, ionic, gas, and liquid pathways within the catalyst layer defined at least in part by the interconnections between the binder-coated nanoparticles and the binder-free catalyst nanoparticles; an electrode having a catalyst layer comprising an electrode catalyst layer composition comprising: subjecting the electrode to an electrochemical reaction during which the catalyst nanoparticles in the catalyst layer are redistributed to form a thin film of the catalyst material on the nano-sized conductive solid nanoparticles; A method comprising:

9. The method of claim 8 , wherein the electrochemical reaction occurs in a fuel cell reactor.

10. The method of claim 8 , wherein the electrode is a cathode of the fuel cell reactor.

11. A plurality of sub-layers stacked on top of each other, a) an innermost layer characterized by a first material packing density; b) an outermost layer opposite the innermost layer, the outermost layer being characterized by a second material packing density; c) one or more intermediate layers between the innermost layer and the outermost layer, each characterized by a respective material packing density different from the first material packing density or the second material packing density; A catalyst layer structure having a multi-layer catalyst layer with multiple sub-layers including:

12. 12. The catalyst layer structure of claim 11, wherein the material packing density of each intermediate layer is less than the material packing density of at least one of the innermost layer and the outermost layer.

13. 13. The catalyst layer structure according to claim 11 or 12, wherein the total thickness of the one or more intermediate layers is greater than the thickness of at least one of the innermost layer and the outermost layer.

14. The multilayer catalyst layer is a catalyst layer composition, Binder-coated nanoparticles coated with a binder as a binding substrate; Binder-free catalyst nanoparticles attached to at least said binder-coated nanoparticles by their binder matrix; regular electrical, ionic, gas, and liquid pathways within the catalyst layer defined at least in part by the interconnections between the binder-coated nanoparticles and the binder-free catalyst nanoparticles; 13. The catalyst layer structure according to claim 11 or 12, which is composed of a catalyst layer composition comprising:

15. 13. The catalyst layer structure according to claim 11 or 12, wherein the multilayer catalyst layer is coated on one side of a solid electrolyte membrane of a membrane electrode assembly, and the other side of the solid electrolyte is coated with another such multilayer catalyst layer composed of multiple sublayers, the packing density of which differs among at least some of the multiple sublayers.

16. 13. The catalyst layer structure of claim 11 or 12, wherein the material packing density of at least one of the innermost layer and the outermost layer is equal to or greater than the packing density of the one or more intermediate layers.

17. 13. The catalyst layer structure of claim 11 or 12, wherein the one or more intermediate layers have the same composition throughout the one or more intermediate layers.

18. 13. The catalyst layer structure of claim 11 or 12, wherein the one or more intermediate layers include at least one intermediate layer having a mixed catalyst nanoparticle composition layer.

19. 13. The catalyst layer structure of claim 11 or 12, wherein the one or more intermediate layers comprise a plurality of intermediate layers having different respective packing densities.

20. Catalyst layer structure according to claim 11 or 12, wherein the innermost layer comprises nanoparticles having an average particle size in the range of 30 to 150 nm.

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