Performance Of Membrane Electrode Assembly Research Articles

Optimization of cathode catalyst layer of membrane electrode assembly for polymer electrolyte fuel cells using machine learning

To optimize the cathode catalyst layer of MEAs for polymer electrolyte fuel cells, we developed a data-driven model to predict the performance of MEAs by using the physical properties of the catalyst layer as a property variable. To use the physical properties of the catalyst layer as an input variable, feature extraction through image processing and measurement data profiles from electron microscopy images, and XRD, were automated to eliminate variation due to differences among analysts. Furthermore, a sensitivity analysis using a data-driven model extracted important features and revealed that diffusion in the interparticle voids within the catalyst layer and intra-particle diffusion of carbon aggregates were the key factors. These results are consistent with the findings of previous numerical and experimental approaches for cathode catalyst layers and demonstrate that data-driven modeling is a powerful tool for developing cathode catalyst layers for MEAs. Furthermore, the combination of data-driven modeling and genetic algorithm optimization techniques guides the optimization of material properties to improve the performance of membrane electrode assemblies. These results are expected to provide valuable insights into improving the performance of polymer electrolyte fuel cells, promoting their widespread use, and realizing CO2 recycling in a carbon-neutral and green manner.

Effective single web–structured electrode for high membrane electrode assembly performance in polymer electrolyte membrane fuel cell

To achieve a sustainable society, CO2 emissions must be reduced and efficiency of energy systems must be enhanced. The polymer electrolyte membrane fuel cell (PEMFC) has zero CO2 emissions and high effectiveness for various applications. A well-designed membrane electrolyte assembly (MEA) composed of electrode layers of effective materials and structure can alter the performance and durability of PEMFC. We demonstrate an efficient electrode deposition method through a well-designed carbon single web with a porous 3D web structure that can be commercially adopted. To achieve excellent electrochemical properties, active Pt nanoparticles are controlled by a nanoglue effect on a highly graphitized carbon surface. The developed MEA exhibits a notable maximum power density of 1082 mW/cm2 at 80°C, H2/air, 50% RH, and 1.8 atm; low cathode loading of 0.1 mgPt/cm2; and catalytic performance decays of only 23.18 and 13.42% under commercial-based durability protocols, respectively, thereby achieving all desirables for commercial applications.

Optimization of the ionomer-to-carbon ratio in the cathode catalyst layer of PtCoMn/C alloy catalysts

The optimization of membrane electrode assembly (MEA) structures based on alloy catalysts can further improve the properties of proton exchange membrane fuel cells and accelerate their commercialization. Herein, novel MEAs with ultra-low platinum loading and high performance were prepared by a decal transfer method using a highly active PtCoMn/C alloy catalyst. The effects of different I/C ratios on the performance of PtCoMn/C cathodes were investigated by polarization curves. The results suggested an optimal I/C ratio of 0.9, leading to a maximum power density of 1.51 W/cm2. The effects of the I/C ratio on catalyst activity and proton conductivity were studied by AC impedance and cyclic voltammetry, and the impact of the I/C ratio on local oxygen transport resistance was evaluated by the limiting current method. The data revealed that the MEA has the highest ECSA of CL combined with the lowest Rct and higher proton conductivity,when the I/C ratio is 0.9. An influencing mechanism of ionomer content on performance of low platinum loading MEA prepared by PtCoMn/C was then drawn, suggesting that The highest activity at the I/C ratio of 0.9 mainly depends on its excellent proton conductivity.

Impact of conditioning protocol on hydrocarbon-based solid polymer electrolyte fuel cells

Freshly prepared membrane-electrode-assemblies (MEA) for fuel cells require conditioning to improve their performance and durability. It is therefore important to choose the appropriate conditioning method to ensure their highest performance and durability using the shortest conditioning time possible. In this report, we describe the impact of standardized conditioning procedures, including US Department of Energy (DOE) and European Union (EU) harmonized protocols, an amperometric protocol, and a cathode starvation protocol for hydrocarbon solid polymer electrolyte-based MEAs. The hydrocarbon polymer employed was sulfophenylated poly(phenylene)biphenyl. The cathode starvation conditioning protocol yields MEAs that exhibit the highest peak power density (1790 mW/cm2, H2/O2, 80 °C, 100% RH, 1 atm pressure). This was found to be 20, 45, and 52% greater than that found for hydrocarbon MEAs conditioned using the EU (1500 mW/cm2), DOE (1240 mW/cm2), and amperometric (1180 mW/cm2) conditioning protocols. Durability studies entailing voltage cycling revealed that the cathode starvation-conditioned MEAs yield the lowest performance losses (41% of initial performance) for the hydrocarbon MEAs. The DOE, and EU conditioning protocols yielded MEA performance losses of 55% and 45% of their initial performance lost after degradation. The amperometric protocol led to conditioned MEAs that lost mechanical integrity during accelerated degradation.

Effects of Electrostatic Force and Network Structure on the Stability of Proton-Exchange Membrane Fuel Cell Catalyst Ink

The stability of the catalyst slurry of a proton-exchange membrane fuel cell (PEMFC) is of great significance to its large-scale production and commercialization. In this study, three kinds of slurries with different stabilities were prepared using different probe ultrasonic powers. The influence of electrostatic force and network structure on slurry stability was also studied. In addition, the catalyst layer (CL) and membrane electrode assembly (MEA) were further tested to determine the relationship between slurry stability, CL, and MEA performance. The results showed that the slurry prepared with 600 W dispersion power had the least agglomeration on day 12, which is due to the clusters in the slurry having the smallest average particle size and the largest surface area, thereby allowing them to absorb the most Nafion and have the largest electrostatic force to inhibit agglomeration. However, the slurry with 1200 W dispersion power had the least sedimentation after 9.4 days because the strength of the network structure in the slurry strengthened the most, resulting in a significant increase in viscosity and inhibition of sedimentation. Electrochemical tests showed that the MEA gradually exhibited worse electrical performance and higher impedance due to the agglomeration of catalyst particles caused by the standing process. Altogether, this study provides insights to better understand and regulate the stability of catalyst slurries.

Effect of membrane deposition methods on the performance of membrane electrode assemblies

AbstractThe performance of proton exchange membrane fuel cells (PEMFCs) is closely related to the preparation process of the membrane electrode assemblies (MEAs). The direct membrane deposition approach can achieve excellent interfacial connection between functional layer, as well as simplifying the MEA manufacturing process. Nevertheless, it has been recognized that for this approach, the permeation of the electrolyte solution into the catalyst layer is a challenge, and it is associated with the deposition method. In this study, three MEAs are prepared by spraying, blade coating, and a combination of the two. The effect of the electrolyte solution deposition methods on the properties of the MEAs is analyzed. The MEA prepared using the combination of spraying and blade coating delivers the highest performance of up to 0.618 W cm−2 (80°C with H2/air conditions at normal pressure). In this method, the spraying layer can alleviate the negative effect of cracks on the gas diffusion electrode surface, and the blade‐coating layer can improve the membrane uniformity. The MEA prepared by this method exhibits excellent cell performance compared to the traditional catalyst coated membrane type MEA, particularly in low‐humidity conditions. This work provides guidance for the preparation of high‐performance MEAs for PEMFCs.

Reconstruction of Thiospinel to Active Sites and Spin Channels for Water Oxidation.

Water electrolysis is a promising technique for carbon neutral hydrogen production. A great challenge remains at developing robust and low-cost anode catalysts. Many pre-catalysts are found to undergo surface reconstruction to give high intrinsic activity in the oxygen evolution reaction (OER). The reconstructed oxyhydroxides on the surface are active species and most of them outperform directly synthesized oxyhydroxides. The reason for the high intrinsic activity remains to be explored. Here, a study is reported to showcase the unique reconstruction behaviors of a pre-catalyst, thiospinel CoFe2 S4 , and its reconstruction chemistry for a high OER activity. The reconstruction of CoFe2 S4 gives a mixture with both Fe-S component and active oxyhydroxide (Co(Fe)Ox Hy ) because Co is more inclined to reconstruct as oxyhydroxide, while the Fe is more stable in Fe-S component in a major form of Fe3 S4 . The interface spin channel is demonstrated in the reconstructed CoFe2 S4 , which optimizes the energetics of OER steps on Co(Fe)Ox Hy species and facilitates the spin sensitive electron transfer to reduce the kinetic barrier of O-O coupling. The advantage is also demonstrated in a membrane electrode assembly (MEA) electrolyzer. This work introduces the feasibility of engineering the reconstruction chemistry of the precatalyst for high performance and durable MEA electrolyzers.

Pt-Based Oxygen Reduction Reaction Catalysts in Proton Exchange Membrane Fuel Cells: Controllable Preparation and Structural Design of Catalytic Layer.

Proton exchange membrane fuel cells (PEMFCs) have attracted extensive attention because of their high efficiency, environmental friendliness, and lack of noise pollution. However, PEMFCs still face many difficulties in practical application, such as insufficient power density, high cost, and poor durability. The main reason for these difficulties is the slow oxygen reduction reaction (ORR) on the cathode due to the insufficient stability and catalytic activity of the catalyst. Therefore, it is very important to develop advanced platinum (Pt)-based catalysts to realize low Pt loads and long-term operation of membrane electrode assembly (MEA) modules to improve the performance of PEMFC. At present, the research on PEMFC has mainly been focused on two areas: Pt-based catalysts and the structural design of catalytic layers. This review focused on the latest research progress of the controllable preparation of Pt-based ORR catalysts and structural design of catalytic layers in PEMFC. Firstly, the design principle of advanced Pt-based catalysts was introduced. Secondly, the controllable preparation of catalyst structure, morphology, composition and support, and their influence on catalytic activity of ORR and overall performance of PEMFC, were discussed. Thirdly, the effects of optimizing the structure of the catalytic layer (CL) on the performance of MEA were analyzed. Finally, the challenges and prospects of Pt-based catalysts and catalytic layer design were discussed.

Insights into Degradation of the Membrane-Electrode Assembly Performance in Low-Temperature PEMFC: the Catalyst, the Ionomer, or the Interface?

Here, we report a study on the structural characteristics of membrane electrode assembly (MEA) samples obtained from a low-temperature (LT) polymer electrolyte membrane (PEM) fuel cell (FC) stack subjected to long-term durability testing for ∼18,500 h of nominal operation along with ∼900 on/off cycles accumulated over the operation time, with the total power production being 3.39 kW h/cm2 of MEA and the overall degradation being 87% based on performance loss. The chemical and physical states of the degraded MEAs were investigated through structural characterizations aiming to probe their different components, namely the cathode and anode electrocatalysts, the Nafion ionomer in the catalyst layers (CLs), the gas diffusion layers (GDLs), and the PEM. Surprisingly, X-ray diffraction and electron microscopy studies suggested no significant degradation of the electrocatalysts. Similarly, the cathode and anode GDLs exhibited no significant change in porosity and structure as indicated by BET analysis and helium ion microscopy. Nevertheless, X-ray fluorescence spectroscopy, elemental analysis through a CHNS analyzer, and comprehensive investigations by X-ray photoelectron spectroscopy suggested significant degradation of the Nafion, especially in terms of sulfur content, that is, the abundance of the -SO3- groups responsible for H+ conduction. Hence, the degradation of the Nafion, in both of the CLs and in the PEM, was found to be the principal mechanism for performance degradation, while the Pt/C catalyst degradation in terms of particle size enlargement or mass loss was minimal. The study suggests that under real-life operating conditions, ionomer degradation plays a more significant role than electrocatalyst degradation in LT-PEMFCs, in contrast to many scientific studies under artificial stress conditions. Mitigation of the ionomer degradation must be emphasized as a strategy to improve the PEMFC's durability.

Boosting oxygen transport through mitigating the interaction between Pt and ionomer in proton exchange membrane fuel cell

The key to operating low-cost and high-power proton exchange membrane fuel cell (PEMFC) is reducing local oxygen transport resistance (Rionomer) from Pt/ionomer interface in cathode with low Pt loading. Herein, we design a high-oxygen mass-transfer Pt/ionomer interface via chemical modification of Pt/C catalyst with 1-Hexadecanethiol (C16SH) by self-assembled monolayers (SAMs) method. With a concentration of 0.3 mM, C16SH is selectively adsorbed on Pt nanoparticles and constructs a hydrophobic Pt/C surface, which can effectively reduce.-SO3H density around Pt active sites and the specific Pt/ionomer interface is obtained after C16SH is removed by in situ electrochemical oxidation. Consequently, compared with the performance of membrane electrode assembly (MEA) from unmodified catalyst, the voltage of C16SH-modified MEA increases by 45 and 82 mV, respectively, at 1500 and 2000 mA cm−2 at RH 100%. The decrease in oxygen transport resistance plays a key role in improving polarization performance, relative to the increase in H+ transport resistance. Moreover, according to limiting current density method, the reduced Rionomer from Pt/ionomer interface is the essential reason for the improved oxygen transport. In general, this work highlights a promising method to boost oxygen transport and enhance performance of PEMFC through mitigating the interaction between Pt and ionomer.

Rationally Designed PGM-Free Catalyst MEA with Extraordinary Performance

Platinum group metal (PGM) catalysts are the major electrocatalysts for oxygen reduction reaction (ORR) in the polymer electrolyte membrane fuel cells (PEMFCs). However, the high cost of PGM catalysts is the major huddler for the widespread applications of fuel cell electric vehicles. To remove this cost obstacle of fuel cell commercialization, PGM-free catalysts have been considered as the replacement of PGM catalysts for ORR because of the low cost and relatively comparable performance with PGM catalyst. Fe-C-N complex is the one of the most active centers in PGM-Free catalyst groups. This type of catalyst shows excellent activity characterized using the rotation disk electrode (RDE), i.e., the half wave potential (E1/2 ) could reach 0.91 V versus standard hydrogen electrode (SHE). However, in a membrane electrode assembly (MEA), the performance of PGM-Free catalysts cannot achieve the comparable performance to PGM catalyst. Since there are so many differences between PGM-free, and PGM catalysts e.g., activity, stability, surface conditions, particle size etc. The fabrication of PGM-Free catalyst MEA cannot simply borrow the methods from that of making PGM MEA. In addition, the thicknesses of catalyst layers of PFM-free are significantly thicker than that of PGM, i.e., 10 times. Hereby, we proposed a novel method of fabricating PGM-Free catalyst MEA, so that the intrinsic catalyst activity from RDE can be translated into MEA performance. The method is based on the catalyst coated membrane (CCM) method using optimized ionomer to carbon (I/C) ratio and solvent mixture of catalyst ink. Such method pushes PGM-free MEA first ever achieved the current density of 50.8 mA cm-2 at 0.9 V iR-free in H2/O2 and over 150 mA cm-2 at 0.8 V in H2/air, which surpassed the 2025 performance targets of US Department of Energy (DOE) for PGM-Free catalyst MEA. Further, the property (solvent composition, dispersion of catalyst and ionomer in an ink), structure (pore structure) and the MEA performance have been characterized using mercury intrusion porosimetry (MIP), MEA testing. A property-structure-performance relationship has been established.

Tuning the Rheology of Anode Inks with Aging for Low-Temperature Polymer Electrolyte Membrane Water Electrolyzers

Low-temperature polymer electrolyte membrane water electrolyzers (PEMWE) are an attractive clean energy technology to produce hydrogen (H2), which is an energy carrier for several applications such as transportation and grid-scale energy storage and distribution (as supported by the US Department of Energy’s H2@Scale initiative). The catalyst layers -- composed of catalyst particles and ionomer, which acts as a binder for the catalyst and a proton conducting medium -- are key components of the PEMWE membrane electrode assembly (MEA). The catalyst layers are commonly fabricated by solution-processing an ink, which is a mixture of catalyst and ionomer often dispersed in a water-alcohol solvent mixture. Tuning the rheological properties of the anode inks (typically composed of iridium oxide catalyst, IrOx), particularly increasing their viscosity without significantly increasing the solids loading, to suit various scalable coating methods, is generally a challenge due to relatively low porosity and high density of the IrOx catalysts compared to the carbon-supported cathode catalysts. The typically low viscosities of the anode inks combined with high particle densities often cause stability/settling issues and challenges obtaining unform coatings, leading to inhomogeneous distribution of the catalyst that may have a negative effect on electrode performance. In this presentation we report on a dramatic enhancement in the viscoelasticity of the anode inks with aging, where the ink transitions from a liquid-like to a weak gel-like structure. The steady-shear and oscillatory shear rheology characterizations of the inks as a function of aging/time, the impact of formulation conditions (ionomer-to-catalyst ratio and dispersion media composition) on the viscoelastic enhancement with aging, and possible mechanisms for the observed behavior will be discussed. In addition to the rheological measurements, X-ray scattering characterization of the ink structure will be presented. The implications of the rheological changes on ink stability and processing will also be discussed. Additionally the impact of ink age on MEA performance will be presented.

Effects of Catalyst Composition, Loading, and Spray Parameters on the Performance of Unitized Regenerative Fuel Cell Membrane Electrode Assemblies

Proton exchange membrane unitized regenerative fuel cells (PEM-URFCs) combine the ability to both produce power (in fuel cell mode) and generate fuel and oxidant (in electrolysis mode) from the same cell. Compared with discrete fuel cell and electrolyzer systems, URFCs provide the potential for lower mass, volume, and cost. The composition and structure of the bifunctional oxygen catalyst layer (CL), which facilitates the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the same electrode, significantly affects performance and stability, particularly given the wide potential differences and different mass transport phenomena involved under operation in fuel cell or electrolysis mode. We previously showed bimetallic nanoframes provide bifunctional oxygen electrocatalysts with significantly higher activity compared with monometallic structures, evaluated using a rotating disk electrode configuration.1 Here, we investigated the effects of the oxygen CL composition, loading, and spray parameters on the performance of URFC membrane electrode assemblies (MEAs). Pt black and IrO2 catalysts were combined at different ratios and deposited at different mass loadings. Catalyst layers were sprayed directly onto membranes using an ultrasonic spray system. Within ultrasonically sprayed catalyst layers, higher spray rates resulted in improved fuel cell performance. Higher catalyst loadings improved both fuel cell and electrolyzer performance, but reached a region of diminishing returns at higher loadings. The ratio of the ORR catalyst (Pt) to the OER catalyst (IrO2) modulated the performance in both fuel cell and electrolyzer modes. Different catalyst ratios influence the catalyst utilization at higher loadings. The comparison of URFC performance at same Pt or IrO2 loadings indicates that in addition to the active catalyst itself, the non-catalytically active component influences MEA performance. This result is in line with our previous evaluation of synergistic effects of Pt and IrO2 within rotating disk electrode measurements1 and supports that in addition to the significant effects of catalyst material structure on performance, the electrode structure plays a critical role in fuel cell and electrolyzer performance in URFC MEAs. Repeated switching of URFC MEAs between fuel cell and electrolysis modes indicates that reasonable performance is maintained over the initial cycles within our single cell test configuration. References Godínez-Salomón, F.; Albiter, L.; Mendoza-Cruz, R.; Rhodes, C.P. Bimetallic Two-dimensional Nanoframes: High Activity Acidic Bifunctional Oxygen Reduction and Evolution Electrocatalysts. ACS Appl. Energy Mater. 2020, 3, 2404-2421. http://dx.doi.org/10.1021/acsaem.9b02051

Modifying the Cathode Catalyst Layer in PEM Fuel Cells with Ionic Liquids for Improved Oxygen Reduction Reaction

Increasing the accessibility of green, affordable hydrogen and reducing the cost of polymer electrolyte membrane fuel cells (PEMFC) devices are critical to the widespread commercialization of hydrogen powered fuel cells. The high cost of PEMFCs is in part due to the high Pt leadings in the cathode catalyst layer (CCL) to compensate for kinetic and transport losses during the sluggish oxygen reduction reaction. Therefore, substantial research efforts have been focused on modifying the CCL and its constituent components to achieve cost parity with other advanced energy technologies, particularly in the transportation sector.Hydrophobic ionic liquids (ILs) have been used as interfacial additives for oxygen reduction reaction (ORR) electrocatalysts, demonstrating enhanced catalyst activity and durability.1,2 However, incorporating ILs or IL-modified catalysts into the electrodes of a PEMFC membrane electrode assembly (MEA) has proven to be challenging. To address this limitation, we developed a new ionomer chemistry with orthogonal properties of protonic conductivity and ionic liquid functionality: sulfonated poly(ionic liquid) block copolymers (S-PILBCPs). The new ionomer in the Pt/C CCLs yields a two-fold improvement in the kinetic activity, both in the half-cell and MEA. Furthermore, a Nafion/S-PILBCP composite ionomer substantially improves the high current density performance as well.3 In this work, we use rotating disk electrode (RDE) techniques to electrochemically characterize the Pt/S-PILBCP interface. Our analysis demonstrates the promise and utility of hydrocarbon-based poly(IL) ionomers over the traditional ionomer-Nafion and also provides important insights about observed MEA performance enhancements.

The Impacts of Membrane Pinholes on Performance and Hydrogen Crossover in PEM Water Electrolysis

Polymer electrolyte membrane (PEM) water electrolysis is a promising energy storage technology to produce highly pure hydrogen with high efficiency 1. However, to implement it on a larger scale, it is essential to understand the effects of defects and the required tolerances and quality controls during manufacturing or subsequent handling. Inhomogeneities in membrane electrode assembly (MEA) component materials caused by the manufacturing process or subsequent handling can lead to performance loss and failure 2. Defects such as membrane pinholes, cuts, tears, abrasions, or perforations can all potentially impact MEA performance. In terms of impact, a loss of integrity of the membrane can allow bulk gas transport (crossover) and/or electrical shorting 3.In particular, hydrogen crossover is a crucial issue for PEM water electrolysis in terms of safe operation and efficiency losses, especially at increased hydrogen pressures. Crossover reduces the overall efficiency of the system and poses flammability hazards under certain conditions 4. Pinholes that form during the manufacturing process or during operation through degradation of the membrane lead to dramatically increased hydrogen crossover.In this study, the impacts of membrane pinholes on the performance and hydrogen crossover of PEM water electrolyzer cells are studied. Pinholes with different sizes are artificially introduced to the MEA to investigate the effects on the initial cell performance and hydrogen crossover rate under various backpressure and current density conditions. Reference Liu, C.; Shviro, M.; Gago, A. S.; Zaccarine, S. F.; Bender, G.; Gazdzicki, P.; Morawietz, T.; Biswas, I.; Rasinski, M.; Everwand, A., Exploring the Interface of Skin‐Layered Titanium Fibers for Electrochemical Water Splitting. Adv Energy Mater 2021, 11 (8), 2002926.Ulsh, M.; DeBari, A.; Berliner, J. M.; Zenyuk, I. V.; Rupnowski, P.; Matvichuk, L.; Weber, A. Z.; Bender, G., The development of a through-plane reactive excitation technique for detection of pinholes in membrane-containing MEA sub-assemblies. Int J Hydrogen Energ 2019, 44 (16), 8533-8547.Phillips, A.; Ulsh, M.; Mackay, J.; Harris, T.; Shrivastava, N.; Chatterjee, A.; Porter, J.; Bender, G. J. F. C., The effect of membrane casting irregularities on initial fuel cell performance. 2020, 20 (1), 60-69.Martin, A.; Trinke, P.; Stähler, M.; Stähler, A.; Scheepers, F.; Bensmann, B.; Carmo, M.; Lehnert, W.; Hanke-Rauschenbach, R. J. J. o. T. E. S., The Effect of Cell Compression and Cathode Pressure on Hydrogen Crossover in PEM Water Electrolysis. 2022, 169 (1), 014502.

High-Platinum-Content PGM Catalysts on Atomically Dispersed and Nitrogen Coordinated Single Manganese Site Carbons for Heavy-Duty Fuel Cells

Fuel cells for heavy-duty vehicles (HDVs) have attracted considerable attention because of their unique scalability, better fuel economy, the less demand for hydrogen refilling infrastructure. However, the potential application requires more stringent fuel cell durability up to 25,000 hours. Membrane electrode assemblies (MEAs) made from platinum group metal (PGM) catalyst with relatively high loading 0.3 mgPt/cm2 play a crucial role in ensuring high-power and long-term durability. Integrating fine PGM nanoparticles and robust carbon support with strengthened interactions is critical for improving MEA performance and durability. Here, a unique atomically dispersed and nitrogen coordinated single Mn site-rich carbon (M-N-C) support was developed for high content (40 wt.%) platinum catalysts for the oxygen reduction reaction (ORR) cathode with reduced thickness. Compared with two controls studied in this work (e.g., a porous graphitic carbon-supported Pt and a commercial TKK Pt/C catalysts), the Pt (40 wt.%)/Mn-N-C catalyst exhibited much enhanced catalytic activity and stability for the ORR in both aqueous acidic electrolyte and polymer electrolyte-based MEA. We carefully elucidated the promotional role of the Mn-N-C support in promoting Pt catalyst concerning its high surface area, partially graphitic structure, and nitrogen dopants, providing better Pt nanoparticle dispersion, and strengthened interactions between Pt and carbon. Consequently, the MEA from the Pt (40 wt.%)/Mn-N-C catalyst can retain 1.2 A/cm2 at 0.7 V (based on HDV conditions (0.2 mgPt/cm2 and 250 kPa air) after 150000 voltage AST cycling. Therefore, the Mn-N-C carbon-supported Pt catalyst holds great promise to meet the challenging DOE target (1.07 A/cm2 at 0.7 V after 150,000 cycles) for HDVs.

Graded Catalyst Layers As a Strategy to Increase Power Density and Reduce Catalyst Loading

Proton exchange membrane fuel cells (PEMFCs) offer an attractive solution to reduce the carbon emissions of the transport sector. Despite the continuous efforts of researchers over the past decades, the current landscape of fuel cell technologies shows limitations at the component level in terms of performance, durability, and production cost. The main objective of the work presented here is to improve the power density of fuel cells by understanding the performance limitations of the membrane electrode assemblies (MEAs). To accomplish this objective, a series of in‐situ performance tests and ex‐situ characterisation methods have been used to create correlations between the observed performance, voltage loss breakdowns at the cell level, and the fundamental material property characteristics of state-of-the-art (SoA) MEA components. Specifically, we have explored the development of graded catalyst layers in the x-, y-, and z-direction to improve catalyst utilization, leading to increased power density while simultaneously decreasing catalyst loadings. The optimized catalyst layer structures, in combination with ultrathin proton exchange membranes, have led to high performance MEAs with reduced catalyst loadings compared to commercially available SoA MEAs.

Engineering Atomic Single Metal–FeN4Cl Sites with Enhanced Oxygen-Reduction Activity for High-Performance Proton Exchange Membrane Fuel Cells

Fe-N-C single-atomic metal site catalysts (SACs) have garnered tremendous interest in the oxygen reduction reaction (ORR) to substitute Pt-based catalysts in proton exchange membrane fuel cells. Nowadays, efforts have been devoted to modulating the electronic structure of metal single-atomic sites for enhancing the catalytic activities of Fe-N-C SACs, like doping heteroatoms to modulate the electronic structure of the Fe-Nx active center. However, most strategies use uncontrolled long-range interactions with heteroatoms on the Fe-Nx substrate, and thus the effect may not precisely control near-range coordinated interactions. Herein, the chlorine (Cl) is used to adjust the Fe-Nx active center via a near-range coordinated interaction. The synthesized FeN4Cl SAC likely contains the FeN4Cl active sites in the carbon matrix. The additional Fe-Cl coordination improves the instrinsic ORR activity compared with normal FeNx SAC, evidenced by density functional theory calculations, the measured ORR half-wave potential (E1/2, 0.818 V), and excellent membrane electrode assembly performance.

Advances in polybenzimidazole based membranes for fuel cell applications that overcome Nafion membranes constraints

High-temperature proton exchange membrane fuel cells (PEMFCs) are becoming more appealing to researchers around the world due to several advantages such as high energy conversion efficiency, lightweight due to the use of polymeric materials, low noise due to the lack of mechanical components, zero or low emission of harmful greenhouse gases, simple design, first reaction kinetics, and simple water management. The performance, limitations, and possibilities for the practical implementation of different high-temperature proton exchange membranes (PEMs) utilized in fuel cells are discussed in this review paper. A suitable PEM must be developed to improve the performance of membrane electrode assemblies for high-temperature PEMFCs (working temperature above 100 °C). Various PEMs such as sulfonated poly(ether ether ketone) (SPEEK), sulfonated polystyrene (SPS), sulfonated polyimide (SPI), sulfonated polysulfone (SPSU), phosphoric acid doped polybenzimidazole (PA-PBI), perfluorosulfonic acid (PFSA) polymer-based membranes have been investigated as PEMs for fuel cell applications by several research groups. Among the various PEMs, PA-PBI membranes are the most promising high-temperature PEM for fuel cell applications because of their higher proton conductivity at high temperatures and anhydrous conditions, good chemical and thermal, mechanical stability, and high durability. However, the performance of high-temperature PEMs based on pristine PA-PBI is insufficient to fulfill the need for practical implementation of high-temperature PEMFCs, which needs to be enhanced further before they can be used commercially. Therefore, PA-PBI composite membranes containing various multifunctional inorganic, organic, and hybrid fillers are being actively explored to produce high-temperature PEMs. The PA-PBI composite membranes’ proton conductivity increases with rising temperature and maintains conductivity in anhydrous conditions, as well as chemical, thermal, and oxidative stability under operating conditions and long-term performance stability.

High-loading Pt-alloy catalysts for boosted oxygen reduction reaction performance

To improve performance of membrane electrode assembly (MEA) at large current density region, efficient mass transfer at the cathode is desired, for which a feasible strategy is to lower catalyst layer thickness by constructing high loading Pt-alloy catalysts on carbon. But the high loading may induce unwanted particle aggregation. In this work, H-PtNi/C with 33% (mass) Pt loading on carbon and monodisperse distribution of 3.55 nm PtNi nanoparticles, was prepared by a bimodal-pore route. In electrocatalytic oxygen reduction reaction (ORR), H-PtNi/C displays an activity inferior to the low Pt loading catalyst L-PtNi/C (13.3% (mass)) in the half-cell. While in H2-O2 MEA, H-PtNi/C delivers the peak power density of 1.51 W·cm−2 and the mass transfer limiting current density of 4.4 A·cm−2, being 21% and 16% higher than those of L-PtNi/C (1.25 W·cm−2, 3.8 A·cm−2) respectively, which can be ascribed to enhanced mass transfer brought by the thinner catalyst layer in the former. In addition, the same method can be used to prepare PtFe alloy catalyst with a high-Pt loading of 36% (mass). This work may lead to a range of catalyst materials for the large current density applications, such as fuel cell vehicles.