Understanding and Engineering of Multiphase Transport Processes in Membrane Electrode Assembly of Proton-Exchange Membrane Fuel Cells with a Focus on the Cathode Catalyst Layer: A Review

Abstract

The development of proton-exchange membrane fuel cell (PEMFC) technology will give rise to a great evolution toward a more sustainable and eco-friendly life by powering clean electric vehicles or stations. However, several vital problems still hinder the commercialization of PEMFCs. The foremost issue is the high cost compared to the contenders, deriving from both the high consumption of Pt catalysts and low service life under practical operations. In this review, deeper investigations on how to further lower the cost of PEMFCs show the importance of understanding and engineering the multiphase transport processes in the membrane electrode assembly (MEA). The definitions, rules, numerical simulations, and experimental validations of various mass transfer processes across the MEA are introduced to provide a holistic evaluation and enable optimization to improve the cell performance and reliability. In addition, because the sluggish oxygen reduction reaction in the cathode catalyst layer (CCL) requires most of the Pt catalysts, the oxygen/water-related multiphase transfer in CCLs is taken as a focus for detailed analysis. Several successful strategies, such as triple-phase boundary engineering, graded design, and novel ordered three-dimensional structure construction, are proven to be promising in greatly reducing the Pt consumption in the CCL and facilitating the microscopic multiphase transfer processes of the MEA. With optimized engineering of the electrode structure and configuration inside the MEA, the mass transfer resistances can be minimized to give the best operating conditions for electrochemical reactions to occur in the catalyst layers. Finally, the main challenges and some perspectives for developing advanced MEAs with lower cost in high-performance and reliable PEMFCs are provided.

How to appropriately assess the oxygen reduction reaction activity of platinum group metal catalysts with rotating disk electrode

“…PEMFCs is of crucial importance to realize the carbon-neutral society for the sustainable development of human kind ( Asset and Atanassov, 2020 ), and enormous advances have been achieved on mechanism study, catalyst synthesis/characterization, MEA simulation/fabrication, and even preliminary commercialization of electric vehicles during the last decade ( Deng et al., 2020 ; E4tech, 2018 ; Wang et al., 2020b ). PGM-based catalysts are still indispensable for the foreseeable largescale application of PEMFCs, nevertheless some fundamental issues concerning potential conversion and activity/durability tests still need to be clarified and standardized for the better development of pivotal ORR catalysts.…”

Phosphate‐Assisted Dispersion of Iron Phosphide in Carbon Nanosheets towards Efficient and Durable ORR Catalysts in Acidic and Alkaline Media

“…This is beneficial to reduce the catalyst usage, and more importantly lower the thickness of catalyst layer, which facilitates the diffusion of O 2 and improves PEMFC performance. [54] The performance of the PEMFC with Fe 2 P/FeP-PNC as the cathode increases with respect to increasing back pressure, and achieved the highest powder density at the pressure of 30 psi for both H 2 and O 2 sides (Figure 9c). This is because that the transfer rate of the reaction gas will be accelerated with increase of back pressure.…”

Cathode Design for Proton Exchange Membrane Fuel Cells in Automotive Applications

“…Thereby, appropriate water/heat management is essential for proton conducting and reactant transport, mitigating severe performance loss in operation [136]. There are two major strategies applied to achieve highpower performance at large-current-density operation: optimization engineering of the electrode structure and MEA configuration, and minimizing mass transfer resistance by providing the best operating conditions for electrochemical reactions in the optimal CL [8]. Ramaswamy and Kumaraguru [137] proposed that the material and design selection in the CL affected the local-O 2 and bulk-H + transport thus improving large current density performance in PEMFCs.…”

“…Lee et al [139] investigated increasing the average pore size from 50 to 60 nm in the CL by introducing PEG addition to catalyst ink to achieve reduced mass transport resistance in operation. Besides the above-mentioned innovation of material and electrode structure, other efforts reported related to mass transfer inside the MEAs were focused on water/heat management, flow field design and the humidification strategy at the fuel cell stack level for a full play of the MEA potential [8].…”

“…Then, research advancements about promoting intrinsic cathodic ORR activities Fig. 1 Flux balance overviews in a simplified PEMFC model [8] in PEMFCs are briefly described. The research efforts on improving mass transport of oxygen and water in the cathode catalyst layer are discussed in detail.…”