Experimental and numerical analysis of a catalyst layer in the membrane electrode assembly of polymer electrolyte membrane fuel cells

Fuel cells constitute an important strategy for carbon-neutral Carbon Dioxide recycling because they utilize the green hydrogen produced from renewable electrical energy. To achieve low-cost and high-performance polymer electrolyte fuel cells, reducing active metals by optimizing the cathode catalyst layer structure is crucial. In this study, we combined image analysis, numerical analysis, and electrochemical approaches to clarify the diffusion characteristics of the cathode catalyst layer in a polymer electrolyte membrane fuel cell. The structure of a catalyst-supported carbon substrate and stacked catalyst-supported carbon substrate was determined using transmission electron microscopy and focused ion-beam scanning electron microscopy. Porosity was analyzed by image analysis and torsion by numerical analysis using the random walk method. Diffusivity near the catalyst and pores was evaluated using a recently developed method by analyzing the active metal surface resistance based on the dependence of the catalyst layer resistance on carbon monoxide coverage. These analytical methods were applied to catalyst-supported carbon materials with different structures. Diffusion through the catalyst surface, carbon support, and carbon support aggregates was also analyzed; furthermore, we obtained following guidelines for improving the specifications. Larger pores and smaller flexures in the cathode catalyst layer may improve the performance of Polymer Electrolyte Membrane Fuel Cells.