Design of multi-layered gradient catalysts for efficient proton exchange membrane fuel cells

Efficient catalyst layers (CLs) in proton exchange membrane fuel cells (PEMFCs) should possess a highly active surface for electrochemical reaction and an ideal platform for simultaneous mass transfer. Efforts have been devoted to lower the widely used Pt and Nafion loading due to their high cost. However, the increase in gas transport resistance and decrease in transfer ability of protons and electrons result in a degraded fuel cell performance. Therefore, CL design with optimal efficiency is important for high performance and stability of PEMFCs. In this study, we design gradient multi-layered CLs in which the loadings of Pt–C catalyst and Nafion ionomer are set differently for each layer to increase efficiency. For ideal cell performance, the ionomer loading should be higher near the membrane layer and Pt–C loading should be higher near the gas diffusion layer. In addition, we confirm that if the loading difference between layers in the gradient CL becomes excessively large, performance can degrade due to the non-uniform Pt active surface. Thus, we compared 1-layer, 3-layer and 5-layer CLs, and designing more layers to reduce the difference in loading between layers results in higher electrochemical surface area (ECSA) and improved performance.