Design of gradient cathode catalyst layer (CCL) structure for mitigating Pt degradation in proton exchange membrane fuel cells (PEMFCs) using mathematical method

The durability of PEMFCs is greatly influenced by the non-uniform degradation of catalyst particles across the thickness of cathode catalyst layer (CCL). Gradient CCL is one of the effective structures to improve both cell performance and durability. Here we employ mathematical modeling to evaluate several gradient CCL structures with Pt/C catalysts in terms of the evolution of electrochemical surface area (ECSA) and Pt mass during cycling. Results based on the two-layer models considering particle size gradient only show that larger Pt particles near the CCL/membrane interface can remarkably mitigate the loss of ECSA and Pt mass, but accelerate the Pt dissolution near the gas diffusion layer (GDL). An increase in the number of layers, corresponding to a more smooth decrease of particle size from the CCL/membrane interface to GDL, can effectively retain high ECSA after cycling. The CCL with an optimum performance is achieved by manipulating the particle size gradient and Pt loading gradient simultaneously, which gains more uniform distribution of Pt active surface for improving the end-of-test performance and durability. This work provides a strategy to achieve highly durable PEMFCs by combining the gradient of particle size and Pt loading in the CCL structure.