Modelling analysis of low platinum polymer fuel cell degradation under voltage cycling: Gradient catalyst layers with improved durability

Improving the durability of polymer electrolyte membrane fuel cells with low platinum loading is a crucial step in the development of next generation electric vehicles. In this work a simplified model of nanoparticle growth is spatially solved across the catalyst layer and combined with a PEMFC model to analyze the heterogeneity of degradation that is induced by accelerated stress test for electrocatalyst durability, which mimics the degradation due to load cycling. The model is calibrated and later validated by analyzing experimental data collected on cathode catalyst layers with 0.1 mg cm⁻² platinum loading and average particle size ranging from 2 nm to 5 nm. Non-uniform degradation is observed in the catalyst layer consequently to the formation of a platinum depleted region next to the membrane, which, according to the model, results from diffusion and precipitation of dissolved platinum into the membrane. Performance of catalyst layers with gradient structure is simulated to get insight into the degradation of non-uniform catalyst layers and results are compared to experimental data. It is concluded that gradient catalyst layers mitigate performance degradation because evolve towards more uniform distribution of active surface and improve transport loss due to low-roughness factor and Ohm loss in the catalyst layer.