Insights to the differences in catalytic performance of under-rib and under-channel regions for PEM water electrolysis

The difference in catalyst utilization in different regions of proton exchange membrane electrolyzer cell (PEMEC) is often overlooked, yet it holds significant implications for understanding the electrochemical reactions in electrolysis and designing novel electrode structures. In this study, we creatively designed catalyst coated membrane (CCM) with non-uniform distribution of catalytic layers in the under-rib and under-channel regions. Combined with the gradient design method of catalytic layers, the electrochemical reactions in the different regions were explored experimentally. The difference in reactant supply between the under-rib and under-channel catalytic layer was revealed by the water starvation experiment. Moreover, a three-dimensional two-phase non-isothermal model was constructed to study the differences in the current density distribution between ribs and channels. The results show that the current density under the rib is higher than under the channel. At the rib: channel catalyst loading of 3:1, the CCM performance is optimal. Based on the findings, the CCM with non-uniform, gradient catalytic layer was designed, which can achieve an 18.33 % reduction in precious metal loading without significant performance loss. This study reveals the genuine differences in catalysis reactions within PEMEC, thus providing new insights for realizing the electrode designs with high electrolysis performance and low catalyst loading.