Lattice Boltzmann simulation of cathode catalyst layer degradation on transport reaction process within a proton exchange membrane fuel cell

Abstract

The degradation of the catalyst layer significantly affects the gas transport and electrochemical processes in the porous electrodes, thus affecting the performance of proton exchange membrane fuel cells. To reveal the catalyst layer degradation impact, the microscopic porous structure of the cathode catalyst layer was reconstructed by a random algorithm in this work. Consequently, Lattice Boltzmann method was used to study the oxygen transport and electrochemical reaction processes at the limiting current density condition with considering the degradation of platinum, carbon particles, and ionomers under uniform and exponential degradation rates, respectively. The results reveal that the degradation of platinum reduces the reaction sites in the catalyst layer, thus deteriorating the electrochemical kinetics and lowering the total reaction rate. On the contrary, the degradation of carbon and ionomer shows two diametrically opposed effects. On the one hand, the oxygen transport is improved due to carbon and ionomer degradation, especially for ionomer degradation, thereby accelerating the total reaction rate. On the other hand, the degradation of carbon and ionomer triggers the detachment of platinum particles, leading to a decrease in reaction rate. In the early stages of the multi-component simultaneous degradation process, the total reaction rate is prohibited by oxygen transport limitation inside the catalyst layer; as the degradation degree increases, the oxygen transport through the ionomer films is enhanced and the electrochemical kinetics becomes the rate determining factor, especially for exponential degradation rate. This study provides a comprehensive assessment of the oxygen transport and electrochemical reaction within the catalyst layers with respect to different degrees of catalyst layer degradation, which can guide the design of high-performance anti-degradation catalyst layers for the next generation of fuel cells.