Ionomer-involved moisture transfer and electrochemical reaction within porous catalyst layer of PEM vapor electrolyzer/dehumidifier: Numerical simulation development and parameter analysis

PEM-based vapor electrolyzers have significant potential, with the porous catalytic layer (CL) with three-phase interfaces (TPIs) being crucial. Hygroscopic and proton-conductive ionomers significantly affect CL performance, especially with humidity as the reactant. This study developed Multiple-Relaxation-Time lattice-Boltzmann Method (MRT-LBM) simulations to visualize coupled moisture transport and electrochemical reaction in microstructured CL. Identifying TPIs as reaction sites allowed accurate calculation of the effects of moisture distribution and ionomer impedance on reaction overpotential. Multiscale simulations, linking a calculation zone (8 × 8 μm²) with the entire CL (35 mm × 8 μm) using periodic circulation, showed less than 9 % error compared to experiments. Results indicated as the random CL structure hinder moisture transport to TPIs, optimizing the structure proved more effective in enhancing electrochemical performance and catalyst utilization than improving catalyst activity, especially at higher air humidity (>70 %). Increasing ionomer content also enhances electrolysis, but excessive amounts (>30 % ωt) reduce performance by blocking moisture supply. An orderly arrangement of ionomers and particles can double current density and increase moisture removal by over 1.5 times. This study advances PEM electrolysis by coupling ionomer-involved moisture transport with electrochemical reaction at TPIs, offering new insights for future electrolyzer design and also the mass transfer mechanism in complex porous media.