Effect of ionomer coverage on Pt surface on local mass transport in the cathode catalyst layer for enhanced proton exchange membrane fuel cell performance

In proton exchange membrane fuel cell (PEMFC), optimizing the ionomer coverage on Pt surface within the cathode catalyst layer (CCL) can enhance the synergistic transport of oxygen and protons. This improvement significantly increases the utilization efficiency of Pt particles, leading to a notable enhancement in cell performance. In this study, an agglomerate sub-model with ionomer partially covering Pt surface is coupled with the PEMFC model to investigate the impact of ionomer coverage on cell performance. It is found that the ionomer coverage substantially effects cell performance, and optimal ionomer coverage vary under different operating conditions to maximize cell performance. In this study, under the typical stationary power generation (0.75 V), the cell exhibits optimal performance at 60 % ionomer coverage, while under a common condition for automotive application (0.5 V), the optimal coverage is 40 %. As ionomer coverage increases, the area of the liquid water region decreases while the liquid film becomes thicker. This leads to reduced oxygen concentration and consequently an increase in concentration overpotential. However, higher ionomer coverage can effectively improve the proton conductivity, thereby reducing the ohmic losses. Additionally, the current density in the liquid water region on the Pt surface consistently increases with higher ionomer coverage regardless of voltage. However, in the ionomer region, the current density decreases with increased coverage under low voltage conditions, while it remains relatively stable under high voltage conditions. This study provides a new perspective for designing high-performance CCL.