Enhancing oxygen transport in the ionomer film on platinum catalyst using ionic liquid additives

The O₂ permeation barrier across the nanoscale ionomer films on electrocatalysts contributes to a major performance loss of proton exchange membrane (PEM) fuel cells under low Pt loading. Enhancing O₂ transport through the ionomer films is essential for developing low Pt loading catalyst materials in high-performance PEM fuel cells. This study found that adding an ionic liquid (IL) can effectively mitigate the dense ionomer ultrathin sublayer formed on the Pt surface, which severely hinders O₂ transport to the catalyst sites. The molecular dynamics simulation results show that adding the IL significantly alters the ionomer ultrathin sublayer structure by inhibiting its tight arrangement of perfluorosulfonic acid chains but scarcely impacts the ultrathin sublayer thickness. Additionally, the IL addition provides a larger free space for O₂ dissolution in the ultrathin sublayer. Consequently, due to IL molecules' presence, the O₂ density in the ultrathin sublayer on the Pt surface is improved by an order of magnitude, which will benefit the catalytic efficiency, and the O₂ permeation flux across the ionomer film is increased by up to 8 times, which will reduce the O₂ transport loss of the catalyst layer.