Interfacial Regulation of Oxygen Transport in PEMFC Catalyst Layers by Functionalized Carbon Supports

The dense layer formed by the strong adsorption of ionomer on platinum (Pt) surfaces in cathode catalyst layers of proton exchange membrane fuel cells is a key factor limiting oxygen transport and can be significantly affected by the surface functional groups on carbon supports. This work employs molecular dynamics simulations to clarify how surface functional groups affect the oxygen transport resistance to the Pt surface and adopts density functional theory to reveal why the interaction between ionomer and Pt is altered by the surface functional groups. Aside from the enriching effects of water on Pt surfaces, we find that the adsorption of sulfonate ions (SO₃^-) is more preferred by the high-affinity functional groups on carbon surfaces, such as COOH, and thus significantly affects the interaction between SO₃^- and Pt surface, thereby reducing oxygen transport resistance. Moreover, the distance of functional group to Pt catalysts exhibits a nonmonotonic effect on the oxygen transport resistance: too close or too far from the Pt catalysts would weaken the effect of surface functional groups, while an optimal distance is around 7.38 Å, located outside the dense layer.