Microenvironment Regulation to Unlock Platinum Catalyst Activity in Membrane Electrode Assemblies

High gas transport resistances and strong absorption of ionomer sulfonate groups onto the Pt surface significantly limit the efficient expression of catalytic activity in membrane electrode assemblies (MEAs), especially with a low Pt loading. Here, we address these challenges by tailoring the ionomer–Pt interface microenvironment with protonated porous carbon nitride (pCN) nanosheets. The N-rich pCN nanosheets disrupt the crystallinity of the ionomer matrix through acid–base interactions with sulfonate groups, creating more amorphous regions that facilitate local oxygen transport. Additionally, the acid–base pairs form a transition layer between the ionomer–Pt interface, which blocks the direct contact of sulfonate groups with Pt. Consequently, the as-prepared MEAs with pCN demonstrate a 1.3-fold increase in mass activity, a 30% reduction in local oxygen transport resistance at the cathode electrode, and only a 7.3% decay in peak power density after 30 000 cycles in an accelerated stress test.