Microenvironment\nRegulation to Unlock Platinum Catalyst\nActivity in Membrane Electrode Assemblies

High gas transport resistances and strong absorption\nof ionomer\nsulfonate groups onto the Pt surface significantly limit the efficient\nexpression of catalytic activity in membrane electrode assemblies\n(MEAs), especially with a low Pt loading. Here, we address these challenges\nby tailoring the ionomer–Pt interface microenvironment with\nprotonated porous carbon nitride (pCN) nanosheets. The N-rich pCN\nnanosheets disrupt the crystallinity of the ionomer matrix through\nacid–base interactions with sulfonate groups, creating more\namorphous regions that facilitate local oxygen transport. Additionally,\nthe acid–base pairs form a transition layer between the ionomer–Pt\ninterface, which blocks the direct contact of sulfonate groups with\nPt. Consequently, the as-prepared MEAs with pCN demonstrate a 1.3-fold\nincrease in mass activity, a 30% reduction in local oxygen transport\nresistance at the cathode electrode, and only a 7.3% decay in peak\npower density after 30 000 cycles in an accelerated stress\ntest.