Reconfiguring Ionomers in Proton Exchange Membrane Fuel Cell Catalyst Layer to Promote Multi‐Species Transport and Durability

Abstract In proton exchange membrane fuel cells (PEMFCs), ionomers in the catalyst layer tend to align lamellar to the catalyst surface, impeding the formation of continuous ionic domains essential for efficient proton transport. This alignment also obstructs oxygen diffusion to the catalyst‐liquid‐gas three‐phase boundary (TPB), which critically limits the PEMFC's power density. Here, we introduce porous graphene‐based nanosheet@Nafion composite ionomers that reconfigure ion transport domains and gas channels at the nanoscale within the catalyst layer. These composite ionomers dramatically enhance proton transport (5.0‐fold) and oxygen diffusion (3.3‐fold), increasing rated power density by 1.70 times and peak power density by 1.48 times compared to Nafion‐based fuel cells. Furthermore, they demonstrate significant durability improvements during accelerated stress tests. This strategy provides an effective approach to optimizing microstructures and constructing efficient multi‐species transport pathways at the TPB, highlighting their potential for maximizing the performance of advanced high‐activity electrocatalytic materials in PEMFCs.