Engineering the Interfacial Microenvironment of Fe–N–C Cathode to Boost Proton Conduction for High-Performance Fuel Cells

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Abstract While atomically dispersed Fe–N–C catalysts represent a compelling nonplatinum alternative for the oxygen reduction reaction (ORR), their practical deployment in proton-exchange membrane fuel cells (PEMFCs) remains severely constrained by a poorly defined catalyst–ionomer–reactant triple-phase interface, which drastically impedes efficient proton transfer within the cathode catalyst layer. Herein, we report a rational interfacial microenvironment engineering strategy that exploits noncovalent interactions between oxygenated functional groups on carbon nanotubes (CNTs) and ionomer side chains to precisely modulate the catalyst–ionomer interfacial structure. The incorporation of oxygen-containing moieties effectively promotes water enrichment at the catalyst–ionomer interface, strengthens intermolecular interactions among water moieties, and facilitates the establishment of a hydrogen-bonded water network. This interconnected network significantly reduces proton transport resistance, boosting the proton conductivity of the Fe–N–C cathode layer by a factor of 2.3 relative to the conventional architecture. Coarse-grained molecular dynamics simulations substantiate that oxygen-functionalized CNTs facilitate long-range proton hopping, directly contributing to the measured conductivity enhancement. As a result, the optimized PEMFC delivers a remarkable peak power density of 1.63 W cm–2 and an exceptional current density of 53 mA cm–2 at 0.9ViR-free, surpassing the U.S. Department of Energy (DOE) 2025 target of 44 mA cm–2. This work establishes a generalized interfacial microenvironment modulation strategy to overcome proton transport limitations in nonplatinum ORR catalysts, opening a new avenue toward advanced fuel cell electrocatalysts.

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