Ammonia Poisoning Behaviors on Pt/C Catalyst Layer in PEMFC

Trace ammonia impurities in hydrogen fuel can severely deteriorate the comprehensive performance of proton exchange membrane fuel cells (PEMFCs). While previous studies have primarily documented macroscopic performance degradation and attributed ammonia poisoning to competitive adsorption or site blocking, the underlying electronic mechanism-particularly how ammonia alters the intrinsic catalytic selectivity of Pt-remains unexplored. This work bridges this gap by systematically combining electrochemical evaluation with density functional theory (DFT) calculations to reveal that ammonia poisoning operates. Experiment shows: after 3 h of ammonia exposure, the electrochemical active surface area for the hydrogen oxidation reaction decreases by 55.86%, and the oxygen reduction reaction (ORR) half-wave potential negatively shifts by a maximum of 0.154 V, with Nafion ionomer inducing an additional 0.056 V potential attenuation. Density functional theory calculations verify that ammonia adsorption triggers Pt-to-N charge transfer and downshifts the Pt d-band center. Such electronic modulation weakens the adsorption of ORR intermediates, increases the four-electron reaction pathway barrier from 0.28 eV to 0.61 eV, and promotes undesirable two-electron H 2 O 2 generation. These findings establish a dual-mechanism framework-site blocking plus electronic perturbation-that fundamentally distinguishes this work from prior macroscopic descriptions, providing a new theoretical basis for designing ammonia-tolerant catalysts.