Atomically dispersed manganese catalysts for oxygen reduction in proton-exchange membrane fuel cells

摘要

Platinum group metal(PGM)-free catalysts that are also iron free are highly desirable for the oxygen reduction reaction(ORR)in proton-exchange membrane fuel cells,as they avoid possible Fenton reactions.Here we report an efficient ORR catalyst that consists of atomically dispersed nitrogen-coordinated single Mn sites on partially graphitic carbon(Mn-N-C).Evidence for the embedding of the atomically dispersed MnN4 moieties within the carbon surface-exposed basal planes was established by X-ray absorption spectroscopy and their dispersion was confirmed by aberration-corrected electron microscopy with atomic resolution.The Mn-N-C catalyst exhibited a half-wave potential of 0.80 V versus the reversible hydrogen electrode,approaching that of Fe-N-C catalysts,along with significantly enhanced stability in acidic media.The encouraging performance of the Mn-N-C catalyst as a PGM-free cathode was demonstrated in fuel cell tests.First-principles calculations further support the MnN4 sites as the origin of the ORR activity via a 4e? pathway in acidic media.