Boosting the Performance and Durability of Fe-N-C Fuel Cell Catalysts via Integrating Mo₂C Clusters

Carbon-supported nitrogen-coordinated iron single-atom (Fe-N-C) catalysts have been regarded among the most promising platinum-group-metal-free catalysts for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). Nevertheless, their limited intrinsic activity and unsatisfactory stability have hindered their practical applications. Here, it is reported that the integration of Mo₂C clusters effectively enhances the ORR activity and stability of Fe-N-C catalysts. The composite catalyst of Fe single atoms and Mo₂C clusters co-embedded on nitrogen-doped carbon (Fe_SA/Mo₂C-NC) exhibits an excellent ORR activity with a half-wave potential of 0.82 V in acidic media and a high peak power density of 0.5 W cm^-2 in an H₂-air PEMFC. Moreover, improved stability is achieved with nearly no decay under H₂-air conditions for 80 h at 0.4 V. Experiments with theoretical calculations elucidate that the etching effect of the phosphomolybdic acid precursor optimizes the pore size distribution of the composite catalyst, thereby exposing more active sites. The Mo₂C clusters modulate the electronic configuration of the Fe-N₄ sites, optimizing adsorption energy for ORR intermediates and strengthening the Fe-N bond to mitigate demetalation. This work provides valuable insights into the construction of single-atom/nanoaggregate hybrid catalysts for efficient energy-related applications.