Remarkable advancement of Platinum group metal-free (PGM-free) catalysts for the oxygen reduction reaction (ORR) in acidic media makes it potentially feasible as an alternate to Pt-based catalysts in polymer electrolyte fuel cells (PEMFCs). The current leading PGM-free catalysts are composed of single transition metal atoms embedded in microporous nitrogen-doped carbon matrix (M-N-C). The commercialization of M-N-C catalysts in PEMFCs has been impeded by the insufficient activity and particularly durability. The limited ORR performance is likely owing to the single metal center configuration that causes low active site density, undesired O₂ binding configuration and energy toward the metal center, etc. These inherent limitations of M-N-C catalysts motivate us to move toward M_x-N-C with multiple metal center (MMC) sites.

On account of this, herein a multidentate ligand platform is utilized to prepare a series of bimetallic coordination complexes. These complexes were then used as the metal precursors to produce M_x-N-C with MMC sites by incorporating them into microporous nitrogen-doped carbon matrix via both pyrolysis and surface deposition approaches without breaking the pre-existing multiple nuclear structure. The formation of MMC sites is supported by multiple characterizations. The high ORR activity achieved is tentatively related to MMC sites that promotes the desorption of oxygen adsorbates and suppress the site-blocking effect at elevated potentials. Further improvement, however, is limited by the low concentration of MMC sites. densification of MMC sites is undergoing.

Acknowledgement

This work was supported by the US Department of Energy under award number DE-EE0008416. The authors declare no competing financial interests. MRCAT operations are supported by the Department of Energy and the MRCAT member institution. This research used resources of the Advanced Photon Source, a DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.