Revealing Distance-Dependent Synergy between MnCo 2 O 4 and Co-N-C in Boosting the Oxygen Reduction Reaction.

Synergistic effects have been applied to a variety of hybrid electrocatalysts to improve their activity and selectivity. Understanding the synergistic mechanism is crucial for the rational design of these types of catalysts. Here, we synthesize a MnCo 2 O 4 /Co-N-C hybrid electrocatalyst for the oxygen reduction reaction (ORR) and systematically investigate the synergy between MnCo 2 O 4 nanoparticles and Co-N-C support. Theoretical simulations reveal that the synergy is closely related to the distance between active sites. For a pair of remote active sites, the ORR proceeds through the known 2e - + 2e - relay catalysis while the direct 4e - ORR occurs on a pair of adjacent active sites. Therefore, the formation of the undesired byproduct (H 2 O 2 ) is inhibited at the interface region between MnCo 2 O 4 and Co-N-C. This synergistic effect is further verified on an anion-exchange membrane fuel cell. The findings deepen the understanding of synergistic catalysis and will provide guidance for the rational design of hybrid electrocatalysts.