Atomically-dispersed Mn-(N-C₂)₂(O-C₂)₂ sites on carbon for efficient oxygen reduction reaction

Owing to their ultimate mass-catalytic activity, simple active site configuration and readily tunable electronic structures, transition-metal single atoms (SAs) on carbon support have emerged as a new category of electrocatalysts for oxygen reduction reaction (ORR). Here, we exemplify the use of atomically dispersed Mn with N, O heteroatoms-coordinated Mn sites to enhance alkaline ORR performance. A combined sol-gel/carbonization approach is developed to controllably anchor Mn-SAs onto graphitic carbon nanosheets via a hybridized N, O coordination configuration of Mn-(N-C₂)₂(O-C₂)₂ (denoted as Mn-SA@CNSs). The obtained Mn-SA@CNSs exhibits superior alkaline ORR electrocatalytic activity with a half-wave potential of 0.88 V vs. RHE in 0.1 M KOH. The rechargeable Zn–air battery assembled using Mn-SA@CNSs air cathode can readily attain a high power density of 177 mW cm⁻² with a narrow voltage gap of 0.76 V at 5 mA cm⁻². Density functional theory calculations unveil that altering the coordination environment of Mn-SAs from N-coordinated Mn-(N-C₂)₄ to N-/O-coordinated Mn-(N-C₂)₂(O-C₂)₂ alters the d-band electronic structures and regulates the binding strength of ORR intermediates on Mn-SA sites to dramatically reduce the energy barrier and enhance ORR activity. The exemplified hybridization coordination approach in this work would be applicable to alter the electronic structures of other transition-metal SAs for ORR and other reactions.