Co(O)4(N)-type single-atom-based catalysts and ligand-driven modulation of electrocatalytic properties for reducing oxygen molecules

Single-atom-based catalysts are intriguing electrocatalytic platforms that combine the advantages of molecular catalysts and conductive carbon-based materials. In this work, hybrids (Co-NrGO-1 and Co-NrGO-2) were generated by wet-reactions between organometallic complexes (Co(CH₃COO)₂ and Co[CH₃(CH₂)₃CH(C₂H₅)COO]₂, respectively) and N-doped reduced graphene oxide at 25°C. Various characterizations revealed the formation of atomically dispersed Co(O)₄(N) species in Co-NrGO-2. Density functional theory (DFT) calculations explained the effect of the aliphatic C7 group in Co2 on the formation processes. The Co-NrGO-2 hybrid showed excellent catalytic performance, such as onset (0.94 V) and half-wave (0.83 V) potentials, for electrochemical oxygen reduction reaction (ORR). Co-NrGO-2 outperformed Co-NrGO-1, which was explained by more back donation to the antibonding orbitals of O₂ from electron-rich aliphatic groups. DFT calculations support this feature, with mechanistic investigations showing favored ORR reactions and facile breakage of double bonds in O₂.