Engineering the Coordination Environment of Single Cobalt Atoms for Efficient Oxygen Reduction and Hydrogen Evolution Reactions

The coordination environment of single-atom catalysts (SACs) plays a crucial role in determining the energy conversion efficiency of related electrochemical devices. Herein, the coordination environment of a series of Co-based SACs (Co1-SACs) was tuned to correlate the chemical structures of these catalysts with their electrocatalytic performance. The optimized Co1-SACs containing Co-S2N2 sites are electrocatalytically active in both the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER), which were carried out in alkaline media. The Co1-SACs containing Co-S2N2 sites exhibit high ORR activity, with an onset potential of 0.99 V vs RHE and good stability, as well as have promising application in a zinc-oxygen battery with a high power density (260 mW cm-2) and open-circuit voltage (1.50 V), remarkable tolerance to large current density, and long-term operation. The ORR of the Co-S2N2 site is attributed to the optimized electron density of the Co atom through its cocoordination with adjacent S and N atoms. Moreover, the Co1-SACs efficiently catalyze the HER, exhibiting a low overpotential (121 mV at 20 mA cm-2), a low Tafel slope (47 mV dec-1), and long-term stability. This work also provides a facile heteroatom-doping strategy to engineer the desired coordination environments in SACs for efficient electrocatalysis. © 2021 American Chemical Society.