Coupling Magnetic Single-Crystal Co2 Mo3 O8 with Ultrathin Nitrogen-Rich Carbon Layer for Oxygen Evolution Reaction.

Transition-metal oxides as electrocatalysts for the oxygen evolution reaction (OER) provide a promising route to face the energy and environmental crisis issues. Although palmeirite oxide A2 Mo3 O8 as OER catalyst has been explored, the correlation between its active sites (tetrahedral or octahedral) and OER performance has been elusive. Now, magnetic Co2 Mo3 O8 @NC-800 composed of highly crystallized Co2 Mo3 O8 nanosheets and ultrathin N-rich carbon layer is shown to be an efficient OER catalyst. The catalyst exhibits favorable performance with an overpotential of 331 mV@10 mA cm-2 and 422 mV@40 mA cm-2 , and a full water-splitting electrolyzer with it as anode catalyst shows a cell voltage of 1.67 V@10 mA cm-2 in alkaline. Combined HAADFSTEM, magnetic, and computational results show that factors influencing the OER performance can be attributed to the tetrahedral Co sites (high spin, t2 3 e4 ), which improve the OER kinetics of rate-determining step to form *OOH.