Coupling magnetic single-crystal $C{o}_{2}M{o}_3{O}_8$ 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 $A_{2}M{o}_3{O}_8$ as OER catalyst has been explored, the correlation between its active sites (tetrahedral or octahedral) and OER performance has been elusive. Now, magnetic $C{o}_{2}M{o}_3{O}_8$@NC-800 composed of highly crystallized $C{o}_{2}M{o}_3{O}_8$ 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, $t_2^3{e}^4)$, which improve the OER kinetics of rate-determining step to form *OOH. (© 2020 Wiley‐VCH Verlag GmbH and Co. KGaA, Weinheim)