Enhanced oxygen evolution reaction by Co-O-C bonds in rationally designed Co3O4/graphene nanocomposites

Nanocomposites between transition metal oxide and carbon materials have been well recognized as the promising OER catalysts. It is believed that the outstanding activity of the nanocomposites is due to the synergetic effect between the oxides and carbon. However, the mechanism of this synergetic effect is not clear. In this work, with the help of sophisticated first-principle simulation, it is revealed that Co-O-C bond plays a critical role in improving the OER activity by introducing an extra reaction step in deprotonation of HO*. Furthermore, it is predicted from the simulation that the effective active sites of the nanocomposites are O atoms near the Co-O-C bonds. On the basis of the simulation results, Co3O4/reduced graphene oxide nanocomposites for OER catalysts was designed, with the purpose of optimizing the percentage of Co-O-C bonds and the neighboring active oxygen sites. The formation and the percentage of Co-O-C bonds were characterized using XANES. By changing the precursor amount, the percentage of Co-O-C bonds could be optimized at similar to 43%. The resultant nanocomposites demonstrated outstanding OER activity, which was consistent with the simulation results. Through this work, the mechanism of the synergetic effect between transition metal oxides and carbon for OER activity was proposed.