Facet dependent oxygen evolution activity of spinel cobalt oxides

Water splitting is a promising technology to produce clean hydrogen if powered by renewable energies, where oxygen evolution is the rate determining step at an anode. Here we adjust the different crystal planes of the cobalt oxides catalyst to expose more effective active sites through a hydrothermal process, so as to improve the reaction activity for oxygen evolution. The samples were well characterized by TEM, SEM and XRD. Among the three synthetic crystal planes (100), (111) and (110) of spinel cobalt oxides, the (100) crystal plane has the highest intrinsic activity. Combining in-situ infrared and DFT calculations, we observed that the oxygen evolution reaction reached the lowest energy barrier on the (100) plane of the cobalt oxide crystal. Further XPS analysis showed that the highest Co3+/Co2+ ratio was observed on the surface of the nanocube samples, indicating that Co3+ is a more active site for oxygen evolution catalytic activity.