Short O-O separation in layered oxide NaCoO enables an ultrafast oxygen evolution reaction.

The layered oxide NaCoO with Na occupying trigonal prismatic sites between CoO layers exhibits a remarkably high room temperature oxygen evolution reaction (OER) activity in alkaline solution. The high activity is attributed to an unusually short O-O separation that favors formation of peroxide ions by O-O interactions followed by O evolution in preference to the conventional route through surface O-OH species. The dependence of the onset potential on the pH of the alkaline solution was found to be consistent with the loss of H ions from the surface oxygen to provide surface O that may either be attacked by solution OH or react with another O; a short O-O separation favors the latter route. The role of a strong hybridization of the O-2 and low-spin Co/Co π-bonding states is also important; the OER on other Co/Co oxides is compared with that on NaCoO as well as that on IrO.