Extensive Active-Site Formation in Trirutile CoSb2O6 by Oxygen Vacancy for Oxygen Evolution Reaction in Anion Exchange Membrane Water Splitting

Abstract

Here, we first report an octahedral Co2+-rich Co oxide with inactive Sb5+ ion as an oxygen evolution reaction (OER) electrocatalyst for efficient H-2 production by lowering the cell voltage in anion exchange membrane water splitting (AEMS). To enhance the OER activity of Co-based oxides, it is crucial to increase the amount of Co4+ at OER potential, known as the fast OER active site. Using in situ X-ray absorption spectroscopy, we observed most of the octahedral Co2+ in trirutile CoSb2O6 oxidized to Co3+ before the OER potential. Furthermore, oxygen vacancies facilitated further oxidation from Co3+ to Co4+ by tuning OH- adsorption energy of Co and then produced extensive active sites for O-O bond formation in OER compared to spinel-type Co3O4. As a result, we obtained a much lower OER overpotential of 360 mV at 100 mA/cm(2), providing 88% of the highest H-2 energy efficiency in the AEMS by applying a cell voltage of 1.7 V.