Active Site Formation in Oxygen Deficient Cobalt Antimonate for Oxygen Evolution Reaction in Alkaline Media

Abstract

Electrochemical water splitting is the one of the promising ways to obtain hydrogen from aqueous media. Oxygen evolution reaction (OER) at the anode is the rate-determining step due to the sluggish kinetics, which leads to reducing energy efficiency. Recently, anion exchange membrane water splitting has been considered as an alternative way because of its capability of producing hydrogen of high purity and the availability of iron-triad element-based catalysts because of their thermodynamically stability in alkaline media. Besides, cobalt oxides such as spinel, layered double hydroxide are being investigated as active OER electrocatalyst. Among them, the spinel-type Co3O4, which contains one Co2+ in the tetrahedral site and two Co3+ ions in the octahedral site, exhibits outstanding OER performance in alkaline media and has been actively investigated.In this study, we investigated oxygen-deficient cobalt antimonate oxide (CoSb2O6) as OER catalyst in alkaline media, which has unique crystal structure and contains abundant octahedral Co2+ compared to spinel-type cobalt oxide. Through in situ X-ray absorption near-edge structure analysis, we observed most of octahedral Co2+ ions were oxidized to Co4+ at OER potential, which leaded to increase the OER activity by extending the active site. We also carried out anion exchange membrane water splitting to confirm the availability as the anode catalyst to produce H2 gas.