A facile corrosion approach to the synthesis of highly active CoOx water oxidation catalysts

Abstract

Ultra-small rock salt cobalt monoxide (CoO) nanoparticles were synthesized and subjected to partial oxidation (‘corrosion’) with ceric ammonium nitrate (CAN) to form mixed-valence CoO_x (1 < x < 2) water oxidation catalysts. Spectroscopic, microscopic and analytical methods evidenced a structural reformation of cubic CoO to active CoO_x with a spinel structure. The superior water oxidation activity of CoO_x has been established in electrochemical water oxidation under alkaline conditions. Electrochemical water oxidation with CoO_x was recorded at a considerably low overpotential of merely 325 mV at a current density of 10 mA cm⁻² in comparison to 370 mV for CoO. Transformation of both octahedral Co^II and Co^III sites into amorphous Co(OH)₂–CoOOH is the key to high electrochemical activity while the presence of a higher amount of octahedral Co^III sites in CoO_x is imperative for an efficient oxygen evolution process.