Electrolytic splitting of saline water: Durable nickel oxide anode for selective oxygen evolution

Increasing generation of renewable electricity offers a source of green electric power, which can be exploited for the sustainable production of hydrogen through the electrolysis of water. Scarcity of fresh water resources promotes the search for electrode materials, which could be used for splitting of saline water into hydrogen and oxygen without formation of hazardous chlorine compounds, and also withstand highly aggressive chloride medium. In the present study we demonstrate that nickel oxide layer formed by means of simple spray-pyrolysis technique on conductive glass substrate can be used as corrosion resistant and 100% O ₂ -selective anode for the electrolysis of alkaline (pH 14) chloride solution. Dimensional stability and durability of the anode is secured by the absence of metallic phase, whereas selectivity towards oxygen evolution and absence of chloride oxidation is shown to be controlled thermodynamically. The obtained experimental evidence that hydrogen peroxide is formed as intermediate in oxygen evolution reaction under conditions investigated has led to new mechanistic insights and the mechanism of Ni(IV)-mediated electrocatalytic oxidation of water molecules in alkaline chloride medium has been proposed.