InGaN/GaN Multiple Quantum Well Photoanode Modified with Cobalt Oxide for Water Oxidation

Indium gallium nitride (InGaN) is an attractive semiconductor, with a tunable direct bandgap for photoelectrochemical water splitting, but it corrodes in aqueous electrolytes. Cobalt oxide (CoO_x) is a promising cocatalyst to protect photoelectrodes and accelerate the charge transfer. CoO_x is earth-abundant and stable in extremely alkaline conditions and shows high activity for the oxygen evolution reaction (OER). In this work, we demonstrate that CoO_x directly deposited onto InGaN/GaN multiple quantum well photoanodes exhibits excellent activity and stability in a strong alkaline electrolyte, 1 M NaOH (pH = 13.7), for water oxidation up to 28 h, while a reference sample without the catalyst degraded rapidly in the alkaline electrolyte. Under simulated solar illumination, the CoO_x-modified InGaN/GaN quantum well photoanode showed a high photocurrent density of 1.26 mA cm^-2 at 1.23 V and an onset potential of -0.03 V versus a reversible hydrogen electrode.