Co3O4 Nanoparticles as Robust Water Oxidation Catalysts Towards Remarkably Enhanced Photostability of a Ta3N5 Photoanode

Despite the fact that Ta3N5 absorbs a major fraction of the visible spectrum, the rapid decrease of photocurrent encountered in water photoelectrolysis over time remains a serious hurdle for the practical application of Ta3N5 photoelectrodes. Here, by employing a Co3O4 nanoparticle water oxidation catalyst (WOC) as well as an alkaline electrolyte, the photostability of Ta3N5 electrode is significantly improved. Co3O4/Ta3N5 photoanode exhibits the best durability against photocorrosion to date, when compared with Co(OH)x/Ta3N5 and IrO2/Ta3N5 photoanodes. Specifically, about 75% of the initial stable photocurrent remains after 2 h irradiation at 1.2 V vs. RHE (reversible hydrogen electrode). Meanwhile, a photocurrent density of 3.1 mA cm−2 has been achieved on Co3O4/Ta3N5 photoanode at 1.2 V vs. RHE with backside illumination under 1 sun AM 1.5 G simulated sunlight. The reason for the relatively high stability is discussed on the basis of electron microscopic observations and photoelectrochemical measurements, and the surface nitrogen content is monitored by X‐ray photoelectron spectroscopic analysis. Nanoparticulate Co3O4 water oxidation catalyst is uniformly deposited onto the surface of a Ta3N5 photoanode with abundant and compact nanojunctions formed between Co3O4 and Ta3N5. Profitting from the unique features of the Co3O4 water oxidation catalyst and the alkaline solution, the improved kinetics of water oxidation cause the Co3O4/Ta3N5 photoanode to have the best durability against photocorrosion shown to date.