Interfacial Design of a Ta₃N₅ Thin-Film Photoanode for Highly Stable Oxygen Evolution over a Wide pH Range

High Resolution Image Download MS PowerPoint Slide Ta 3 N 5 -based visible-light-absorbing semitransparent photoanodes for the oxygen evolution reaction (OER) are one of the most promising candidates for the construction of photoelectrochemical (PEC) water-splitting devices with a tandem configuration. Although the PEC properties of Ta 3 N 5 have been evaluated in alkaline aqueous solutions, those in acidic or near-neutral pH aqueous solutions are still unclear. An efficient OER by Ta 3 N 5 in acidic and near-neutral pH aqueous solutions is still challenging because it requires surface modifiers with chemical durability and efficient electrocatalytic properties for the OER. This study focuses on the interfacial design of Ta 3 N 5 semitransparent photoanodes to achieve an efficient and stable OER over a wide pH range. The results of PEC measurements and X-ray photoelectron spectroscopy reveal that self-photooxidation occurs on the bare Ta 3 N 5 surface regardless of the pH values, resulting in photocurrent decrease. A uniform coating of IrO x applied using spin-coating successfully protected Ta 3 N 5, and the IrO x /Ta 3 N 5 photoanodes maintained ∼80% of their initial OER photocurrent even after 4 h. The pH dependence of the photocurrent value of IrO x /Ta 3 N 5 was found to follow that of the electrocatalytic OER rate of IrO x . Furthermore, the onset potential for the OER on IrO x /Ta 3 N 5 was independent of the pH value and was fixed at 0.7 V versus a reversible hydrogen electrode.