Surface-Modified Ta₃N₅ Nanocrystals with Boron for Enhanced Visible-Light-Driven Photoelectrochemical Water Splitting

Photocatalysts for water splitting are the core of renewable energy technologies, such as hydrogen fuel cells. The development of photoelectrode materials with high efficiency and low corrosivity has great challenges. In this study, we report new strategy to improve performance of tantalum nitride (Ta₃N₅) nanocrystals as promising photoanode materials for visible-light-driven photoelectrochemical (PEC) water splitting cells. The surface of Ta₃N₅ nanocrystals was modified with boron whose content was controlled, with up to 30% substitution of Ta. X-ray photoelectron spectroscopy revealed that boron was mainly incorporated into the surface oxide layers of the Ta₃N₅ nanocrystals. The surface modification with boron increases significantly the solar energy conversion efficiency of the water-splitting PEC cells by shifting the onset potential cathodically and increasing the photocurrents. It reduces the interfacial charge-transfer resistance and increases the electrical conductivity, which could cause the higher photocurrents at lower potential. The onset potential shift of the PEC cell with the boron incorporation can be attributed to the negative shift of the flat band potential. We suggest that the boron-modified surface acts as a protection layer for the Ta₃N₅ nanocrystals, by catalyzing effectively the water splitting reaction.