Enhanced oxygen evolution on visible light responsive TaON photocatalysts co-loaded with highly active Ru species for IO3− reduction and Co species for water oxidation

Abstract

Loading an appropriate cocatalyst significantly enhances the activity of semiconductor photocatalysts in both conventional one-step water splitting and Z-scheme-type water splitting with a redox couple. In the present study, we examined the catalytic activity of Ru-based cocatalysts for IO₃⁻ reduction to improve the efficiency of O₂ evolution on a TaON photocatalyst under visible light with an IO₃⁻ acceptor, which is an important half component in Z-scheme water splitting systems. X-ray photoelectron spectroscopy analyses and electrochemical measurements revealed that the calcination temperature in the loading of Ru species from aqueous RuCl₃ significantly affected the catalytic activity for the reduction of IO₃⁻. Calcination at or below 200 °C produced Ru(OH)_xCl_y species that drastically enhanced the reduction of IO₃⁻, whereas that at 300 °C generated conventional RuO₂ that showed lower activity for IO₃⁻ reduction than Ru(OH)_xCl_y but considerably enhanced the water oxidation. Co-loading the Ru(OH)_xCl_y and Co cation species as water oxidation cocatalysts significantly improved O₂ evolution on the TaON photocatalyst by more than a factor of two compared to that loaded with only the conventional RuO₂ cocatalyst. This suggests the effectiveness of co-loading two different cocatalysts that are independently optimized for reduction and oxidation.