Fe/Ru Oxide as Versatile and Effective Cocatalyst for Boosting Z-Scheme Water Splitting: Suppressing Undesirable Backward Electron Transfer

Artificial Z-scheme is a promising and rational strategy for solar-to-chemical energy conversion such as water splitting. In the Z-scheme, backward redox processes are an essential drawback that should be overcome to increase its efficiency. Here we demonstrate that simple co-loading of Fe/Ru oxide, (Fe,Ru)Ox, onto various photocatalysts effectively improve the efficiency of water oxidation by suppressing the undesirable backward oxidation of a redox reagent Fe2+. The (Fe,Ru)Ox co-loading on Bi4TaO8Cl afforded the highest water splitting activity (apparent quantum efficiency of 1.6% at 420 nm) among the Z-scheme systems employing mixed-anion compounds as an O2-evolving photocatalyst. The results on photoelectrochemical and electrochemical measurements along with time-resolved spectroscopy clarified the key roles of Fe/Ru oxide; the Ru oxide component functions as a ‘collector’ of photogenerated carriers and active sites for surface redox reaction, while the Fe oxide component acts as a ‘blocker’ against u...