A Redox-Mediator-Free Solar-Driven Z-Scheme Water-Splitting System Consisting of Modified Ta3N5 as an Oxygen-Evolution Photocatalyst

Tantalum nitride (Ta3N5) modified with various O2‐evolution cocatalysts was employed as a photocatalyst for water oxidation under visible light (λ>420 nm) in an attempt to construct a redox‐mediator‐free Z‐scheme water‐splitting system. Ta3N5 was prepared by nitriding Ta2O5 powder under a flow of NH3 at 1023–1223 K. The activity of Ta3N5 for water oxidation from an aqueous AgNO3 solution as an electron acceptor without cocatalyst was dependent on the generation of a well‐crystallized Ta3N5 phase with a low density of anionic defects. Modification of Ta3N5 with nanoparticulate metal oxides as cocatalysts for O2 evolution improved water‐oxidation activity. Of the cocatalysts examined, cobalt oxide (CoOx) was found to be the most effective, improving the water‐oxidation efficiency of Ta3N5 by six to seven times. Further modification of CoOx/Ta3N5 with metallic Ir as an electron sink allowed one to achieve Z‐scheme water splitting under simulated sunlight through interparticle electron transfer without the need for a shuttle redox mediator in combination with Ru‐loaded SrTiO3 doped with Rh as a H2‐evolution photocatalyst. Split me! A redox‐mediator‐free Z‐scheme water‐splitting system capable of working under simulated sunlight was achieved by using Ir/CoOx/Ta3N5 in combination with Ru/SrTiO3:Rh as a H2‐evolution photocatalyst.