Solar-Driven Z-scheme Water Splitting Using Modified BaZrO3–BaTaO2N Solid Solutions as Photocatalysts

A two-step photocatalytic water splitting (Z-scheme) system consisting of a modified BaZrO 3 –BaTaO 2 N solid solution, a paired photocatalyst, and a reversible donor/acceptor pair (i.e., redox mediator) was constructed. BaZrO 3 –BaTaO 2 N (Zr/Ta = 0.05) having a band gap of 1.8 eV has sufficient potential to reduce and oxidize water by absorbing visible photons of up to 660 nm. Upon suitable modification of this material with nanoparticulate cocatalysts, both H 2 and O 2 were evolved individually in the presence of reversible redox couples (viz., IO 3 – /I – and Fe 3+ /Fe 2+ ), although O 2 evolution from aqueous solution containing Fe 3+ was negligible. Among various combinations tested, BaZrO 3 –BaTaO 2 N modified with Pt nanoparticles was the most suitable for H 2 evolution in the presence of an IO 3 – /I – pair, achieving Z-scheme water splitting into H 2 and O 2 in combination with either PtO x /WO 3 or TiO 2 rutile as an O 2 evolution photocatalyst even under simulated sunlight.