Unleashing the Potential of Coupled Substituted 3D Niobate Perovskite Oxides in Cocatalyst-free Photocatalytic Hydrogen Evolution

Many 3D titanate and niobate perovskites are useful photocatalysts for hydrogen evolution but are active only under UV-light. Various strategies, including the use of noble metal-based catalysts/cocatalysts and heterojunction formation, are adopted to induce visible-light absorption and enhance photocatalytic activity. Here, a simple coupled-substitution approach in 3D niobate perovskite oxides, Na0.5Ca0.5M0.25Nb0.75O3 (M = Cr, Mn, Fe, and Co), is demonstrated to show enhanced hydrogen evolution without using heterojunction systems or noble metal catalysts/cocatalysts. The approach is innovative since the incorporation of a non-Jahn–Teller transition metal ion induces local octahedral distortion in the structure, while the Jahn–Teller active ions show negligible to no distortion in the presence of Nb5+, a d0 system, that is known to undergo second-order Jahn–Teller distortions. The effects of octahedral distortion on the structure, optical absorption, and in cocatalyst-free hydrogen evolution are discussed. The Cr compound shows a hydrogen evolution of ∼200 μmol g–1 h–1, the highest rate among all the compounds in the series, due to its fast charge transfer dynamics. The study offers important insights into the understanding of underlying factors influencing the photocatalytic activity of the perovskite-based materials for the development of practical photocatalytic systems.