Effect of heat treatment on local structure and photocatalytic water splitting activity of Ni-loaded LiCa₂Ta₃O₁₀

Abstract

The photocatalytic activity of 0.5 wt% Ni-loaded LiCa₂Ta₃O₁₀ for water splitting into a stoichiometric H₂/O₂ mixture increased about 4-fold after heat treatment at ≥ 500°C in a flow of N₂. Local structures of the photocatalysts before and after heat treatment have been studied using XRD and XAFS. Rietveld refinement of XRD patterns revealed that the heat treatment decreased the thickness of a triple-layered perovskite slab and thus increased the distortion of octahedral TaO₆ units in the both side of triple-layers. The resulting increase of dipole moment is considered to be efficient for promoting a charge separation step in the photocatalytic process. The heat treatment also converted the Ni cocatalysts from NiO/Ni core-shell to fully oxidized structure, but its effect on the photocatalytic activity was negligible.