Distinguishing the effects of altered morphology and size on the visible light-induced water oxidation activity and photoelectrochemical performance of BaTaO2N crystal structures

Abstract

Factors, including crystallinity, morphology, size, preferential orientation, growth, composition, porosity, surface area, etc., can directly influence the optical, charge-separation, charge-transfer and water oxidation and reduction properties of particle-based photocatalysts. Therefore, these factors must be considered when designing high-performance particle-based photocatalysts for solar water splitting. Here, a flux growth method was applied to alter the morphology and size of Ba₅Ta₄O₁₅ precursor oxide crystals using BaCl₂, KCl, RbCl, CsCl, KCl + BaCl₂ and K₂SO₄ at different solute concentrations, and the impact of nitridation with and without KCl flux was studied. Specifically, the effects of altered morphology and size on the visible light-induced water oxidation activity and photoelectrochemical performance of the BaTaO₂N crystal structures were investigated. Upon nitridation, the samples became porous due to the lattice shrinkage caused by the replacement of 3 O²⁻ with 2 N³⁻ in the anionic network. The BaTaO₂N crystal structures obtained by nitridation without KCl flux show higher surface areas than do their counterparts prepared by nitridation with KCl flux because of the formation of porous networks. All of the samples exhibited a high anodic photocurrent upon nitridation without KCl flux compared with those of the samples obtained by nitridation with KCl flux. These findings demonstrate that it is important to specifically engineer photocatalytic crystals to reach their maximum potential in solar water splitting.