Al ³⁺ ‐Dependent Anisotropic Facet Tailoring on SrTiO ₃ Single Crystal for Photocatalytic Overall Water Splitting

Controllable fabrication of single-crystal metal oxide is of paramount importance for advanced photo(electro)catalytic applications, but achieving nonequilibrium crystal shapes with tailored facets through molten salt synthesis still remains a challenge. Herein, we systematically explored the effect of Al³⁺ concentration in tailoring crystal facets of SrTiO₃ single crystals and developed a one-step molten salt strategy for engineering anisotropic structures by using miscible AlCl₃ as Al³⁺ additive. By progressively increasing Al³⁺ concentration, a series of high-quality SrTiO₃ single crystals exposing {100}, {111}, and {110} facets were sequentially synthesized. Theoretical calculations reveal an Al-doping stabilized {111} surface reconstruction and provide further atomistic insights into the surface structural evolution with Wulff constructions as Al³⁺ concentration increases. Experimental results demonstrate that the anisotropic facets dominate the efficient charge separation for the enhanced photocatalytic overall water splitting activity. Consequently, SrTiO₃ single crystals enclosed by well-defined {100} and {111} facets exhibit a remarkable hydrogen evolution rate of 2621.85 µmol·h^-1 and an apparent quantum yield value of 50.5% at 350 nm for stoichiometric overall water splitting. This work offers a molten-salt synthetic strategy and valuable insight for preparing facet-controlled single-crystal semiconductors.