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

Abstract 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 Al 3+ concentration in tailoring crystal facets of SrTiO 3 single crystals and developed a one‐step molten salt strategy for engineering anisotropic structures by using miscible AlCl 3 as Al 3+ additive. By progressively increasing Al 3+ concentration, a series of high‐quality SrTiO 3 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 Al 3+ concentration increases. Experimental results demonstrate that the anisotropic facets dominate the efficient charge separation for the enhanced photocatalytic overall water splitting activity. Consequently, SrTiO 3 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.