Al3+‐Dependent Anisotropic Facet Tailoring on SrTiO3 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 non‐equilibrium 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.