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BaTiO₃heated in an excess of SrCl₂at 1150 °C converts to SrTiO₃through an ion exchange reaction. The SrTiO₃synthesized by ion exchange produces hydrogen from pH 7 water at a rate more than twice that of conventional SrTiO₃treated identically. The apparent quantum yield for hydrogen production in pure water of the ion exchanged SrTiO₃is 11.4% under 380 nm illumination. The catalyst resulting from ion‐exchange differs from conventional SrTiO₃by having ≈2% residual Ba, inhomogeneous Cl‐doping at a concentration less than 1%, Kirkendall voids in the centers of particles that result from the unequal rates of Sr and Ba diffusion together with the transport of Ti and O, and nanoscale regions near the surface that have lattice spacings consistent with the Sr‐excess phase Sr₂TiO₄. The increased photochemical efficiency of this nonequilibrium structure is most likely related to the Sr‐excess, which is known to compensate donor defects that can act as charge traps and recombination centers.

SrTiO₃polycrystalline ceramics with polished surfaces are annealed at 1250 °C in air. This treatment causes the flat surfaces to break up into facets meeting at sharp edges and corners. An analysis of the orientations and topography of the faceted surfaces demonstrates that all are either {100} or {110} oriented. The {100} surfaces are photocathodically active and reduce Ag⁺to Ag metal. The {110} surfaces are photoanodically active and oxidize Mn²⁺and Pb²⁺to Mn⁴⁺and Pb⁴⁺, respectively. The chemical properties of both surfaces appear to be uniformly photocathodic or photoanodic. However, after annealing at 1100 °C with Sr₃Ti₂O₇, the {110} facets have a combination of photocathodic and photoanodic terraces. The results show that the photocathodic‐to‐photoanodic surface area ratio, which influences the overall rate of a photochemical reaction, can be controlled for arbitrarily oriented SrTiO₃surfaces by using thermal treatments to create low index facets and to control the chemical terminations on these facets.