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Abstract The hydrogen produced by Al‐doped SrTiO₃/TiO₂core‒shell catalysts with a range of Al‐doped SrTiO₃cores and the same TiO₂shell are compared. The study included SrTiO₃cores doped with different amounts of Al (0, 1, 2, or 3 mol%) added at different points in the synthesis (prior to or during the molten salt treatment) and at different temperatures (900°C, 1000°C, and 1100°C). It was found that core‒shell catalysts with different cores had hydrogen generation rates that varied by a factor of more than 40 and varied with the processing parameters in the same way as the hydrogen generation rates of the cores alone. The best catalysts had 2 or 3 mol% added Al, added during treatment in a SrCl₂molten salt at 1000°C or 1100°C. Because the core absorbs most of the light, its ability to separate and transport photogenerated charge carriers dominates the properties of the core‒shell catalyst. This indicates that, to optimize the properties of core‒shell catalysts, it is essential to optimize the properties of the core. While the shell can be important to protect the core from degradation, it is not as important to the overall reactivity as the core. 

Abstract Ferroelastic BiVO₄has charged surface domains, even though its crystal structure is non‐polar. These charged domains can be detected by piezo‐force microscopy and lead to spatially selective photochemical reactions. The photochemical reactivity of (Bi_0.96Na_0.04)(V_0.92Mo_0.08)O₄is studied above and below the ferroelastic transition temperature to better understand the origin of charged ferroelastic domains. The results demonstrate that spatially selective reactivity occurs above the ferroelastic transition temperature, similar to what is observed below the transition temperature. Furthermore, when the sample is cooled after brief excursions above the transition temperature, the domains reform with a microstructure that is indistinguishable from what is observed before the transition. The results are consistent with the idea that inhomogeneous distributions of charged point defects, created by stress in the ferroelastic domains, lead to charged domains that promote spatially selective photochemical reactions. If these inhomogeneous defect distributions are not homogenized above the transition temperature, they can template the re‐creation of the original domain microstructure after the transformation back to the ferroelastic phase. 

Abstract 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.