Effect of the Spatial Dopant Distribution on the Photocatalytic Properties of Rhodium-Doped Strontium Titanate Nanoparticles

Scalable water splitting photocatalyst systems do not yet meet the efficiency targets for commercialization of solar-driven hydrogen production. Strontium titanate (SrTiO₃) is a promising material candidate with reports of stable performance on large scale, and outstanding quantum efficiency. Nevertheless, a large band-gap limits its solar-to-hydrogen conversion efficiency. The doping of SrTiO₃ with Rhodium (Rh) and co-dopants is a common strategy to enable visible light harvesting. However, doping results in enhanced charge carrier recombination, making charge separation and transport the limiting factors for the efficiency in sacrificial hydrogen evolution and Z-schemes for overall water splitting. Tuning the spatial distribution of dopants offers additional control of the charge carrier dynamics but the influence of this approach and the underlying mechanisms are not yet fully understood.
In this presentation, we compare techniques for synthesizing SrTiO₃ nanoparticles with controlled dopant distributions, such as controlling the kinetics of diffusion-based doping and the direct synthesis of homojunctions as core-shell particles. We identified the critical role of the surface morphology during diffusion-based doping leading to a reduced calcination time of 30 minutes. Samples with maintained UV photocatalytic performance and additional visible light harvesting compared to undoped references have been synthesized. We perform comprehensive characterization including the photocatalytic performance at 365 and 415 nm illumination in a purged-type reactor, the dopant distribution by STEM-EDX mapping, oxidation states by XPS, and charge carrier dynamics by surface photovoltage spectroscopy. This work provides new insights on the effect of the dopants’ spatial distribution as result of the position-dependent energy landscape, light-absorption, and charge recombination in the nanoparticles. Along-side we report suitable synthesis techniques to control the dopant distribution on a nanometer scale, which may be translated to other systems.