La,Al-Codoped SrTiO3 as a Photocatalyst in Overall Water Splitting: Significant Surface Engineering Effects on Defect Engineering

Suppressing the formation of defects such as oxygen vacancies and Ti3+ in SrTiO3 perovskite lattice has been regarded as an effective way to improve photocatalytic performance in overall water-splitting reaction. In this work, a series of La,Al-codoped SrTiO3 catalysts are synthesized by a flux treatment method after grounding. An appropriate doping amount of La3+ and Al3+ ions into perovskite will lead to fewer defects, responsible for enhancing photocatalytic performance. Al3+ ion doping will introduce the oxygen vacancies into the perovskite, resulting in a decreasing number of Ti3+ ions. During the defect engineering, more Sr2+ will precipitate onto the perovskite surface caused by the introduction of Al3+. Hence, surface engineering is applied through appropriate La3+ ion doping contributing to the lattice distortion, allowing surficial Sr2+ to re-enter the perovskite lattice, leading to the promoted conversion of Ti3+ to Ti4+. Simultaneously, the La3+ ion doping is also beneficial to the decrease in oxygen vacancies. As a result, the essential relationship between the La3+ doping amount and photocatalytic performance in overall water splitting is revealed. The optimized 0.6% La and 1% Al codoped SrTiO3 sample loading Rh (0.1 wt %)/Cr2O3 (0.05 wt %)/CoOOH (0.05 wt %) gives the highest activity and good stability, with gas evolution rates of 1.79 mmol·h–1 (H2) and 0.91 mmol·h–1 (O2). In comparison, the apparent quantum efficiency is 78.43% under 365 nm irradiation.