SrTiO 3 Sol–Gel Synthesis Enables Enhanced Photocatalytic Overall Water Splitting Activity by Al and/or Ga (co-)Doping and in-situ Formation of a SrTiO 3 /SrCO 3 Heterojunction

High Resolution Image Download MS PowerPoint Slide SrTiO 3 is a well-known photocatalyst for overall water splitting due to its suitable band edge positions and perovskite structure, which allows for versatile doping strategies that alter electronic or optical properties. However, side phase formation in SrTiO 3 syntheses is common, and SrCO 3 formation on SrTiO 3 surfaces is known to be ubiquitous and independent of the synthesis method. Herein, we address this phenomenon in the context of photocatalytic overall water splitting, and we introduce a sol–gel synthesis that allows for more control over SrCO 3 formation and lower calcination temperatures than common SrTiO 3 molten salt syntheses. We show how aliovalent (co-)doping at the Ti 4+ lattice position is feasible with Al 3+ and Ga 3+ ions but incomplete at 850 °C and therefore contributing to the formation of a SrCO 3 side phase. The highest overall water splitting activity was measured for an Al,Ga:SrTiO 3 /SrCO 3 composite (3.5% Al, 3.5% Ga, and 3% Sr excess), comparable to the activity of Al:SrTiO 3 /SrCO 3 obtained from a common molten salt approach while saving 71% in energy consumption during calcination. This direct approach of doping and in-situ formation of a beneficial SrTiO 3 /SrCO 3 heterojunction was transferred to a calcination temperature as low as 550 °C, allowing for the synthesis of porous composite materials.