Unveiling the Role of the Ti Dopant and Viable Si Doping of Hematite for Practically Efficient Solar Water Splitting

Doping engineering is of key importance for controlling the electrical, optical, and structural properties of a semiconductor. In more expanded doping systems, codoping with deep insight and understanding of interactions between impurities is necessary to make an efficient photoelectrode. Here, we show that the high formation energy of a Si-doped hematite can be decreased with the introduction of a host Ti-dopant, making easy and cost-efficient solution-based Si doping possible. The effect of the positive interaction between dopants lowers the formation energy in a standard atmosphere to the one under extreme conditions of about 10–10 atm. By taking advantage of formation energy control, we achieved a photocurrent density of 4.3 mA cm–2 at 1.23 VRHE in the optimized Si:Ti codoped hematite with a cocatalyst without using any demanding experimental processes. Our study suggests a ground rule for the facile incorporation of the high-formation-energy dopant into photocatalysts, which can be readily extended to other doped systems to achieve a substantial improvement in PEC performance.