Spontaneous Exciton Dissociation in Sc-Doped Rutile TiO₂ for Photocatalytic Overall Water Splitting with an Apparent Quantum Yield of 30%

Achieving high-efficiency photocatalytic overall water splitting with earth-abundant materials like TiO₂ under ambient conditions is a compelling renewable energy solution. However, this remains challenging due to both the presence of rich deep-level defects and lack of strong driving force in particulate photocatalysts, limiting the separation of photogenerated charges. Here, we developed a scandium (Sc)-doped rutile TiO₂ with fully passivated detrimental Ti³⁺ defects and very strong built-in electric field arising from engineered (101)/(110) facet junctions. The Sc³⁺ doping enables a much lower exciton binding energy of 8.2 meV (28.6 meV for undoping) than room-temperature thermal fluctuation energy, indicating spontaneous exciton dissociation. These features enable the photogenerated electrons and holes to selectively transfer to the (110) and (101) facets, respectively. The resulting Sc-doped TiO₂ with cocatalyst delivers photocatalytic overall water splitting with an apparent quantum yield of 30.3% at 360 nm and a solar-to-hydrogen conversion efficiency of 0.34%, representing the highest values reported for TiO₂-based photocatalysts under ambient conditions.