Favorable Energy Band Alignment of TiO₂ Anatase/Rutile Heterophase Homojunctions Yields Photocatalytic Hydrogen Evolution with Quantum Efficiency Exceeding 45.6%

Developing the technology for high yielding photocatalytic hydrogen evolution reactions is an important challenge. Development and optimization of photocatalytic junctions is a likely route for achieving this if heterojunctions with suitable band alignments can be achieved in sufficiently high‐density form. Here, a novel anatase‐TiO 2 /H‐rutile‐TiO 2 heterophase homojunction system with near optimum energy band alignment is reported. The resulting as‐prepared catalyst exhibits an excellent photocatalytic hydrogen evolution rate of 29.63 mmol g –1 h –1 under UV–vis light irradiation and an outstanding apparent quantum efficiency of 45.6% at 365 nm. The significant improvement is ascribed to near perfect lattice matching in combination with the rapid separation and transfer of photogenerated carriers in anatase‐TiO 2 /H‐rutile‐TiO 2 heterophase homojunctions. In situ X‐ray photoelectron spectroscopy, electron spin resonance spin‐trapping tests, femtosecond transient absorption spectroscopy, steady‐state surface photovoltage spectroscopy, and transient‐state surface photovoltage with additional ex situ characterizations and theoretical calculations show that the mechanism is enhanced transfer of photogenerated carriers in the anatase‐TiO 2 /H‐rutile‐TiO 2 catalyst. This work provides a pathway for enhancing photocatalytic performance through optimization of heterojunctions.