Enhanced hydrogen evolution reaction performance of anatase–rutile TiO2 heterojunction via charge transfer from rutile to anatase

Abstract

In light of recent doubts surrounding the industrial viability of photo(electro)catalysis technology for sustainable hydrogen production, it becomes imperative to align materials development with rationalized synthesis protocols. In this study, we present an innovative technique utilizing atmospheric-pressure chemical vapor deposition (APCVD) to rapidly produce TiO₂ in just 5 minutes using pure TiCl₄ as the sole reagent. The resulting photoanode exhibits exceptional photoelectrochemical (PEC) water-splitting performance, achieving a photocurrent density of 2.06 mA cm⁻² at 1.23 V RHE. Moreover, the photoanode demonstrates sustained operation for 16 hours, leading to the successful collection of 138 μmol of H₂ and 62 μmol of O₂. These remarkable results are attributed to the controlled formation of an anatase–rutile phase-junction, the presence of well-balanced oxygen vacancies, and the bifrustum nanoparticle–nanoflake structure with a unique light trapping effect and large surface area. Density functional theory calculations confirm that the water-splitting reaction primarily occurs at undercoordinated Ti and O atoms in both anatase and rutile TiO₂. Notably, the calculated Gibbs free energy values for the hydrogen evolution reaction (HER) differ significantly between rutile (−0.86 eV) and anatase TiO₂ (0.22 eV). In the heterojunction, charge transfer enhances the HER performance through shared electronic density, resulting in a synergistic effect that surpasses the capabilities of individual surfaces and underscores the importance of electronic interactions within the junction.