Energy band modulation of N-doped rutile/anatase TiO₂ photoanode promoting charge separation toward prominent photoelectrochemical performance

To solve the problem of high photogenerated carrier recombination rate and low photoelectric conversion efficiency of TiO₂-based materials, a simple N-doped anatase/rutile TiO₂ heterophase nanorod film was designed by a low-temperature hydrothermal method in this work. The enhanced separation and transport of photogenerated charges were facilitated by the smaller contact barrier and appropriate band matching between anatase TiO₂ nanoparticles and rutile TiO₂ nanorods. The introduction of N doping in anatase TiO₂ resulted in an upward shift of the valence band and a narrowing of the band gap, consequently enhancing the efficiency of visible light utilization. The combination of the heterophase junction and N-doping exhibited a synergistic effect, effectively suppressing the recombination of photogenerated charges and enhancing the photoelectric conversion efficiency of the photoanode. Under AM 1.5G irradiation, the photocurrent density (J) of the A-TO(N)@R-TONR photoanode reached 2.19 mA·cm⁻² (V_{RHE, 1.23 eV}). Additionally, the incident photon-electron conversion efficiency (IPCE) and the charge injection efficiency (η) reached 81.4% and 51.6% at 320 nm. Furthermore, the J, IPCE, and η values of the A-TO(N)@R-TONR photoanode were 2.96, 2.1 and 3.2 times those of pure R-TONR photoanode, respectively. This work presents a rational strategy for designing efficient TiO₂-based photoanodes.