Fluorination of the WO₃ Photoanode to Promote Interfacial Charge Transfer for Efficient Photoelectrocatalytic Performances

To improve the interfacial charge transfer over a tungsten oxide (WO3) photoanode for an efficient photoelectrocatalytic (PEC) process, WO3 was fluorinated in a solvothermal process in the presence of NH4F. It was shown that, after the fluorination with the molar ratio of NH4F to WO3 at 0.4, the charge separation and charge injection efficiencies increased from 22.02 to 61.15% at 0.5 V vs Ag/AgCl and from 44.71 to 72.69% at 0.5 V vs Ag/AgCl, respectively, significantly enhancing the PEC performances for synergetic tetracycline degradation and H2 evolution. Various characterization and density functional theory calculation results revealed that the incorporation of fluorine into the WO3 lattice by fluorination substantially raises the Fermi level of WO3, which bends the energy bands of WO3 more upward at the semiconductor/electrolyte interface. The intensified upward bending bands effectively promote charge transfer at the fluorinated WO3 photoanode/electrolyte interface, achieving the observed efficient PEC performances.