Fluorination of\nthe WO<sub>3</sub> Photoanode to Promote\nInterfacial Charge Transfer for Efficient Photoelectrocatalytic Performances

To improve the interfacial charge transfer over a tungsten\noxide\n(WO<sub>3</sub>) photoanode for an efficient photoelectrocatalytic\n(PEC) process, WO<sub>3</sub> was fluorinated in a solvothermal process\nin the presence of NH<sub>4</sub>F. It was shown that, after the fluorination\nwith the molar ratio of NH<sub>4</sub>F to WO<sub>3</sub> at 0.4,\nthe charge separation and charge injection efficiencies increased\nfrom 22.02 to 61.15% at 0.5 V vs Ag/AgCl and from 44.71 to 72.69%\nat 0.5 V vs Ag/AgCl, respectively, significantly enhancing the PEC\nperformances for synergetic tetracycline degradation and H<sub>2</sub> evolution. Various characterization and density functional theory\ncalculation results revealed that the incorporation of fluorine into\nthe WO<sub>3</sub> lattice by fluorination substantially raises the\nFermi level of WO<sub>3</sub>, which bends the energy bands of WO<sub>3</sub> more upward at the semiconductor/electrolyte interface. The\nintensified upward bending bands effectively promote charge transfer\nat the fluorinated WO<sub>3</sub> photoanode/electrolyte interface,\nachieving the observed efficient PEC performances.