Fluorine doped copper tungsten nanoflakes with enhanced charge separation for efficient photoelectrochemical water oxidation

Inefficient electron-hole separation greatly restricts the performance of CuWO₄ toward photoelectrochemical oxygen evolution reaction. To address such issue, we developed a facile fluorine doping approach, in which F⁻ anions were incorporated into the crystal lattice of n-type CuWO₄ nanoflakes and served as effective electron donors to increase the electron density. The dopant concentration in CuWO₄ could be easily controlled by varying the added amount of F precursor solution. The obtained F-doped CuWO₄ retained the two-dimensional network structure of the undoped CuWO₄ nanoflakes. The obtained F-doped CuWO₄ nanoflakes exhibited a highly-enhanced activity and an excellent stability for photoelectrochemical oxygen evolution reaction. The activity of F-doped CuWO₄ depended on the F-doping concentration. The 2.50 at.% F-doped CuWO₄ showed the highest photocurrent density of 0.57 mA cm⁻² at 1.23 V vs. reversible hydrogen electrode, which is ca. 1.8 times that of the pristine CuWO₄ (0.32 mA cm⁻²) and stands among the highest values reported for CuWO₄-based photoanode. The high activity of F-doped CuWO₄ was ascribed to the significantly-improved electron-hole separation efficiency, which resulted from F-doping induced high electron density in F-doped CuWO₄. This work suggests that anion doping is an effective way to further improve the photoactivity of CuWO₄ toward photoelectrochemical oxygen evolution reaction.