Hydrothermally Grown Halogen-Doped ZnO Nanorods for Photoelectrochemical Water Oxidation: Experimental and DFT Insights

This study demonstrates the photoelectrochemical (PEC) aspects of hydrothermally grown halogen-doped ZnO nanorods, analyzing their structural, morphological, optical, and electrical properties under visible light illumination. We find that halogen doping in the ZnO matrix significantly enhances the PEC water splitting performance. Among the four halogen atoms (Cl, Br, F, and I), Cl yields the highest photocurrent density of 0.75 mA/cm2 at 1.5 V vs Ag/AgCl, nearly 5 times that of pristine ZnO nanorods (0.16 mA/cm2). This improvement in PEC activity is attributed to the increased light absorption, higher charge carrier density, and efficient separation of the photoexcited electron–hole pairs. Cl doping in ZnO increases the free electron concentration and tends to substitute oxygen vacancies, thereby reducing the recombination of photogenerated electron–hole pairs. In addition, the density functional theory calculations provide theoretical insights into the effect of halogen doping on the photocatalytic activity of ZnO. These findings pave the way for the design of efficient and cost-effective photoanode materials for PEC applications.