Enhancing Photoelectrochemical Water Oxidation on WO 3 via Electrochromic Modulation: Universal Effects and Mechanistic Insights

Abstract Although WO 3 exhibits both electrochromic and photoelectrochemical (PEC) properties, there is no research conducted to investigate the correlation between them. The study herein reports the electrochromic enhancement of PEC activity on WO 3 . The electrochromic WO 3 (e‐WO 3 ) exhibits a significantly enhanced activity for PEC water oxidation compared to raw WO 3 (r‐WO 3 ), with a limiting photocurrent density three times that of r‐WO 3 . The electrochromic enhancement of PEC activity is universal and independent of the type of cations inserted during electrochromism. Decoloring reduces the PEC activity but a simple re‐coloring restores the activity to its maximum value. Electrochromism induces large amounts of oxygen vacancies and surface states, the former improving the electron density of WO 3 and the latter facilitating the hole transfer across e‐WO 3 /electrolyte interface. It is proved that the electrochromic enhancement effect is due to the significantly improved electron–hole separation efficiency and the charge transfer efficiency across the WO 3 /electrolyte interface.