Enhancing Photoelectrochemical Water Oxidation on WO₃ via Electrochromic Modulation: Universal Effects and Mechanistic Insights

Although WO₃ 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 WO₃. The electrochromic WO₃ (e-WO₃) exhibits a significantly enhanced activity for PEC water oxidation compared to raw WO₃ (r-WO₃), with a limiting photocurrent density three times that of r-WO₃. 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 WO₃ and the latter facilitating the hole transfer across e-WO₃/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 WO₃/electrolyte interface.