Structural reconstruction of TiO2/WO3 heterojunctions for efficient photoelectrocatalytic hydrogen evolution

Understanding the active species is paramount for the rational design of high-efficiency photoelectrocatalysts, especially given that material structures frequently undergo substantial reconstruction under operando conditions. We address this challenge by investigating the dynamic phase evolution of a TiO 2 /WO 3 (WTO) heterostructure during the photoelectrocatalytic hydrogen evolution reaction (HER). Crucially, cathodic bias drives a rapid and profound surface reconfiguration, enabling the in situ creation of the true catalytic species, H 0.53 WO 3 , while simultaneously introducing numerous oxygen vacancies (O V ). This structural transition is macroscopically evident as electrochromism, shifting from a W 6+ -rich yellowish-white state to a W 5+ -rich deep blue state. Mechanistic analysis identifies this dynamic phase change as the key to catalyst activation, driving an exponential enhancement in performance by facilitating a nearly 30-fold increase in carrier concentration (from 9.4 × 10 20 to 2.7 × 10 22 cm −3 ), superior charge transport kinetics, and significantly expanded visible-light absorption. Consequently, the reconfigured TiO 2 /H 0.53 WO 3 (H-WTO) exhibits a hydrogen evolution rate of 274.1 μmol·h −1 ·cm −2 at −1.0 V vs. RHE in pure water, which is approximately 480 times higher than that of pure TiO 2 . These findings highlight the critical role of electrochromism-induced phase transitions in activating transition-metal oxides and provide mechanistic insights into designing dynamically reconfigurable heterostructures for efficient PEC hydrogen production.