Oxygen vacancy induces self-doping effect and metalloid LSPR in non-stoichiometric tungsten suboxide synergistically contributing to the enhanced photoelectrocatalytic performance of WO3−x/TiO2−x heterojunction

Abstract

A WO_3−x/TiO_2−x nanotube array (NTA) heterojunction photoanode was strategically designed to improve photoelectrocatalytic (PEC) performance by establishing a synergistic vacancy-induced self-doping effect and localized surface plasmon resonance (LSPR) effect of metalloid non-stoichiometric tungsten suboxide. The WO_3−x/TiO_2−x NTA heterojunction photoanode was synthesized through a successive process of anodic oxidation to form TiO₂ nanotube arrays, magnetron sputtering to deposit metalloid WO_3−x, and post-hydrogen reduction to engender oxygen vacancy in TiO_2−x as well as crystallization. On the merits of such a synergistic effect, WO_3−x/TiO_2−x shows higher light-harvesting ability, stronger photocurrent response, and resultant improved photoelectrocatalytic performance than the contrast of WO_3−x/TiO₂, WO₃/TiO₂ and TiO₂, confirming the importance of oxygen vacancies in improving PEC performance. Theoretical calculation based on density functional theory was applied to investigate the electronic structural features of samples and reveal how the oxygen vacancy determines the optical property. The carrier density tuning mechanism and charge transfer model were considered to be associated with the synergistic effect of self-doping and metalloid LSPR effect in the WO_3−x/TiO_2−x NTA.