Metal-Reduced WO_3–x Electrodes with Tunable Plasmonic Resonance for Enhanced Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting is one of the most promising green technologies for producing renewable clean hydrogen energy. Developing plasmonic semiconductors with tunable plasmonic resonance to visible light has drawn increasing attention in view of utilizing abundant low-energy photons for solar-to-chemical conversion. Herein, we demonstrate for the first time that the WO3 electrode can be partly reduced by various metal foils in acid solution, showing strong localized surface plasmon resonance (LSPR) in the visible-to-near-infrared (vis–NIR) region. The LSPR can be precisely tuned using metal foils with different standard electrode potentials for different reaction times, and the LSPR peak position strongly depends on the concentration of W5+ in the WO3–x electrodes. A photocurrent density of 0.79 mA·cm–2 at 1.23 VRHE, which is twice that of pristine one, is obtained over an optimally reduced WO3–x electrode. The enhanced PEC water splitting performance is ascribed to the increased light absorption, conductivity, and charge-carrier concentration.