Efficient WO3−x nanoplates photoanode based on bidentate hydrogen bonds and thermal reduction of ethylene glycol

Abstract

In this study, an efficient WO3−x nanoplates photoanode was generated based on bidentate hydrogen bonds and in subsequent thermal reduction of ethylene glycol (EG). An appropriate number of controllable oxygen vacancies (Ov) was generated in-situ on the surface of the WO3 nanoplates without deep defects by bidentate hydrogen bonds. Density functional theory (DFT) calculations indicate that the distance between two alcoholic hydrogens (5.124 Å) in EG matches that of the diagonal oxygens (5.483 Å) in the WO3 (002) surface, which allows EG to combine through the most stable bidentate hydrogen bonds with O–H intervals of approximately 2.5 Å. Diagonal oxygens are captured directly from the surface, leaving Ov owing to the special hydrogen-bond structure and moderate reducibility of EG under appropriate thermal conditions. The photocurrent density of the WO3−x nanoplates improves considerably to 2.07 from the 0.91 mA cm−2 of pristine WO3 with the introduction of Ov, which demonstrates the superior surface reaction kinetics from the reduced holes-to-water resistance and increase in surface injection efficiency. DFT calculations of the oxygen evolution reaction reveal that surface Ov could substantially decrease the reaction energy barrier for a lower overpotential of 0.494 V compared to that of WO3 (1.037 V), which is consistent with the reduction in the Tafel slope from 412 to 243 mV dec−1. Therefore, this study provides an innovative method to obtain an efficient WO3 photoanode based on the treatment of EG.