Modulating WO<sub>3</sub> Crystal Orientation to Suppress Hydroxyl Radicals for Sustainable Solar Water Oxidation
Xiaobing Shi, Qianbao Wu, Chunhua Cui
Abstract
Tungsten trioxide (WO 3 ) is one of the promising semiconductors suitable for photoelectrochemical water oxidation, but its hydroxyl radical ( • OH)-induced intrinsic performance degradation remains unclarified. Here, we demonstrate that quenching-treated WO 3 with preferred {021} facets shows a highly improved Faradaic efficiency (from 57 to 95%) and its performance stability is more than 36 h relative to that of nontreated WO 3 with less than 1-h stability. Using electron paramagnetic resonance (EPR), we find that the • OH could be highly suppressed on the treated WO 3 photoanode, while abundant • OH is generated on the nontreated WO 3 . In situ ultraviolet–visible (UV–Vis) spectroscopy is used to track the presence of surface W–O–O–W intermediates on the treated WO 3, suggesting the favorable formation of O–O and thus better oxygen evolution Faradaic efficiency, while the nontreated WO 3 favors the formation of • OH, which accumulates on the WO 3 surface, thus changing the photoanode/electrolyte interfacial properties and poisoning the oxygen evolution process. This work provides an intrinsic understanding of the degradation of the WO 3 photoanode under acidic and neutral conditions.