Transforming glyoxal to value-added glyoxylic acid (GA) is highly desirable but challenging due to the uncontrollable over-oxidation. In this work, we report on a first demonstration of semi-oxidation of glyoxal with high selectivity (86.5%) and activity on WO3 nanoplate photoanode through the photoelectrochemical strategy. The optimization of reactivity was achieved via crystal facet regulation, showing a satisfactory GA production rate of 308.4 mmol m-2 h-2, 84.0% faradaic efficiency, and 4.3% total solar-to-glyoxylic acid efficiency on WO3 with enriched {200} facets at 1.6 V versus RHE. WO3 with a high {200} facet ratio exhibits more efficient electron-hole transfer kinetics, resulting in the facilitated formation of hydroxyl radicals (•OH) and glyoxal radicals. Meanwhile, the theoretical calculation results indicate that the high selectivity and activity come from the strong adsorption ability for glyoxal and the low reaction energy for glyoxal radical generation on the (200) facets of WO3. Moreover, the high energy demand toward oxalic acid production on WO3 leads to the exciting semi-oxidation process.
Keywords: WO3 nanoplates; crystal facet engineering; glyoxal; photoelectrochemistry; selective oxidation.