Defect Engineering of WO3 by Rapid Flame Reduction for Efficient Photoelectrochemical Conversion of Methane into Liquid Oxygenates

Photoelectrochemical (PEC) conversion is a promising way to utilize methane (CH4) as a chemical building block without harsh conditions. However, PEC CH4 conversion to value-added chemicals remains challenging due to the thermodynamically favorable over-oxidation of CH4 to CO2. Here, we report WO3 nanotubes (NTs) photoelectrocatalysts for PEC CH4 conversion with high liquid product selectivity through defect engineering. By tuning the flame reduction treatment, the oxygen vacancies of WO3 NTs were carefully controlled. The optimized reduced WO3 NTs suppressed over-oxidation of CH4 and showed high C1 liquid selectivity of 69.4% and production rate of 0.174 μmol cm-2 h-1. Scanning electrochemical microscopy revealed that oxygen vacancies can restrain the production of hydroxyl radicals, the presence of which in excess could further oxidize C1 intermediates to CO2. In addition, optical characterization and computational studies elucidated that oxygen vacancies thermodynamically suppress over-oxidation. This work introduces a strategy to understand and control the selectivity of photoelectrocatalysts for direct CH4 conversion to liquids.