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 (CH 4 ) as a chemical building block without harsh conditions. However, PEC CH 4 conversion to value-added chemicals remains challenging due to the thermodynamically favorable over-oxidation of CH 4 . Here, we report WO 3 nanotubes (NTs) photoelectrocatalysts for PEC CH 4 conversion with high liquid product selectivity through defect engineering. By tuning the flame reduction treatment, the oxygen vacancies of WO 3 NTs were carefully controlled. The optimally reduced WO 3 NTs suppressed over-oxidation of CH 4 showing high total 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, which in excess could further oxidize C1 intermediates to CO 2 . Additionally, band diagram analysis 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 CH 4 conversion to liquids.