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

Photoelectrochemical (PEC) conversion is a promising way to use methane (CH₄) as a chemical building block without harsh conditions. However, the PEC conversion of CH₄ to value-added chemicals remains challenging due to the thermodynamically favorable overoxidation of CH₄. Here, we report WO₃ nanotube (NT) photoelectrocatalysts for PEC CH₄ conversion with high liquid product selectivity through defect engineering. By tuning the flame reduction treatment, we carefully controlled the oxygen vacancies of WO₃ NTs. The optimally reduced WO₃ NTs suppressed overoxidation of CH₄ showing a high total C1 liquid selectivity of 69.4% and a 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 CO₂. Additionally, band diagram analysis and computational studies elucidated that oxygen vacancies thermodynamically suppress overoxidation. This work introduces a strategy for understanding and controlling the selectivity of photoelectrocatalysts for direct conversion of CH₄ to liquids.