Simultaneously Accelerating Carrier Transfer and Enhancing O₂/CH₄ Activation via Tailoring the Oxygen-Vacancy-Rich Surface Layer for Cocatalyst-Free Selective Photocatalytic CH₄ Conversion

Solar energy-driven direct CH₄ conversion to liquid oxygenates provides a promising avenue toward green and sustainable CH₄ industry, yet still confronts issues of low selectivity toward single oxygenate and use of noble-metal cocatalysts. Herein, for the first time, we report a defect-engineering strategy that rationally regulates the defective layer over TiO₂ for selective aerobic photocatalytic CH₄ conversion to HCHO without using noble-metal cocatalysts. (Photo)­electrochemical and in situ EPR/Raman spectroscopic measurements reveal that an optimized oxygen-vacancy-rich surface disorder layer with a thickness of 1.37 nm can simultaneously promote the separation and migration of photogenerated charge carriers and enhance the activation of O₂ and CH₄, respectively, to •OH and •CH₃ radicals, thereby synergistically boosting HCHO production in aerobic photocatalytic CH₄ conversion. As a result, a HCHO production rate up to 3.16 mmol g^–1 h^–1 with 81.2% selectivity is achieved, outperforming those of the reported state-of-the-art photocatalytic systems. This work sheds light on the mechanism of O₂-participated photocatalytic CH₄ conversion on defective metal oxides and expands the application of defect engineering in designing low-cost and efficient photocatalysts.