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 O-2 and CH4, respectively, to center dot OH and center dot CH 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 O-2-participated photocatalytic CH4 conversion on defective metal oxides and expands the application of defect engineering in designing low-cost and efficient photocatalysts.

Automated summary

This study reports a defect-engineering strategy that selectively converts CH4 to formaldehyde through aerobic photocatalytic reactions without the use of noble-metal cocatalysts. The optimized oxygen-vacancy-rich surface disorder layer on TiO2 promotes charge carrier separation and migration, enhances the activation of O-2 and CH4, and synergistically boosts formaldehyde production. This work sheds light on the mechanism of O-2-participated photocatalytic CH4 conversion and expands the application of defect engineering in designing low-cost and efficient photocatalysts.