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

ABSTRACT

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.