Defect-Expedited Photocarrier Separation in Zn2In2S5 for High-Efficiency Photocatalytic C─C Coupling Synchronized with H2 Liberation from Benzyl Alcohol

Photocatalytic carbon-carbon (C─C) coupling of benzyl alcohol is a promising means to coproduce the value-added chemicals with H 2 but is generally subject to low efficiency in terms of photon utilization. Here, efficient benzyl alcohol C─C coupling is achieved over Zn 2 In 2 S 5 containing a tunable content of Zn vacancies ( V Zn ). The V Zn tends to form shallow defect states below the conduction band that can expedite photocarrier separation by collecting the photo-generated electrons. The V Zn -collected electrons are essential for a high selectivity of the C─C coupling reactions because they enable a fast elimination of the byproduct benzaldehyde by catalyzing its reduction back to the ketyl radicals. Under simulated sunlight, the V Zn -containing Zn 2 In 2 S 5 accomplishes ≈100% conversion of benzyl alcohol for merely 1 h and attains ≈100% selectivity for the C─C coupling compounds for 2 h, delivering an apparent quantum yield as high as 7.7% at 420 ± 20 nm. The benefits of V Zn have also been verified by the theoretical calculations that indicate reduced energy barriers for various surface reactions in the presence of V Zn . This work brings fresh mechanistic insights into the role of V Zn and can serve as a useful guideline in the design of efficient photocatalysts.