Potassium-Doped g-C3N4 Achieving Efficient Visible-Light-Driven CO2 Reduction

The visible-light-driven CO2 reduction efficiency is largely restrained by the negative photoabsorption and high recombination rate of electron–hole pairs. It is an effective method to increase the efficiency of CO2 photoreduction by doping alkali metal elements to engineer the electronic properties of the catalyst. Here, we report a new study on the potassium-doped g-C3N4 (K-CN) being used for CO2 reduction irradiated by visible light. DFT calculations and XPS tests show that the potassium doping is interlayer doping, changing the electronic structure of g-C3N4. The higher ID/IG value indicates more structural distortion and defects caused by K doping. K-CNs have enhanced visible-light absorption, and PL spectra demonstrate that the introduction of potassium advances the separation and transmission of photoexcited charge carriers, further confirmed by transient photocurrent response experiment. Under visible light, K-CN-7 achieved efficient CO2 reduction without any noble metal as a cocatalyst, with CO formation rates of 8.7 μmol g–1 h–1, which is 25 times that of ordinary g-C3N4. Our work further validates the importance of inhibiting e–/h+ recombination in improving solar energy conversion efficiency while also bringing hope for efficient solar fuel production using g-C3N4.