Photocatalytic CO2 conversion to hydrocarbon fuels, the solar fuels, making possible simultaneous solar energy harvesting and CO2 reduction, is considered a killing two birds with one stone approach to solving the energy and environmental problems. However, the development of solar fuels has been hampered by the low conversion efficiency and lack of product selectivity of the photocatalysts. Here, we present defect engineering (interstitial, substitutional, and vacancy) in chalcogenides as a viable method towards promising photocatalysts for CO2 reduction reaction (CO2RR). Three cases will be illustrated: the carbon- and nickel-doped SnS2 (abbreviated as SnS2-C and SnS2-Ni, respectively) nanosheets and single layer MoS2.
For the first case, the SnS2-C nanosheets with a typical layer thickness of ~40 nm were synthesized using an L-cysteine-based hydrothermal process. Compared with undoped SnS2, the interstitial carbon doping induced microstrain in the SnS2 lattice, resulting in different photophysical properties. Density functional theory calculations were performed for the formation energy, along with the CO2 adsorption and dissociation on differently configured SnS2-C for CO2RR. Experimentally, the SnS2-C exhibited a highly effective photocatalytic activity in gas phase with a photochemical quantum efficiency exceeding 0.7 % under visible light, which is ~250 times higher than that of its undoped counterpart, and also a world-record high value reported for inorganic catalyst. For the second case, substitution doping of Ni is also found to be effective for enhancing the performance of SnS2. For the third case, the MoS2 single layers were prepared by chemical vapor deposition, followed by hydrogen plasma post-treatment. With increasing hydrogen plasma treatment time, we observed a trend of blue-shift in the A1g peak and red-shift in E2g peak in their Raman spectra, implying creation of sulfur vacancies, of which the resultant stoichiometry ratio of Mo/S was further investigated by X-ray photoelectron spectroscopy. In addition, scanning tunneling microscopic images clearly supported that there were missing atoms in the MoS2 layers after hydrogen plasma treatment. Productivity and selectivity of CO2RR were found to be strongly dependent with the different Mo/S ratios of the MoS2 single layers. The role and interplay of the defects and the hosting materials as well as their effects on CO2RR will be discussed in this presentation.