Silicon-doped graphene edges: an efficient metal-free catalyst for the reduction of CO2 into methanol and ethanol

Abstract

Inspired by a recent study (Nature Catalysis, 2019, 2, 46–54) in which silicon nanosheets decorated with palladium clusters have shown an excellent CO₂ reduction activity with the Si atom acting as the catalytic active site, we for the first time identify a metal-free Si-based material for the CO₂ reduction reaction (CRR). In experiments, Si atom doped graphene edges (Si@G) have already been realised, and during the preparation of Si@G, Si chain doped graphene edges (Si chain@G) have also been observed with a high percentage (ACS Nano, 2016, 10, 142–149). Due to the “acceptance and back-donation” of electrons between the Si dopant and CO₂ molecule, CO₂ can be well captured and activated on Si, and in the subsequent reduction process, the formation of CH₃OH at the single Si doped armchair edge has the highest activity with a limiting potential of −0.49 V. Since multiple Si active sites are located at the Si chain doped graphene edge, the formation of C₂ products, including CH₃CH₂OH and C₂H₄, has great probability. DFT calculations have shown that at Si chain@G, the formation of C₂H₅OH is energetically favourable as compared to C₂H₄, with a limiting potential of only −0.60 V, which is lower than those of other reported Cu-based materials (such as −1.0 V on the Cu (100) surface). However, the generation of CO and HCOOH has a lower selectivity because of the strong binding strength with the Si atom, making the product desorption difficult. Because of the strong interaction, low limiting potentials and high selectivity, Si@G can be a promising metal-free catalyst to achieve the reduction of CO₂, which paves a new way for advancing CO₂ conversion.