Silicon-doped graphene edges: an efficient metal-free catalyst for the reduction of CO 2 into methanol and ethanol

Inspired by a recent study ( Nature Catalysis , 2019, 2 , 46–54) in which silicon nanosheets decorated with palladium clusters have shown an excellent CO 2 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 CO 2 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 CO 2 molecule, CO 2 can be well captured and activated on Si, and in the subsequent reduction process, the formation of CH 3 OH 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 C 2 products, including CH 3 CH 2 OH and C 2 H 4 , has great probability. DFT calculations have shown that at Si chain@G, the formation of C 2 H 5 OH is energetically favourable as compared to C 2 H 4 , 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 CO 2 , which paves a new way for advancing CO 2 conversion.