Ultrastable nickel single-atom catalysts with high activity and selectivity for electrocatalytic CO2 methanation

Electrochemical conversion of CO2 into valuable hydrocarbon fuel is one of the key steps in solving carbon emission and energy issue. Herein, we report a non-noble metal catalyst, nickel single-atom catalyst (SAC) of Ni-1/UiO-66-NH2, with high stability and selectivity for electrochemical reduction of CO2 to CH4. Based on ab initio molecular dynamics (AIMD) simulations, the CO2 molecule is at first reduced into CO2- when stably adsorbed on a Ni single atom with the bidentate coordination mode. To evaluate its activity and selectivity for electrocatalytic reduction of CO2 to different products (HCOOH, CO, CH3OH, and CH4) on Ni-1/UiO-66-NH2, we have used density functional theory (DFT) to study different reaction pathways. The results show that CH4 is generated preferentially on Ni-1/UiO-66-NH2 and the calculated limiting potential is as low as -0.24 V. Moreover, the competitive hydrogen evolution reaction is unfavorable at the activation site of Ni-1/UiO-66-NH2 owing to the higher limiting potential of -0.56 V. Furthermore, the change of Ni single atom valence state plays an important role in promoting CO2 reduction to CH4. This work provides a theoretical foundation for further experimental studies and practical applications of metal-organic framework (UiO-66)based SAC electrocatalysts with high activity and selectivity for the CO2 reduction reaction.