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.