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 Ni₁/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 Ni₁/UiO-66-NH₂, we have used density functional theory (DFT) to study different reaction pathways. The results show that CH₄ is generated preferentially on Ni₁/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 Ni₁/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.