Theoretical simulations inspired the design of Ni nanoparticles-NiN4 single atom composites for efficient CO2 electro-reduction at ultralow overpotential

Ni, especially Ni single atom catalysts (SACs) are the most promising electrocatalyst in the reduction of CO₂ to CO. However, the high energy barrier for the formation of *COOH on Ni SA sites leads to a high overpotential for CO₂RR, which severely hinders the CO production efficiency. How the coupling effect of Ni SAs and Ni nanoparticles (NPs) sites improve the performance of Ni-based electrocatalysts is interesting to be investigated. Herein, theoretical calculations revealed that the synergy of Ni SAs and Ni NPs could efficiently lower the energy barrier of the *COOH formation via promoting the H₂O dissociation process to accelerate the *H supply for CO₂ protonation as well as promote the CO₂ adsorption and CO desorption, thus improving catalytic activity. Based on the theoretical study, Ni-N₄ SA coupled with Ni nanoparticles supported on nitrogen-doped carbon nanotubes (Ni-N₄Ni_NP/NCNT) was designed. As electrocatalyst, the Ni-N₄Ni_NP/NCNT showed an ultralow onset overpotential of 60 mV for CO₂RR-to-CO, and achieves a FE_CO of ∼99 % from an overpotential of as low as 160 mV, outperforming state-of-the-art Ni SACs. This work not only sheds new light for the rational synthesis of Ni-based catalysts with both Ni SAs and Ni NPs sites to achieve efficient CO₂RR to CO, but also offers an in-depth insight for the origin of efficient performance of cooperative Ni_SA-Ni_NP catalysts.