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 CO 2 to CO. However, the high energy barrier for the formation of *COOH on Ni SA sites leads to a high overpotential for CO 2 RR, 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 H 2 O dissociation process to accelerate the *H supply for CO 2 protonation as well as promote the CO 2 adsorption and CO desorption, thus improving catalytic activity. Based on the theoretical study, Ni-N 4 SA coupled with Ni nanoparticles supported on nitrogen-doped carbon nanotubes (Ni-N 4 Ni NP /NCNT) was designed. As electrocatalyst, the Ni-N 4 Ni NP /NCNT showed an ultralow onset overpotential of 60 mV for CO 2 RR-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 CO 2 RR to CO, but also offers an in-depth insight for the origin of efficient performance of cooperative Ni SA -Ni NP catalysts.