Revealing the synergistic effect of Ni single atoms and adjacent 3d metal doped Ni nanoparticles in electrocatalytic CO2 reduction

Abstract

Herein, we report the successful fabrication of a series of transition metal doped Ni nanoparticles (NPs) coordinated with Ni single atoms in nitrogen-doped carbon nanotubes (denoted as Ni_1+NPsM-NCNTs, M = Mn, Fe, Co, Cu and Zn; Ni₁ = Ni single atom). X-ray absorption fine structure reveals the coexistence of Ni single atoms with Ni–N₄ coordination and NiM NPs. When applied for electrocatalytic CO₂RR, the Ni_1+NPsM-NCNT compounds show the Faradaic efficiency of CO (FE_CO) with a volcano-like tendency of Mn < Fe ≈ Co < Zn < Cu, in which the Ni_1+NPsCu-NCNT exhibits the highest FE_CO of 96.92%, a current density of 171.25 mA cm⁻² and a sustainable stability over 24 hours at a current density of 100 mA cm⁻², outperforming most reported examples in the literature. Detailed experiments and theoretical calculations reveal that for Ni_1+NPsCu-NCNTs, the electron transfer from NiCu NPs to Ni single atoms strengthens the adsorption of *COOH intermediates. Moreover, the d-band center of Ni–N in Ni_1+NPsCu-NCNT is upshifted, providing stronger binding with the reaction intermediates of *COOH, whereas the NiCu NPs increase the Gibbs free energy change of the Volmer step, suppressing the competitive HER.