Modulating Electronic Density of Single-Atom Ni Center by Heteroatoms for Efficient CO Electroreduction.

Single-atom catalysts (SACs) with unique geometric and electronic configurations have triggered great interest in many important reactions. However, controllably modulating the electronic structure of metal centers to enhance catalytic performance remains a challenge. Here, the electronic structure of Ni centers over Ni-NC SACs by introducing electron-rich phosphorus or electron-deficient boron for electrochemical CO reduction (CORR) is systematically tailored. It is found that the Ni-PNC with Ni-NP site exhibits superior performance with a current density of 14.6 mA cm and a Faradaic efficiency of 90.6% at -0.8 V versus RHE for CO production, far exceeding Ni-NC and Ni-BNC SACs. Detailed characterizations and theoretical calculations reveal a linear relationship between the valence state of Ni species and the CORR performance. The incorporation of P species facilitates the electronic localization around the Ni center, significantly promoting the adsorption of CO and the formation of key *COOH intermediate to enhance CORR. This work provides a feasible approach to quantitatively manipulate the electronic structure of single-atom metal sites and to rationally design highly efficient catalysts for boosted performance.