Spin Regulation of Nickel Single Atom Catalyst via Axial Phosphor‐Coordination Achieves Near Unity CO Selectivity in Electrochemical CO₂ Reduction

Abstract

The engineering of the spin state and axial coordination of the metal center of single‐atom catalyst (SAC) represents an effective strategy for regulating the catalytic activity, selectivity, and stability toward electrocatalytic reduction of CO2 (ECO2R). However, rational design and deliberate fabrication of SACs with axial coordination of specified atoms remain challenging. Herein, Ni single atoms with axial coordination of phosphorus (NiP−N4−C) and four planar nitrogen atoms are fabricated, which induces reorientation of the 3d orbitals of the Ni atom and shift of the spin state from low (S = 0) to high (S = 2). The enhanced d−p orbital coupling between the Ni and the adsorbents enhances CO2 activation and reduces energy barrier for formation of *COOH, a key intermediate in the ECO2R to produce CO, enabling the high activity and near unity selectivity of CO in ECO2R in a broad potential range of 600 mV (−0.4–−1.0 V vs reversible hydrogen electrode vs RHE), achieving a turnover frequency of 37.2 s−1 at −1.0 V versus RHE. As a bifunctional cathode electrocatalyst, NiP−N4−C demonstrates a peak power density of 18.5 mW cm−2 and maintains cycling durability over 70 h in rechargeable Zn−CO2 batteries.