Modulating the spin state of the nickel site through axial phosphorus coordination to enhance CO2 electroreduction

Abstract

Carbon-based single-atom catalysts have demonstrated excellent performance in electrochemical CO₂ reduction reactions. However, the traditional planar, highly symmetric MN₄ structures seriously restrict their activities due to relatively weak interactions between the catalyst and CO₂. In this work, we demonstrated a novel and controllable method for axial P coordination of single-atom Ni catalyst through low-temperature post-functionalization. This modification significantly regulates the spin state of the Ni sites, thereby increasing the interaction between CO₂ and the active sites. The axially P-coordinated single-atom Ni catalyst exhibits markedly improved performance for CO₂ conversion to CO, achieving a maximum CO Faradaic efficiency of ∼ 99 % at −0.98 V (vs. RHE) and a partial current density for CO of −45.1 mA cm⁻² at −1.48 V (vs. RHE), which is 18.4 % higher than that of the pristine single-atom Ni catalyst. Density functional theory calculations indicate that axial P coordination modulates the magnetic moment of the Ni active center and the 3d orbital splitting energy levels, thereby promoting CO₂ adsorption and facilitating CO desorption by optimizing the binding energies of reaction intermediates. These findings are confirmed by experimental electron spin resonance measurements. This work provides a facile strategy for regulating the electronic structures of single-atom catalysts and highlights the potential for spin-state modulation to significantly enhance CO₂ electroreduction.