Manipulating Spin States by Metal Axial Coordination of Active Sites for Generating Valuable CH4 in CO2 Reduction.

Dual-atom catalysts (DACs) exhibit superior catalytic performance with more active sites and diverse electronic structures. However, electronic spin state as the crucial factor is rarely explicitly studied, and the in-depth understanding of the electronic structures remains a great challenge. Herein, double-solvent method is adopted to encapsulate the Ni and Mn ions into the channels of Mn-based ZIF -8 (Ni→Mn DAC) and Ni-based ZIF -8 (Mn→Ni DAC), respectively. The introduced metal exhibits axial coordination around the metal active site with the distinct coordination environments, indicating the diverse electronic structures. Experimental investigations and theoretical calculations demonstrate that the improved CO2 reduction (CO2RR) activity of Ni→Mn DAC derives from the axial coordinated Ni atom-induced spin-state transition of Mn 3d3 from low-spin (dxy↑↓ dz 2↑) to high-spin (dxy↑ dxz↑ dyz↑). This is attributed to the splitting of Mn 3d orbital with specific C─Ni─N─Mn─N3 coordination structure, which makes Mn d-band center push toward the Fermi level and further strengthens the adsorption of *CO. Based on the accelerated reaction kinetics, the strong interaction between Mn active sites and *CO leads to the rapidly completion eight-electron process for generating CH4. This work provides an efficient spin-manipulation strategy for accelerating the generation of valuable CH4.