Spin-Polarization in Rigid/Soft Layered Oxide Catalyst Regulates Key Intermediates for Efficient CO2-to-Formate Conversion.

Precise control of metal oxidation states is pivotal in regulating the adsorption energetics of *OCHO intermediate during CO2 electroreduction. However, the stabilization of oxidation states to enable effective intermediate adsorption-desorption behavior remains a critical challenge for enhancing formate yield. Herein, we synthesize a rigid/soft layered oxides (CuInAlO4) with rigid Al-O framework and soft Cu-O active units. Spin-polarized electrons derived from the unpaired electrons in the dz2 orbital of CuO5 units transfer to the empty 5s/5p orbitals of In3⁺ via the superexchange interaction of 3d(Cu) - 2p(O) - 5s/5p(In). The enhanced spin polarization promotes spin-orbit coupling between metal sites (Cu, In) and *OCHO intermediates (O), forming In─*O─CH─O*─Cu electronic bridge and greatly improving the formation efficiency of formate. CuInAlO4 catalyst achieves exceptional formate selectivity (faradaic efficiency of 95% at 500 mA cm-2, energy efficiency of 80.3%, overpotential of 180 mV), outperforming conventional In─O*─CH─O*─In pathways by reducing the *OCHO-to-HCOOH energy barrier by 1.31 eV. Experimental and theoretical analyses reveal that the rigid AlO5 units stabilize metal-oxygen bonds, preventing oxygen dissolution, while accelerating formate production kinetics through spin-polarized charge transfer.