Spin Polarization Enhanced Ethanol Selectivity in Electrocatalytic CO₂ Reduction on the Paramagnetic CuO Surface

We report an electrochemical CO₂ reduction reaction catalyzed by a paramagnetic and conductive CuO/Cu interface with spins polarized by a moderate external magnetic field (MF) of ∼800 gauss, achieving a ∼30% increase in CO₂-to-C₂₊ Faradaic efficiency (FE) compared to that in the absence of the MF in a flow cell electrolyzer. At a current density of 400 mA/cm², the CO₂-to-C₂₊ FE reached 86.7 ± 2.7% with 47.9 ± 1.4% cathodic energy efficiency (EE) in contrast to the CO₂-to-C₂₊ FE of 67.6% with 36.4% of EE in the absence of MF. Notably, ethanol production exhibits a much higher response to the MF (∼55.6% increase in FE) than ethylene (∼6.4% increase in FE) at 400 mA/cm². In situ surface-enhanced Raman spectroscopy (SERS) captured magnetic-field-enhanced *CO coverage and ethanol-forming C₂ intermediates on CuO/Cu, providing direct spectroscopic evidence of spin-modulated pathway selection. Computational study suggests that the enhancement of ethanol selectivity is due to the reduced reaction kinetic barrier under MF, while the ethylene selectivity is less affected, mainly due to the insensitivity of the kinetic barriers under MF.