Electronic State Modulation of Cu by Ge for Post C─C Steps in Electrochemical CO2 Reduction

The precise control of product selectivity in the electrochemical CO 2 reduction reaction (ECR) toward specific multi-carbon (C 2+ ) compounds remains a significant challenge. This work demonstrates that incorporating germanium (Ge) into copper (Cu) nanoparticles to form a solid solution effectively tunes the surface electronic states of Cu, thereby steering the C 2+ product distribution from ethylene toward ethanol. First-principles calculations predict that an optimal Ge content (Cu 94 Ge 6 ) optimizes the Cu 3d orbital hybridization and shifts the d-band center, strengthening the adsorption of the critical * CH 2 CHO intermediate and favoring its hydrogenation pathway. Experimentally, the Cu 94 Ge 6 catalyst exhibits an ethanol-to-ethylene ratio of ∼1.8, significantly higher than that of pure Cu (∼0.6). Comprehensive characterization, including in situ ATR-FTIR and quasi in situ XPS, reveals that the Ge-induced electronic modulation enhances the adsorption of COCHO/CH 2 CHO intermediates and promotes the presence of isolated interfacial water, which collectively facilitates ethanol formation. This study presents a viable strategy for regulating C 2+ product selectivity through solid-solution electronic engineering in Cu-based electrocatalysts.