Electrolysis-Mode-Dependent Valence Reconstruction of Cu-Based Catalysts Enables Selective CO2 Electroreduction toward CH4 or C2+ Products.

Electrochemical CO2 reduction (eCO2R) provides a promising route for converting CO2 into value-added fuels and chemicals, yet controllable selectivity between CH4 and C2+ products remains challenging due to complex proton-coupled electron transfer and sluggish C-C coupling kinetics. Herein, we systematically investigate the influence of galvanostatic electrolysis (GE) and pulsed galvanostatic electrolysis (PGE) on the catalytic behavior of Cu3Al1-LDH toward eCO2R. Under GE, the catalyst undergoes deep reduction to form a Cu0-enriched surface that promotes *CO adsorption and C-C coupling, achieving a high C2+ Faradaic efficiency (FE) of 83.4% at 500 mA cm-2. In contrast, PGE stabilizes a Cu2+/Cu+/Cu0 mixed-valence interface through periodic oxidation-reduction reconstruction, shifting the reaction pathway toward CH4 with an FECH4 of 59.5% at 200 mA cm-2. In situ Raman and attenuated total reflection surface-enhanced infrared absorption spectroscopy reveal that periodic oxidation-reduction during PGE dynamically regulates Cu valence evolution and key reaction intermediates, thereby suppressing C-C coupling while promoting the deep hydrogenation of *CO toward CH4. This work establishes a direct correlation among electrolysis mode, catalyst reconstruction, intermediate evolution, and eCO2R selectivity, providing a new strategy for programmable control of eCO2R pathways.