Efficient CO₂ electroreduction requires catalysts for enhanced energy conversion efficiency and carbon product selectivity with low overpotential, in consideration of the interference of competitive H₂ evolution reaction and complex intermediate species involved. We proposed that adaptive electronic structures based on dynamic mixed-valence interconversion would facilitate electron transfer and intermediate turnover during the catalysis, ensuring high activity, selectivity, and durability. Herein, a novel mixed-valence Cu-based metal-organic framework was prepared using an electron-rich linker for electrocatalytic reduction of CO₂. The designed material delivered a remarkable Faradaic efficiency of 99.2% for C₁ liquid fuels at a low reduction potential of −0.1 V versus reversible hydrogen electrode, considerably higher than that of the commercial copper foam and competitive to the Cu-based electrocatalysts reported. The experimental data and theoretical calculations verified the Cu(I)/Cu(II) interconversion and the much higher energy barrier of H₂ evolution than carbon product generation. Such a feasible strategy, simultaneously improving energy conversion efficiency, carbon product selectivity, and structural robustness, provides great insights into rational catalyst customization for sustainable CO₂ conversion.