Crystallinity-Directed In Situ Reconstruction of Cu–Al Oxides Yielding Tunable Cu^δ+ Sites for Electrochemical CO₂-to-C₂₊ Conversion

During the electrochemical CO₂ reduction reaction (CO₂RR), copper catalysts continuously undergo structural evolution, which is less controllable, and its impact on the product distribution of CO₂RR remains unclear. Here, crystallinity-tunable Cu-Al mixed metal oxide (CuAl-MMO-<i>T</i>) precatalysts were first synthesized via layered double hydroxide calcination. These precatalysts subsequently underwent in situ electrochemical reconstruction to form active CuAl-MMO-<i>T</i>R catalysts with tailored Cu^δ+ valence states. The moderately crystalline-derived CuAl-MMO-600R achieves a C₂₊ Faradaic efficiency of 76.8% with 44.6% ethylene selectivity at -300 mA·cm^-2, outperforming both its low- and high-crystallinity counterparts. In situ Raman and density functional theory showed that residual Al species stabilize Cu⁺ active sites via strong electronic interactions, while oxygen vacancies promote *CO adsorption and OH^- enrichment, synergistically lowering the C-C coupling energy barrier. Furthermore, system integration assisted by the glycerol oxidation reaction reduces the full-cell voltage by 17%, enabling simultaneous CO₂-to-C₂₊ conversion and biomass-derived chemical production. This crystallinity-directed reconstruction strategy provides a pathway to tailoring CO₂RR electrocatalysts and controlling the product selectivity.