Hierarchical Cavity Cu Nanostructures with Coordinative Microenvironment Engineering for pH‐Universal Electrocatalytic CO₂‐to‐C₂₊ Conversion

Abstract The rational design of copper‐based electrocatalysts with optimized *CO intermediate coverage and OH⁻‐enriched microenvironments remain critical yet challenging for achieving efficient CO₂‐to‐C₂₊ conversion across varied pH conditions. This study presents a Kirkendall effect‐driven synthesis of hierarchical copper nanostructures featuring precisely engineered cavity architectures and tunable coordination environments. Through systematic coordination number (CN) modulation, it is demonstrated that the d‐band center position of Cu sites is positively correlated with *CO adsorption energy. Specifically, the moderate‐coordinated Cu (111) facets in three‐layered cavity structures (3L‐Cu) exhibit optimal *CO dimerization energetics. Benefiting from the synergistic effects of spatial confinement and ionic diffusion gradients, the 3L‐Cu catalyst establishes self‐sustaining alkaline microdomains even in acidic media (pH 1), as evidenced by in situ Raman spectroscopy. This unique microenvironment engineering enables state‐of‐the‐art C₂₊ Faradaic efficiencies of 78.74 ± 2.36% (alkaline), 69.33 ± 2.08% (neutral), and 58.32 ± 1.75% (acidic) with sustained stability, outperforming existing pH‐universal CO₂RR catalysts. First‐principles calculations further reveal that the multilayer confinement effect of 3L‐Cu reduces the coupling energy barriers of *CO‐*CO and *CO‐*COH in alkaline and acidic electrolytes, respectively. This work establishes a new paradigm for designing adaptive electrocatalysts through coordinated structural and electronic microenvironment control.