Synergistic Coupling between Nanoconfinement and Grain Boundary Improves Electrocatalytic CO₂ Reduction to n-Propanol

Cu-based nanomaterials are recognized as the most promising catalysts for electrocatalytic CO₂ reduction to produce valuable multicarbon products (C₂₊). However, the low localized concentration of *C₁ and *C₂ intermediates and poor availability of active sites limit the CO₂ conversion efficiency and selectivity for C₂₊. Herein, a three-dimensional interconnected self-supporting Cu nanowire array with rich grain boundaries (GB-ICCu) is designed to obtain high production of C₂₊, especially n-propanol (n-PrOH), due to the synergistic coupling between the nanoconfinement effect and the grain boundary. The finite element simulations and experimental results reveal that the three-dimensional interconnected structure between Cu nanowires, like a nanoscaffolding, induces a pronounced nanoconfinement of *C₁ and *C₂ intermediates and consequently enhances the selectivity toward n-PrOH. Meanwhile, the rich grain boundaries of the (111) and (200) on the surface of each Cu nanowire also strengthen CO₂ activation and intermediate adsorption, thereby reducing the energy barrier for C-C coupling. As a result, a high Faradaic efficiency of 17.47% and a partial current density of 10.44 mA cm^-2 for n-PrOH are achieved in the H-type cell, while 12.05% and 77.7 mA cm^-2 are achieved in the flow cell, respectively, which present an advance in partial current density of n-PrOH, i.e., the yield rate of n-PrOH. This work provides a strategy and a Cu-based electrocatalyst for C₃ synthesis via CO₂ reduction.