Harnessing high faradaic efficiency for n-butanol over Cu-cubic nanocrystals: New insights into CO₂reduction via GC-DFT and operando Raman spectroscopy

n-Butanol is a valuable chemical commodity with a market price of approximately $1300/ton. It is usually made from propylene and syngas via the oxo process, but its reliance on fossil fuels is unsustainable. However, its direct electrochemical production from CO₂ in a single step remains a significant challenge due to high energy requirements and the need for specialized catalysts. In this study, we report a facile single-step electrochemical CO₂ conversion into n-butanol with high faradaic efficiency, bypassing the need for a cascade system. C-C coupling via dimerization into C₄ products (n-butanol) was facilitated on the size dependent Cu-cubic morphology (average 30 nm), having dominate crystal facet orientation {100}. The process achieved a Faradaic efficiency of 21 % for n-butanol and 54.4 % for ethylene at a current density of 750 mA cm⁻², demonstrating stability of over 25 h of operation. Mechanistic insights were gained through Grand Canonical Density Functional Theory (GC-DFT) calculations, which revealed the favored energetics for the C–C coupling pathway on Cu-cubic {100} rather than C₁ products desorption. Furthermore, operando Raman spectroscopy tracked the CH₂CHO* intermediate, which is important for the C-C coupling. This scalable flow cell system could offer a promising and sustainable route for industrial n-butanol production from CO₂.