Enhancing C₂₊ product selectivity in CO₂ electroreduction by enriching intermediates over carbon-based nanoreactors

Electrochemical CO₂ reduction reaction (CO₂RR) to multicarbon (C₂₊) products faces challenges of unsatisfactory selectivity and stability. Guided by finite element method (FEM) simulation, a nanoreactor with cavity structure can facilitate C-C coupling by enriching *CO intermediates, thus enhancing the selectivity of C₂₊ products. We designed a stable carbon-based nanoreactor with cavity structure and Cu active sites. The unique geometric structure endows the carbon-based nanoreactor with a remarkable C₂₊ product faradaic efficiency (80.5%) and C₂₊-to-C₁ selectivity (8.1) during the CO₂ electroreduction. Furthermore, it shows that the carbon shell could efficiently stabilize and highly disperse the Cu active sites for above 20 hours of testing. A remarkable C₂₊ partial current density of-323 mA cm^-2 was also achieved in a flow cell device. In situ Raman spectra and density functional theory (DFT) calculation studies validated that the *CO_atop intermediates are concentrated in the nanoreactor, which reduces the free energy of C-C coupling. This work unveiled a simple catalyst design strategy that would be applied to improve C₂₊ product selectivity and stability by rationalizing the geometric structures and components of catalysts.