Carbon Nanotube CO Reservoir Enables Efficient Tandem CO₂ Electroreduction to Multicarbon Products with >1 A cm^-2...

The tandem strategy for electrochemical CO₂ reduction (ECO₂R), which utilizes CO gas as the essential intermediate, offers a promising route for converting CO₂ into multicarbon (C₂₊) products. However, inefficient retention and utilization of the CO intermediate remain fundamental issues limiting the practical viability of these tandem systems. Here, we introduce a proof-of-concept "CO reservoir" strategy to directly address this bottleneck. With a well-defined bilayer tandem ECO₂R system, we show that incorporating N-doped carbon nanotube (NCNT) as a CO reservoir into the downstream Cu catalyst layer simultaneously enhances the retention time, local concentration, and utilization efficiency of the CO intermediate, a discovery validated by COMSOL simulations, potential-step chronoamperometry, theoretical calculations, and in situ Raman spectroscopy. Enabled by this reservoir effect, the tandem electrocatalyst demonstrates exceptional CO₂-to-C₂₊ performance, achieving a peak C₂₊ Faradaic efficiency $({\mathrm{FE}}_{C_{2+}}$) of 87.1 ± 2.7% and, notably, an optimal C₂₊ partial current density $\left(j_{C_{2+}}\right)$ exceeding 1 A cm^-2. The CO reservoir strategy constitutes a promising approach for effective intermediate management in tandem ECO₂R systems, establishing a viable tandem route toward industrial-level C₂₊ production from CO₂.