Carbon Nanotube CO Reservoir Enables Efficient Tandem CO2 Electroreduction to Multicarbon Products with >1 A cm–2 Partial Current Density

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 (FEC2+) of 87.1 ± 2.7% and, notably, an optimal C2+ partial current density (jC2+) 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.