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

Abstract

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 <math xmlns="http://www.w3.org/1998/Math/MathML"><mo>(</mo><msub><mrow><mi>FE</mi></mrow><mrow><msub><mrow><mi>C</mi></mrow><mrow><mrow><mn>2</mn></mrow><mo>+</mo></mrow></msub></mrow></msub></math>) of 87.1 ± 2.7% and, notably, an optimal C₂₊ partial current density <math xmlns="http://www.w3.org/1998/Math/MathML"><mo>(</mo><msub><mi>j</mi><msub><mi>C</mi><mrow><mn>2</mn><mo>+</mo></mrow></msub></msub><mo>)</mo></math> 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.