Reframing Porous Carbon as a Transport Framework for High-Rate CO₂ Electroreduction

Porous carbons are widely used as supports for Cu-based CO₂ reduction electrodes, yet how their pore structures regulate reactant transport within the catalyst layer remains insufficiently understood. Here, carbon blacks with distinct hierarchical textural characteristics are systematically investigated, revealing a consistent association between more developed pore architecture and higher C₂H₄ productivity. Guided by this trend, a hierarchically integrated Cu/C catalyst is designed by forming Cu nanodomains throughout the carbon framework and compared with a benchmark prepared by physically mixing commercial Cu nanoparticles with the same carbon support. The integrated Cu/K6 catalyst achieves a C₂H₄ partial current density of 355 mA cm^{- 2} with a C₂H₄ Faradaic efficiency of 50.7% at a total current density of 700 mA cm^-2. Under these conditions, Cu/K6 exhibits a cathode potential approximately 0.3 V less negative and a 20% higher C₂H₄ partial current density than the physically mixed benchmark. Mixed kinetic-transport analysis indicates that the integrated architecture shifts the apparent transport-limitation threshold to higher current densities. Multiphysics computational fluid dynamics simulations further reveal shorter effective CO₂ diffusion paths and mitigated local CO₂ depletion. These findings establish hierarchical Cu-carbon integration as an effective strategy for alleviating CO₂ transport limitations and enhancing C₂H₄ production.