Porous Cu/C nanofibers promote electrochemical CO₂-to-ethylene conversion via high CO₂ availability

In the CO₂ reduction reaction (CO₂RR), efficient CO₂ mass transport is important to facilitate CO₂-to-ethylene (C₂H₄) conversion which requires *CO dimerization. Here, we report carbon (C) shell-augmented Cu-embedded porous C nanofibers (CNFs) to elucidate the effects of mesoporous C on CO₂-to-C₂H₄ conversion. The mesoporous C structures were controlled by harnessing blended polymers (PAN + PMMA) which have distinct thermal decomposition behaviors and by inducing selective C oxidation during calcination. Furthermore, we found that selective C oxidation can induce the C precipitation from the CO (g) and CO₂ (g) by the Boudouard reaction. This enabled the formation of C shells on the surface of Cu active sites. C shell-augmented Cu/CNFs having the highest surface area of mesopores enhanced the CO₂ mass transport and CO₂ adsorption for high CO₂ availability. Porous Cu/CNFs, fabricated by the calcination of electrospun Cu-precursor + blended polymer nanofibers (NFs) with the 60% PMMA ratio and selective C oxidation, induced an efficient C₂H₄ faradaic efficiency (FE) of 39.5% at −1.27 V (vs. RHE), 1.7-fold improvement from the C₂H₄ FE of 23.2% at −1.25 V (vs. RHE) in Cu/CNFs, fabricated by full reduction without PMMA (the lowest surface area of mesopores). Investigating the CO₂RR under CO₂ deficient conditions and analyzing the in situ Raman spectra reveal that enhanced CO₂ mass transport and CO₂ adsorption can facilitate CO₂ availability with high *CO coverage for efficient C₂H₄ production.