Bipolar ethylene electrosynthesis from CO₂ and biowaste acid with total faradaic efficiency over 118

Ethylene (C₂H₄), a cornerstone of the chemical industry, is produced predominantly via fossil-intensive high-temperature processes that contribute significantly to global energy consumption and CO₂ emissions. Here, we report an ambient bipolar C₂H₄ electrosynthesis system that concurrently decarboxylates propanoic acid, a prevalent biorefinery waste, at nanoporous Pt microparticles-coated anode and reduces CO₂ at W-doped CuO_x-loaded cathode. Physicochemical and operando spectroscopy characterizations, along with theoretical modeling reveal that the polarized Pt-PtO₂ interface formed in situ downshifts the d-band relative to Fermi level which favors the desorption of *CH₂CH₂ intermediate to promote selective propanoic acid decarboxylation toward C₂H₄. Remarkably, the resulting electrocatalyst couple delivers an unprecedented C₂H₄ faradaic efficiency (FE_C2H4) of 118.7% and a large current density of 1000 mA cm^-2, and sustains a FE_C2H4 exceeding 103.4% for over 265 h at an industrial current density of 400 mA cm^-2, offering a promising pathway to carbon-neutral C₂H₄ production from waste feedstocks.