CO electrolysers with 51% energy efficiency towards C2+ using porous separators

Electrochemical CO2 reduction can generate multi-carbon (C2+) products via a CO2-to-CO cascade followed by CO reduction (COR). However, COR energy efficiency remains below 40% due to sluggish ion transport within charge-selective membranes. Here we introduce an uncharged porous separator that enables facile transport of both ion types, reducing ohmic resistance and superconcentrating cations at the catalyst surface—lowering COR voltage by 150 mV at 200 mA cm−2. In previous electrolyser designs, porous separators were limited by cathode-to-anode H2 crossover; the low diffusivity of C2H4 and CO in water allows a separator three times thinner and 1.6 times more porous, markedly reducing overpotential. Operating at elevated temperatures with a nickel–iron-based anode further lowers voltage by 330 mV, leading to a full-cell voltage of 1.95 V at 200 mA cm−2 and an energy efficiency of 51% to C2+ products sustained over 250 h. The system also achieves a CO single-pass conversion of 97% and a C2H4 concentration of 87 wt% in the product gas stream. Electrochemical COx reduction to multi-carbon products is hindered by low energy efficiency, in part due to sluggish ion transport across charge-selective membranes used in electrolysers. Here the authors use a porous, non-charge-selective separator that enhances ion transport and improves performance for CO electrolysis.