Carbon dioxide electroreduction (CO2R) is being actively studied as a promising route to convert carbon emissions to valuable chemicals and fuels. However, the fraction of input CO2 that is productively reduced has typically been very low, <2% for multicarbon products; the balance reacts with hydroxide to form carbonate in both alkaline and neutral reactors. Acidic electrolytes would overcome this limitation, but hydrogen evolution has hitherto dominated under those conditions. We report that concentrating potassium cations in the vicinity of electrochemically active sites accelerates CO2 activation to enable efficient CO2R in acid. We achieve CO2R on copper at pH <1 with a single-pass CO2 utilization of 77%, including a conversion efficiency of 50% toward multicarbon products (ethylene, ethanol, and 1-propanol) at a current density of 1.2 amperes per square centimeter and a full-cell voltage of 4.2 volts.

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CO 2 reduction is a promising strategy to synthesize valuable multi-carbon products (C 2+ ) while sequestering CO 2 and utilizing intermittent renewable electricity. Here, we present a stable membrane electrode assembly (MEA) electrolyzer that converts CO 2 to C 2+ products. This strategy achieves $50% and $80% selectivity for ethylene and C 2+ products, respectively, with cathode outlet concentrations of $30% ethylene and the direct production of $4 wt % ethanol. We characterize stability by operating continuously for 100 h with steady ethylene production.

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The carbon dioxide reduction reaction (CO 2 RR) presents the opportunity to consume CO 2 and produce desirable products. However, the alkaline conditions required for productive CO 2 RR result in the bulk of input CO 2 being lost to bicarbonate and carbonate. This loss imposes a 25% limit on the conversion of CO 2 to multicarbon (C 2+ ) products for systems that use anions as the charge carrierand overcoming this limit is a challenge of singular importance to the field. Here, we find that cation exchange membranes (CEMs) do not provide the required locally alkaline conditions, and bipolar membranes (BPMs) are unstable, delaminating at the membrane−membrane interface. We develop a permeable CO 2 regeneration layer (PCRL) that provides an alkaline environment at the CO 2 RR catalyst surface and enables local CO 2 regeneration. With the PCRL strategy, CO 2 crossover is limited to 15% of the amount of CO 2 converted into products, in all cases. Low crossover and low flow rate combine to enable a single pass CO 2 conversion of 85% (at 100 mA/cm 2 ), with a C 2+ faradaic efficiency and full cell voltage comparable to the anion-conducting membrane electrode assembly.

The electrochemical conversion of CO 2 produces valuable chemicals and fuels. However, operating at high reaction rates produces locally alkaline conditions that convert reactant CO 2 into cell-damaging carbonate salts. These salts precipitate in the porous cathode structure, block CO 2 transport, reduce reaction efficiency, and render CO 2 electrolysis inherently unstable. We propose a self-cleaning CO 2 reduction strategy with short, periodic reductions in applied voltage, which avoids saturation and prevents carbonate salt formation. We demonstrate this approach in a membrane electrode assembly (MEA) with silver and copper catalysts, on carbon and polytetrafluoroethylene (PTFE)-based gas diffusion electrodes, respectively. When operated continuously, the C 2 selectivity of the copper−PTFE system started to decline rapidly after only ∼10 h. With the self-cleaning strategy, the same electrode operated for 157 h (236 h total duration), maintaining 80% C 2 product selectivity and 138 mA cm −2 of C 2 partial current density, at a cost of <1% additional energy input.

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