Limiting Ethanol Crossover in the Electrochemical Reduction of Carbon Dioxide By Integrating a Dual Membrane Electrolyzer

As the world faces the need to limit global warming significantly by 2050, the transition from fossil fuels to renewable energy is necessary. Carbon dioxide can be converted into renewable energy and carbon products via the electrochemical reduction of CO2. Through the use of a fuel cell and Cu electrocatalysts, multi-carbon products are produced. Sn dopants in the catalyst increase product selectivity to ethanol, which can be used as a fuel. This system's product yield is limited by crossover of ethanol from the cathode to the anode where it is oxidized to acetic acid. In order to limit crossover and increase product yield, a dual layer membrane consisting of an anion exchange membrane and a cation exchange membrane was implemented. An inner layer between the dual membranes was flushed with DI water. This captured ethanol before it crossed over to the anode side and facilitated conductivity across the cell. The system was optimized using 1M KOH (pH 14) through the inner layer, 1M KOH+H₃PO₄ (pH 6) anolyte, Nafion CEM, and Sustainion AEM. Performance was assessed by measuring ethanol concentration and faradaic efficiency at the anode, inner layer, and cathode via nuclear magnetic resonance and gas chromatography. Results demonstrated significant improvements in ethanol production and retention. The cathode and inner layer together produced ethanol at 51.92% Faradaic efficiency (FE), which corresponds to more than 10 wt% ethanol directly from the cathode. Importantly, crossover to the anode was minimal, with less than 1.07% FE detected. This novel approach effectively limited crossover, with the majority of the product being captured at the inner layer, thereby substantially improving the efficiency of CO₂-to-ethanol conversion in this electrochemical system