Strategies for CO2 electroreduction in cation exchange membrane electrode assembly

Abstract

For a CO2 reduction reaction (CO2RR), cation-exchange membrane (CEM)-based membrane electrode assembly (MEA) electrolyzers are among the most commercially viable systems; however, the acidic environment in these electrolyzers lowers the CO2RR selectivity. Herein, we outline broad methods for enhancing the performance of CEM MEA electrolyzers by providing an alkaline environment for the cathode. An appropriate amount of anion exchange ionomer, high-alkali cation concentration, and thick catalyst layer with carbon increase the pH gradient for neutralization and minimize the neutralization boundary layer, thus turning most of the catalyst layer into an alkaline environment with high CO2RR selectivity. To take advantage of cation effects, local cation concentrations must be controlled to avoid losing energy efficiency due to high membrane resistance of large cations. Furthermore, the operating conditions of the MEA electrolyzer influence cation concentration. Our study provides various insights into facilitating the development of CEM CO2 MEA electrolyzers for practical application.