How membrane characteristics influence the performance of CO2 and CO electrolysis

Abstract

Due to the ability to produce sustainably carbon-based chemicals and fuels, CO₂ electrolysis and the closely related CO electrolysis are advancing rapidly from fundamental studies toward industrial applications. Many near-room temperature CO₂ and CO electrolysis (CO₍₂₎E) technologies adopt features from proton exchange membrane fuel cells and H₂ electrolyzers. However, CO₍₂₎E's selectivity and overall performance are highly sensitive to a multitude of parameters, adding an extra degree of complexity. One often-overlooked parameter in optimizing these devices is the ion exchange membranes (IEM). Here we critically review the IEM performance variables of most relevance to CO₍₂₎E, which leads to identifying several parameters in need of substantial more scientific understanding. We begin with a summary of the working principles of the three main IEM types for CO₍₂₎E, then focus on anion exchange membranes (AEM) since AEMs provide the most favorable local alkaline environment for CO₍₂₎E at the cathode. Critical issues for AEMs in CO₂E include (i) ion and water transport in the membrane, (ii) ionic conductivity, and (iii) chemical stability. We conclude with an overview of the state-of-the-art IEM reported in high current density (j ≥ 100 mA cm⁻²) CO₂ and CO electrolysis devices.