In the course of achieving industrially relevant energy efficiencies and current densities, different kinds of CO₂ electrolyzers were auditioned. These electrolyzers utilize gas-diffusion electrodes (GDEs) where a gaseous CO₂ is directly fed to catalysts. One promising architecture among these designs is a membrane electrode assembly (MEA) in which a cathode GDE is pressed to an ion-exchange membrane (IEM) in the absence of a catholyte. For the engineering of such devices, it is required to employ active, selective, and stable electroctalysts as well as highly ion-conducting and chemically stable solid polymer electrolytes. These ion-exchange polymers (or ionomers) can serve both as membranes and binders for GDEs.
An ionomer is a polymer where a small proportion of the constitutional units have ionic (or ionizable) groups. Ionomers can be used to constitute (a) ion-exchange membranes and (b) binders added to a catalyst layer in a zero-gap reactor for electrochemical CO₂ reduction or fuel-cell systems. Representative examples include a Sustainion® membrane and ionomers developed by Dioxide Materials. It is important for ionomers to conduct specific ions selectively at high rates for these applications. The transport of ions is enabled by water-filled hydrated ionic domains present in the polymer matrix. We design and synthesize anion-exchange ionomers for anion-exchange membranes (AEMs) and catalyst binders that will show desired properties.