Monitoring Carbonate and Bicarbonate within an Anion Exchange Membrane during Self-Purge Using Infrared Spectroelectrochemistry

The carbonation of anion exchange membranes (AEMs) upon exposure to atmospheric CO 2 can have a significant impact on their performance in electrochemical energy technologies since the replacement of OH – anion charge carriers with less mobile HCO 3 – and CO 3 2– results in a loss of ionic conductivity. In the case of AEM fuel cells (AEMFCs) and water electrolyzers (AEMWEs) this is at least in part mitigated against by the self-purge mechanism, in which electrochemical processes taking place during operation replenish the lost OH – at the cathode. While the self-purge process is reasonably well understood, it is not clear what the speciation of HCO 3 – and CO 3 2– is within the AEM phase and how this is correlated to membrane ionic conductivity. In this work, we developed a spectroelectrochemical method based on attenuated total reflection infrared (ATR-IR) spectroscopy enabling estimation of the relative concentration of HCO 3 – and CO 3 2– anions within an AEM during self-purge alongside periodic measurement of in-plane ionic conductivity. We show that for the AEM PiperION (HCO 3 – form), the self-purging behavior is qualitatively similar to that observed during chemical anion exchange with 1 M KOH, in which HCO 3 – anions are rapidly converted to CO 3 2– followed by the much slower displacement of CO 3 2– by OH – . The in-plane membrane conductivity is shown to correlate well with the relative CO 3 2– concentration under both transient and equilibrated conditions. The method presented offers insights into the behavior of AEMs in the context of anion exchange and self-purging, thus offering a route to a more complete understanding of AEM performance.