Model-based insights into the decarbonation dynamics of anion-exchange membranes

Abstract

We present a model-based analysis of the transport of anions in anion exchange membranes (AEMs) with the aim of understanding the decarbonation process and its dynamics. The dynamic simulation model covers the diffusive and migrative transport of water, carbonate anions, and hydroxide anions through an AEM. To the best of our knowledge, this is the first model studying decarbonation process in AEMs. The model is validated using decarbonation data from anion conductivity measurements of ten different AEM materials. Driven by migrative transport, strong concentration gradients develop inside the membranes. A parameter study reveals that the ion-exchange capacity and the applied current have the largest effect on the decarbonation dynamics. Further, high hydroxide diffusivities increase the decarbonation time constant, whereas high carbonate diffusivities decrease it. The results further indicate that high diffusivities of both carbonates and hydroxide result in slower membrane decarbonation. This work provides new insights into properties determining the carbonation and decarbonation of AEMs, which is critical for AEM-based electrochemical devices such as fuel cells and electrolysers.