(Invited) Molecular Insights into Water Structure and Proton Transfer at the Interfaces in Bipolar AEM/PEM Membranes

Bipolar membranes (BPMs) are polymeric membranes composed of an acidic proton exchange membrane (PEM) and an alkaline anion exchange membrane (AEM). Bipolar membranes are operated in two different configurations, forward bias and reverse bias, based on the orientation of membranes and electrodes, when the cathode faces the PEM, it is operated in a reverse bias configuration. In reverse bias BPMs facilitates the dissociation of water at the interface of its junction. This unique feature makes it attractive to many industrial applications, including chemical industries, energy conversion and storage, environmental protection, and food processing. It was determined that the rate of water dissociation at the interface of a bipolar membrane increases with the addition of a weak acidic head group material, which acts as the catalyst for the water dissociation reaction and thus referred as the catalyst layer. BPMs have a better ion transport framework because of the amphiphilic nature of all three layers, resulting in well-connected water channels. Hence it is crucial to understand the interaction of water molecules with the functional groups at the molecular level and the morphology at mesoscale to understand the water aggregation and phase separation which helps in the asymmetric transport of proton and hydroxide ions through PEM and AEM respectively. This talk will communicate our efforts to undertake a multiscale approach involving both electronic structure calculations and mesoscale simulations to elucidate: (1) water interaction of water with the headgroups; proton transfer, and (2) connectivity of a TMA AEM, a PFSA PEM, and a phosphonic acid-based catalyst.