Ion transport and membrane architecture: from monopolar fundamentals to scalable bipolar membrane design

Abstract

Our growing energy needs and continued dependence on fossil fuels are depleting resources and increasing greenhouse gas emissions. This has created a need for electrochemical energy storage and conversion technologies, which can capture and use renewable energy sources. Ion conducting polymer membranes are key components in these electrochemical devices. Cation exchange membranes (CEMs) offer high conductivity, but rely on expensive catalysts, while anion exchange membranes (AEMs) enable earth-abundant catalysts but suffer from limited stability. Bipolar membranes (BPMs) enable water dissociation reaction and the use of non-noble group catalysts, but their lifetimes are limited by degradation at the interface due to blistering and delamination. This degradation may be due to inadequate adhesion and poor contact between the layers of the BPM, primarily caused by differences in the properties of the materials used. In this work, AEM and CEM materials are functionalized from the same precursor polymers and monopolar membranes are fabricated and characterized to investigate structure-property property relationships. Next, a scalable BPM was fabricated from anion exchange layer and cation exchange layer having the same polymer backbone, resulting in a BPM with good adhesion and superior performance in an electrodialysis cell as compared to commercial BPM. Lastly, asymmetric and catalyst-included BPMs were fabricated and evaluated. These advanced version BPMS showed the effects of asymmetry of the AEL vs CEL thickness and the inclusion of a catalyst layer at the interface.