Understanding Electrochemical and Mechanical Durability of Bipolar Membranes Used in Electrodialysis

Using renewable energy to drive direct carbon capture systems is a powerful way to contribute to net negative emissions. When using liquid alkaline sorbents for CO 2 direct air capture, it is critical to reduce the energy demand for CO 2 concentration and sorbent regeneration. Electrodialysis is an ideal candidate technology to integrate renewable energy into this process, however, to enable this ion-exchange membrane separators that can operate at high ion flux and low voltage are needed. Bipolar membranes (BPMs), that generate protons and hydroxide ions from the dissociation of water when operated in reverse bias, are the enabling component to generate acid and base in electrodialysis systems. Bipolar membrane electrodialysis (BPMED) uses a BPM to create acidifying and basifying chambers which are well suited to concentrate and release CO 2 and concentrate the remaining alkaline effluent to cycle back to the capture process. Current BPM durability, however, sufferers at high current density (ion flux) and physical scale. BPMs have several known degradation mechanisms including chemical breakdown of ion exchange polymers, loss of junction adhesion, or physical breakdown due to shearing force and pressure swings in an electrodialysis cell. To assess the electrochemical and mechanical durability of BPMs under operational conditions, we investigated how fabrication conditions (including preconditioning, hot pressing, and catalyst loading) impact the adhesion of custom made BPMs. T-peel studies were performed ex-situ to quantify adhesive forces of BPMs made of different compositions and prepared under different conditions, and BPMED experiments were performed to assess the electrochemical performance of the corresponding BPMs. The BPMED results show that, while adhesion is necessary to physically maintain the BPM junction, mechanical adhesion alone cannot overcome poor ion and water transport management at the water dissociation junction. The results of this systematic comparison indicate that in order for BPMs to operate at high current densities, high adhesion forces made during fabrication of BPMs will need to be balanced with water dissociation kinetics and ion/water transport through the individual membrane layers.