Separation of Polymeric Charge Enables Efficient Bipolar Membrane Operation

Efficient charge separation at the membrane-membrane junction is key to the operation of bipolar membranes (BPMs). Beyond co-ion crossover, there is a lack of understanding of the fundamental processes that control charge separation in BPMs. Herein, we employ polyelectrolytes to investigate the factors controlling charge separation in a cell devoid of co-ion crossover. We find that mobile polymeric charges at the bipolar interface can undergo charge-pairing and quenching in a process that we term bipolar pairing. This phenomenon attenuates membrane voltages and inhibits reverse bias water dissociation kinetics, leading to large overpotential penalties exceeding 7.5 V in some cases. However, we find that a sequential approach to constructing the catalyst and ionomeric binder layers of a BPM can more effectively minimize bipolar pairing than codepositing the two as a single mixed layer. These studies expose a hitherto unknown mechanism of efficiency loss in BPMs with implications for the design of high-efficiency bipolar interfaces.