Methodology for Selecting Anion and Cation Exchange Membranes Based on Salt Transport Properties for Bipolar Membrane...

Bipolar membranes (BPMs) are a unique construction of ion exchange membranes with anion exchange and cation exchange layers in series. Due to the unique transport processes in BPMs, they are becoming an increasingly attractive option for many electrochemical devices, especially in water electrolysis and carbon dioxide reduction. However, because a large number of anion and cation exchange membranes are available, it can be difficult to select the layers for BPM fabrication, particularly when targeting specific properties for use in a device. In this study, a survey of nine anion and nine cation exchange membranes was conducted to assess their steady-state ion transport properties. The primary application of this work is seawater electrolysis; therefore, measurements of salt flux and area resistance in 0.5 mol/L sodium chloride solutions were performed. These measurements displayed a trade-off behavior, with membranes displaying higher area resistance and having a lower salt flux. Conversely, membranes with lower area resistance had a higher salt flux. From these individual membrane results, a methodology was formulated to select component membranes for BPM fabrication, primarily considering their transport characteristics. Three BPMs were fabricated using this methodology. A model was developed to integrate the parameters and ion transport properties measured from individual membranes to predict salt flux and area resistance values for a BPM. Values produced from the model were then compared with experimental salt flux and area resistance BPM measurements. Both the model and experimental salt flux and area resistance BPMs exhibited an area resistance-flux trade-off, like that of the component membranes.