Tuning the Interfacial Electrical Field of Bipolar Membranes with Temperature and Electrolyte Concentration for Enhanced Water Dissociation

A coupled experimental and numericalstudy was performedfor afundamental understanding of the impact of operating conditions, i.e.,temperature and electrolyte concentration, as well as interfacialabruptness, on the bipolar membrane (BPM) performance. A comprehensivemultiphysics-based model was developed to optimize the operation conditionand interfacial properties of BPM, and the model was used to guidethe design and engineering of high-performing BPMs. The origin ofthe enhanced BPM performance at a high temperature was identified,which was attributed to the intrinsic reaction rate enhancement aswell as the increase in electrolyte ionic conductivity. The experimentallydemonstrated current density-voltage characteristics of BPMsclearly exhibited three distinctive regions of operation: ion-crossoverregion, water dissociation region, and water-limiting region, whichagreed well with the multiphysics simulation results. In addition,the model revealed that a sharper interfacial abruptness led to improvedBPM performance due to the enhanced interfacial electric field atthe water dissociation region. The decrease of the electrolyte concentration,which increased the dielectric constant of the electrolyte, enhancedthe interfacial electric field, leading to improved electrochemicalperformances. The present study offers an in-depth perspective tounderstand the species transport as well as water dissociation mechanismunder various operation conditions and membrane designs, providingthe optimal operation conditions and membrane designs for maximizingthe BPM performance at high current densities. The performance of BPM can be enhancedto save energy byoperating at higher temperatures and with a lower electrolyte concentration.