A coupled experimental and numerical
study was performed
for a
fundamental understanding of the impact of operating conditions, i.e.,
temperature and electrolyte concentration, as well as interfacial
abruptness, on the bipolar membrane (BPM) performance. A comprehensive
multiphysics-based model was developed to optimize the operation condition
and interfacial properties of BPM, and the model was used to guide
the design and engineering of high-performing BPMs. The origin of
the enhanced BPM performance at a high temperature was identified,
which was attributed to the intrinsic reaction rate enhancement as
well as the increase in electrolyte ionic conductivity. The experimentally
demonstrated current density–voltage characteristics of BPMs
clearly exhibited three distinctive regions of operation: ion-crossover
region, water dissociation region, and water-limiting region, which
agreed well with the multiphysics simulation results. In addition,
the model revealed that a sharper interfacial abruptness led to improved
BPM performance due to the enhanced interfacial electric field at
the water dissociation region. The decrease of the electrolyte concentration,
which increased the dielectric constant of the electrolyte, enhanced
the interfacial electric field, leading to improved electrochemical
performances. The present study offers an in-depth perspective to
understand the species transport as well as water dissociation mechanism
under various operation conditions and membrane designs, providing
the optimal operation conditions and membrane designs for maximizing
the BPM performance at high current densities.