Bipolar membranes (BPMs), a special class of ion exchange
membranes
with the unique ability to electrochemically induce either water dissociation
or recombination, are of growing interest for environmental applications
including eliminating chemical dosage for pH adjustment, resource
recovery, valorization of brines, and carbon capture. However, ion
transport within BPMs, and particularly at its junction, has remained
poorly understood. This work aims to theoretically and experimentally
investigate ion transport in BPMs under both reverse and forward bias
operation modes, taking into account the production or recombination
of H+and OH–, as well as the transport
of salt ions (e.g., Na+, Cl–) inside
the membrane. We adopt a model based on the Nernst–Planck theory,
that requires only three input parameters—membrane thickness,
its charge density, and pKof proton adsorption—to
predict the concentration profiles of four ions (H+, OH–, Na+, and Cl–) inside
the membrane and the resulting current–voltage curve. The model
can predict most of the experimental results measured with a commercial
BPM, including the observation of limiting and overlimiting currents,
which emerge due to particular concentration profiles that develop
inside the BPM. This work provides new insights into the physical
phenomena in BPMs and helps identify optimal operating conditions
for future environmental applications.