Bipolar membranes: A review on principles, latest developments, and applications

Electrochemical carbon dioxide capture to close the carbon cycle

“…However, in addition to the extra energy needed for heating up the electrolytes, the thermal stability of the ion exchange membranes poses a limitation on high temperature processes. For instance, the commercial bipolar membranes are cannot withstand temperatures higher than 40-60°C for a long duration [99]. Moreover, CO 2 solubility decrease at higher temperatures (up to 100°C) [100][101][102].…”

The Acid–Base Flow Battery: Sustainable Energy Storage via Reversible Water Dissociation with Bipolar Membranes

“…Oppositely, when H + and OH − ions are recombined at the junction (battery discharging mode, i.e., forward bias in BPM literature), the formed water must be able to diffuse out of the junction fast enough to avoid water accumulation at the junction and the consequent delamination of the bipolar membrane layers. Unlike all other bipolar membrane assisted processes [ 23 ], the acid–base flow battery uses the BPMs under both reverse bias (i.e., water dissociation) and forward bias (water recombination). Current commercial membranes are designed only for dissociating water, while operating BPMs under water recombination (which occurs during the discharging process in the ABFB), has been so far overlooked by membrane scientists and manufacturers.…”

“…However, uncontrolled mixing of such concentrated acid and base can be explosive, which raises new safety concerns when operating the battery. Furthermore, reaching such high acid–base concentrations in the battery is unpractical today, as for current commercial bipolar membranes 1 M acid–base concentration (theoretical energy density of ~25 kWh/m 3 ) is the maximum practical value without sacrificing permselectivity [ 23 ]. Likewise, commercial monopolar membranes would suffer from severe co-ion leakage at such high concentrations.…”

“…The design of an acid–base flow battery resembles the typical design of a 3-compartment BMED stack [ 23 ], where a series of CEM, BPM, and AEM is used to create the repeating unit, or “triplet” ( Figure 2 ). Each membrane is separated from its adjacent membranes with net spacers to create the compartments for salt, acid, and base solutions, and promote mixing.…”

“…In contrast to CEM or AEM that allow selective ion transport, the BPM (ideally) allows no transport of ions across it. Instead, the BPM is used to produce ions by dissociating water at the junction of its two layers [ 22 , 23 ]. Notably, unlike conventional water splitting occurring on electrode surfaces that produces gas (H 2 and O 2 ), the BPM-assisted water dissociation only generates ions (H + and OH − ), and occurs at a lower voltage (i.e., 0.83 V across a BPM separating 1 M HCl and 1 M NaOH instead of 1.23 V needed for water splitting in conventional electrolysis).…”