An overview of the development of polymer electrolyte membranes for brine electrolysis applications

The state- of- the- art of membrane technology is characterized by a number of mature applications like PEM fuel cells, electrolyzers, electrodialysis and etc. Amongst them, brine electrolysis technology is considered as an intensive energy consumption (۰.۶% of global power) [۱,۸]. This is further underlined that membrane electrolysis is favored as an efficient energy consumption technology in comparison with mercury and diaphragm ones [۷]. It is apparent that, cation exchange membranes (CEMs) is regarded as a prominent component in such systems which are currently composed of established materials including polymeric or inorganic material and feasibly can be scalable manufacturing procedures like interfacial polymerization, casting and coating. Furthermore, some efficient polymers for tremendous potential in various sub-disciplines of electrochemistry and polymer engineering. The present overview explicitly provides the specifications of brine electrolysis membranes that conduct sodium cations with respect to prevention back migration of hydroxide anions, namely chlor- alkali cation exchange membrane.One of the critical considerations for CEMs is their long-term stability to alkaline and oxidative media, and as such, a wide range of polymer backbones and appended cations have been evaluated as potential constructs for this purpose. The progresses provide opportunities for development of membrane materials with advanced functionalities and superior characteristics that can effectively be employed for synthesis of high performance membranes. To date, the most advanced membrane used in brine electrolysis is the perfluorinated ion exchange membranes (PIEMs) which contains a sodium perfluorosulfonic acid layer and a perfluorocarboxylic acid layer that reinforced by a polytetrafluoroethylene (PTFE) fabrics [۲,۷]. Although the perfluorosulfonic acid type of polymers such as Flemion, have attracted enormous attention from the polymer electrolysis membrane cells, the drawbacks of this PFSA-based polymers, such as high cost in production. The fluoropolymers are highly aerophilic in liquid electrolytes [۱,۴]. As a result, gas products are easily absorbed on the membrane surface, which blocks the contact between the electrolyte and membrane, thus underwater bubble wettability is a major focus on the electrode materials and separators [۳]. The modified aromatic-hydrocarbon based CEMs can meet and even surpass the durability targets for electrolysis applications that are suitable such as sulfonated poly (ether ether ketone) (SPEEK), sulfonated poly(styrene) (SPS), and sulfonated poly(benzimidazole). Styrene- based polymers has been known as one of the promising candidates for this application since it has high thermo-oxidative stability and extraordinary mechanical properties as well as high cost effectiveness[۶]. The most mitigation strategy is to synthesize a double- layer membrane that incorporated in hydrocarbon- based membranes. This double- layer membrane can be synthesized via two prominent functional groups containing sulfonated and carboxylated groups. Table۱ represent some of research works related to CEMs.The results demonstrated the role of constructing a hydrophilic interface layer with efficient iontransport on the surface of the PIEM is a simple and effective method to solve the gas productadhesion issue in chlor- alkali applications. Also, as it can be seen, there are few researches basedon non- fluorinated- based membranes in this application and it can be addressing the urgent needsin developing new IEM and research in brine electrolysis applications.

Keywords:

Cation exchange membrane electrolysis , Brine electrolysis , Stability