Elaboration and characterisation of ion-exchange films used in the fabrication of bipolar membranes

Bipolar membranes (BMs) were elaborated by assembling two ion-exchange membranes (IEMs) of opposite polarities. The two IEMs were prepared by using the semi-interpenetrating polymer networks (s-IPN) technique. Poly(vinyl alcohol) (PVA) was chosen as the polymer matrix. Commercial poly(sodium styrenesulfonate) (PSSNa) was used as anionic polyelectrolyte (Pe) and synthesised poly(N-ethyl-4-vinylpyridinium bromide) (PEVPBr) as cationic Pe. Both IEMs were obtained by mixing PVA and Pe solutions, followed by solvent evaporation and crosslinking with gaseous 1,2-dibromoethane. Ion-diffusion experiments, membrane conductivity measurements and ion-transport numbers calculations were performed on the two IEMs to highlight their ion-exchange properties. The BMs were elaborated by pressing together a wet PVA/PEVPBr membrane on a wet PVA/PSSNa membrane using a PVA/PSSH (acidic form of PSSNa) solution as glue and by crosslinking the junction by heat treatment. Current–voltage (I–V) experiments were performed on the BMs. Bipolar behaviour was observed only when a water dissociation catalyst was introduced in the BM, the best result was obtained with chromium(III) cations as catalysts in the cation-exchange layer.