Creating Bipolar Junction by Depositing Ultrathin Anion-Exchange Coating on CationExchange Membrane to Dissociate Water in Electrodialysis

Document Type : VSI: Membr. for Develop.&Sustain.

Authors

1 Department of Chemistry, Lahore Garrison University, DHA Phase VI, Lahore, Pakistan.

2 School of Natural Sciences, National University of Science & Technology, H-12, Islamabad, Pakistan.

Abstract

Ultrathin anion-exchange films have been created by employing layer-by-layer (LBL) deposition method. The LBL  deposited protonated poly(allylamine) (PAH)/poly(4-styrenesulfonate) (PSS) polyelectrolyte multilayers (PEMs) behave as  anionexchange films when PAH and PSS polyelectrolyte solutions are prepared in NaSCN as a supporting electrolyte (SE). Reflectance FTIR studies indicate that when PAH is prepared in 0.5 M NaSCN and PSS is prepared in 1 M NaSCN, the thickness of the film and the number of anion-exchange sites in the film are manifold greater than those in the film  fabricated from PAH and PSS polyelectrolytes when either of them is prepared in 0.5 M NaSCN. Transmembrane potential measurements were performed to measure the permselectivity of thus fabricated PEMs. These measurements indicate  that the fabricated films demonstrate high anion-exchange properties at neutral pH. However, the ion-exchange  character of the films switches from anions- to cations-exchange when pH of the surrounding solutions changes from 7  to 8.4. Diffusion dialysis results through the coated alumina membranes confirm such a change in the net charge of the  films with a change in the pH. Current density-voltage curve studies indicate plenty of formation of H+ and OHions  through water dissociation occurring at the interfacial bipolar junction created by depositing these anion-exchange  coatings on Nafion cation-exchange membrane (CEM). Donnan dialysis studies also indicate the formation of bipolar  junction through deposition of such films on cationexchange membranes. 

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