Using Layer-by-layer\nAssembled Clay Composite Junctions\nto Enhance the Water Dissociation in Bipolar Membranes

Bipolar membranes (BPMs) with a layer-by-layer (LbL)\nassembled\nmontmorillonite (K30 MMT) clay-polyelectrolyte (PE) composite junction\ncoated onto a sulfonated poly(ether ether ketone (SPEEK)) electrospun\nsupport are prepared, characterized and their water dissociation performance\nis analyzed. In particular, the focus is on the effect of the presence\nof the K30 MMT clay as a catalyst for water dissociation, the bilayer\nnumber (three, six, and nine), and the PE strength (poly(ethylenimine)\n(PEI) as a weak PE and poly(diallyl dimethylammonium chloride) (PDADMAC)\nas a strong PE) on the BPM performance. The BPMs are prepared by electrospinning\nand hot pressing SPEEK and the Fumion FAA-3 polymer. Adding the composite\nmultilayers in the BPM junction decreases the membrane area resistance\nin reverse bias from 560 to 21 Ohms cm<sup>2</sup> for the best-performing\nmodified BPM. The bilayer number has limited influence on the overall\nmembrane resistance, while the PDADMAC BPMs outperform the PEI BPMs\ndue to the higher and more stable PE and clay adsorptions. Electrochemical\nimpedance spectroscopy shows that the depletion layer thickness decreases\nexponentially with the number of bilayers as the water dissociation\nreaction becomes less dependent on the junction electric field. Furthermore,\nthe higher Donnan exclusion at the modified junctions improves the\nBPM permselectivity 3-fold compared to the BPM containing no catalyst.\nAltogether, these improvements lead to 6.7 times less energy being\nused in BPM electrodialysis for the production of acid and base when\na BPM with composite LBL junction is used compared to a BPM without\ncatalyst. Thus, adding MMT clay composite LbL catalyst to BPM junctions\nis a promising method to improve the efficiency and reduce the energy\nconsumption of electrochemical processes that rely on BPMs.