The layer-by-layer casting technique was adopted to fabricate bipolar membranes (BPMs) comprising a cation-exchange layer (CEL), an interfacial layer (IL, phosphorylated graphene oxide (PGO) and/or quaternized graphene oxide (QGO)), and an anion-exchange layer (AEL). Under applied dc potential gradient, water molecules dissociate at the IL and generate H+ and OH–. The effect of the IL nature (PGO, QGO, and mixed PGO/QGO) on the water splitting performance of the BPM was thoroughly studied. Well optimized BPM-PGO/QGO exhibited high current efficiency (CE) and low energy consumption and was assessed to be superior in comparison with different commercial BPMs. The reported BPM showed improved water splitting performance, significant reduction in resistance, and high permselectivity (low co-ion leakage) for over 10 experimental cycles. Relatively stable performance of BPM-PGO/QGO made it industrially viable for water splitting.

For developing acid-/oxidative-resistant aliphatic-polymer-based cation-exchange membrane (CEM), macromolecular modification of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) was carried out by controlled chemical grafting of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS). To introduce the unsaturation suitable for chemical grafting, dehydrofluorination of commercially available PVDF-co-HFP was achieved under alkaline medium. Sulfonated copolymer (SCP) was prepared by the free radical copolymerization of dehydofluorinated PVDF-co-HFP (DHPVDF-co-HFP) and AMPS in the presence of free radical initiator. Prepared SCP-based CEMs were analyzed for their morphological characteristics, ion-exchange capacity (IEC), water uptake, conductivity, and stabilities (mechanical, chemical, and thermal) in comparison with state-of-art Nafion117 membrane. High bound water content avoids the membrane dehydration, and most optimal (SCP-1.33) membrane exhibited about ∼2.5-fold high bound water content in comparison with that of Nafion117 membrane. Bunsen reaction of iodine-sulfur (I-S) was successfully performed by direct-contact-mode membrane electrolysis in a two-compartment electrolytic cell using different SCP membranes. High current efficiency (83-99%) confirmed absence of any side reaction and 328.05 kJ mol-H2(-1) energy was required for to produce 1 mol of H2 by electrolytic cell with SCP-1.33 membrane. In spite of low conductivity for reported SCP membrane in comparison with that of Nafion117 membrane, SCP-1.33 membrane was assessed as suitable candidate for electrolysis because of its low-cost nature and excellent stabilities in highly acidic environment may be due to partial fluorinated segments in the membrane structure.