Sulfonated poly (vinylidene fluoride‐co‐hexafluoropropylene) nanocomposite membranes with high selectivity, stability, and vanadium‐ion barrier for vanadium redox flow batteries

Abstract

Polyethyleneimine-functionalized reduced graphene oxide (PEI-RGO)-embedded sulfonated poly (vinylidene fluoride-co-hexafluoropropylene) (SPVDF-co-HFP) acid-base composite membranes are fabricated by solution casting method for vanadium redox flow battery (VRFB) applications. The denser and crumbled morphology revealed by FESEM images and EDX results indicates the successful synthesis of PEI-RGO nanosheets. The interfacial acid-base pairs formed between PEI-RGO and SPVDF-co-HFP matrix of composite membranes result in improvement of ion exchange capacity, water uptake, proton conductivity, as well as effective control in swelling ratio and vanadium-ion permeability. In addition, the dispersing ability of PEI-RGO in the SPVDF-co-HFP matrix improved the thermal and mechanical stability of the composite membranes. Homogeneous dispersion of PEI-RGO nanosheets at the SPVDF-co-HFP surface is revealed by the FESEM images of the composite membranes, and their presence is confirmed by EDX results. The SPVDF-co-HFP membrane with 0.75 wt% PEI-RGO exhibited the highest proton conductivity of 5.69 × 10 −3 Scm −1 at 25 C, membrane selectivity of 25.52 × 10 −4 Scm −3 min, and lowest vanadium-ion permeability of 2.23 × 10 −8 cm 2 min −1. Overall results suggested that the SPVDF-co-HFP-0.75 nanocomposite membranes are found to be a suitable alternative for commercially costly Nafion in VRFB applications.

Deciphering the role of 2D graphene oxide nanofillers in polymer membranes for vanadium redox flow batteries

“…217 Similarly, rGO-PEI was considered to increase the effectivity of sulfonated poly(vinylidene uoride-co-hexa-uoropropylene) (sPVDF-co-HFP) membrane. 216 The proton conductivity of sPVDF-co-HFP was signicantly increased by the presence of rGO-PEI in the polymer matrix. The initial proton conductivity of sPVDF-co-HFP was 1.37 mS cm −1 .…”

“…The increase in water uptake in the membrane effectively altered the internal microstructure of the membrane, which probably affected its stability. 215,216 Therefore, efforts were made to develop GO with a decreased oxygen-containing functional group in the reduced graphene oxide (rGO) form. The establishments were focused on developing the polymer membrane hybrid membrane with rGO.…”

“…Based on the proton conductivity and lowered vanadium ion permeation, the rGO-PEI-sPVDF- co -HFP membrane (25.52 × 10 4 S cm −3 min) revealed greater ion selectivity than the Nafion 212, Nafion 117, and sPVDF- co -HFP membranes. 216 Altering the membrane's internal structure through interfacial interaction enhances the membrane's properties. The acid–base pair formation in the membrane and the existence of the Donnan exclusion effect by the presence of the NH 3 + group and 2D nanosheets in the hybrid membrane containing rGO-PEI are the major reasons for attaining efficient ion selectivity and unit cell performances.…”

Two‐Dimensional Materials Applied in Membranes of Redox Flow Battery

“…Nagendran et al fabricated an acid-base composite membrane embedded polyethyleneimine-functionalized rGO (PEI-rGO) in sulfonated poly (vinylidene fluoride-co-hexafluoropropylene) (SPVDF-co-HFP) polymer matrix. [76] PEI provides additional charge carriers (NH 2 /NH), and forms interfacial acid-base pairs between PEI-RGO and SPVDF-co-HFP matrix, both of which improve the ion exchange capacity (IEC) and proton conductiv- Where PVP is polyvinylpyrrolidone, MVP is (mono)vinylpyrrolidone, CL is ɛ-caprolactam, NMCL is N-methylcaprolactam, PVA is polyvinyl alcohol. [69] Copyright (2019), American Chemical Society.…”

An efficient and eco‐friendly route to prepare graphene nanosheet and its effect on the flammability of polypropylene composites

“…Nowadays, two‐dimensional nanomaterials have attracted enormous attention in academia and industry. Graphene is one of the most promising two‐dimensional nanomaterials, which have devoted to develop many potential applications such as advanced composites, 1 high‐capacity batteries, 2 flame retardancy, 3 energy conversion and storage, 4 owing to its high surface area, extraordinary physical properties, and outstanding electron charge transport properties 5 …”