We report on the synthesis and characterization of polyethylene-styrene-divinylbenzene-based interpolymer cation exchange membrane (ICEM) and its applicability as a separator in vanadium redox flow battery (VRFB). ICEM preparation involved radical...

Zinc-based energy storage is increasingly getting attention owing to its outstanding characteristics over to the other systems. Their high abundance, user-friendliness, environmental benignity, and low reduction potential which can avoid unwanted hydrogen evolution are some of the attractive features. Appropriate membrane selection for the zinc-based redox flow battery is challenging. Herein we report the composite of SPEEK (sulfonated polyether ether ketones) with covalent organic frameworks (COF) as a potential membrane for zinc-based redox flow battery. Biphenyl-based knitting type COF was prepared, post sulfonated, and blended with SPEEK. In a Zn/I2 redox flow battery system, the discharge capacity was found to be 19.8 AhL-1, 17.4 AhL-1, 15.1 AhL-1 for 20%, 15%, 10% SCOF loading, respectively, against 14.5 AhL-1 for pristine SPEEK at 20 mAcm-2 current density. The capacity was improved by about 36% higher than the neat SPEEK membrane. This improvement in the battery performance might be due to the higher ionic conductivity and hydrophilicity after SCOF loading. We found that the 15% loading was the maximum limit for the battery performance, beyond which the energy efficiency was found to be fading, which is due to the excessive dendrite growth on the membrane surface.

We describe the synthesis of N-sulfonated poly(arylene-oxindole) by metal-free superacid, denoted IDB, IBP, and IFP by polycondensation of isatin with 1,4-diphenoxybenzene, biphenyl, and fluorene, monomer, respectively. All three polymers provide flexible transparent films with high decomposition temperatures (400 to 500 °C) as well as good mechanical and oxidative stability. The physiochemical and electrochemical characteristics of the IDB membrane were better, in comparison to IBP and IFP. The presence of an ether linkage in IDB facilitates the formation of a highly negative charge amide ion, resulting in a high degree of N-sulfonation. To evaluate performance in VRFB, relevant physical properties and stability in a highly oxidative environment (2.1 M H2SO4 and 1.6 M VO2 +) were evaluated. In a single cell VRFB test, the peak power density for IDB, IBP, and IFP was 275 mW cm–2, 240 mW cm–2, and 225 mW cm–2 respectively, at 300 mA cm–2 current density. The IDB membrane showed 97% Coulombic, 68% energy, and 66% voltage efficiencies at 100 mA cm–2 over 200 charge/discharge cycles. In comparison to Nafion 117 in identical experimental settings, the OCV studies validated the low rate of self-discharge, showing the IDB membrane is better suited for VRFB applications.

Here, we report the synthesis of nickel nanoparticles thermally encapsulated in multiwalled carbon nanotubes (MWCNTs) and its utility in alkaline water splitting by combining with composite thermoset anion-exchange membrane. Ni@MWCNT displayed both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). It provided 10 mA cm –2 current density at an overpotential of 300 mV for OER and 254 mV for HER on a glassy carbon electrode, respectively. Base-catalyzed N-methly-4-piperidone-formaldehyde-based prepolymer was grafted on to poly(vinyl alcohol) and cross-linked via thermal annealing followed by quaternization using methyl iodide to obtain thermoset anion exchange membrane (NMPi). Composite NMPi membranes were synthesized using additives tetraethyl orthosilicate (TEOS) and zirconium oxychloride. The water splitting performance on the fabricated membrane electrode assembly was tested and compared with commercially available Neosepta membrane. The obtained faradic efficacy of the water splitting was 94.33% for ZrO 2 -NMPi membrane followed by 80.23%, 77.70%, and 65.10% for SiO 2 -NMPi, NMPi, and Neosepta membranes, respectively. The best membrane ZrO 2 -NMPi achieved maximum current density of ∼0.776 A cm –2 in 5 M KOH electrolyte at 80 °C and 2 V applied constant voltage. The excellent alkaline stability of MEA indicates its potential utility in hydrogen generation applications.

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The use of redox flow batteries (RFBs) has become popular for preserving renewable energy. For widespread commercialization, the appropriate selection of redox-active species and ion exchange membranes (IEM) is essential. Herein, we synthesized a robust PVA-Silica (PVA-SiO2) composite membrane and demonstrated its essential use in an aqueous hybrid RFB. A proton-conducting, chemically and physically stable membrane was created by combining the traditional hydrophilicity of PVA with well-defined interconnecting ion-conducting channels produced by uniformly distributed silica particles. We believe that thermal crosslinking ensured substantial dimensional and chemical durability, whereas silica permitted good ionic conductivity. The utility of the membrane was proved in a hybrid redox flow battery consisting of newly synthesized 1,4-phenoxy bis-propane sulfonic acid (PPS) and vanadium (III) salt in 2 M H2SO4. A detailed battery analysis was carried out with a rate performance study, cycling test, polarization curve, and OCV. Over 100 charge/discharge cycles, it demonstrated 95% coulombic efficiency, 61% voltage efficiency, and 57% energy efficiency at a current density of 50 mA cm-2, indicating the best utility of an oxidatively susceptible functional group-free robust proton conducting membrane.

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