Metal oxides supported on carbon materials are reported as catalysts for the positive and negative electrodes of vanadium redox flow battery (VRFB). In this study, thermally activated graphite felt (TGF) is decorated with Co3O4 nanostructure by a low-temperature hydrothermal method. The functional groups on the TGF are believed to nucleate the Co3O4 particles establishing a covalent bridging between them. The bridge improves the electron tunnelling across the electrolyte/electrolyte interface, reducing the overpotential of vanadium redox reactions. The covalent bridge, coupled with the enhanced surface area of the nanostructured-Co3O4 coated TGF (TGF/Co-100–12), are responsible for improved VO2 +/VO2+ and V3+/V2+ redox kinetics in VRFB. A 25 cm2 VRFB employing TGF/Co-100–12 electrodes, compared to TGF, enhances the specific capacity from ∼ 38 Ah l−1 to ∼ 45 Ah l−1 and energy efficiency (EE) from 81 to 87.6% at 100 mA cm−2 and its capacity retention (after 50 cycles) is ∼ 100% higher than that of TGF based VRFB. Besides, a two-cell stack is demonstrated with an EE of 84% and 89% of initial capacity even after 50 cycles, and 3% loss in EE vis-à-vis single cell is mainly due to the additional contact resistance arising out of coupling the cells.

Styrene–DVB copolymer grafted semi-interpenetrating type PVDF-based proton exchange membranes (PEMs) have been designed for vanadium redox flow battery (VRFB) applications.

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2,5-bis((dimethylamino)methyl)benzene-1,4-diol (H2QDMA), a redox-active molecule and its derivatives are synthesised by a one-step chemical method using Mannich reaction and studied as a potential catholyte with vanadium (V2+/V3+) anolyte for aqueous redox flow battery applications. The solubility of H2QDMA was ~ 0.75 M in 3 M H2SO4. H2QDMA showed one sharp redox peak at the formal potential 0.6 V ± vs Ag/AgCl, and it was stable for 100 continuous CV cycles without any appreciable change in color. The battery delivered a discharge capacity of ~ 2 Ah L-1, which faded with cycles. We have carried out a post cycle analysis of catholyte and anolyte to understand the origin of the capacity fading. Toward this end, the oxidized form of H2QDMA, i.e., QDMA, was synthesized. The stability of QDMA in acidic solution was low, and the color of the solution changed to intense brown with time. The UV-Visible spectrum and CV curves of the QDMA reflects the same behavior as observed with the catholyte solution obtained post galvanostatic charge-discharge analysis. This study concluded that the QDMA undergoes faster chemical transformation, presumably through the Michael addition reaction process, compared to its participation in the desired electrochemical process.

The paradigm shift in cationic polyelectrolyte membrane design has offered efficient vanadium redox flow battery (VRFB) performance. Herein, we report a facile room-temperature cross-linked hydrophilic modification of halogen end groups in brominated poly (2,6-dimethyl-1,4-phenylene ether) to afford an efficient cationic polyelectrolyte membrane for VRFB application. A progressive assessment of hydrophilic cross-linking followed by long side chain architecture was strategically designed. The influence of microstructure modifications was evaluated with respect to galvanostatic charge−discharge performance, peak power densities, and self-discharge attributes. The long side chain membrane (LSCM) with terminal -N + R 4 exhibits minimal cell resistance of ∼56 mΩ with coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) as high as 91.0−97.0%, ∼70.0−86.0%, and 68.0−78.0% between 50 and 150 mA cm −2 operations. Polarization studies revealed peak power density in the range of 475−500 mW cm −2 . On improving the functional charge density, the self-discharge was also improved by ∼3.8 times in contrast to the un-cross-linked membrane. Finally, the thickness was optimized to acquire the lowest cell resistance of ∼18 mΩ and the maximum power density of ∼555 mW cm −2 (∼30.0% higher than that of Nafion-117) was observed with average CE, VE, and EE of >90.0%, >85.0%, and ∼80.0% at 100 mA cm −2 , respectively. Moreover, the importance of our report highlights that such combinatorial performance outputs of EEs, peak power density, and electrochemical properties are critically rare in literature with previously studied cationic polyelectrolyte membranes. Thus, this work contributes a strategic chemical designing approach and introduces a platform to fabricate an efficient cationic polyelectrolyte membrane for VRFB application.