Stable Poly(2,6-dimethyl-1,4-phenylene ether) Based Cross-Linked Cationic Polyelectrolyte Membrane with Ionic Microstructure Modification for Efficient VRFB Performance

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+R4 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.