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...

In this work, we report a thermally annealed porefilled anion exchange membrane (PFAEM) with excellent mechanical and chemical stability effected by a polypropylene support and impressive electrochemical properties induced by a pore-filled poly (4-vinyl pyridine) matrix followed by its successful demonstration in vanadium redox flow batteries (VRFBs). As expected, a low swelling ratio synergized with Donnan exclusion resulted in low vanadium ion diffusion. The calculated permeability rates for V +3 , VO 2+ , and VO 2 + were 4.80 × 10 −7 , 7.11 × 10 −7 , and 9.4 × 10 −7 dm s −1 , respectively. An exceptionally low dimension change (∼4.5%) was observed in 1.6 M VO 2 + /2 M H 2 SO 4 solution over 15 days. The assembled VRFB exhibited a Coulombic efficiency (CE) of 98.6% and energy efficiency (EE) of 69.2% over 50 charge/discharge cycles at 150 mA cm −2 with a high-capacity retention of 70% and average capacity decay of 0.63% per cycle. The observed peak power density was 340 mW cm −2 . Finally, the autopsy of the membrane after battery performance suggested negligible depreciation in mechanical and electrochemical properties, confirming its potential applicability in VRFBs.

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.