Lei Hu,Yue Du,Li Gao,Mengting Di,Ning Zhang,Yu Pan,Xiaoming Yan,Baigang An,Gaohong He
Nanoscale solid superacid SO42–/ZrO2/WO3 is coupled into imidazole-hydroxyl-quaternary ammonium co-functionalized polybenzimidazole (PG112) to address the trade-off effect of membrane for large-scale flow battery application. Nanoscale SO42–/ZrO2/WO3 particles with high sulfonic groups are dispersed in membrane as redox-active ion barriers and proton carriers, which mitigate the electrolyte crossover and maintain high ion conductivity. The VO2+ permeability of the prepared membrane (7.86 × 10–10 cm2 s–1) is significantly lower than those of PG112 (3.93 × 10–9 cm2 s–1) and Nafion 212 (7.76 × 10–8 cm2 s–1) membranes. The vanadium flow battery with this membrane exhibits a longer self-discharge duration time of 231 h compared with Nafion 212 (35 h) and PG112 (88 h) membranes. High coulombic efficiencies of 97.5–99.2% at 40–120 mA cm–2 are obtained for the prepared membrane, which are higher than those for Nafion 212 (78.0–92.8%) and PG112 membranes (96.2–98.6%). Stable cycle performance and low retention capacity are also observed, suggesting the excellent chemical stability of the prepared membrane in vanadium flow battery operation. This work provides a prospective and applicable membrane to enhance the performance of flow battery.
To solve the stability issue of cost-effective nonfluorinated membranes, an ether-free poly(arylene piperidinium) (PBPip)-based membrane is first applied in redox flow batteries (RFBs). For improved efficiencies of RFB, amphoteric side chains are introduced onto the PBPip. Without an ether bond in the polymer backbone, the membrane shows a good stability in a strong oxidation environment. The Fourier transform infrared (FTIR) spectra exhibit no obvious changes over 30 days of oxidation test. Different from traditional blended amphoteric membranes, the amphoteric side chain allows both cation- and anion-exchange capacities to increase with grafting degree, which leads to a very high total ion-exchange capacity (IEC) (4.19 mmol g–1). Outstanding ion-conduction ability (area resistance: 0.22 Ω cm2) comparable to Nafion 212 (0.24 Ω cm2) is consequently achieved. Ionic cross-linking structure between cationic and anionic groups results in a low swelling rate (13.9%). Combined with the repelling effect of positively charged piperidinium, a low VO2+ permeability (1.31 × 10–8 cm2 s–1) is accomplished. On the basis of these good properties, the membrane exhibits excellent vanadium battery performances, especially at high current densities. The VE and EE both exceed 80% even at 200 mA cm–2. The battery performances have no obvious reductions after 500 cycles. These results indicate that this work provides a new orientation to design the membrane for RFB.
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