Efficiency and Oxidation Performance of Densely Flexible Side-Chain Piperidinium-Functionalized Anion Exchange Membranes for Vanadium Redox Flow Batteries

Abstract

In order to improve the performance of vanadium redox flow batteries (VRFBs), a series of anion exchange membranes (PAES-8mPip-x) containing multiple flexible side-chain piperidinium structures were selected for use as ionic membranes for VRFBs. The relationship between their battery performance and chemical structure was systematically investigated, and their oxidation stability and degradation mechanism in strong oxidizing solution were studied in detail. These membranes exhibited high SO4 2– conductivity as well as low area specific resistance due to the incorporation of densely flexible side-chain piperidinium. Their SO4 2– conductivity and area-specific resistance are in the range of 9.6–18.1 mS cm–1 and 0.19–0.34 Ω cm2 at 20 °C, respectively. The single battery assembled with the representative PAES-8mPip-0.25 displayed high efficiencies, and its coulombic efficiency, voltage efficiency, and energy efficiency were 94.78, 90.15, and 85.44% at a current density of 60 mA cm–2, respectively, which were higher than those of Nafion 212 (94.19, 89.08, and 83.90%) at the same testing condition. What is more, it was found that these AEMs had good stability in strong oxidizing solution. Although their polymer backbone was degraded to a certain extent in 1.5 mol L–1 VO2 +/3 mol L–1 H2SO4 at 40 °C, the flexible piperidinium in side chains did not undergo significant chemical degradation. Related research results provide a scientific basis for the design of high-performance anion membrane materials for VRFBs.

Ether-Free Poly(p-terphenyl-co-acetylpyridine) Membranes with Different Thicknesses for Vanadium Redox Flow Batteries

“…The self-discharge performance of PTAP-55μm and Nafion 212 based cells further confirmed above deduction. As shown in Figure S1 (Supporting Information), Nafion 212 achieved an OCV of 27 h, which is comparable with previous reports. , However, the OCV of PTAP-55μm was up to 102 h, indicating good vanadium ion resistant.…”

“…Our recently works depicted that side-chain QA groups grafted poly­(terphenylpiperidinium) membranes degraded into pieces during the test within 250 h. , However, PTAP membranes exhibited good chemical stabilities and almost kept their original shape and weight during the chemical stability test. In addition, both PBI and PTAP membranes exhibited increased weight, probably resulting from the absorption of vanadium ions in the membranes. , As shown in the photos in Figure , the color of the membranes became darker, which also indicated the absorption of vanadium ions . Nevertheless, not only Nafion membranes but also PBI and PTAP membranes remained robust after a 400 h chemical stability test, proving that PTAP membranes had a good stability under strong acid and oxidizing conditions.…”

“…19,45 As shown in the photos in Figure 6, the color of the membranes became darker, which also indicated the absorption of vanadium ions. 46 Nevertheless, not only Nafion membranes but also PBI and PTAP membranes remained robust after a 400 h chemical stability test, proving that PTAP membranes had a good stability under strong acid and oxidizing conditions. Performance of VRFBs.…”

“…As shown in Figure S1 (Supporting Information), Nafion 212 achieved an OCV of 27 h, which is comparable with previous reports. 41,46 However, the OCV of PTAP-55μm was up to 102 h, indicating good vanadium ion resistant.…”

Role of Ionic Concentration and Distribution in Anionic Conductivity: Case Study on a Series of Cobaltocenium-Containing Anion Exchange Membranes with Precise Structure Control

“…To investigate this effect, some pioneers such as Bai, Hickner, Wang, Xu, and Hu demonstrated the possibility of preparing AEMs with different ionic concentrations, and the ion-conducting property of the corresponding AEMs was also improved by structure optimization (Figure ). In addition, different functional groups, such as quaternary ammonium, − piperidinium, − imidazolium, and other cationic groups, were also introduced into AEMs to study their influence on the AEM property . However, the influence of ionic concentration and substituent on the ion-conducting property was only studied by a few groups, which may be owing to the complicated synthetic chemistry and the lack of suitable polymer precursors.…”