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Fluorine functionalized ion-conductive membrane for high-performance vanadium flow batteries

Authors： WANG Herong1, TIAN Li1, LIU Yupeng1, CHEN Zeyu1, PANG Bo1, JIANG Xiaobin1,CUI Fujun2, WU Xuemei1, HE Gaohong1

Units： 1. State Key Laboratory of Fine Chemicals, Research and Development Center of Membrane Science and Technology, Dalian University of Technology, Dalian 116024, China; 2. Panjin Institute of Industrial Technology, Dalian University of Technology, Panjin 124221, China

KeyWords： proton exchange membrane; vanadium redox flow batteries; fluorine functionalized side chain; H+/Vn+ selectivity

ClassificationCode：TM912.1

year,volume(issue):pagination： 2026,46(2):38-46

Abstract：

The selectivity between proton(H+) and vanadium ions(Vn+) is a key factor for the ion-conductive membranes in vanadium redox flow batteries (VRFBs). Currently, the commercially Nafion 212 membrane suffers from low proton conductivity and poor selectivity, which severely restricts further performance improvements for vanadium redox flow batteries. In this work, the construction of highly selective ion-conductive membranes (PBI-8F) by incorporating fluorinated functionalized side chains was proposed for VRFBs. By grafting fluorinated functionalized side chains, the microphase-separated structure of the ion-conductive membrane could be enhanced, forming both high proton conductivity and low vanadium ions permeability. After introducing fluorinated side chains, the ion cluster size of PBI-8F membrane increased to approximately 12 nm, indicating stronger microphase separation capability. Molecular dynamics simulations revealed that the enhanced microphase separation in the PBI-8F membrane originated from the self-aggregation of both fluorine atoms and sulfonic acid groups. Additionally, the incorporation of fluorinated hydrophobic side chains restricted the water uptake (9.8%) and swelling ratio (3.2%), improving the dimensional stability of the membrane. Moreover, the area resistance of the PBI-8F membrane was 0.21 Ω·cm2, which was 69.6% lower than that of the pristine PBI membrane, while the vanadium ion permeation rate remained low at 2.35×10-10 cm2/s, two orders of magnitude lower than that of Nafion 212(3.41×10-10 cm2/s), demonstrating high H+/Vn+ selectivity. The PBI-8F membrane exhibited high coulombic efficiency (99.6%), voltage efficiency (80.4%), and energy efficiency(80.1%) at 200 mA/cm2. No changes in the characteristic peaks of the ion-conducting membrane were observed before and after cycling, confirming the excellent VRFB performance of the PBI-8F membrane.

Funds：

国家青年基金(C类)(22408039); 国家自然科学基金面上项目(22378042, 22021005); 国家资助博士后人员计划(GZC20240184)

AuthorIntro：

王鹤蓉（2005-），女,陕西汉中人，研究方向为质子交换膜材料

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