Polybenzimidazole membranes functionalised with 1-methyl-2-mesitylbenzimidazolium ions via a hexyl linker for use in vanadium flow batteries

• Published in: Polymer (Guilford) Vol. 174; pp. 210 - 217
• Main Authors: Lee, Yona, Kim, Sangwon, Maljusch, Artjom, Conradi, Oliver, Kim, Hyoung-Juhn, Jang, Jong Hyun, Han, Jonghee, Kim, Jihyun, Henkensmeier, Dirk
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 12.06.2019; Elsevier BV
• Subjects: 2-Mesityl benzimidazolium; Batteries; Energy efficiency; Functional groups; Ion exchange; Mechanical properties; Membranes; Modulus of elasticity; Permeability; Polybenzimidazole; Polybenzimidazoles; Rechargeable batteries; Sulfuric acid; Vanadium; Vanadium redox flow battery (VRFB); X-ray scattering; Polybenzimidazole; Vanadium redox flow battery (VRFB); 2-Mesityl benzimidazolium
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2019.04.048

1-(6-bromohexyl)-3-methyl-2-(2,4,6-trimethylphenyl)-2H-benzimidazolium bromide was synthesised and grafted onto polybenzimidazole (PBI). The highest obtained degrees of functionalisation were 0.7 and 1.1 ionic groups per repeat unit, corresponding to ion exchange capacities of 1.25 and 1.55 mmol chloride/g. While the latter material had much reduced tensile strength and Young's modulus, the material with a lower degree of functionalisation showed properties similar to PBI and was therefore further investigated. X-ray scattering showed that the functional group reduced the crystallinity. Conductivity was in the range of 2–3 mS cm−1, but increased to 23 mS cm−1 after doping in 2 M sulfuric acid, 2–4 times higher than for doped PBI. Permeability for VO2+ ions was 0.8 × 10−12 m2 s−1. In the vanadium redox flow battery, the grafted PBI showed higher coulomb and voltage efficiency than PBI, and therefore also higher energy efficiency. [Display omitted] •PBI was functionalised with hexyl tethered 1-methyl-2-mesityl-benzimidazolium ions.•Highest reached ion exchange capacity was 1.55 mmol chloride/g.•Conductivity of the 2 M sulfuric acid doped membrane was 23 mS cm−1.•Permeability for VO2+ ions was 0.8 × 10−12 m2 s−1•CE, VE and EE were higher than for a cell using pristine PBI.