Highly Selective Anion Exchange Membrane Based on Quaternized Poly(triphenyl piperidine) for the Vanadium Redox Flow Battery

Abstract

Vanadium redox flow batteries (VRFBs) have attracted great attention recently owing to the increasing supply of intermittent renewable energies. However, VRFBs usually suffer from serious vanadium ion crossover and high cost when perfluorinated membranes are employed as the separator. In this study, a highly selective anion exchange membrane (AEM) is synthesized from the aryl ether-free poly­(terphenyl piperidine) (PTP). Using 3-chloro-2-hydroxypropyltrimethyl ammonium chloride (CHPTMA-Cl) as the quaternization reagent, not only are the piperidinium cations formed in the PTP main chain, but also the side-chain quaternary ammonium cation and hydroxyl group are introduced into the PTP backbone. Compared with pure PTP-TFA and methyl quaternized PTP (PTP-Me) membranes, the obtained hydroxypropyltrimethyl ammonium grafted poly­(terphenyl piperidinium) (PTP-CHPTMA) membrane exhibits high H+ permeability (1.82 × 10–5 cm2 min–1) and low area resistance (0.35 Ω cm2) mainly due to the presence of the hydrophilic hydroxyl group. Owing to the electrostatic repulsion effect of main-chain piperidinium and side-chain quaternary ammonium cations to vanadium ions, the PTP-CHPTMA membrane achieves a low vanadium ion permeability (1.21 × 10–8 cm2 min–1). Consequently, the PTP-CHPTMA membrane reaches 2 orders of magnitude higher ion selectivity than Nafion 115. The assembled single VRFB with PTP-CHPTMA possesses high Coulombic efficiencies of close to 100% at 60–160 mA cm–2 and higher energy efficiencies than the cell with Nafion 115. The self-discharge duration of the cell with PTP-CHPTMA (381 h) is nearly 4.5 times longer than that of Nafion 115 (86 h). Meanwhile, the VRFB based on PTP-CHPTMA displays excellent cycle stability and discharge capacity retention over 580 charge–discharge cycles at 100 mA cm–2.

Poly(terphenylene) and Bromohexylated Polystyrene-b-poly(ethylene-co-butene)-b-polystyrene Cross-Linked Anion Exchange Membrane with Excellent Comprehensive Performance

“…When completely quaternized ( n = 1), the chemical shift peak of H5 disappears (as shown in Figure e). It is basically consistent with the results in the same position in the literature. , It illustrates the successful synthesis of polymers with different degrees of quaternization.…”

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

“…31 In addition, the diagnostic signal at 2.3 ppm (H 1 ) is ascribed to the methyl protons. 30,31 In addition, the FT-IR spectra of PTAP and PBI polymers are shown in Figure 2B. As to PBI, the characteristic absorption bands at 1452 and 1627 cm −1 are attributed to the stretching vibration of C�N groups and in-plane deformation of benzimidazole rings, respectively, indicating the presence of benzimidazole rings.…”

“…However, the area resistance of the pure PTP membrane was as high as 2.01 Ω• cm 2 , which could not be applied in VRFB. 30 Therefore, it is still of great significance to develop alternative membranes with high physicochemical stability, reasonable cost, and good selectivity for VRFBs.…”

“…The VRFBs were assembled and tested according to our recent work using a Neware CT-3008 (5 V/6 A) system. 30 The battery charge−discharge cycling test was conducted under different current densities, which decreased from 160 mA cm −2 to 40 mA cm −2 and then increased to 160 mA cm −2 . In order to avoid electrode corrosion and hydrogen evolution, setting a cutoff voltage was necessary, which was between 1.0 and 1.65 V in this work.…”

“…Jannasch et al recently synthesized a series of ether-free poly­(arylene piperidine)­s (PAPs) through a superelectrophilic activation . Subsequently, different side chains quaternized PAP membranes have been successfully developed for anion exchange membrane fuel cell and high temperature proton exchange membrane fuel cell. , Inspired by the above works, our group prepared different quaternized poly­(triphenylpiperidine) (PTP) membranes for VRFBs, using (5-bromopentyl)­trimethylammonium bromide and 3-chloro-2-hydroxypropyltrimethyl­ammonium chloride as quaternization reagents, respectively. The obtained long side-chain quaternary ammonium grafted poly­(terphenylpiperidinium) membranes (i.e., PTP-QA and PTP-CHPTMA) exhibited much lower vanadium ion permeability and higher ion selectivity than Nafion 115.…”