Study of Anion Exchange Membrane Properties Incorporating N-spirocyclic Quaternary Ammonium Cations and Aqueous Organic Redox Flow Battery Performance

Abstract

Flexible cross-linked anion exchange membranes (AEMs) based on poly (p-phenylene oxide) grafted with N-spirocyclic quaternary ammonium cations were synthesized via UV-induced free-radical polymerization by using diallylpiperidinium chloride as an ionic monomer. Five membranes with ion exchange capacity (IEC) varying between 1.5 to 2.8 mmol Cl−·g−1 polymer were obtained and the correlation between IEC, water uptake, state of water in the membrane and ionic conductivity was studied. In the second part of this study, the influence of properties of four of these membranes on cell cycling stability and performance was investigated in an aqueous organic redox flow battery (AORFB) employing dimethyl viologen (MV) and N,N,N-2,2,6,6-heptamethylpiperidinyl oxy-4-ammonium chloride (TMA-TEMPO). The influence of membrane properties on cell cycling stability and performance was studied. At low-current density (20 mA·cm−2), the best capacity retention was obtained with lower IEC membranes for which the water uptake, freezable water and TMA-TEMPO and MV crossover are low. However, at a high current density (80 mA·cm−2), membrane resistance plays an important role and a membrane with moderate IEC, more precisely, moderate ion conductivity and water uptake was found to maintain the best overall cell performance. The results in this work contribute to the basic understanding of the relationship between membrane properties and cell performance, providing insights guiding the development of advanced membranes to improve the efficiency and power capability for AORFB systems.

Anion Exchange Membranes Incorporating Multi N-Spirocyclic Quaternary Ammonium Cations via Ultraviolet-Initiated Polymerization for Zinc Slurry-Air Flow Batteries

“…The DAPCl yield (%) increased with the increase of the DAPCl to polymer ratio due to, probably, the higher number of double bonds and/or low viscosity of the solution. It can be noted that the conversion for this class of copolymers is higher than that for our previous results in which the CH 2 Br was directly bonded to the PPO backbone …”

“…The increase of IEC of the membranes induces a large water-uptake because of the lengthening of the hydrophilic chains and decreases of the cross-linking density and stiffness. The water uptake of the prepared membranes is lower when compared to membranes based on PPO containing poly­(DAPCl) with similar IEC, in which the allyl function was directly bonded to the PPO backbone …”

“…It can be noted that the conversion for this class of copolymers is higher than that for our previous results in which the CH 2 Br was directly bonded to the PPO backbone. 51 3.3. Water Uptake, Ionic Conductivity, and Surface Morphology.…”

“…Four AEMs with different IECs were prepared using UV-initiated polymerization in a similar way to our previous study . The membrane preparation was performed as follows.…”

“…Four AEMs with different IECs were prepared using UV-initiated polymerization in a similar way to our previous study. 51 The membrane preparation was performed as follows. The appropriate amounts of each species (polymer, DAPCl monomer, and initiator) were solubilized in a mixture of 1, 2dichloroethane and NMP, and the solutions are cast on a petri dish.…”