Effects of the N-alicyclic cation and backbone structures on the performance of poly(terphenyl)-based hydroxide exchange membranes

Abstract

By using different synthetic strategies, the structures of the cyclic cation and the backbone polymer of hydroxide exchange membranes were systematically varied to study the effects on stability and conductivity.

Functionalizing Polystyrene with N-Alicyclic Piperidine-Based Cations via Friedel–Crafts Alkylation for Highly Alkali-Stable Anion-Exchange Membranes

“…Aryl ether bonds in the polymer backbone are reported to be particularly sensitive to scission reactions, especially in the proximity of electron-withdrawing groups. 15 This finding motivates the use of ether-free polymer backbones, such as poly(arylene alkylene)s 11 − 14 , 16 − 20 and polynorbornenes. 21 − 24 Polystyrene (PS) is another example of an ether-free polymer that has been extensively investigated for the preparation of AEMs in the form of block and graft copolymers.…”

Ether-free polyfluorenes tethered with quinuclidinium cations as hydroxide exchange membranes

“…5,6 The vast number of studies on AEMs based on different aromatic polymer backbones, including polyethers, polysulfones, polyphenylenes, polybenzimidazoles, etc., has shown that aryl ether links are sensitive to hydrolysis under alkaline conditions, especially if this reaction is activated by nearby electron-withdrawing groups such as sulfone links. [9][10][11][12][13][14][15][16][17][18][19][20] Hence, AEMs based on ether-free aromatic backbones, such as polyphenylenes, 9,[21][22][23] poly(arylene alkylene)s [24][25][26][27][28][29][30][31][32] and sterically protected polyimidazoliums, [33][34][35][36] as well as on aliphatic backbones such as poly(diallyldialkyl ammonium) 37 and polynorbornenes, 38,39 have shown excellent alkaline stability.…”

“…42 The high stability of the alicyclic QAs has been rationalized by a low ring strain combined with the constrained conformations imposed by the ring structure, which increase the transition state energy of both substitution and elimination reactions. 42 Later studies by us and others on AEMs functionalized with alicyclic cations such as piperidinium 25,26,44 and different spirocyclic QAs 32,37,[45][46][47][48][49][50][51] have conrmed a high alkaline stability. However, the results also indicate that the stability is highly dependent on precisely how the cations are attached to the polymer backbone.…”

“…However, the results also indicate that the stability is highly dependent on precisely how the cations are attached to the polymer backbone. 32,47,49,51 If the alicyclic cations are placed in positions where their ring conformation can be deformed, e.g., in a rigid polymer backbone, there is a tendency for the stability to decrease. 25,32 In the present work we have prepared and studied AEMs based on aryl ether-free uorene-based copolymers tethered with quinuclidinium (Qui) cations placed on exible hexyl spacers.…”

Progress of Alkaline Anion Exchange Membranes for Fuel Cells: The Effects of Micro-Phase Separation

“…Fuel cells are electrochemical devices that directly convert the chemical energy of a fuel (such as hydrogen or methanol) into electrical energy (Noonan et al, 2012;Chu et al, 2015;Feng et al, 2016;Wang et al, 2019). Compared to that of the fuel cells with liquid electrolytes, polymer electrolyte membrane fuel cells, which use solid polymer electrolyte membranes, possess higher power densities, simplified operations, and easier maintenance and have attracted much attention during the last decades (Olsson et al, 2018;Pham et al, 2019). Based on the polymer electrolyte membrane, the polymer electrolyte membrane fuel cells could be classified as proton exchange membrane fuel cells (PEMFCs), and alkaline anion exchange membrane fuel cells (AEMFCs).…”