One-Pot Synthesis of Proton Exchange Membranes from Anion Exchange Membrane Precursors

Abstract

Proton exchange membranes (PEMs) play a critical role in many electrochemical devices that could solve the shortcomings of current energy storage and conversion systems. Hydrocarbon-based PEMs are an attractive alternative for replacing the state-of-the-art perfluorosulfonic acid PEMs; however, synthetic routes are generally limited to sulfonation of aromatic units (pre- or postpolymerization functionalization). Here we disclose a facile and scalable one-pot synthetic method of converting an alkyl halide functionality to a sulfonate in polymer systems. With this method, sulfonated hydrocarbon PEMs can be conveniently prepared from a precursor polymer of anion exchange membranes which have recently experienced significant advances. Polyphenylene type PEMs (BPSA and mTPSA in this report) were generated in one-pot SN2 reaction of bromoalkyl side chains of polymers followed by oxidation. These PEMs showed excellent proton conductivity with BPSA showing 250 mS/cm in water at 80 °C, nearly 1.5 times higher than that of Nafion 212. Furthermore, the separation of the sulfonic acid group from the rigid backbone with a flexible alkyl chain mitigates excessive water uptake and in-plane swelling ratio of the polymer, despite having a high ion exchange capacity of 2.6 mequiv/g. Oxidative stability was also shown to be superior for hydrocarbon-based PEMs with negligible changes in mass, NMR, and proton conductivity.

Poly(arylene alkylene)-Based Ion-Exchange Polymers for Enhancing Capacitive Desalination Capacity and Electrode Stability

“…Their corresponding synthesis procedure and chemical structures are presented in Scheme and further confirmed by 1 H NMR in Figure S3. On the other hand, cation-exchange polymer SPFL was synthesized through two steps, which involve a nucleophilic substitution reaction and subsequent oxidation . First, FLBr-55 reacted with potassium thioacetate to afford a thioacetate-tethered precursor, FLTA-55.…”

“…On the other hand, cation-exchange polymer SPFL was synthesized through two steps, which involve a nucleophilic substitution reaction and subsequent oxidation. 33 First, FLBr-55 reacted with potassium thioacetate to afford a thioacetate-tethered precursor, FLTA-55. The complete conversion was confirmed by the disappearance of the bromomethyl proton resonance at 3.25 ppm in FLBr-55 along with the appearance of new signals at 2.72 (−CH 2 −S−) and 2.27 ppm (−S−C�O−CH 3 ) in FLTA-55 (in DMSO-d 6 , Figure S2).…”

Highly proton conductive and stable sulfonated poly(arylene-alkane) for fuel cells with performance over 2.46 W cm−2

“…[31][32][33][34] Facile and efficient sulfonation of poly(phenyl-alkane)s remains a great challenge. In 2020, Pagels et al 23 presented an effective and simple method of converting an alkyl halide functionality, a common precursor of AEMs, 35 to a sulfonate group. The Br-of bromoalkyl side chains was replaced by nucleophilic substitution with potassium thioacetate (KSAc), and then the thioacetate groups were converted to sulfonate groups using m-chloroperoxybenzoic acid (mCPBA) as the oxidant.…”

High performance poly(isatin alkyl-terphenyl)s proton exchange membranes with flexible alkylsulfonated side groups

“…Still, in most cases, the sulfonic group is directly connected to the polymer backbone, limiting the phase separation of hydrophilic and hydrophobic domains. 22 Researchers have attempted several approaches to address these shortcomings, including synthesizing polymers free of ether bonds in the backbone 23,24 and introducing aliphatic flexible side chains. [25][26][27] The PEMs containing aromatic structures should provide significantly better oxidation stability in an electrochemical reaction environment due to being free of heteroatom bonds, but they are difficult to synthesize.…”