Versatile Synthetic Route to Tailor-Made Proton Exchange Membranes for Fuel Cell Applications by Combination of Radiation Chemistry of Polymers with Nitroxide-Mediated Living Free Radical Graft Polymerization

Abstract

A versatile method for the preparation of proton exchange membranes (PEMs) by the combination of radiation chemistry of polymers with nitroxide-mediated living free radical graft polymerization with subsequent sulfonation is presented. Thus, poly(vinylidene fluoride) (PVDF) membranes were first irradiated with electron beam and then the free radicals formed were immediately quenched with 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO). In the second step, the produced TEMPOcapped macroinitiator sites were utilized in nitroxide-mediated living free radical graft polymerization of styrene or for the controlled graft copolymerization of styrene and N-phenylmaleimide onto the PVDF membrane. In the final step, the membranes were either directly sulfonated, or in the former case, alternatively the alkoxyamine moieties at the polymer chain ends were substituted by a maleimide derivative prior to sulfonation. The introduction of the N-phenyl maleimide moieties into the grafted chains significantly increased the thermo-oxidative stability of the PEMs as determined by thermogravimetric analysis (TGA). In this work, also a comparison between these membranes prepared by the controlled nitroxide-mediated graft polymerization and those membranes prepared by the conventional preirradiation grafting method in terms of grafting yields, thermo-oxidative stability, water uptake, and ion exchange capacity, proton conductivity, etc. is presented. Noteworthy is the fact that the membranes using the controlled grafting technique are grafted through the membrane already at a degree of grafting of 14%, whereas the penetration limit for the membranes prepared by conventional radiation-induced grafting is approximately 30% as determined by SEM-EDX analysis. Furthermore, preliminary H 2/O2 fuel cell tests showed promise for the development of this type of PEMs prepared by means of a nitroxidemediated living free radical grafting process. Thus, already the PVDF membrane that had been grafted with styrene by means of controlled radical polymerization could after sulfonation be used in a fuel cell for 930 h at 70 °C without any drop in current density. In contrast, according to our previous studies, PVDF membranes prepared by conventional preirradiation grafting of styrene fail within 150 to 200 h under similar conditions.

A Biomimetic Actuator Based on an Ionic Networking Membrane of Poly(styrene‐alt‐maleimide)‐Incorporated Poly(vinylidene fluoride)

“…[4] What is more, the fluorinated polymer is less environmentally friendly, and its cost is at least 1 order of magnitude too high. [11] So many efforts have been undertaken to replace the Nafion membrane, which is widely used in the fields of the fuel cell and the polymer actuator, by much cheaper and ecologically more acceptable materials over the past few years. [12,13] So far, the work done has been only partially successful.…”

Nanocomposite proton conducting membranes based on amphiphilic PVDF graft copolymer

“…In general, partially fluorinated graft copolymer electrolyte membranes with proton conducting properties have been synthesized by multi-step procedures via high energy intensive radiation. [14][15][16][17][18] In this work, however, an amphiphilic proton conducting polymer was effectively synthesized via single step reaction using P(VDF-co-CTFE) as a matrix, as shown in Scheme I. Hydrophilic proton conducting PSSA chains and hydrophobic inorganic PTMSPMA chains were directly grafted from P(VDF-co-CTFE) backbone at 90 o C for 24 h using secondary chlorine atoms as an ATRP initiator. Thus, the comb-like amphiphilic graft copolymer is expected to consist of hydrophobic P(VDF-co-CTFE) main chain and the side chains of proton conducting PSSA and inorganic PTMSPMA with statistical arrangement.…”

“…[7][8][9][10][11][12][13] A partially fluorinated polymer electrolyte membrane is an interesting candidate for replacing Nafion because of easy synthesis, a lower methanol permeability and low costs along with electrochemical properties comparable to perfluorinated membranes. [14][15][16][17][18] It is also well known that partially fluorinated polymer electrolyte membranes possess unique properties, such as low surface energy, high chemical and thermal stabilities, and good mechanical properties. Poly (vinylidene fluoride) (PVDF) is a representative partially fluorinated polymer and grafting polymerization of PVDF has been carried out mostly using high energy beam methods, e.g.…”

Preparation of proton exchange membranes by radiation-induced grafting of alpha methyl styrene–butyl acrylate mixture onto polyetheretherketone (PEEK) films

“…One of the important requirements of solid polymer electrolyte membranes in fuel cells is their high proton conductivity of the order of 10 -2 S cm -1 for complete electrochemical combustion and best performances [3]. This has led to the enormous efforts in developing proton exchange membranes by radiation-induced graft polymerization technique [4][5][6][7]. The appeal of this approach arises from the flexibility of using any type of radiation, such as gamma rays and electron beam irrespective of the shape and size of the polymer matrix.…”