Controlling the degree of sulfonation and its impact on hybrid cross-linked network based polyphosphazene grafted butylphenoxy as proton exchange membrane Amina Ouadah * , Tianwei Luo, Shuitao Gao, Changjin Zhu School of Chemistry and Chemical Engineering, Beijing Institute of Technology, No.5, Zhongguancun South Street, Beijing, 100081, China article info Article history: Received 17 January 2018 Received in revised form 13 June 2018 Accepted 16 June 2018 Available online xxx Keywords: Proton exchange membrane Polyphosphazene Atom transfer radical polymerization Cross-linking abstract A new hybrid based polyphosphazene backbone is synthesized via a series of reactions (ring opening of polyphosphazene, bromination, grafting groups, Atom transfer radical polymerization (ATRP) and sulfonation) with a controlled degree of sulfonation. The syn- thesis is proved via the 1 H NMR analysis at different steps. The corresponding membranes were elaborated via a casting method and characterized by 1 H NMR, FTIR, and XPS. Con- ductivity of the synthesized proton exchange membranes is as good as that of the com- mercial Nafion and displays at the same time a low swelling ratio and water uptake due to the cross-linking process. The membrane's activation energies are very low confirming the easy transport through the channels. As matter of fact, the morphology study reveals a well hydrophilic/hydrophobic nanophase separation. The present membranes are chemi- cally and thermally very stable, no significant weight loss was observed after the Fenton's reagent test and no thermal degradation occurs at temperatures lower than 250  C (considered high temperature for nowadays proton exchange membranes). © 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Introduction Finding a good alternative energy to fossil fuels is one of nowadays challenge; normally gasoline is the most used source of energy in automobile; however, its use is facing some problems like the low efficiency and the environmental pollution which leads to substituting with different fuels like hydrogen or methanol that will be converted to electrical en- ergy using fuel cells [1,2]. Fuel cell device was invented in 1839 by Sir William Grove [3] and later on, this industry became one of the most attrac- tive industries [4]. Indeed, fuel cell is a device converting chemical energy into electricity providing a good clean potential and alternative power source especially for portable electronic devices [5] due to its efficiency for producing more energy, its friendly environment technique [4,6] and the good conversion regarding wearable devices application [1,7,8]. While the fuel cell is operating, an element is the heart of its performance which is the electrolyte membrane; the electro- lyte is a trigger component for the fuel cell performance [9,10]; it is an ion conducting membrane sandwiched between the two electrodes inside the fuel cell assembly [10]. As matter of fact, H. Chen et al. have provided fuel cell classification depending on the ion type; two categories have been widely studied: proton exchange membrane (PEM) based on the proton's con- ductivity, it is a good alternative due to its advantages; * Corresponding author. E-mail address: ouadahamina@outlook.com (A. Ouadah). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy xxx (2018) 1 e15 https://doi.org/10.1016/j.ijhydene.2018.06.105 0360-3199/© 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Ouadah A, et al., Controlling the degree of sulfonation and its impact on hybrid cross-linked network based polyphosphazene grafted butylphenoxy as proton exchange membrane, International Journal of Hydrogen Energy (2018), https:// doi.org/10.1016/j.ijhydene.2018.06.105