Graphene oxide-naphthalene sulfonate blends as possible proton exchange membranes

Abstract

This work presents a study on the preparation of novel self-assembling naphthalene sulfonate-functionalised graphene oxide membranes, whose analysis aims at assessing their potentiality as an alternative to perfluorinated proton conductors. Three different graphene oxide-to-naphthalene sulfonate molar ratios and two different process temperatures were combined to identify the most suitable conditions to perform an effective functionalisation. ATR-FTIR, Raman and EDX spectroscopies, thermogravimetric analysis, static contact angle evaluation and XRD aimed to point out the introduction of sulfonic acid groups (–SO3H) in the GO framework, while optical and scanning electron microscopies verified the good membrane uniformity. The evaluation of the ion exchange capacity (IEC) demonstrated the proton-exchanging ability of the prepared membranes. The most promising sample underwent water uptake (WU) and electrochemical impedance spectroscopy (EIS) tests to examine the dependence of its water sorption and proton conductivity with respect to relative humidity and temperature, in order to deepen the assessment of its feasibility as a possible future electrolyte in alternative energy generators. A preliminary investigation of the mechanical properties of the above-mentioned sample was performed as well to expand the characterisation of its behaviour.