Development of self-assembling sulfonated graphene oxide membranes as a potential proton conductor

Abstract

A simple method is reported for the preparation of self-assembling sulfonated graphene oxide membranes (SGO-X) to be studied as a potential proton conductor for proton exchange membrane fuel cells (PEMFCs). The effect of three different sulfuric acid-to-GO molar ratios is investigated, the main aim being the identification of an optimal sulfonation interval ensuring a successful trade-off among composition, structural stability and functional properties. ATR-FTIR and EDX spectroscopies, SEM, thermogravimetry and static contact angle measurements allow to analyze the efficacy of the functionalization of graphene oxide (GO) with sulfonic acid groups (–SO3H) and the uniformity of the component's structure. A preliminary examination of the proton conductivity is performed on the most promising samples (SGO-1, SGO-20) by means of electrochemical impedance spectroscopy (EIS), together with the evaluation of water uptake, ion exchange capacity and degree of sulfonation. This introductory work demonstrates that the proposed SGO-X membranes exhibit notable water-retaining and proton-exchanging properties at elevated temperatures and reduced humidity, compared to pristine GO and Nafion® 212 benchmark specimens. Therefore, these innovative self-standing materials are proved to be worthy of additional studies for the optimization of their features, foreseeing the assessment of their behavior as a possible electrolyte in a PEM fuel cell.