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

Abstract

A simple method is reported for the preparation of selfassembling 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.

Reduced Graphene Oxide Membranes as Potential Self-Assembling Filter for Wastewater Treatment

“…Finally, the progressive weight loss associated to the 550-1000 • C range corresponds to the breakdown of the GO framework [18].…”

“…In this scenario, membranes based on graphene oxide (GO) and related materials have attracted great interest from both academia and industry, even though GO structures are still debated [14][15][16][17], because of the complexity of the material and its non-stoichiometric composition [14,[18][19][20].…”

Investigation of Sulfonated Graphene Oxide as the Base Material for Novel Proton Exchange Membranes

“…Graphene oxide was purchased from Graphenea, Inc. (Cambridge, MA, USA) as a 0.4 wt.% aqueous dispersion with average particle size of less than 10 µm and a pH between 2.2 and 2.5. Starting from an elemental analysis performed by the vendor [ 19 ], the authors extrapolated an empirical GO formula (C 1.5 H 0.2 N 0.01 S 0.03 O) by exploiting the oxygen atoms content as normalization factor [ 14 ]. The associated molecular mass of 35.3 g mol −1 was compatible with literature values [ 20 , 21 ] and preliminary energy dispersive X-ray (EDX) analyses executed on a pristine sample [ 14 ].…”

“…Six samples were prepared in this work by adopting different acid-to-GO molar ratios, namely, 1, 2.5, 5, 10, 15 and 20, a range that was identified as the most promising one in a previous work by the authors [ 14 ]. The GO molecular mass discussed in Section 2.1 was employed to evaluate the corresponding required acid volumes, as summarized in Table 1 .…”

“…The former is prepared via a thermal or chemical reduction with the intent of increasing the C-to-O ratio up to values approaching pristine graphene [ 5 ], and finding employment in Li-ion batteries [ 11 ] and filters for water softening [ 6 ]. The latter is characterized by sulfonic acid groups grafted on the GO surface, which bestow a high ionic conductivity thanks to the facilitated solvation of movable protons [ 12 ], and it is mainly applied in the field of fuel cells [ 13 , 14 , 15 , 16 , 17 , 18 ].…”