Graphene oxide and sulfonated-derivative: Proton transport properties and electrochemical behavior of Nafion-based nanocomposites

An organo sulfonated-derivative (sGO) of the graphene oxide (GO) was synthesized using a basically new approach. NMR investigations (¹³C-MAS, PFG, relaxation) highlighted the structural and composition changes of the carbon surfaces subsequent to GO functionalization, as well as especially the different capacity of hydration and retention that the two GO and sGO materials manifest. Two self-diffusion coefficients for the water inside the interlayer spaces were detected, spaced by an order of magnitude. sGO evidences higher ability to incorporate and retain water up to 130 °C than GO, whereby much higher proton conductivity, approximately 3 mS cm⁻¹ at 90%RH, confirming how a proper organo-modification of the graphene platelets with highly hydrophilic groups can favor the proton transport. Such proton-conductive materials GO-based can be exploit as additives in membranes for applications PEMFCs. Homogeneous and exfoliated nanocomposite membranes based were successfully prepared by using Nafion ionomer. The organo-derivative sGO produces a considerable gain in proton conductivity, also at very low RH conditions, due to the formation of extremely connected path for protons, which is, instead, absent in Naf-GO composite, where the chemical reaction between epoxy and sulfonic groups, of filler and polymer respectively, subtracts a fraction of acid functionalities for the proton exchange.