Highly efficient synthesis of reduced graphene oxide–Nafion nanocomposites with strong coupling for enhanced proton and electron conduction

Abstract

The synthesis of a reduced graphene oxide (RGO)–Nafion nanocomposite membrane with both high electron and proton conductivity was successfully achieved using a simple solution casting method followed by a hot press thermal reduction process. Interestingly, in the hybrid material, the strong-coupling effects, exerted by the functional groups of RGO and the electron withdrawing groups of Nafion, have played a significant role in the enhancement of both proton and electron conductivity. The strong coupling interaction phenomena are evidenced by Raman and X-ray photoelectron spectroscopy (XPS). The proton conductivity of the composite increased by around 30 times, from 7.30 × 10⁻³ for recast Nafion to 2.20 × 10⁻¹ S cm⁻¹ while the electron conductivity reached 2.20 × 10⁻² S cm⁻¹ with 5 wt% of RGO–Nafion nanocomposite in wet condition. The electron conductivity of this same nanocomposite increased 5 times, from 4.40 × 10⁻³ for RGO to 2.15 × 10⁻² S cm⁻¹ at ambient conditions. The presence of RGO in Nafion increases the water uptake by left oxygen-containing functional groups. The electron withdrawing groups of Nafion (–CF₂ & –SO₃H) are responsible for the increased RGO's electron conductivity. The proton conductivity of composite is further enhanced by the alignment or morphological change of the membrane's proton channels during hot press thermal reduction. The proposed synthesis is a simple, environmentally benign and scalable process to produce Nafion–RGO nanocomposites without complex dispersion or chemical reduction processes.