Highly Efficient Synthesis of Strongly Coupled Reduced Graphene Oxide/Nafion Nanocomposites with Enhanced Mixed Proton and Electron Conduction

Hydrogen fuel production from solar water splitting using an artificial photosynthetic device is the Holy Grail for sustainable energy generation. In the design of such a device, the development of new functional materials with high simultaneous transport of protons and electrons is an important quota of the work for an efficient energy system. In here, reduced graphene oxide (RGO)-Nafion nanocomposite membrane with both high proton and electron conductivity was successfully synthesized using a simple solution casting method followed by a hot press thermal reduction process at a temperature higher than the thermal stability of Nafion. Interestingly, in the hybrid material, the strong-coupling effects, exerted by the electron withdrawing groups of Nafion and the functional groups of RGO, have played an important role in the improvement of both electron and proton conductivity. The strong coupling interaction phenomena are proved by IR, Raman and X-ray photoelectron spectroscopy. The proton conductivity of the material increased by two order of magnitude (~30 times), from 7.30x10^-3 for recast Nafion to 2.20x10^-1 S cm^-1 while the electron conductivity reached 2.20x10^-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 4.40x10^-3 for RGO to 2.15x10^-2 S cm^-1 at ambient condition. 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 electron conductivity of RGO. 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.