Graphene oxide nanofibers: A nanocarbon material with tuneable electrochemical properties

We report the electrochemical properties of a novel nanocarbon material obtained by chemical oxidation and ultrasound-assisted exfoliation of fishbone carbon nanofibers (CNF). The resulting material maintains its tubular morphology and presents a characteristic interlayer spacing of graphene oxide (above 0.75 nm). Thus, this is called graphene oxide nanofibers (GONF). The new rearrangement of the accessible sp2-carbon domains makes the GONF a potential alternative for electrochemical energy conversion/storage applications, showing a developed porosity and tuneable surface chemistry. The influence of the oxidation degree of GONF on its electrochemical behaviour in 0.5 M H2SO4 is reported. Cyclic voltammetry and electrochemical impedance spectroscopy evidenced a significant increase of the capacitance for GONF, being 4–27 times higher than that obtained for pristine CNF. An optimum in the capacitance (49.2 F g−1) was obtained using an oxidation ratio (OR = KMnO4/Sample) of 6 and 60 min of sonication. The latter is ascribed to the unique structure of this material containing both graphitic and graphene oxide domains. Higher OR or longer sonication times led to a partial loss of graphitic domains and higher contribution of micropores, which worsen the fast ion/electrolyte transport. Additionally, the optimized material exhibited an improved activity for the hydrogen evolution reaction.