Reduced graphene oxides prepared via explosive and non-explosive thermal reduction: Structural evolution, functional properties and reinforcing efficacy

Abstract

The present study reveals the influences of heating rate, as employed during thermal reduction of graphene oxide (GO) to reduced graphene oxide (rGO), on the degree of exfoliation and defect structure of the resulting rGO, and, in turn, the effects of the same on the physical properties, electronic properties, performances as electrode material for electrochemical energy storage and efficacy as mechanical reinforcement in brittle materials. Faster heating (@ 10 °C/min) of GO to 350 °C has been found to result in efficient thermal exfoliation, yielding rGO (R10) with ∼400% increase in specific surface area, but with a highly disordered structure. By contrast, slower heating (@ 1 °C/min; as for R01) causes reduction in surface area by ∼30% (w.r.t. GO) due to failure of exfoliation. However, both the rGOs exhibit high defect density (viz., distance between defect sites; Ld ∼1.12–1.3 nm), corresponding to stage 2 of disorder (as per analysis based on Raman spectra). Higher sp2 C fraction in R01 results in higher electronic conductivity, whereas significantly larger specific surface area, along with relatively lower crystallite size and Ld, bestows R10 with higher capacity and rate-capability in the context of electrochemical Li-/Na-storage. As reinforcement in alumino-borosilicate glass-ceramic, while GO and R10 have been found to improve the resistances towards crack propagation and abrasive wear damage (w.r.t. unreinforced alumino-borosilicate), incorporation of R01 deteriorates both these aspects primarily due to inefficient exfoliation of R01, concomitant poor dispersion, failure of reinforcing mechanisms and presence of thicker flakes acting as sites of excessive material damage.