Optimisation of electrolytic solvents for simultaneous electrochemical exfoliation and functionalisation of graphene with metal nanostructures

Abstract

The development of a simple, simultaneous electrochemical exfoliation and functionalisation of graphene with metal nanostructures in a one-pot, single step process is reported. This approach is useful in terms of the reduction in processing time and cost, as well as aiding the control of the aggregation of graphene sheets. This first part of this work compares the efficiency of electrochemical graphite exfoliation in dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP) and in a mixture of dimethyl carbonate (DMC) and ethylene carbonate (EC) in an electrolyte consisting of LiClO4 and tetraethylammonium tetrafluoroborate. In the second part, the best performing electrolytic solvent was used for in-situ functionalisation of graphene sheets with gold or cobalt nanostructures. The formation of solid layer electrolyte interface in the DMC/EC system is believed to stabilise the graphite from premature exfoliation and allowed the ions to intercalate efficiently to produce a relatively high yield of monolayer graphene sheets. By contrast, the electrochemical exfoliation of graphite in the other two solvents (DMSO and NMP) produced lower yields of few layer graphene. In particular, the co-intercalation of DMSO fragments the electrode by its decomposition by-products (sulfur/carbon oxides) before sufficient cation intercalation occurs. The simulations electrochemical exfoliation and functionalisation of graphene at a single applied potential in the presence of Au salt in DMC/EC solution resulted in the functionalisation of graphene sheets with a variety of high surface area Au nanowhiskers, nanodendrites, nanowires and lamellar nanoparticles. Alternatively, the use of Co(II) salt in the exfoliation solution resulted in the co-deposition of uniformly grown Co nanoparticles on graphene sheets. The metal-functionalised graphene sheets showed high catalytic activity and stability when used as an electrocatalyst for hydrogen evolution reactions. This process could be extended to other metal salts, or mixtures of metal salts, to form graphene-metal alloy composites for use in various applications.