A high charge efficiency electrode by self-assembling sulphonated reduced graphene oxide onto carbon fibre: towards enhanced capacitive deionization

Abstract

Sulphonated reduced graphene oxide (SRGO) is self-assembled onto carbon fibre cloth (CFC) by electrophoresis deposition as a composite (CFC–SRGO) electrode for high-performance capacitive deionization (CDI). The resulting CFC–SRGO composite shows a cross-linked nanotubular structure and the individual carbon fibre is fully encapsulated by SRGO nano-sheets, forming a cylindrical-shell microstructure. The electrosorption performance of the CFC–SRGO composite electrode is determined by carrying out a batch-mode electrosorption experiment, showing a great improvement in charge efficiency of more than twice that of a bare CFC electrode. Remarkably, this result is comparable with that of membrane enhanced capacitive deionization. Further, the low exponential decay constant of the CFC–SRGO composite electrode derived from the electrosorption kinetics demonstrates that the deposited SRGO favors a decrease in the internal electrode resistivity and therefore improves the ion electrosorption rate which contributed to the enhanced charge efficiency significantly. Another possible reason accounting for the high charge efficiency of the CFC–SRGO electrode is that the functionalized SRGO is analogous to a cation-exchange membrane which can block the co-ions during electrosorption. In addition, the electrosorption isotherm of the CFC–SRGO film follows Langmuir adsorption, indicating the monolayer adsorption mechanism. Meanwhile, the thermodynamic analyses imply that the electrosorption of salt ions onto the CFC–SRGO electrode is driven by a physisorption process.