Layer-by-layer (LBL) assembly of graphene with p-phenylenediamine (PPD) spacer for high performance supercapacitor applications

Abstract

A novel route to perform the layer-by-layer (LBL) assembly of graphene sheets through the covalent functionalization of graphene oxide is reported. The two-dimensional (2D) graphene sheets have the tendency to aggregate or stack which reduces the available surface area and limits the ion transport during the electrochemical process. This makes it hard for the stacked graphene assembly to achieve optimum device performance. Herein, we report a strategy to solve these problems by transforming the aggregated graphene sheets into an open structure by introducing a spacer between the layers. In this study, a highly reliable, efficient and very simple modification route is reported, where p-phenylenediamine (PPD) is covalently functionalized onto graphene oxide (GO) nanosheets through the reaction between two amine groups of PPD and the epoxy groups on the basal plane of GO. The modified graphene sheet (GPPD) is capable of delivering a much higher specific capacitance and energy density of 282.33 F g⁻¹ and 39.24 W h kg⁻¹, respectively at a discharge current of 0.75 mA. The GPPD electrode also displays excellent electrochemical stability of 92.82% after 1000 charge–discharge cycles. A comparison is made with the existing electrochemical performance and it is found that the results obtained in our study using such a simple process are superior to most of the results reported in the literature.