Self-Assembled 1T-MoS2/Functionalized Graphene Composite Electrodes for Supercapacitor Devices

Two-dimensional (2D) materials such as graphene and molybdenum disulfide (MoS2) have been investigated widely for applications in energy storage, including supercapacitors, due to their high specific surface area, potential redox activity, and mechanical flexibility. However, electrodes comprising either pure graphene and MoS2 have failed to reach their potential due to restacking of the layered structure and poor electrical conductivity. It has been shown previously that composite electrodes made from a mixture of graphene and MoS2 partially counteract these issues; however, performance is still limited by poor mixing at the nanoscale. Herein, we form a true composite electrode by chemically functionalizing the graphene so that the negatively charged surface can self-assemble with the positively charged 1T-MoS2 to give an alternating layer structure. These alternately restacked 2D materials were then used to produce supercapacitor electrodes, and their energy storage properties were characterized. This stacked structure has increased the interlayer spacing of 1T-MoS2 which was indicated by the increase in the intensity of the (001) peak in the X-ray diffraction spectra. Furthermore, the typically metastable 1T-MoS2 was stabilized by the interaction with the functionalized graphene, preventing it reverting back to the 2H phase, which was observed when pristine graphene was used. The graphene was functionalized using either 4-bromobenzenediazonium or 4-nitrobenzenediazonium, with the latter giving optimal capacitance when mixed with the MoS2. The alternative layer graphene–MoS2 structure was confirmed by Raman spectroscopy and electron microscopy, leading to a high specific capacitance (290 F cm–3 at 0.5 A g–1) and 90% retention of capacitance after 10 000 cycles.