Electrode Material based on 2D MoS₂ and rGO Aerogels for Supercapacitor Applications

Supercapacitors are of great interest as they bridge the gap of energy density versus power density between conventional capacitors and batteries. The development of new materials for electrodes of supercapacitors is the challenge addressed in this work. The semiconductor phase of MoS₂ (H-MoS₂) is the stable phase while the metallic conducting phase (T-MoS₂) is metastable and will transition to H-MoS₂ with heating and ageing. However, when layers of MoS₂ contact rGO they may transition and remain in the T-MoS₂. In this work, a composite of 2D MoS2 and an rGO aerogel was investigated to produce an effective supercapacitor electrode. Aerogels have potential in this application as their porous morphology give the material a high surface area in which electrolyte can diffuse and electric double layers can form. MoS2 monolayers were prepared by intercalating MoS2 with lithium and exfoliating with sonication, this produced a suspension of monolayer MoS2 with a mean diameter of 500 nm. The rGO aerogel was produced in a self-assembly reduction reaction of GO with ascorbic acid. The MoS2 suspension could be dripped onto the aerogel’s sponge-like structure that effectively soak up the suspension, depositing the MoS2 on the rGO surface. The obtained materials were examined by scanning electron microscopy with element mapping, transmission electron microscopy, atomic force microscopy in contact mode, X-ray diffraction and Raman spectroscopy. Cyclic voltammetry was used to determine the electrochemical window of the electrode, galvanostatic charge-discharge to determine the specific capacitance and electrochemical impedance to analyze the charge transfer kinetics, all experiments were conducted using a three-electrode flooded cell in a 1M solution of Li₂SO₄. The tested devices showed capacitance of 140.4 F g^-1at 0.5 A g^-1 for the supercapacitor with rGO-MoS₂, which is 60% higher than the device using only rGO in the electrode. Moreover, the rGO-MoS₂ electrode based supercapacitor evidenced great cyclability maintaining 85% efficiency after 5000 cycles. Its superior performance over a pure rGO aerogel electrode can be attributed to the increase in surface area of the porous electrode and the increase of interaction with the electrolyte.