Technology Outline (Process Description)

We started the project by working on three different materials Co3O4, MnO2 and MoS2 and then we focused on MoS2 as a promising electrode material for the supercapacitor. We studied its two different morphologies (sheet- like morphology and wire-like morphology). MoS2 nanosheets were prepared from the bulk by exfoliation technique, and MoS2 nanowires were directly grown over the Ni foam substrate by a simple hydrothermal process. The latter helped in the large-scale preparation of MoS2. The growth time played a crucial role in determining the surface orientation of nanowires over the substrate, which in turn affects the energy storage performance. The MoS2 nanotube electrode with brush-like arrangement over nickel foam exhibited the best performance as compared to the electrodes grown for 12, 24, and 48 h. For the first time, a symmetric supercapacitor based on MoS2 with very high mass loading of active materials (~30 mg cm^-2) is fabricated. In symmetric configuration the electrode prepared at 36 h having a mass loading of 30 mg cm^-2, exhibited a specific capacitance value of 244 F g^-1 with an energy density of 12.2 Wh kg^-1 at 1 A g^-1. The capacitor retained nearly 92% its maximum capacitance even after 9000 charge-discharge cycles at a constant current density 5 A g^-1. The study confirms that MoS2 nanostructures of high mass loadings grown over conducting substrates have great potential as promising electrodes for energy storage applications.

To further improve the electrochemical performance of the supercapacitors, we decorated the surface of MoS2 with 25% of fine nanoparticles of RuO2 . By depositing the metal oxide, we could achieve the good capacitance value. The as-prepared electrode material was tested for supercapacitor application in symmetric two-electrode configuration. A maximum specific capacitance value (based on the mass loading of RuO2/MoS2 composite in a single electrode) of 719 F/g is obtained for the supercapacitor at a constant current density of 1 A/g. At a constant power density of 0.6 kWkg^-1, the energy density value obtained for supercapacitors is 35.92 Whkg^-1 (the calculation is based on the mass loading of RuO2 /MoS2 alone = 2 mg).

We have also fabricated Coin cell supercapacitor and based on the last review committee suggestion we visited C-MET Thrissur and measured our cells from the lab. we got promising values for real application. As of now with a mass loading of 6 mg of RuO2/MoS2 per electrodes we are able to fabricate coin cell capacitors with a capacitance of 1.2 F, consistently.

As an offshoot for helping the JRF to complete his Ph.D, we also worked on MoSe2 and its compounds as well. The project resulted in 6 journal publications and 6 conference presentations. The project helped develop basic infrastructure for supercapacitor research at CSIR-NIIST.