Synthesis, Characterization and Energy Applications of Transition Metal Chalcogenide Nanostructures

Abstract

The thesis titled “Synthesis, Characterization and Energy Applications of Transition Metal Chalcogenide Nanostructures” encompass the work on transition metal chalcogenide nanostructures for their prospective use as electrode materials for supercapacitors and electrochemical water-splitting. Herein, the hydrothermal method is employed for the synthesis of different transition metal chalcogenide nanostructures, namely cobalt chalcogenides (CoTe2 and CoSe2), nickel chalcogenides (NiTe2, NiSe2 and NiSe), molybdenum chalcogenides (MoS2, MoSe2 and MoTe2) and copper chalcogenides (Cu2S and Cu2S-Ni3S2). The synthesis is followed by some of the important physiochemical characterization techniques, such as XRD, SEM, HRTEM, XPS and etc. CoTe2 and CoSe2 as supercapacitor electrodes delivered the specific capacitances of 360 F g-1 and 951 F g-1 at 5 mV s-1 scan rate. NiTe/NiTe2 nanosheets as HER electrocatalyst required an overpotential of -432 mV to deliver 20 mA cm-2 current density. While, it required overpotential of 679 mV for the OER. Further, NiSe2 nanosheets and NiSe nanoflakes required the overpotentials of -198 mV and - 217 mV, respectively, to deliver 10 mA cm−2 current density for the HER. MoX2 (X= S, Se, Te) nanostructures as HER electrocatalyst rank their performance in the order: MoSe2>MoS2>MoTe2. On the other hand, isoelectronic tungsten (W) doping enhanced the specific capacitance of MoSe2 supercapacitor electrodes. Specific capacitance as a function of W-doping indicated 2 M % as an optimum doping amount, delivering the maximum specific capacitance of 147 F g-1. Furthermore, graphene composites of these nanostructures delivered enhanced specific capacitance (248 F g-1) and superior cycle life. Cu2S micro-hexagons could catalyze the HER in both basic (1 M KOH) and acidic solutions (0.5 M H2SO4), corresponding to the extreme pH values of 14 and 0, respectively. On the other hand, Cu2S enhanced the alkaline water-splitting characteristics of nickel sulfide (Ni3S2), requiring the overpotentials of -149 mV and 329 mV to deliver current density of 10 mA cm-2 for the HER and OER, respectively. Furthermore, overall-water splitting required the cell-voltage of 1.77 V to deliver 10 mA cm-2 and demonstrated ultra-long term stability for 100 h.