Nanostructured Transition Metal Tellurides: Thin Film Fabrication, Characterization, and their applications to Electrochemical Devices

Currently, metal oxides and chalcogenide nanostructures are the most visible energy sources. Numerous metal oxides are used in solar cells, batteries, and transistors. Among them, metal telluride nanostructures have not been widely used but have a structure similar to that of metal oxides, and they are actively under investigation. The metal telluride nanostructure has a narrow bandgap and is highly sensitive to light and has high electric conductivity, thus being a solar cell and a material having high thermal conductivity. Firstly, molybdenum ditelluride thin film was made by electrodeposition. It is an economical way, an easily adjustable way for thickness and can make grain size particle. Molybdenum ditelluride has a layer structure likely graphene. And molybdenum dioxide, molybdenum disulfide and molybdenum diselenide are have a layer structure and used as an anode of lithium battery. Electrodeposited molybdenum thin films on copper foil are made an anode of lithium ion battery. Since the size of tellurium atoms is similar to lithium ion and molybdenum ditelluride is layer structure likely graphene, molybdenum ditelluride is suitable as an anode of lithium ion battery. Secondly, The present work demonstrates a highly controllable, facile and environmentally friendly aqueous solution based synthetic method for oxide contamination-free Ag2Te thin films on desired substrates at room temperature using ion exchange induced chemical transformation of Ag/AgxO thin films. The films before and after chemical transformation reaction are characterized using an energy dispersive X-ray analyzer, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, thin film X-ray diffraction technique, high resolution transmission electron microscopy, and the selected area electron diffraction analysis technique. The as-deposited Ag2Te films show a highly crystalline nature even without thermal treatment. Furthermore, the electrochemistry for lithiation/delithiation of the Ag2Te film is studied for exploring its feasibility in the application as an anode material in a Li-ion battery. The experimentally estimated capacity of the Ag2Te electrode for Li storage is found to be about two and half fold larger than the theoretical capacity of the Ag2Te material. This implies that the binder-free Ag2Te film prepared by the current method could find a potential application in the Li-ion or other similar charge storing devices. Lastly, metal telluride nanostructures have demonstrated several potential applications particularly in harvesting and storing green energy. Metal tellurides are synthesized by tellurization process performed basically at high temperature in reducing gas atmosphere, which makes the process expensive and complicated. The development of a facile and economical process for desirable metal telluride nanostructures without complicated manipulation is still a challenge. In an effort to develop an alternative strategy of tellurization, herein we report a thin film formation of self-standing cobalt telluride nanotubes on various conducting and nonconducting substrates using a simple binder-free synthetic strategy based on anion exchange transformation from a thin film of cobalt hydroxycarbonate nanostructures in aqueous solution at room temperature. The nanostructured films before and after ion exchange transformation reaction are characterized using field emission scanning electron microscope, energy dispersive X-ray analyzer, X-ray photoelectron spectroscopy, thin film X-ray diffraction technique, high resolution transmission electron microscope, and selected area electron diffraction analysis technique. After the ion exchange transformation of nanostructures, the film shows conversion from insulator to highly electrical conductive semimetallic characteristic. When used as a counter electrode in I3���/I��� redox electrolyte based dye-sensitized solar cells, the telluride film exhibits an electrocatalytic reduction activity for I3��� with a demonstration of solar-light to electrical power conversion efficiency of 8.10%, which is highly competitive to the efficiency of 8.20% exhibited by a benchmarked Pt-film counter electrode. On the other hand, the telluride film electrode also demonstrates electrocatalytic activity for oxygen evolution reaction from oxidation of water.Docto