Electrochemical Preparation Of Bismuth,Bismuth Telluride Alloys And Properties Of Bismuth Oxide

Bi elemental nanomaterials have aroused people's attention due to their unique morphology and size as well as excellent optical properties,magnetic properties and catalytic properties.Bismuth-tellurium alloy is widely used thermoelectric materials,while the bismuth oxide has good optoelectronic properties.In this thesis,bismuth,bismuth-tellurium alloy films were prepared by electrodeposition,and the kinetics of the preparation process were studied.The bismuth film was converted into bismuth oxide by anodization,and its photoelectric properties were tested.Cyclic voltammetry,chronoamperometry and chronopotentiometry were used to study the kinetic parameters such as redox potential,diffusion coefficient and electron transfer number of bismuth ion in choline chloride-urea(1:2 molar ratio).The elemental structure and morphology of the deposited films obtained by potentiostatic deposition were characterized by scanning electron microscopy and X-ray diffraction.The results show that the electrode reaction of bismuth ion in the molten salt is one-three-electron irreversible reaction,and the initial position of reduction peak is near-0.5 V.The coatings obtained by potentiostatic electrodeposition at different potentials and different potentials are pure bismuth.The morphology of the bismuth particles obtained by electrodeposition at-0.5 V,-0.7 V,-0.8 V,-0.9 V,-1.0 V for 15 min were hexagonal,sharp synaptic,petal-like,fishbone-like,twig-like respectively.However,all the nuclear types belong to three-dimensional continuous nucleation under these potentials.Cyclic voltammetry,chronoamperometry and chronopotentiometry were used to study the kinetic behavior of ions in a molten salt system containing tellurium ions and choline chloride-urea containing bismuth ions and tellurium ions(molar ratio of 1:2).Pure tellurium plating and bismuth-tellurium alloy plating were obtained.The tellurium plating are composed of spheres particles with different sizes.The deposition potential has great effects on the morphology of bismuth-tellurium alloy.Spherical particles with different sizes are obtained at-1.2 V,while flower-like particles with uniform size was obtained at-1.5 V.The nucleation of bismuth telluride alloy at-1.2 V belongs to continuous nucleation,while it is instantaneous nucleation at-1.5 V.Different types of bismuth oxide were obtained bythermal oxidation and electrooxidationusing the electrodeposited bismuth plating,and the influence of preparation conditions and oxidation conditions on the structure,morphology and photoelectric properties of the oxide was studied.After thermal oxidation at 250?for 12 h,the photocurrent of the bismuth oxide increased with the decrease of electrodeposition potential of the bismuth.When the bismuth was electrodeposited at-1.0 V,the obtained bismuth oxide presents the highest photocurrent of 0.64 ?A/cm2.Cyclic voltammetry method was used to obtain different bismuth oxide with different potential ranges,scanning rates and scanning numbers.The highest photocurrent of oxide was 16.5 ?A/cm2 which was obtained with potential scan range of 0?5 V,scan rate of 0.02 V/s,scanning cycle of 6.In addition,it was found that the test potential had a great influence on the photocurrent value.The photocurrent was positive when it was at the open-circuit potential,while it was negative at the bias potential which was negative to the open-circuit potential.