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• Main Authors: Yen-chun Kuo, 郭妍均
• Other Authors: Shueh-lin Yau
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/27173906436079533859

碩士 === 國立中央大學 === 化學學系 === 102 === In situ scanning tunneling microscopy (STM) and cyclic voltammetry (CV) were used to examine two topics: Effects of anions and pH on the electrodeposition of cobalt on Pt(111) electrode. Part I was the electrodeposition of cobalt onto a Pt(111) electrode in 0.1 M K2SO4 + 1 mM H2SO4 (pH3). Cobalt deposited tended to nucleate uniformly on the terrace and accompanied by hydroxide adsorption, then assembled into ordered honeycomb-like structured film at -0.34 V( vs. Ag/AgCl ). While the potential was shifted to -0.6 V, hydroxide was reduced and local ordered moiré patterns were displaced by rough patches immediately. Chloride ions and cobalt were coadsorbed to form a disordered bilayer. Cobalt monolayer accompanied with a layer of bromide to arrange in honeycomb structure. Adsorption strength of anion and cobalt: Br- > Cl- > OH-. In potassium sulfate solution containing chloride and bromide, the deposition efficiency of cobalt was highest in presence of bromide, followed by chloride, and potassium sulfate yielded the worst efficiency. For the first five layers of cobalt, deposition proceeded mainly in a two-dimensional mode, producing a regular moiré pattern in potassium sulfate solution. The in-plane interatomic spacing between cobalt atoms decreased gradually from 0.257 to 0.254 nm. Spiral islands were observed starting from the sixth layer, yielding well-defined, stacked triangules defined by <110> aligned steps. By contrast, islands with irregular shapes were found in the presence of chloride. In the presence of bromide, cobalt was deposited in three-dimensional (Volmer-Weber mode). Electrodeposition of cobalt onto a Pt(111) electrode in potassium sulfate solutions made of unlike pH. Deposition efficiency reached as high as (72.5 %) in pH6 solution, by opposed to 8.0 % found in pH2 solution. Similarly, nickel was deposited more efficiently in pH3 than pH2 solution. Due to the higher proton concentration in acidic solution, charge wasw mostly consumed by protons to yield hydrogen, leading to lower reduce deposition efficiency of nickel and cobalt. It was observed that the first layer of cobalt or nickel grew in fractals and in extended fractal at pH2. In addition, the deposition of cobalt or nickel accompanied by hydroxide adsorption into ordered honeycomb-like structure at pH3 solution. At more negative potential, hydroxide was desorbed, producing partially ordered honeycomb-like structure. The dgree of ordering of honeycomb-like structure was poorer in pH6 electrolyte. Multilayer deposition of cobalt or nickel in pH2 and pH3 potassium sulfate solution occurred in two-dimensional, producing regular moiré patterns until the sixth layer, where three-dimensional islands were imaged by the STM. However, the deposition at pH6 followed the VW mode. Cobolt deposit could pack in fcc at pH2, whereas it adopted hcp stacking at higher pH(~6) sulfate solution.