The Effects of Underpotential Deposition and Crystallographic Orientation Toward Electrochemical Reactions on Gold and Platinum Electrodes

• Main Authors: Chi Wang, 王琦
• Other Authors: Chung-Sun Chung
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/65847656628193229276

博士 === 國立清華大學 === 化學系 === 88 === Described in this thesis are electrochemical studies utilizing the solutin flushing tactics recently developed in this laboratory, which can change the solution condition during electrochemical reaction while maintain the surface from being altered. When conducting electrochemical surface analysis, there usually exist several factors that affect the reaction, making it difficult to resolve the results. With this technique, one can reserve specific factors and remove others so as to understand the roles these factors play. In chapter 2 anion effects upon upd behavior of copper on platinum electrodes was studied. By flushing with fresh electrolyte solution to remove halide ions existed during deposition process before anodic stripping of the upd copper, the measurement was not interfered by halide. Comparison of flushing and conventional methods gave quantitatively the effects of chloride in solution upon deposition/stripping of copper. In chapter 3 the effects of copper adlayer structure upon nitrobenzene reduction on Au(111) surface was studied. It is known that upd copper hinders the reduction of nitrobenzene on gold electrode. The solution was flushed after copper adlayer of various coverages was obtained. Electroreduction of nitrobenzene was then carried out on this modified electrode. The dependence of half-wave potential (Ep/2) upon copper coverage (theta(Cu)) was found to be closely related to the structure of the adlayer. In sulfuric solution, the copper adatoms was randomly arranged on Au(111) when theta(Cu) < 0.25, while formed an ordered (root 3 ×root 3 )R30 when 0.25 < theta(Cu) < 0.65. At even higher coverage, it formed a (1 ×1) structure. Ep/2 decreased as coverage increased when theta(Cu) < 0.25, reached a platau when 0.25 < theta(Cu) < 0.65 and decreased again when theta(Cu) > 0.65. The the electroreduction of nitrobenzene on Au(111), -(110), -(100), -(210) and polycrystalline electrodes was studied in chapter 4. The electroreduction of nitrobenzene is very sensitive to the surface condition of the electrode. The reduction on Au(110), -(210) and -(poly) electrodes can lead to a stably adsorbed redox intermediate, not reported before, at 0.33 V vs. SCE. The intermediate was deduced as phenyldihydroxylamine and phenyldihydroxylamine cation redox couple. The unusual stability of the redox intermediate is found to correlate with the orientation of adsorbed water molecules that can be intimately controlled by an applied potential in relationship to the potential of zero charge on the surface.