Author: Grzegorz (Gregory). JerkiewiczPublisher:
ISBN:
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Languages : en
Pages : 0
Book Description
The main body of research reported in this thesis was concerned with studies of H, and OH or O, chemisorption on polycrystalline and single-crystal Pt surfaces, including studies of the anodic growth of thick oxide films and distinction between the several states in which they are formed. In the work reported in the first part of this thesis, a standard procedure has been worked out for preparing polycrystalline Pt electrodes. Such electrodes reveal and sustain the same physical and electrochemical properties over long periods of time; this is probably the result of the discovery and use of the "electrochemical annealing" phenomenon. Thus, polycrystalline Pt electrodes can be well characterized in a reproducible way after selected controlled thermal and/or electrochemical pretreatments and are found to become reconverted to the same, stable and final state (the "electrochemically annealed" state) after prolonged cycling between 0.05 and 1.40 V, RHE, regardless of their initial pretreatment. At Pt anodes subjected to regimes of anodization at high controlled potentials for various periods of time, it was found that at least five states of the oxide film can be distinguished, in reduction, using the cyclic-voltammetry technique. The extent of growth of the oxide film at Pt proceeds according to a direct logarithmic law in time of growth for polarization potentials between 1.80 and 2.30 V, RHE. Upon further increase of the polarization time, the oxide growth rate increases some 400 times due to the onset of the high-field oxide growth mechanism of Mott and Cabreta. Upon increase of the polarization potential and time, it has been shown that multilayer phase oxide is generated on top of the quasi-2-d oxide. It is found that the quasi-2-d oxide can be reduced independently from the bulk-type oxide, leading to a situation where the thick-oxide film resides on bare Pt. It is also demonstrated that the quasi-2-d oxide resides between Pt and the thick oxide film. The oxide growth rate depends on the crystallographic orientation of the underlying metal surface. Cycling of "quenched" Pt(111) and Pt(100) into the oxide region results in surface restructuring (probably enhanced by the stress from quenching). Such pretreated Pt(111) and Pt(100) surfaces exhibit the same electrochemical behaviours as those of annealed Pt(111) and Pt(100). (Abstract shortened by UMI.).
