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The Electrochemical Behaviors Of Sb Irreversible Adsorption On Pt Single Crystal Electrodes And Kinetics Of Hcooh Oxidation

Posted on:2003-04-05Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y Y YangFull Text:PDF
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The Electrochemical Behaviors of Sb Irreversible Adsorption on Pt single Crystal Electrodes and Kinetics of HCOOH OxidationThe oxidation of C, molecules, such as HCOOH, CH3OH, HCHO and CO et al, is of fundamental importance in electrocatalysis and fuel cell applications. Single crystal planes can provide surface models of well-defined atomic arrangement. The use of single crystal electrodes has contributed to reveal the intrinsic relationship between surface structure of electrodes and their properties at an atomic level in electrocatalysis.In order to explore the surface modification of Pt single crystal electrodes by Irreversibly Adsorption (IRA) of Sb and the electrocatalytic effects of modified electrodes for HCOOH oxidation, three basal planes (100), (110), (111) and two stepped surface (320)(3(110)x(100)), (331)(3(lll)x(lll)) of Pt single crystal were prepared and used in the study of this thesis. Cyclic voltammetry, ECSTM, in situ time resolved FTIR spectroscopy, programmed potential step technique were employed in the study. Based on the data processing method of integration transform developed in our group, the kinetics of HCOOH oxidation on Pt(hkl)/Sb electrodes of different 9Sb has been investigated quantitatively, and both the rate constant kf, the transfer coefficient f! and the factor of activation energy correction /were determined.The main results and conclusions are summarized as follows.1. Electrochemical characterization of surface modification of Pt(hkl) with IRA Sb adatomsThe results obtained in cyclic voltammograms demonstrated that the electrochemical behavior of IRA Sb is sensitive to the structure of Pt single crystal electrodes. Since Pt(lOO)Vand Pt(320) surfaces contain both (100) symmetrical sites, the redox peak of Sbad is measured at 0.37V on these two electrodes. However, Pt(lll) and Pt(331) include (111) symmetrical sites, the redox peak of Sbad is shifted negatively to 0.20V. The surface coverage of Sb^ (0Sb) can be conveniently monitored under electrochemical condition. Starting from the saturated adsorption, Pt(hkl)/Sb of different coverage can be obtained conveniently by controlling the up limit of potential scan (EJ and the number of potential cycles. The Sb adatoms formed in irreversible adsorption on Pt(lOO), Pt(llO) and Pt(lll) are stable at potentials below 0.45 V, below 0.40V on Pt(320) and below 0.35V on Pt(331). The behaviors of surface redox process of Sbad varied with the surface atomic arrangement of Pt single crystal electrodes. It was attributed to the electronic effect that the presence of a small amount of Sbad on Pt(llO), Pt(320) and Pt(331) can inhibit almost completely hydrogen adsorption. The geometric effect was manifested in the case of Pt(lOO) modified with Sb adatoms where the 0H varied with 0Sb linearly. It has determined that the irreversible adsorption on Pt(l 11) is a complex process, due to the Sb adatom may enter into the Pt(l 11) surface atomic layer to form Pt-Sb alloy at high coverage of Sbad. The surface atomic arrangement can be disturbed through the adsorption of Sb. In comparison the surface disturbance degree, the surface structure of stepped planes are confirmed to be more stable than the basal planes.2. Electrocatalyric properties of Pt(hkl) modified with IRA Sb adatoms towards HCOOH oxidationThe results of cyclic voltammeter and time resolved FUR specrroscopy have revealed that the dissociative adsorption of formic acid can be suppressed by the presence of Sb^ on platinum single crystal surfaces. Even at a low coverage of Sb^, the dissociative adsorption can be partially impeded. Since the adsorption of Sb on the Pt(hkl) planes may influence the reaction activation energy, the peak potential of HCOOH oxidation are all measured in the potential range between 0.20V and 0.30V. The electrocatalytic effects of Sbad for HCOOHVIoxidation on the five Pt single crystal electrodes consist in the enhancement of oxidation current and the negatively shift of oxidation potential. It has been measured that t...
Keywords/Search Tags:Pt single crystal electrodes, Formic acid, Irreversible adsorption Sb, Electrooxidation, Kinetics
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