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UPD Behavior And Reaction Mechanism Of Cobalt (Ⅱ) On Polycrystalline Platinum And Gold Electrodes

Posted on:2022-02-11Degree:MasterType:Thesis
Country:ChinaCandidate:M Y SongFull Text:PDF
GTID:2491306347451504Subject:Physical chemistry
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UPD has long been an important topic in electrochemical research because of its important theoretical and practical value.In this paper,polycrystalline Pt electrode and polycrystalline Au electrode are used as working electrode,platinum plate electrode as auxiliary electrode,saturated calomel electrode as reference electrode,and sulfate,perchlorate and chloride containing Co2+ as electrolyte solution,the Underpotential deposition behavior of cobalt ion on the polycrystalline platinum electrode and the polycrystalline gold electrode in different anionic systems has been studied by the combination of CV,EIS and CHR,the effects of different electrochemical parameters on the electrode surface dynamics were also discussed.The findings are as follows:(1)In the four systems of ammonium sulfate,ammonium perchlorate,ammonium sulfate(Cl-added)and ammonium perchlorate(Cl-added),Co has obvious UPD behavior on Pc Pt electrode and Pc Au electrode,and they all have wide potential range and complex peaks,it can be considered as a surfacelimited electrodeposition process to some extent.(2)Under different anionic conditions(SO42-、ClO4-、SO42-+Cl-and ClO4-+Cl-),it was found that Co has different UPD kinetics on Pc Pt electrode and Pc Au electrode.In the UPD process of Co on Pc Pt electrode,there are usually two times constants,and the phase angle peak moves to the high frequency region with the negative shift of potential,and there is also the phenomenon of diffusion impedance,the impedance modulus decreases with the negative shift of potential.On the Pc Au electrode,with the negative shift of the electrode potential,the phase angle gradually superposes from two peaks to one,and its position gradually moves towards the high frequency region.(3)The coupling mechanism of 2D instantaneous nucleation and 2D continuous nucleation under electrochemical control and Langmuir type adsorption is followed in four systems:ammonium sulfate system,ammonium perchlorate system,ammonium sulfate(Cl-)system and ammonium perchlorate(Cl-)system However,due to the influence of anion adsorption,the charge density of UPD of Co is different in the same time,the order is QUPD(ClO4-+Cl-)>QUPD(SO42-+Cl-)QUPD(ClO4-)>QUPD(SO42-).The results show that the interaction between cobalt ion and polycrystalline electrode is different in different systems.In the UPD process of Co on the Pc Au electrode,compared with the Pt electrode,Co has smaller charge density,shorter adsorption process and nucleation growth process in the same time,it is shown that the UPD process of Co on the Pc Au electrode is weaker than that of Co on the Pc Pt electrode,but the continuous nucleation charge density(Q2Dp-Li)is always higher than the instantaneous nucleation charge density(Q2Di-Li),the results show that 2D continuous nucleation and growth is the main process of Co UPD.
Keywords/Search Tags:Cobalt, Underpotential deposition, Cyclic voltammetry, Electrochemical impedance spectroscopy, Chronoamperometry
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