Alternative TitleSteady-state Voltammetry at Glass-coated Nanoelectrodes
Note (General)Ultramicroelectrode now plays a significant role in the study of the mechanism and kinetics of fast electron transfer under the steady-state condition because of the existence of high mass transport. On the other hand, excess electrolyte is necessary in order to keep electroneutrality. But electrolyte often makes the reactions complicated because of the electric neutrality step. Fortunately microelectrode techniques can affbrd to measure current voltage curves with out electrolyte. However, the experimental data reported are not consistent, and vary from researchers to researchers. The wide variation by microelectrode techniques may be ascribed to instability or an irreproducibility of microelectrodes, delay of a potentiostat at fast measurements, uncompensated resistance, and/or participation of capacitive currents. A strategy of overcoming these complications is to establish a commonly available fabrication technique. So the aim of this thesis deals with fabrication of a number of endurable nanoelectrodes at high success rate with minimal artifacts Thus the fabricated electrodes are applied to fast electron transfer kinetics and electrode reaction in low ionic strength solutions under the steady-state condition. Consequently, the microelectrodes are predicted to provide reliable electrokinetic data. Introduction of this thesis is devoted to the overview, properties and fabrication of nanoelectrodes. The experimental procedures are described in chapter 2. The following chapters are devoted to fabrication of glass-coated nanoelectrodes (Chapter 3), fast electron transfer reactions by steady-state microelectrode techniques and fast scan voltammetry (Chapter 4), and voltammetry of two-electron transfer reaction in low ionic strength solutions(Chapter 5), Conclusion is given in Chapter 6. Chapter 3 deals with fabrication of glass-coated electrodes with nano- and micrometer size by means of dissolutionwith HF.A key of the process was to make a thin glass film on the Pttip and toe xpose the Ptsurface by HF dissolving. 50 electrodes thus fabricated had diameters ranging from l nm to 5 μm, estimated from the steady-state current of diffUsion-controlled current of ferrocene in acetonitrile and ferroceny lderivative in aqueous solution. They exhibited reproducible and stable voltammograms without hysteresis, withstanding 6 hours,continuous use and l5 hours' iterative processes of heat and voltammetry. Chapter 4 is devoted to fast electron transfer reaction by steady-state microelectrode. Rate constants of fast electron transfer reactions of six species, which have been determined equivocally by fast voltammetry, are attempted to be evaluated with steady-state voltammetric measurements at ultramicroelectrodes. This work is motivated by the experimental feasibility of high current density at ultramicroelectrodes without effbcts of capacitive currents or solution resistance. By increasing mass transport, electron transfer becomes the rate determining step,and then potential shift will be found. Unfortunately no potential shift is observed. This fact implies that the rate constants are at least larger than lOcm s-1. Fast voltammetry is carried out at a large electrode for scan rates less than lOVs-1. Peak-to-peak potentials become larger with an increase in the scan rates. This variation is fitted to the mass transport equation complicated by the electrode kinetics for the rate constant of O.Ol7cms-1. The inconsistency between the two methods is ascribed to solution resistance at fast scan Voltammetry. Chapter 5 deals with electrode reaction without supporting electrolyte. 1,4-Benzoquinone (BQ) and tetracyanoquinodimethane (TCNQ), which are reduced consecutively to mono-anions and dianions under conventionally voltammetric conditions, cannot be reduced up to the dianions without supporting electrolyte in acetonitrile solution. Voltammograms without supporting electrolyte at microelectrodes with the diameters less than O.4μm do not include noticeably IR-drop. With an increase in the conductivity of the solution by addition of electrolyte, the second reduction wave appears, involving the potential shift. The electrolyte does not influence the first reduction waves but varies the second one. The salt effect specific to the second wave is ascribed to non-stoichiometric association of the redox anion with the salt cation.
Collection (particular)国立国会図書館デジタルコレクション > デジタル化資料 > 博士論文
Date Accepted (W3CDTF)2020-01-16T18:57:33+09:00
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