| Summary: | 博士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 99 === In this research, Ni-Pt thin films were prepared by the electrochemical deposition method. The experiment data were analyzed and presented by electrochemical method (ex: cyclic voltammetry and linear voltammetry), XRD, SEM, ICP-MS, EQCM, WDS, nano-AEM and XAS. The experiments are divided into four part of themes including: (1) the performance of electrochemically amperometric ethanol sensor with Ni-Pt thin films; (2) the electrochemistry and reaction kinetics of sensing ethanol on Ni-Pt thin films; (3) the electrochemical aging effect on the phase transformation of Ni(OH)2/NiOOH in the Ni-Pt thin films; (4) the rate of producing Ni(OH)2 on the Ni-Pt films and structure effect of Ni-Pt thin films. The results are summarized as follows briefly.
For the performance of ethanol sensor with Ni-Pt thin films, the sensitivity decreased with the increase of Pt content of the Ni-Pt thin film in KOH solution at the applied potential of 520 mV. The response time of sensing ethanol decreased with the increase of Pt content. The addition of Pt could reduce the decline of sensitivity with time and improved the stability of sensing ethanol. In addition, the Ni-Pt thin film which contained 70 at % Pt had best stability during 63 days. The Ni-Pt presented bad selectivity toward the interferences such as methanol, glucose and vitamins C.
For kinetics behavior of sensing ethanol on Ni-Pt thin films, although the addition of Pt in Ni-Pt thin films could not aid the rate of ethanol oxidation with NiOOH. It could promote the rate for electrochemical reaction of Ni(OH)2/NiOOH and accelerate the rate of sensing ethanol further. This could help to reduce response time. The rate of Ni(OH)2/NiOOH redox reaction would be faster than that on pure Ni film at the applied potential which is more than 0.63 V. Furthermore, the oxide which may increase the resistance of the Ni films could be restrained by the addition of Pt during Ni(OH)2/NiOOH redox reaction. This could reduce the increase of the potential of Ni(OH)2/NiOOH redox reaction with the increase of scan rate.
For the phase transformation of Ni(OH)2/NiOOH in the Ni-Pt thin films, Ni(OH)2 gradually grew and concerted to β-Ni(OH)2 in the Ni-Pt thin films during cyclic voltammetry. The rate of Ni(OH)2 converting to β-Ni(OH)2 could be accelerated with long-time cyclic voltammetry of Ni(OH)2/NiOOH. The addition of Pt could reduce the rate of Ni(OH)2 converting to β-Ni(OH)2 in Ni-Pt thin films. The thicker the Ni-Pt films were, the more the films contained the amount of α-Ni(OH)2. This fact also hindered the transformation of Ni(OH)2 to β-Ni(OH)2 in the Ni-Pt thin films. These are helpful to stabilize in α-Ni(OH)2. Aging in KOH solution for a long time could assist Ni(OH)2 in transforming to β-Ni(OH)2 in Ni-Pt films. Some H2O and O2 would enter into the Ni-Pt films to form extra amount of Ni(OH)2 while aging in a humid O2 environment. After long time of ethanol oxidation, the phase of most Ni(OH)2 in the Ni-Pt films was β-Ni(OH)2 although the films still contained a little number of α-Ni(OH)2. The phase of β-Ni(OH)2 in the Ni-Pt films could be stable in KOH solution rather than in a humid O2 environment where the structure of β-Ni(OH)2 may be destroyed by H2O an O2.
For rate of producing Ni(OH)2 and structure of the films, dispersion of nickel atom and structural change arose from the addition of Pt in the films. Various producing rates of Ni(OH)2 were found in the films of different content of Pt. Ni atoms were efficiently oxidized to Ni(OH)2 in the Ni-Pt films. However, Ni atoms were inefficiently formed to Ni(OH)2 during cyclic voltammetry.
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