전기화학3

전기화학3

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1 Faradaic and Nonfaradaic Processes Two types of processes can be occurred at electrodes. 1) Faradaic Process § Charges (e.g. electrons) are transferred across the electrode-electrolyte interface. § Electron transfer causes oxidation or reduction to occur. § Since such reactions are governed by Faraday's law (i.e., the amount of electrochemical reaction caused by the flow of current is proportional to the amount of charge passed), they are called Faradaic Processes . § Electrodes at which faradaic processes occur are called charge transfer electrodes. Faradaic and Nonfaradaic Processes
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2 2) Nonfaradaic process § Under some conditions, a given electrode-electrolyte interface shows a range of potentials where no charge-transfer reactions occur. § However processes such as adsorption and desorption can occur and the structure of the electrode-electrolyte interface can be changed with changing potentials or solution composition. ⇒ These processes are called Nonfaradaic Processes . § Even if charge does not across the interface, external currents can flow when the potential or solution composition changes. § Both faradaic and nonfaradaic processes occur when electrode reactions take place. § Although the faradaic processes are usually of primary interest in the investigation of an electrode reaction, the effects of the nonfaradaic processes must be taken into account in using electrochemical data to obtain information about the charge transfer and associated reactions. § We next proceed by discussing the simple case of system where only nonfaradaic processes occur.
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3 A. Nonfaradaic Processes Ideal Polarized Electrode(IPE) § An electrode at which no charge transfer can occur across the electrode-electrolyte interface, regardless of the potential imposed by an outside source of voltage, is called an “ideal polarized electrode(IPE)”. § While no real electrode can behave as an IPE over the whole potential range available in a solution, some electrode-electrolyte systems can approach ideal polarizability over limited potential ranges. § For example, a mercury electrode in contact with a deaerated potassium chloride solution approches the behavior of an IPE over a potential range about 2 V wide. § At sufficiently positive potentials, the mercury can oxidize in a charge
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전기화학3

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