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能源材料-2

能源æ...

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能源材料 (Energy Materials) 幹程 -2 授幹教師:穆帯著 中央大學 材料與化學工程學系 油化學基本原理與應用 油極反應動力學與熱力學
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Electrochemical cell and reaction Electronic conductor : electrode Ionic conductor: electrolyte We will be concerned with the electrode/electrolyte interface and the events that occur there when an electric potential is applied and current passes.
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Electrode Material Charge is transported through the electrode by the movement of electrons (and hole) 1. solid metal (Pt, Au,..) 2. liquid metal (Hg, amalgams) 3. carbon (graphite); 4. semiconductor
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Electrolyte In the electrolyte phase, charge is carried by the movement of ions. 1.Liquid solution containing ionic species 2. Fused salt: molten NaCl-LiClO 4 eutectic 3. Ionic conductive polymer (Nafion, PEO-LiClO 4 ) 4. Solid electrolyte (sodium b-alumina)
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Electrochemical Cell Zn/Zn 2+ ,Cl - /AgCl/Ag Pt/H 2 /H + ,Cl - /AgCl/Ag
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Reference Electrode 1. Constant makeup 2. Potential is fixed 3. Any change in the cell are ascribable to the working electrode 1. SHE 2. SCE 3. Ag/AgCl Internal reference: 1. Aqueous solution: Fe(CN) 6 4- /Fe(CN) 6 3- 2. Organic solution Fe(C 5 H 5 ) 2 /Fe(C 5 H 5 ) 2 +
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Reduction Process
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Oxidation Process
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Typical Electrochemical experiment
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Background limits HBr is a supporting electrolyte Br 2 + 2e - 2Br -
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H 2 Overpotential
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Reduction Wave for Cd 2+
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Pt electrode in 1M HCl Au electrode in 1M HI
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Hg electrode in 1M HCl
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Faradaic and Nonfaradaic Processes Faradaic process : electron transfer causes oxidation or reduction to occur. Reactions are governed by Faradaic raw. Nonfaradaic process : ions adsorption and desorption on the electrode-solution interface
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Faradaic process Faradaic process: electron transfer process which causes oxidation or reduction to occur. Non-faradaic process: electron flow due to the adsorption and desorption processes, or the structure change of the electrode/solution interface. Electrode Solution Red Ox n e - n e - Electrode Solution Electrode Solution H H O H H O H H O - - - - + + + + H H O H H O H H O Current Time Current Time
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Nonfaradaic Processes IPE : ideal polarized electrode , no charge transfer can occur across the metal-solution interface Hg electrode in a deaerated KCl solution Potential range about 2V wide IN the potential range, Hg E’d is an IPE .
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Redox reaction on Hg E’d Oxidizing limit Reducing limit In the potential range, thermodynamically possible but occurs at a very low rate
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Capacitance and Charge of an Electrode
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q M = -q S M = q M /A, C/cm 2
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