Introduction to electrochemical systems
description
Transcript of Introduction to electrochemical systems
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Introduction to electrochemistry
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Electrochemical cell
load
electrically charged species medium+ = electrolyte
ions
complex ionsmolecules
waterorganic solvent
ceramics
molten saltsionic liquids
membranes
electrodes
external circuitload or measuring equipment
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Electrochemical reaction
electrode
e-electrochemical reaction = heterogeneous redox reaction
The rate of an electrochemical reaction depends on the potential of the electrode
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Redox-reactions in the cell
load
PtPt
acidic aqueous electrolyteH2SO4, HClO4, …
AnodeH2 2H+ + 2e-
Eo = 0.00 V
Cathode O2 + 4H+ + 4e- 2H2OEo = 1.23 V
reaction of interest = working electrode
counter electrodereference electrodeauxillary electrode
I = nFr Q = It = nzFnF
GE
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Metal bonding, Fermi level and work function
Fermi Dirac distribution
Fermi level P(E) = 1/2
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Potential and voltage
f inner or galva potential
outer or voltapotential surface potential
faasi a
charge invacuum
nFGE
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Electrode potential, potential difference and voltage
electrode
probability for finding an electron
solution
Ef
elec
trod
pote
ntia
l
+
- electrode
occupiedstates
unoccupie
d
occupied states
unoccupie
d
0.50 1
Ef’
0.50 1
solutionen
ergy
nFGE
kTEEeEP
/)( f1
1)(
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Electron transfer on the electrode
Ef
electrode
occupiedstates
unoccupied
Ef’
ener
gy
HOMO
LUMOe-
HOMO
LUMOe-
electrode
a molecule in a solvent
a molecule in a solvent
Ag+(aq) + e- Ag Ag+(aq) + e- Ag
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Potential window
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polarizability
ideally nonpolarizable
ideally polarizable
reaction rate ~
reaction rate ~ 0
Li4Ti5O7 electrode for lithiun ion battery
ultra capacitor