Electrochemical Properties of Materials for Electrical Energy Storage Applications Lecture Note 6 November 11, 2013 Kwang Kim Yonsei Univ., KOREA [email protected] 39 Y 88.91 8 O 16.00 53 I 126.9 34 Se 78.96 7 N 14.01
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Electrochemical Properties of Materials for Electrical Energy Storage Applications
Lecture Note 6
November 11, 2013
Kwang Kim
Yonsei Univ., KOREA
39Y
88.91
8O
16.00
53I
126.9
34Se
78.96
7N
14.01
Galvanic cell vs. Electrolytic cell
Electric load
Zn Zn2+ + 2e
Electron generation
Anodic oxidation
Cu2+ + 2e Cu
Electron consumption
Cathodic reduction
Electron flow Electron flow
+ve‐ve
Current flow
DC power supply
Zn2+ + 2e Zn
Electron consumption
Cathodic reduction
Cu Cu2+ + 2e
Electron generation
Anodic oxidation
Electron flow Electron flow
+ve‐ve
Current flow
Galvanic cell Electrolytic cell
Electrochemical cell determines the polarity of electrodes.
DC power supply determines the polarity of electrodes.
Discharge Charge
Galvanic cell vs. Electrolytic cell
DC power supply
Zn2+ + 2e Zn
Electron consumption
Cathodic reduction
Cu Cu2+ + 2e
Electron generation
Anodic oxidation
Electron flow Electron flow
+ve‐ve
Current flow
Electrolytic cell
DC power supply determines the polarity of electrodes.
Charge
Current
potential
EoCu2+/Cu
Eo Zn2+/Zn
Change in electrode potential with current during galvanostatic discharge
‐veCathodicpolarization
+veAnodicpolarization
Cell voltage
Inet = ic ‐ ia
Galvanic cell vs. Electrolytic cell
Electric load
Zn Zn2+ + 2e
Electron generation
Anodic oxidation
Cu2+ + 2e Cu
Electron consumption
Cathodic reduction
Electron flow Electron flow
+ve‐ve
Current flow
Galvanic cell
Electrochemical cell determines the polarity of electrodes.
Discharge
potential
EoCu2+/Cu
Eo Zn2+/Zn
Change in electrode potential with current during galvanostatic discharge
+veAnodicpolarization
‐veCathodicpolarization
Cell voltage
Inet = ic ‐ ia
Current
Pourbaix diagram
Many electron-transfer reactions involve hydrogen ions and hydroxide ions.
Because multiple numbers of H+ or OH– ions are often involved, the potentials
given by the Nernst equation can vary greatly with the pH.
It is frequently useful to look at the situation in another way by considering what
combinations of potential and pH allow the stable existence of a particular species.
This information is most usefully expressed by means of a E-vs.-pH diagram, also
known as a Pourbaix diagram.
Stability of water
As was noted in connection with the shaded region, water is subject to decomposition
by strong oxidizing agents such as Cl2 and by reducing agents stronger than H2.
The reduction reaction can be written either as
2 H+ + 2 e– → H2(g)
or, in neutral or alkaline solutions as
H2O + 2 e– → H2(g) + 2 OH–
These two reactions are equivalent
and follow the same Nernst equation.
E H+/H2= Eo
H+/H2+ (RT / 2F) ln {[H+]2 / PH2
}
at 25°C and unit H2 partial pressure reduces to
E = E° – 0.059 pH = –0.059 pH
Stability of water
Similarly, the oxidation of water
H2O → O2(g) + 4 H+ + 2 e–
is governed by the Nernst equation.
EO2/H2O = EoO2/H2O + (RT/4F) ln {PO2
[H+]4}
at 25°C and unit H2 partial pressure reduces to
E = 1.23 – 0.059 pH
1 gram‐equivalent weight : 96485C or 26.8 Ah
[Coulomb] = [Ampere] x [second] = [Ampere] x [h/3600]
Zn(s) Zn2+(aq) + 2e‐
Atomic weight : 65.4 g
g‐equi. weight : 65.4 / 2 = 32.7g
Capacity : 26.8Ah/32.7g = 0.82Ah/g
1.22 g/Ah
Cu2+(aq) + 2e‐ Cu(s)
Atomic weight : 63.5 g
g‐equi. weight : 63.5 / 2 = 31.75g
Capacity : 26.8Ah/31.75g = 0.84Ah/g
1.19 g/Ah
Theoretical Capacity (Ah/g or mAh/g) of LiCoO2
1 gram‐equivalent weight : 96485C or 26.8 Ah
[Coulomb] = [Ampere] x [second] = [Ampere] x [h/3600]
CoO2 + Li+ + e‐ LiCoO2 ; discharge
Molecular weight of LiCoO2 : 97.871 g
g‐equi. weight : 97.871 / 1 = 97.871 g
Capacity : 26.8 Ah / 97.871 g = 0.274 Ah/g
= 274 mAh/g
Lead - Acid Battery
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