Electrochemical Properties of Materials for Electrical Energy …€¦ · 11-11-2013  · Electrochemical Properties of Materials for Electrical Energy Storage Applications Lecture

Electrochemical Properties of Materials for Electrical Energy Storage Applications

Lecture Note 6

November 11, 2013

Kwang Kim

Yonsei Univ., KOREA

kbkim@yonsei.ac.kr

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