1. 19 Maret 2012 (Revision)
Hydrogen Overpotential
Phenomena
Irwin Maulana
333409293
T. Metalurgi
1

2. Outline
1 Introduction
2 Thermodynamics aspect
3 Kinetics aspect
4 References
2

3. Introduction
 OVERPOTENTIAL?
The difference of equilibrium with applied
potential.
 = Eapplied – Eequilibrium
 Types of Overpotential
1. Concentration
2. Activation
3

4. Thermodynamics aspect
Polarization Curve
Tidak Perlu Perlu Perlu
Overpotensial Overpotensial Overpotensial
Aqueous Solution Aqueous Solution Non Aqueous Solution
4

5. POLARIZATION CURVE
(I vs E)
Equilibrium reaction M+ + e- M which is
occured on the electrode surface will cause the
current which is depend on the potential given.
5

6. Condition 1
M / M2+
i
(a)
Noble
Metals
H2 / H+
0 +
_
E
6

7. Condition 1
• For noble metal
• In general, metal has lower hydrogen
overpotential
• Electrolysis can be occurred with high
current efficiency.
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8. Condition 2
M / M2+
i
(b)
Metals with
H2 / H+
Intermediate
Reactivity
0 +
_
E
8

9. Condition 2
 Intermediate reactivity
 For Ni, Zn, Cd dan Fe
 Can be extracted with aqueous solution
electrolysis method
 Hydrogen overpotential is higher
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10. Condition 3
M / M2+
(c)
Reactive
Metals
i
H2 / H+
_ 0 +
E
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11. Condition 3
 Very reactive metals
 Cannot be extracted with aqueous solution
media
 because ηH2 increase quickly
 fused salt as used media
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12. Kinetics aspect
Ion movement which is occurred slowly
cause the potential deviate from Nerst
formulation.
In Hydrogen : 2H+ + 2e- H2
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13. Kinetics aspect
 Mass Transfer-Controlled Reaction-
Concentration Overpotential
Interfacial Reaction Rate Control-Activation
Overpotential
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14. Kinetics aspect
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15. Kinetics aspect
I. H3O+ diffusion from Bulk Solution to double layer
II. H3O+ go through Double Layer
III. Decomposition
H3O+ H2O + H +
IV. Electrochemical
H3O+ + M + e-  M-H + H2O
2 M-H  2M + H2
V. H2 (g) desorption from NBL
VI. H2 (g) diffusion from Bulk Solution menjauhi
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electrode

16. References
 H. S. Ray  A. Ghosh. 1991. Principles of
Extractive Metallurgy : New Age International
 Rosenqvist. Principles of Extractive Metallurgy.
McGraw-Hill Kogakusha Ltd., Tokyo. 2nd ed.
1983.
 Bard, A.J.; Faulkner, L.R. Electrochemical
Methods: Fundamentals and
Applications. New York: John Wiley & Sons,
2nd Edition, 2000
[http://en.wikipedia.org/wiki/Overpotential,
Diakses tanggal 19 Maret 2012]
 http://electrochem.cwru.edu/encycl/art-t01-
16
tafel.htm [Diakses tanggal 19 Maret 2012]

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