Hydrogen Overpotential

Phenomena

Irwin Maulana

333409293

T. Metalurgi

19 Maret 2012 (Revision)

1

Outline

2

1 Introduction

2 Thermodynamics aspect

3 Kinetics aspect

4 References

Introduction

3

OVERPOTENTIAL?

The difference of equilibrium with applied

potential.

= Eapplied – Eequilibrium

Types of Overpotential

1. Concentration

2. Activation

Thermodynamics aspect

4

Polarization Curve

Tidak Perlu

Overpotensial

Aqueous Solution

Perlu

Overpotensial

Perlu

Overpotensial

Aqueous Solution Non Aqueous Solution

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.

Condition 1

6

(a)

Noble

Metals

0E

+

M / M2+

H2 / H+

i

_

Condition 1

7

• For noble metal

• In general, metal has lower hydrogen

overpotential

• Electrolysis can be occurred with high

current efficiency.

Condition 2

8

(b)

Metals with

Intermediate

Reactivity

0

E

+

M / M2+

H2 / H+

i

_

9

Condition 2

Intermediate reactivity

For Ni, Zn, Cd dan Fe

Can be extracted with aqueous solution

electrolysis method

Hydrogen overpotential is higher

10

(c)

Reactive

Metals

0E

+

M / M2+

H2 / H+

i

_

Condition 3

11

Condition 3

Very reactive metals

Cannot be extracted with aqueous solution

media

because ηH2 increase quickly

fused salt as used media

Kinetics aspect

12

Ion movement which is occurred slowly

cause the potential deviate from Nerst

formulation.

In Hydrogen : 2H+ + 2e- H2

Kinetics aspect

13

Mass Transfer-Controlled Reaction-Concentration Overpotential

Interfacial Reaction Rate Control-Activation

Overpotential

Kinetics aspect

14

Kinetics aspect

15

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

electrode

References

16

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-tafel.htm [Diakses tanggal 19 Maret 2012]

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