The document discusses kinetics of electrochemical reactions and mass transfer in electrochemical systems. It covers the following key points: 1) Chemical kinetics is the study of reaction rates and mechanisms. In industrial synthesis, reaction rates are as important as equilibrium constants. Kinetics answers how fast reactions occur, while thermodynamics addresses if they will occur. 2) Applying a potential increases the reaction rate by reducing the activation energy barrier. Current increases with increasing driving force from an applied potential. Catalysts also reduce the activation energy. 3) The rate of electrochemical reactions depends on parameters like materials, composition, and temperature. Increasing the reaction rate improves fuel cell performance. Reactions occur at electrode-elect

1. UNIT-ONE
1.2. Kinetics of Electrochemical Reactions
1.3. Mass transfer in electrochemical systems
BY Brhane Amha
Mekelle Institute of technology
MU

2. Reactions Kinetics
• Chemical kinetics, also called reaction kinetics, is the study of the rates and
mechanisms of chemical reactions.
• In the industrial synthesis of compounds, reaction rates are as important as
equilibrium constants.
• The thermodynamic equilibrium constant tells us the maximum possible yield of
NH3 obtainable at any given T and P from N2 and H2, but if the reaction rate
between N2 and H2 is too low, the reaction will not be economical to carry out.
• We can, from thermodynamics, address the question; Will the reaction occur?
• We need kinetics, however, answer the question: How fast will the reaction occur?
• In summary, to understand and predict the behavior of a chemical system, one
must consider both thermodynamics and kinetics.

5. Fuel Cell Reactions Kinetics
• Applying a potential to an electrode generates an electric field at the
electrode/electrolyte interface that reduces the magnitude of the
activation energy barrier increasing the ET reaction rate, Electrolysis
works on this principle.
• An applied potential acts as a driving force for the ET reaction.
• Expect that current should increase with increasing driving force
• Catalysts act to reduce the magnitude of the activation energy barrier .

11. Fuel Cell Reactions Kinetics
• Each electrochemical reaction event results in the transfer of one or more electrons,
the current produced by a fuel cell (number of electrons per time) depends on the
rate of the electrochemical reaction (number of reactions per time).
• Rate of electrochemical reaction is dependent on various parameters electrode
material, electrolyte composition, temperature etc.
• Increasing the rate of the electrochemical reaction is therefore crucial to improve
fuel cell performance.
• Electrochemical processes are heterogeneous.
• Electrochemical reactions take place at the interface between an Electrode and an
electrolyte.

14. Fuel Cell Reactions Kinetics
• One of the fundamental laws of electrochemistry is
Faraday’s Law, which relates the charge passed in
an electrochemical experiment (Q) to the number of
moles of analyte electrolyzed (N): Q = nFN

15. O + ne- ⇄ R
(electrode reaction)
nFA
I
v 
Electric current (I) measured at the
electrode is proportional to the rate (v)
of the electrode reaction!
(q – charge, t – time, F – Faraday constant; A –
electrode surface area; n – number of electrons, n(O)
– number of moles of the reactant O)
Rate of an electrode reaction: the flux
R (reduced species)
O (oxidized species)
- e
electrode|solution Interface
AnF
I
AnFt
q
v
tA
n
v
nFnq
t
q
I




1
d
d
d
)O(d
)O(
d
d Flux (the rate of the
heterogeneous electrode
reaction) is equal to the
amount of reacted
material per unit of time
per unit of electrode
surface area
(mol s -1 cm-2). This
chemical rate is equal to
the ratio of the electric
current, number of
exchanged electrons in a
unit reaction and
electrode surface area.

16. Fuel Cell Reactions Kinetics

17. Fuel Cell Reactions Kinetics

18. Fuel Cell Reactions Kinetics

19. Fuel Cell Reactions Kinetics

20. Fuel Cell Reactions Kinetics

21. Fuel Cell Reactions Kinetics

22. Fuel Cell Reactions Kinetics

23. Fuel Cell Reactions Kinetics

24. Fuel Cell Reactions Kinetics

25. Fuel Cell Reactions Kinetics
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26. 1.3. Mass transfer in electrochemical
systems

27. 1.3. Mass transfer in electrochemical systems

28. 1.3. Mass transfer in electrochemical systems
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29. 1.3. Mass transfer in electrochemical systems
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30. 1.3. Mass transfer in electrochemical systems
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31. 1.3. Mass transfer in electrochemical systems
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