The document provides an overview of electrochemistry, focusing on electrochemical cells, including galvanic, electrolytic, and concentration cells, and their applications in energy conversion and corrosion. It discusses the principles of electrostatics, standard electric potential, and the functioning of fuel cells, along with the effects of different factors on galvanic corrosion. The content is framed within the context of materials engineering, highlighting the interplay between chemical and electrical engineering.

1. Electrochemistry
By
Aqeel Hadi Ali
M.Sc. Student
Supervisor: Prof. Dr. Ali Sabea Hammood
Department Of Materials Engineering
Faculty of Engineering
University of Kufa-Najaf-Iraq

2. Contents
1- Introduction
2- Electrostatics
3- Electrochemical Cells
3-1 Galvanic Cell
3-2 Electrolytic Cells
3-3 Concentration Cells
4- Standard Electric potential
5- Fuel cells
6- References

3.  Many Redox reactions occur in aqueous solutions or
suspensions. In this medium most of the reactants
and products exist as charged species (ions) and their
reaction is often affected by the medium . When an
electrochemical cell is arranged with the two half-reactions
separated but connected by an electrically conducting
path, a voltaic is created. The maximum voltage which can be
produced between the poles of the cell is determined by the
standard electrode potentials.
 •Batteries are the most familiar devices for converting
between electrical and chemical energies. Objects like
laptops, cell phones, portable music players and other
devices rely on batteries to provide the electricity needed for
operation. •Electrochemistry is the study of relationships
between electricity and chemical reactions. It includes the
study of both spontaneous and non- spontaneous process.
1- Introduction

4. And the difference between Spontaneous and Nonspontaneous
Reactions are :-

5.  This section deals with a brief review of the physics
of electric charges at rest on a particular phase being
electrically neutral. Consider that an electrical
conductor, such as aqueous solutions containing
known ions, is electrically neutral and that there
exists an infinitesimal current flow. Thus, an electric
field strength vector E at a point P in space and an
inner electric potential of the system are defined as
…
2- Electrostatics(1)

6. …………..1
………….2
…………..3
…………4

7. Fig. 1.1 Schematic electric
poles in a phase being
electrically neutral. Denote
the direction of the electric
field strength components: E1
and E2 at point P. (a) Monopole.
(b) Dipole
• Monopole Let ф be defined at a point P in space around a charge
Q ⁺ (ion) in an electric monopole Q⁺ -P path shown in Fig.1.1a.
• …………5
• ………….6
• Dipole Consider the charge couple shown in Fig.1.1b, in which the
negative and positive charges are separated by a distance d << ri,
making an electric dipole for which the electric dipole moment has a
magnitude of Mx = Qd
• …………..7
• …………..8

8. Example. Let a monopole contain a net charge (Q) due to moles of a
particle in an electrically neutral system. Calculate the electric potential
(фx), the electric potential strength (Ex), and the electric force (Fx)
acting on the particle within a distance of 7 cm from a charged particle
in the x-direction. Plot ф=ƒ(r) to determine how fast ф decays from
the monopole at a distance r. Solution.
Q = zFX =(2)96.500 C/mol) mol)
Q = 1.93x C = 1.93 μC
Inserting these values into Eq. down gives the magnitude of the
electric potential on a monopole system. Thus,

9. which is a high value for the isolated monopole case. The magnitude of
the electric potential strength is expected to have a very high
magnitude given by Eq. Thus,
Thus, the electric force acting on the particle becomes ..
The required plot is given below.

10.  Obviously, the electric potential ф×=ƒ(r) = 1.737/r , decays very fast
as a function of monopole distance r. According to the above plot,
ф× has a negative slope , dф×/ dr =-1.737/ r2 , at any point on the
curve ,and it is a potential gradient . A3D plot reveals a different
trend. Thus, Ex =фx/r gives…

11.  Electrochemical cells (systems) are significantly useful as technological
tools for producing or consuming electrical energy in ionic mass
transport processes . The size and number of poly functional
electrodes of an electrochemical cell play an important role in
technological applications or electrochemical engineering . In fact ,
electrochemical engineering is an overlap between chemical and
electrical engineering fields. Generally, the transport of charge across
the interface between a poly functional electrode (electric conductor)
and an electrolyte (ionic conductor) depends mainly on temperature,
pressure, ion concentration , homogeneity of the electrolyte, electrode
surface roughness , the magnitude of the applied or generated
electric potential (E)
 There are three type of electrochemical cells :
1- Galvanic cells and its application .
2- Electrolytic cells .
3- Concentration cells .
3- Electrochemical
Cells(1)

12. figure 1-2

13. In general, Fig.1.2 schematically depicts three
electrochemical cells called (a) galvanic cell, (b) electrolytic
cell, and (c) concentration cell. These types of cells can be
classified as a one-electrolyte and two-electrode system.
With respect to the concentration cell, it is a galvanic cell
with a high initial concentration of an ion at the anode.
See Appendix B for other cell arrangements.
Electrochemical cells having two half-cells separated by
either a porous diaphragm or a salt bridge are common.
Each half-cell contains an electrode phase immersed in
an electrolyte solution. If the electrodes are electrically
connected using a wire, then the electrochemical cell is
complete and ready to work as an energy-producing
device (galvanic cell) or as an energy consumption device
(electrolytic cell).
3-1 Galvanic cells(1)

14. The application of these devices as
technological tools leads to
electrochemical engineering, which deals
with electroplating , electrowinning ,
electrorefining , batteries , fuel cells ,
sensors , and the like . The types of
electrochemical cells are then classified as….
(1) galvanic cells which convert
chemical energy into electrical
energy while electron and current flows
exist. The electrochemical reactions are
spontaneous.
(2) Electrolytic cells for converting
electrical energy into chemical energy .
The electrochemical reactions are not
spontaneous.

15. (3) Concentration cells when the two half-cells are equal,
but the concentration of a species j is higher in the anode
half-cell than in the cathodic counterpart. Figure 1.3
schematically shows two different galvanic cells and their
macrocomponents. Figure 1.3a contains one electrolyte
and two iron (Fe) electrodes.
Figure 1.3

16. having different microstructures, despite that the
common metallurgical phase is ferrite. The annealed
microstructure is constituted by soft equi-axed grains ,
having insignificant or no microstructural defects and no
residual stresses. On the other hand, the cold-worked
microstructure has hard elongated grains as a result of the
cold-working deformation process, which is a mechanical
deformation method that causes a high level of residual
stresses due to atomic plane distortion and high
dislocation density . Dislocations are line defects in
crystalline solid phases, such as cold-worked ferrite .
Normally , cold-worked structures exhibit deformed grain
structures with significant slip (BCC and FCC metals) or
mechanical twining(HCP metals).

17. Consequently, a galvanic cell forms due to differences in
microstructures and residual stress levels. In multiphase
alloys, phase differences with different electric potentials
cause galvanic corrosion. Furthermore, Fig.1.3b can be
used as the point of departure for developing the
thermodynamics of electrochemical cells containing at
least two half-cells. In a conventional galvanic cell setup ,
the cathode is the most positive electrode kept on the
right-hand side, while the anode is the most negative
electrode on the left hand side of the cell [10]. Thus,
electron flow occurs from left to right through the
terminals (Fig1.3). The schematic cell in Fig.1.3b has two
half-cells separated by a porous membrane. The
macrocomponents of this galvanic cell are:

18. • Anode Half-Cell: It is an electric conductor containing metallic
α- phase called the anodic electrode (plate or cylinder) immersed
into an electrolyte ε-phase (liquid, paste, gel, or moist soil). The α-
phase is a metal M1, such as Zn.
• Cathode Half-Cell: It is also an electric conductor containing
metallic β-phase called the cathode electrode (plate or
cylinder) immersed into an electrolyte δ-phase (liquid, paste, gel,
or moist soil). The β-phase is a metal M2, such as Cu.
The figure below represents the galvanic cell …
Fig. 2.4 The Zn/Cu galvanic (voltaic) cell, also known as Daniell cell.The inset shows the atomic
level at the electrode surfaces..

19. Galvanic corrosion(3)
Galvanic corrosion (also called “dissimilar metal corrosion”
or wrongly “electrolysis”) refers to corrosion damage induced
when two dissimilar materials are coupled in a corrosive
electrolyte. In a bimetallic couple, the less noble material
becomes the anode and tends to corrode at an accelerated
rate, compared with the uncoupled condition and the more
noble material will act as the cathode in the corrosion cell.
Factors Affecting Galvanic Corrosion(2)
The following factors significantly affect the magnitude
of galvanic corrosion:
A. Position of metals in the galvanic series.
B. The nature of the environment.
C. Area, distance and geometric effects.

20.  Figure 1.4 Factors affecting galvanic corrosion(1)
Galvanic Cells in Concrete(2)
In addition, galvanic micro-cells and macro-cells are
contributing factors for reinforced concrete corrosion.
Thus, the concrete acts as the electrolyte, and the metallic
conductor is provided by wire ties and the steel bars.
Figure 1.4a illustrates how a galvanic macro-cell can
develop from differences in chloride ion concentration and
potential .

21.  Figure 1.5 Galvanic macro-cells in reinforced concrete.
(a) Model of a galvanic macro-cell.
(b) (b) Galvanic macro-cell recently built for this section.
(c) (c) Corrosion due to galvanic macro-cells

22. Figure 1.5b shows an actual galvanic macro-cell built
recently for this section, and Fig.1.5c clearly elucidates a
galvanic macro-cell found in a 17-year-old residence
located in the Caribbean. The obvious step for
eliminating spotty corrosion sites on reinforced concrete
structures is to prepare the damaged areas for patching
with fresh concrete. However, another corrosion
mechanism may develop due to the three-phase patched
areas, which are…
(a) the old chloride-contaminated concrete having its own
chloride concentration.
(b) the cleaned steel bars.
(c) the fresh or new chloride-free concrete. Consequently, a
new and strong galvanic macro-cell may develop on the
steel surface due to a large chloride concentration.

23. An electrolytic cell (electrolyzer) is a reversed galvanic cell
in which the current flows counter clockwise and the source
of power is external .The cell has bimetallic or monometallic
electrodes. This cell consumes power, P=EI where E is the
applied external potential and I is DC current , and the cell
reactions are driven in the reverse direction as opposed to
galvanic reactions; that is, the galvanic reactions are driven
backward. This is possible if the applied potential is E >
Ecell. In fact, Faraday’s laws of electrolysis are obeyed for
generating electrochemical reactions under the principles
of electrochemical stoichiometry ,and therefore, the electro
chemical reactions occur with the aid of an external power
supply . This type of cell is very useful:--
3-2 Electrolytic Cells(1)

24. (1) in the electrometallurgical field
for recovering metals from treated
oxide ores by electroplating the
metal cations on cathodes.
(2)in the decomposition of water into
hydrogen and oxygen.
(3)in converting bauxite into
aluminum and other compounds.
Hence, if current flows, then the
principles of electrochemical
stoichiometry are used for
producing electrochemical reactions
through the process of electrolysis.

25. This process stands for an electrochemical event in which the
electrochemical reactions are forced (non-spontaneous)to
occur by passing a direct current (DC) through the electrolyte.
Therefore, E electrolytic > E galvanic, but the measurable cell
potential difference in an electrolytic cell (or galvanic cell) can
be influenced by the Ohm’s potential (E=IR) drop. .
Table 1.1 summarizes generalized comparisons between
galvanic and electrolytic cells ,including the free energy change
(ΔG) not being defined yet, but it determines the direction of
a reaction.

26. In this type of cells , the electric potential aris esasaresult
of direct charge transfer of the electrolyte from the more
concentrated solution to the less concentrated solution. As
a matter of fact, a concentration cell acts to dilute the more
concentrated electrolyte solution, creating a potential
difference between the electrodes as the cell reaches
an equilibrium state. This equilibrium occurs when the
concentration of the reactant, say, Ag⁺ cations , in both
cells is equal. This electrochemical process is achieved by
transferring the electrons from the half-cell containing
the lower cation concentration to the half-cell having the
higher concentration.
3-3 Concentration Cells(1)(2)

27. Furthermore , concentration cell
corrosion is also a phrase being used to
indicate that corrosion occurs when
different areas of a metal surface are in
contact with different concentrations of
the same solution. This particular case
can be found in buried steel pipes
exposed to varying pH of the soil.
There are three general types of
concentration cells:
(1) metal ion concentration cells due to
the presence of water.
(2) oxygen concentration cells due to
dissolved oxygen in solution.
(3) active passive cells due to a passive
film formation for corrosion protection.

28. 4- Standard Electric potential(1)
In general, the reference electrode selected to measure the
standard potential (Eo) of a metal has to be reversible since
classical thermodynamics applies to all reversible processes. The
standard hydrogen electrode (SHE) is used for this purpose. The
standard potential is also known as the electromotive force
(emf ) under equilibrium conditions: unit activity, 25 Ċ, and 1 atm
(101 kPa)pressure. The Eo measurements are for reducing
metallic cations (Mz+). Figure 2.7 shows the SHE cell diagram ,
and Fig. 2.8 schematically illustrates the SHE electrochemical
cell..
As can be seen in Fig.2.8, the electric potential of M at the
surface is measured against the SHE. and it is also known as the
interfacial cell potential, which depends on the chemical
potential of the ions into solution at equilibrium. On the other
hand, the electrons flow toward the cathode electrode M, where
the metal cations Mz+ gain these electrons and enter the

29. Fig. 1.6 Metal/SHE standard cell diagram
Fig. 1.7 Schematic metal/SHE cell

30. The standard potential for metal
reduction

31. Fuel cells are like batteries, except that they are
continuously receiving an external supply of hydrogen gas
(H2) as the fuel and oxygen (O2) or air as the oxidant to
form water (H2O). Figure 1.8 schematically shows a
simplified fuel cell known as photon exchange
membrane fuel cell (PEMFC) , where the membrane
thickness is <100m.
Fig. 1.8 Schematic photon exchange membrane fuel cell (PEMFC)
5- Fuel cells(1)

32. 2.5 Calculate the standard potential for the formation of ferric
hydroxide Fe(OH)3 (brown rust).
Solution:
4Fe + 12OH- 4Fe(OH)3 + 12e Eo a = 0.771 V
3O2 + 6H2O + 12e 12(OH- ) Eo c = 0. 401 V
4Fe + 3O2 + 6H2O 4Fe(OH)3 Eo = 1.172 V
The standard potentials were taken from Table 2.3. Thus Eo = Eo a + Eo
c =1.172v
2.7 If zinc and copper rods are placed in salt water, a direct chemical
reaction may slightly corrode zinc. Why?
Solution:
Because Zn is more active than Cu and therefore, Zn is anodic to Cu.
2.8 Is the cell potential a surface potential? If so, why?
Answer: Ecorr must be a surface potential because it arises due to
simultaneous anodic and cathodic reactions on the metal surface.
Solutions of four question from chapter two ..

33. 2.10 A battery (Example 2.2) containing 0.4 moles of MnO2
delivers 1.5 V . For 4 -hour operation , calculate the electric
current and the power (in watts).
Solution:
From example 2.2, MnO2 + H+ + eMnOOH and
Q = zFXMnO2 = (1)(96500 A.s/mol) (0.4 mol)
Q = 38.600 A.s = 38.600 C = 38.60 kJ/V
Then…
I = Q / t = 38.600 A.s / 4 × 60 × 60 s =2.68 A
P= E I = (1.5 V) ( 2.68 A ) = 4.02 V A = 4.02 Watts

34. 1- Nestor Perez, Electrochemistry and
Corrosion Science, 2nd
Edition, 2016
2- Zaki Ahmad, Principles of Corrosion
Engineering and Corrosion Control, 1st
edition , BH , 2006.
3-PIerre R. Robarge, Corrosion
Engineering: Principles and Practice,
McGraw-Hill companies, 2008.
References