EFFECTS OF ELECTROLYTE SOLUTION TO THE PROPERTIES OF RECHARGEABLE BATTERY lani4 5 ge0 5

VIETNAM NATIONAL UNIVERSITY, HANOI
VNU UNIVERSITY OF SCIENCE
FACULTY OF PHYSICS

Nguyen Thi Thu Huyen

EFFECTS OF ELECTROLYTE SOLUTION TO
THE PROPERTIES OF RECHARGEABLE
BATTERY LaNi4.5 Ge0.5

International Standard Program

Hanoi - 2016


VIETNAM NATIONAL UNIVERSITY, HANOI
VNU UNIVERSITY OF SCIENCE
FACULTY OF PHYSICS

Nguyen Thi Thu Huyen

EFFECTS OF ELECTROLYTE SOLUTION TO
THE PROPERTIES OF RECHARGEABLE
BATTERY LaNi4.5 Ge0.5

International Standard Program

Supervisor: Prof. Dr. Luu Tuan Tai

Hanoi - 2016

ACKNOWLEDGEMENT
First and foremost, I would like to express my special thanks of
gratitude to my teacher Prof. Dr. Luu Tuan Tai who gave me the precious
opportunity to do and finish this wonderful project. My sincere thanks for
your continuous support, your patience, enthusiasm and immense knowledge.
I could not have imagined having better advisors for my study.
My sincere thanks also go to teachers, officers and friends at Faculty of
Physics University of Natural Sciences for always supply best conditions to
me to do this thesis.
Finally I would like to thank all relatives and friends for all the support
and active my staff when I made this thesis.
Ha Noi, 7 June 2016
Student
Nguyen Thi Thu Huyen


Numerical calculation and graphed
Figure 1.1: Crystal structure of LaNi5 intermetallic compound[9].
Figure 1.2: Dependence of LnPH2 to 1/T
Figure 1.3: Shematic representation of an interphase for a hydrogen
absorbing metal (a)absorption plan; (t) charge tranfer plane; (l) lattice[9].
Figure 1.4: Schematic charge/discharge of Ni-MH battery[8].
Figure 1.5: Schematic representation of the concept of a sealed
rechargeable Ni- MH battery[8]
Figure 1.6: Charge characteristics of Ni-MH battery
Figure 1.7 : Discharge characteristic of Ni-MH battery
Figure 1.8: Schematic representation of the hydride
formation/decomposition via a gas phase(a) and electrochemical charge
transfer reaction(b)

Figure 1.9 : Reaction scheme proposed by Bode et al[8] for the Ni
electrode reactions in alkaline solutions.
Figure 1.10: Schematized solid- state transition mechanism for the
Ni(OH)2/NIOOH charge transfer reaction
Figure 2.1: Making sample system using arc melting(ITIMS)
Figure 2.2: X-diffraction device
Figure 2.3: Three electrodes electrochemical cell
Figure 2.4 : E0 measurement of an working electrode.
Figure 2.5: Charge- discharge measurement schema
Figure 2.6 Cyclic Voltammetric measurement system
Table 3.1: Lattice parameters of sample before and after
charge/discharge cycles
Figure 3.1. The sites for H in lattice LaNi5 intermetallic compound
Figure 3.2 : X-ray diffraction spectra of LaNi4.5Ge0.5 and its hydride


Figure 3.3: Magnetization curve of LaNi4.5 Ge0.5 before charge/
discharge
Figure 3.4: Magnetization curve of LaNi4.5 Ge0.5 after 5th cycle in
KOH (6M)
Figure 3.5: Magnetization curve of LaNi4.5 Ge0.5 after 5th cycle in
KOH(5M)and LiOH(1M)
Figure 3.6: Magnetization curve of LaNi4.5 Ge0.5 after 5th cycle in
KOH(5,1M)and LiOH(0.9M)
Figure 3.7: Cycle performance of LaNi4.5Ge0.5 in KOH (6M ) and
LiOH(1M)
Figure 3.8: Cycle performance of LaNi4.5Ge0.5 in KOH(5M) and
LiOH(1M)
Figure 3.9: Cycle performance of LaNi4.5Ge0.5 in KOH(6M)
Figure 3.10: Cycle performance of LaNi4.5Ge0.5 in KOH (5.1M ) and

LiOH(0.9M)


Content
Introduction...........................................................................................................................................1
Chapter 1: Intermetallic hydride material and rechargeable nickel- metal hydride battery..................2
1.1 The intermetallic hydride material..............................................................................................2
1.1.1Crystal structure of intermetallic compounds base on LaNi5...............................................2
1.1.2 Kinetics of sorption and desorption of hydrogen.................................................................3
1.1.3 Hydrogen adsorption capability of intermetallic compounds.............................................4
1.1.4 Hydro sorption in electrochemical systems.........................................................................5
1.1.5 Magnetic properties..............................................................................................................6
1.2 Rechargeable Nickel-Metal hydride (Ni-MH) battery................................................................6
1.2.1 The reactions........................................................................................................................6
1.2.2 Structure of nickel Hydride Batteries...................................................................................7
1.2.3 Charge charateristics............................................................................................................8
1.2.4 Discharge characteristics......................................................................................................9
1.2.5 Discharge characteristics......................................................................................................9
1.2.6 The nickel oxide electrode.................................................................................................12
Chapter 2: Experimental techniques...................................................................................................16
2.1 Sample preparation...................................................................................................................16
2.2 X-ray diffraction measurement.................................................................................................17
2.3 Magnetic measurements............................................................................................................18
2.4 Electrochemical studies.............................................................................................................18
2.4.1 Three electrodes electrochemical system...........................................................................18
2.4.2 Open- circuit potential measurement.................................................................................19
2.4.3 Galvanostatic charge-discharge cycles...............................................................................20
2.4.4 Cyclic Voltammetric technique..........................................................................................21
Chapter 3: Results and discussion.......................................................................................................24
3.1 Crystal structure analysis..........................................................................................................24

3.3 The electrochemical results.......................................................................................................27
Conclusion...........................................................................................................................................32


Introduction
Hydrogen absorption capacity of the inter-metallic diatomic
compounds materials were first discovered in the late 60s of the 20th century.
Since then, the compounds RT5 have been known and studied a lot because of
the ability to absorb and disabsorb the very large amounts of hydrogen at
atmospheric pressure and room temperature [9] which does not damage the
lattice structure. Hydrogen accumulation in the crystal lattice of the material
creates a permanent-form hydrogen container and energy reserves. This
feature has been applied in many fields of science and technology, one of the
applications that is built rechargeable battery cathode Ni-MH[[3,4]. The
advantages of Ni-MH battery are high-capacity battery and its waste does not
pollute the environment[7]. On the other hand, compared with Ni-Cd or the
lithium battery are familiar products in the electronics and communications
handed, Ni-MH battery have longer lifetime and lower cost.[7]
Currently, NiMH batteries are widely used, thus improving the quality
and innovation are necessary. There are many ways to improve the battery
performance has been studied as: doping 3d elements capable of absorbing
hydrogen, reducing particle size which increase the surface area of the
electrode in contact with the electrolyte solution to increase the level of
hydrogen absorption, changes capable of releasing hydrogen absorption and
by acting on the electrolyte solution.The third way takes very few interested,
earlier with NiCd batteries, the electrolyte solution has been carefully studied
and selected by the 6M KOH electrolyte solution thus selected now for the
same type of positive electrode is NaOH.
In this work, we focus on the influence of the electrolyte solution
to the electrochemical properties of the LaNi4,5Ge0,5 compound.

The thesis contains three chapters and some conclusions:
Chapter 1: Intermetallic hydride material and rechargeable nickelmetal hydride battery
Chapter 2: Experimental technique
Chapter 3: Results and discussion

1


Chapter 1: Intermetallic hydride material and
rechargeable nickel- metal hydride battery
1.1 The intermetallic hydride material
1.1.1Crystal structure of intermetallic compounds base on LaNi5
The intermetallic compound system LaNi5 crystallizes with the
hexagonal CaCu5- type structure. The structure consists of two alternating
types of plane: the basal plane with Lanthanum and Nickel atom which
occupy the 1a and 2c sites respectively the z=1/2 plane with only Nickel
atoms on the 3g site[[1].

Lanthanum 1a
NickelI

2c

NickelII

3g

Figure 1.1: Crystal structure of LaNi5 intermetallic compound[9].
The studies of the absorption and the disabsorption have been carried
out on their compounds showed that in the process of hydrogenation material,

elements entered the hole tetrahedron, octahedron and network failures filled
interstitial mechanism alters the lattice constant without changing the material
structure.

2


1.1.2 Kinetics of sorption and desorption of hydrogen
Hydrogen absorption process can be studied by isotherm of pressure
balance as a function of concentration (x) of the oxidizing compound.
However, according to Bureau, Planagan and Oast, its kinetic process can be
studied by a simpler way. When hydrogenation occurs with 2-phases to
distinguish the values ΔH and ΔF can be obtained from the temperature
dependence of the pressure balance. Hydrogenation reaction occurs between
LaNi5 and hydrogen compounds are represented as follows:
LaNi5 + mH2 = LaNi5H2m
In thermodynamics, kinetics Vanhoff equation is represented:
LnPH2 = -ΔF/R + ΔH/RT
where R is the gas constant, the value of ΔH and ΔF is the thermodynamic
quantities corresponding to 1 mol hydrogen. Considering the temperature
range can be considered small enough isothermal, then ΔH and ΔF will not
depend on the temperature. By plotting the dependence of RnH2 with the
inverse of temperature (1 / T) will be obtained 1 superlative line. Based on the
graph it is easy to find the value of ΔH (corresponding to the slope of the line)
and the value ΔS. ΔH can get different values, it can have a positive or
negative value. Hydrogenation occurs in two phases: the first phase to the
process of decomposition of hydrogen molecules into atoms, this process
consumes energy (ΔH> 0). The second stage occurs as hydrogenation, the
process is radiating energy (ΔH <0). Thus, depending on the dominant
process that ΔH yet received a positive or negative value. For Entropy (ΔS),

on the other, its value does not depend on inter-metallic compounds. The
study showed that the entropy of hydrogenation mainly contributed by the
entropy of hydrogen (ΔSgas = 130 J / mol H2 at room temperature).
Considering all of the hydrogenation reaction has advantages in terms
of energy (exothermic reaction, ΔH <0) for the reaction to occur, so when
plotting the dependence of LnPH2 to 1 / T, toys market will look like the
figure below:

3


50
40

LnPH2

30
20
10
0

2.2

2.4

2.6

2.8

3

3.0

3.2

-1

10 /T(K )

Figure 1.2: Dependence of LnPH2 to 1/T.
1.1.3 Hydrogen adsorption capability of intermetallic compounds
In kinetic and catalysts, it is known that transition metals, such as
Nickel , Conalt, Iron…are capable to a adsorb amounts of hydrogen on the
surface. Due to the unfill shell they can establish weak bonds with hydrogen
atoms. Adsorbed amount depends on the chemical potential of each d element
on the surface area of the metal, the hydrogen pressure and the temperature.
It is also necessary to mention here the surface effect phenomena.
There are several processes causing the composition of the surface of
intermetallics to be different from the bulk concentration. It is the fact that the
surface energy of 3d element is bigger than that of the rare earth, which can
lead the surface equilibrium concentration of the rare earth atoms to exceeds
that of the bulk. Surface segregation is quite a general phenomenon, and is
expected to occur whenever the constituent elements have sufficiently
different properties. Often small amounts of oxygen or water present as
impurities in the hydrogen gas. These give rise to the formation of rare earth
oidation enenly results in a surface relatively rich in 3d transition metals.
Under this point of view we can assume that the hydrogen adsorption of
intermetallic compounds is dominated by the 3d elements on the surface.
4

1.1.4 Hydro sorption in electrochemical systems
Due to the non-autonomous character of the electrode/electrolyte
interphase, a substantial greater number of factors affect the sorption process
than in the gas phase. An interphase region is formed whenever an electrode
is in contact with an electrolyte. In the simplest case, the interphase region
takes the form of the electrical double layer. In the more complex cases and in
particular, during the charge tranfer reaction, it consists of layers, each
associated with a participating elementary process.
In this presentation, the inter phase region is an open system in which a
number of consecutive process take place of which the slowest one
determines the rate. These processes include transport of the reactants from
the bulk to the electrode surface by diffusion, absorption on the electrode
surface, charge transfer, desorption of the reaction products away from the
electrode surface. In a discharging battery, these same processes occur,
however, in a battery the electrons ultimately flow into an external circuit
where the electrical work is delivered [3].
The role of the inter phase may vary from that of an inhibitor to an
accelerator of both charge tranfer and molecular transport. This concept,
although not explicitly stated, was implied in the discussion of hydrogen
absorption from the gas phase where it was shown that small metal alloy
clusters absorb more hydrogen via a mechanism that becomes inoperative as
the cluster size increases. The inter phase may be modified in the course of
battery operation, especially as a result of cycling.

5


SOLUTION
PHASE

INTER
PHASE

ELECTRODE
INTERIOR/SOLID
PHASE
Figure 1.3: Shematic representation of an interphase for a hydrogen
absorbing metal (a)absorption plan; (t) charge tranfer plane; (l) lattice[9].
1.1.5 Magnetic properties
The LaNi5 is an enhance Pauli paramagnet with an almost fieldindependent susceptibility at low temperatures that amount to 3,7.10 -3 µB T-1
at 4.2K [5] and is slowly decreasing with increasing temperature up to
300K.The hydrogenation process of this compound changes their magnetism
considerably. Cyclic absorption and adsorption of hydrogen by LaNi 5 cause
super paramagnetic Ni cluster to precipitate on the surface of the melt
particles. Continued cycling eventually causes ferromagnetic behavior of
LaNi5 compound .
1.2 Rechargeable Nickel-Metal hydride (Ni-MH) battery
1.2.1 The reactions
Nickel metal hydride batteries employ nickel hydroxide for the positive
electrode similar to Ni-Cd batteries. The hydrogen is stored in a hydrogen
absorbing alloy for the negative electrode, and an aqueous solution consisting
mainly of potassium hydroxide for the electrolyte. Their charge and discharge
reaction shown below
Positive electrode
Negative electrode

Ni(OH)2 + OH- ↔ NiOOH + H2O + e- (1)
M + H2O + e- ↔ MHab + OH- (2)
6

Overall electrode

Ni(OH)2 + M ↔ NiOOH + MHab (3)

(M : hydrogen absorbing alloy, Hab : absorbed hydrogen)
As can be seen by the overall reaction given above, hydrogen moves
from the positive to negative electrode duringcharge and reverse during
discharge with the electrolyte taking no part in the reaction, which mean that
there is no accompanying increase in the electrolyte. The H absorbing alloy
negative electrode during overcharge by sufficiently increaseing the capacity
of negative electrode which is the same method employed by Ni-Cd batteries.
By keeping battery’s internal pressure constant in this manner, it is possible to
seal the battery.

Figure 1.4: Schematic charge/discharge of Ni-MH battery[8].
1.2.2 Structure of nickel Hydride Batteries
A schematic representation of a Ni-MH battery containg an AB 5-type
hydride-forming electrode and a Ni electrode [8]. The electrodes are
electrically insulated from each other by a separator. Both separtor and
electrodes are impregnated with an alkaline solution that provides for the
ionic conductivity between the two electrodes.

7


Figure 1.5: Schematic representation of the concept of a sealed
rechargeable Ni- MH battery[8].
1.2.3 Charge charateristics

Charge charactertics of nickel metal hidride batteries are affected by
current, time and temperature. The battery voltage rise when the charge
current is increased or when the temperature is low. The charge efficiency
differ depending on the current, time, temperature and other factors.

Figure 1.6: Charge characteristics of Ni-MH battery .
8


1.2.4 Discharge characteristics
Discharge characteristics of nickel metal hidride depend on current,
temperture…and the discharge voltage characteristics are flat at 1.2V which is
almost the same as for Ni-Cd batteries. The discharge efficience and the
discharge voltage decrease in proportion as the current rises or temperature
drops. Compare with Ni-Cd batteries, nickel-metal hydride batteries have
inferior high-rate discharge characteristics, making them less suitable for use
in applications requiring high-current discharge. As with Ni-Cd batteries,
repeated charge and diccharge of these batteries under high discharge cut-off
voltage conditions causes a drop in the discharge voltage ( which is
sometimes accomplanied by a simultaneous drop in capacity). The discharge
characteristics can be restored by charge and discharge to a discharge end
voltage of down to 1V per cell.

Figure 1.7 : Discharge characteristic of Ni-MH battery.
1.2.5 Discharge characteristics
In gas phase reaction hydrogen gas is brought in to contact with a
hydride-forming compound and the gaseous molecules dissociate at the solid
interface. Atomic hydrogen is strongly adsorbed at the metal surface as the
metal hydrogen interaction energetically very favorable. The adsorbed
hydrogen atoms can, subsequently, be converted into the absorbed state by

jumping into the interstitial sites beneath the first atomic layer. Further
transportation into the bulk of the solid occurs via diffusion. The occurence of
a possible phase transformation is omitted in this simplified representation.
9


Figure 1.8: Schematic representation of the hydride
formation/decomposition via a gas phase(a) and electrochemical charge
transfer reaction(b).
The electrochemical analogy is shown in fig 1.8.b. The overall
electrochemical reaction has already been presented by hydride-forming
reaction. Here we will go into some detail and consider the various partial
steps involed in the electrochemical hydride formation reaction. The
following steps can successively distinguished:
i. The supply of reactants by means of diffusion from the bulk (b) of the
electrolyte to the solid interface
H2O(s) ↔H2O

(4)

ii. The charge transfer reaction occuring at interface
10


H2O+e-↔Had+OH-

(5)

H(ad) is atomic hydrogen adsorption. As the results of reduction
reaction, atomic hydrogen Had is again adsorbed on the surface.

iii. The removal of electrochemical formed reaction products from the
interface by mean of diffusion. This include absorption of adsorbed
hydrogen Habs by the RT5 compound through which the hydride is
formed
Had↔Habs
And transport of OH- ions into the bulk of the electrolyte
OH-s↔OH-b
iv. Depending on the materials composition and on the hydrogen
concentration in the solid, either an α phase is formed
Habs(α) ↔Habs(β)
v. Recombination of two Had atoms has to be taken into account. This
lead to the formation of H2, Which is released, from the electode
surface as a gas
2Had↔H2
The hydrogen absorption and desorption properties of intermetallic
compound are generally characterized by pressure-composition isotherms. It
has long been recognized that there is a direct relationship between the
equilibrium pressure for absorption and desorption of hydrogen gas and the
equilibrium potential (E0) of metal hydride electrode. This relationshiphas
been expressed by:
E0 = -[RTln(P(H2))]/nF
where:
R: gas constant
n: number of electrons
E0: measure against a reference electrode
11

(6)

The plateau pressure of the hydride-forming material employed in a
rechargeable Ni-MH battery may not be too high for different reasons (i) the
gas pressure inside a battery should be relatively low for obvious safety
reason (ii) to reduce the battery self-discharge rate (iii)competition between
the hydrogen evolution reaction and the hydride formation reaction becomes
more severe when high plateau material are employed. On the other hand, an
important electrochemical requirement to met for Ni-MH battery is a high cell
voltage.
1.2.6 The nickel oxide electrode
Numerous studies have been devoted to the Ni-electrode over the last
few decades. Excellent reviews on this topic have recently been writen [[1].
These reviews include the various preparation methods and manufacturing
processes of active electrode materials. In contrast to what is suggested by Eq
1.1, the charge and discharge reactions of a Ni- electrode are much more
complex. This is further accentuated by the fact that different electro-active
modifications of both divalent and trivalent Ni have to be considered. The
existance of these modification has first been extensively discussed by Bode
et al, and has, since then, been the subject of many investigations.
Oxidation
state

Ni

+2

+3

12

Modification

Ni

α- Ni(OH)2

Β-Ni(OH)2

13

γ-NiOOH

β-NiOOH


Figure 1.9 : Reaction scheme proposed by Bode et al[8] for the Ni
electrode reactions in alkaline solutions.
Figure summarizes the various Ni species, most relevant for energy
storage applications. Starting with metallic Ni the highly hydrated αmodification of divalent Ni(OH) 2 can be electrochemically prepared at
relatively negative potentials, in accordance with thermodynamic
considerations. Upon cycling and ageing at more positive potentials this
modification is dehydrated in to the β form, which can be further oxidized to
trivalent β-NiOOH. During overcharging, β-NiOOH can be irreversibly
converted into the hydrated
γ-modification, γ-NiOOH can be
electrochemically reduced into α-Ni(OH)2.
The charge transfer reaction between the β-modifications of a
nickeloxide battery electrode is generally considered to occur via a solid-state
transition mechanism is schematically in Fig 1.9.

14


Figure 1.10: Schematized solid- state transition mechanism for the
Ni(OH)2/NIOOH charge transfer reaction.
During charging both protons and electrons are liberate within the β –
Ni(OH)2 solid:
Ni(OH)2 =NiOOH +H+ +e-

(7)

The electrons are transported to the current collector at the back of the
electrode. On the other hand, protons are transported through the solid by
means of diffusion to the solid by means of diffusion to the solid/solution
interface, where they react with OH- ions to give water:
H++OH- = H2O

(8)

Since the electrolyte consists of a strong alkaline solution, supply of
OH- is generally not considered to be a rate-limiting facter. Despite the fact
that the electronic conductivity of β-Ni(OH) 2 is found to be poor, solid state
diffusion of cations is the rate-limiting step in the charge transfer reaction.

15


Chapter 2: Experimental techniques
2.1 Sample preparation
The compound LaNi4.5Ge0.5 was prepared by arc melting in an Argon

atmosphere with purities > 99.9wt% . A slight excess of rare earth element La
was used to compensate the weight loss during the melting process. The
melting procedure with reversing samples was repeated several times to
ensure the homogeneity of the product.
Powder sample with the average particle size of 50µm was obtained by
pulverizing the as- melting samples in an agate mortar.
The electrode was made from approximately 0.4g of alloys powder
compacted into a pellet (4mm in diameter) under pressure of 8000kg/cm 2 at
room temperature for three minutes. Copper wires were pressed with the
powder in order to provide electrical contacts. The pellet was converted by
epoxy resin but one side was kept open as a reacting surface. The electrode
surface was polished using abrasive paper of grade subsequently 600, 800,
1000. After polishing, this surface was cleaned in distilled water for several
times.

Figure 2.1: Making sample system using arc melting(ITIMS).

16


2.2 X-ray diffraction measurement
The structure of free powder samples and samples after 10 th cycle
charge/discharge were checked by X-ray diffraction D5005 at CMS,
Univesity of Nature Science. In all experiments, monochromatic X-ray of CuKα were used.
Crystallographic structure determination:
The X-ray diffraction patterns of powder samples prepared were
compared with X-ray diffraction patterns of LaNi 5. All LaNi5 –based
compounds have the hexagonal CaCu5 structure, thus the lattice parameters of
this were calculated by the following equation

where h,k,l are the Miller indexes; a,c are the lattice parameter and d hkl is the
distance between two lattice layers. Therefore, from every two diffraction
peaks in the diffraction patterns the values of a and c can be calculated basing
on the relation Brag’s law
λ= 2dhklsinϴhkl
where ϴ is the angle between the direction of incident beam and the
direction perpendicular to sample surface.
The lattice parameters(a and c) are the average values of all
above calculated value. From the lattice parameters, the volume of hexagonal
unit cell can be obtained by the following relation
Vhex = a2c.sin1200

17


Figure 2.2: X-diffraction device.
2.3 Magnetic measurements
Magnetic properties of the samples were studied by measuring
magnetization curves and thermomagnetization curves. Magnetic
measurements were carried out on a sensitive Vibrating Sample
Magnetometer (VSM) system at ITIMS
Magnetization curves were measured on the as-prepared bulk samples,
free powder samp;es and after samples 10 th charge/discharge cycle in applied
field from -1,3 Tesla to 1,3 Tesla at room temperature.
The temperature dependence of the magnetization M(T) of free powder
samples was measured in a nitrogen gas enviroment. The temperature range
was from 300K to above 680K. The applied field was 0,1 Tesla. The
temperature was raised about 5K.
2.4 Electrochemical studies
2.4.1 Three electrodes electrochemical system

The electrochemical cell for electrochemical experiments
conventionally consists of three electrodes , which are immersed in 5.9M
KOH+ 0.1M LiOH solution in fig 2.3. the working electrode is the prepared
18


sample. The counter electrode is made from inert metal, Platinum. The
reference electrode is constructed so that it has a negligible contact potential
regardless of the Saturation Calomel Electrode(SCE). The all three electrodes
are connected to a potential control device called a potentiostat.

Figure 2.3: Three electrodes electrochemical cell.
2.4.2 Open- circuit potential measurement
When a metal is immersed in a given solution , an electrochemical
reaction, characterizing the metal/solution interface, occur at the surface of
the metal. This reaction creates an electrochemical potential, at open circuit
that is usually called corrosion potential Ecorr or open circuit potential E0
( measured in milivolt). Since the open circuit potential E 0 is determined by
the specific chemistry of the system.
The open circuit potential E0 of the electrode can only be determined by
comparison to the potential of a referent electrode. The fig2.2 shows how can
be measured E0 of the working electrode (WE) with a reference electrode(RE)
placed into the same solution. In this experiment the Bi- potentiostat 366A
was used to measure E0 as a function of the immersion time

19