ISSN: 1847-9286
Open Access Journal
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Journal of
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J. Electrochem. Sci. Eng. 4(1) 2014, 1-44
Volume 4 (2014)
No.
01
pp.
1-44
IAPC
J. Electrochem. Sci. Eng. 4(1) (2014) 1-44
Published: January 25, 2014
Open Access : : ISSN 1847-9286
www.jESE-online.org
Contents
RICHARD HONG PENG LIANG, TANGSHENG ZOU, KARTHIK SOMASUNDARAM, WEI TONG,
ERIK BIRGERSSON
Mathematical modeling and reliability analysis of a 3D Li-ion battery...................................................... 1
THOMMANDRU RAVEENDRANATH BABU, SARVAREDDY RAJASEKHAR REDDY,
PUCHAKAYALA SUJANA
Comparative voltammetric study and determination of carbamate pesticide residues in soil at
carbon nanotubes paste electrodes ...................................................................................................... 19
TSUNG-WEI CHANG, SHAO-YU HU, WEN-HSI LEE
Synthesis of CuInSe2 thin films from electrodeposited Cu11In9 precursors by two-step annealing ............ 27
ANA M. ESTEVA, ELÍAS BLANCO, JUAN J. PIÑA, ABEL I. BALBIN, CARMEN QUINTANA,
PEDRO HERNÁNDEZ
Determination of nevirapine in the presence of cucurbit(7)uril with a gold electrode............................. 37
J. Electrochem. Sci. Eng. 4(1) (2014) 1-17; doi: 10.5599/jese.2013.0040
Open Access : : ISSN 1847-9286
www.jESE-online.org
Original scientific paper
Mathematical modeling and reliability analysis of a 3D Li-ion
battery
RICHARD HONG PENG LIANG, TANGSHENG ZOU, KARTHIK SOMASUNDARAM*,
WEI TONG*, ERIK BIRGERSSON**
Raffles Science Institute, Raffles Institution, One Raffles Institution Lane, Singapore 575954
*Department of Mechanical Engineering, National University of Singapore, Singapore 117576
**Department of Chemical and Biomolecular Engineering, National University of Singapore,
Singapore 117576

Corresponding Authors: E-mail: vivekarthik81@yahoo.co.in; Tel.: +65-6516 4657; Fax: +65-6779 1936
Received: July 24, 2013; Revised: October 24, 2013; Published: January 25, 2014
Abstract
The three-dimensional (3D) Li-ion battery presents an effective solution to issues affecting
its two-dimensional counterparts, as it is able to attain high energy capacities for the
same areal footprint without sacrificing power density. A 3D battery has key structural
features extending in and fully utilizing 3D space, allowing it to achieve greater reliability
and longevity. This study applies an electrochemical-thermal coupled model to a
checkerboard array of alternating positive and negative electrodes in a 3D architecture
with either square or circular electrodes. The mathematical model comprises the transient
conservation of charge, species, and energy together with electroneutrality, constitutive
relations and relevant initial and boundary conditions. A reliability analysis carried out to
simulate malfunctioning of either a positive or negative electrode reveals that although
there are deviations in electrochemical and thermal behavior for electrodes adjacent to
the malfunctioning electrode as compared to that in a fully-functioning array, there is little
effect on electrodes further away, demonstrating the redundancy that a 3D electrode
array provides. The results demonstrate that implementation of 3D batteries allow it to
reliably and safely deliver power even if a component malfunctions, a strong advantage
over conventional 2D batteries.
Keywords
3D batteries, Li-ion battery, mathematical model, reliability analysis, thermal model
doi: 10.5599/jese.2013.0040
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J. Electrochem. Sci. Eng. 4(1) (2014) 1-17
MODELING AND RELIABILITY ANALYSIS OF A 3D LI-ION BATTERY
Introduction
The demand for small scale, high power density sources has increased with the advent of
miniaturized electronic devices such as micro-electromechanical systems (MEMS), micro-robots,
micro-sensors and implantable medical devices. The lithium-ion battery is considered as a viable
energy storage system that can cater to many of these applications, as it is able to attain the high
energy densities required.
Conventional batteries with planar cathode and anode layers arranged in a parallel-plate
configuration with a separator in between are known as two-dimensional (2D) cells, in which
transport of Li-ions between the electrodes is one-dimensional (1D) in nature. This 2D cell
currently used in commercial applications still face several constraints, especially regarding power
limitations [1–3] and reliability which affect millions of industrial and small-scale consumers [4,5].
As a result, three-dimensional (3D) architectures have been developed for the lithium-ion
battery [1,3,6] partly to ameliorate some of these concerns and further harness its potential as a
key energy solution for the future. This nascent concept describes cells with key structural features
extending in and fully utilizing 3D space. As shown in Fig. 1a, a 3D cell typically consists of anodes
and cathodes which have active surface areas exposed in three dimensions in closely-spaced
arrays in a 2D plane. With this, we have to reconsider the phenomena of mass and charge
transport, electronic and ionic conductivity and electron-transfer kinetics in the form of 3D
batteries.
The 3D cell promises many benefits: it can attain enhanced energy capacity without
compromising on power density, while maintaining the same areal footprint [6–8]; it enables us to
take advantage of more extensive interactions between the active materials [1,9,10], allowing us
to adopt a design that improves reliability in the event that an active component ceases to
function. The flow of energy and current in the conventional parallel-plate design essentially stops
when an intermediate component fails. On the other hand, even if one of the electrodes in a 3D
design fails, the battery can potentially continue to operate (albeit with reduced capacity and
performance) as repeating units of electrodes arranged in a tessellation can provide redundancy.
Experiments have been able to produce working precursors to fully functional 3D batteries
through the use of a variety of electrochemical deposition techniques. For instance, C-MEMS
(Carbon-Microelectromechanical Systems), [11–13] a solution for miniaturization, uses photolithography to implement photoresist arrays on a SiO2 surface, followed by pyrolysis at high temperatures in an oxygen-free environment. Changing conditions under which these steps are carried out
allows one to vary design shapes, and also mechanical and transport properties [2,9,14,15].
Lithographic techniques vapour deposition techniques are being used to prepare independent
arrays of the electrodes [1,2,16–21]. Recently, interdigitated Li-ion microbatteries are prepared
using 3D printing techniques [22].
However, computational studies and mathematical modelling have yet to be entirely developed
for the 3D Li-ion cell, as they either do not completely solve for coupled electrochemistry,
transport phenomena and heat generation, or consider only electrochemical phenomena for
optimization studies. Hart et al. [6] modelled and estimated current densities and potentials for
arrays of electrodes with different geometries, while Zadin et al. [23–25] focused on simulating the
ionic transport mechanisms in liquid and polymer electrolytes inside a 3D microbattery assuming
non-porous solid electrodes to show how cell geometry can give rise to qualitatively non-uniform
current densities and thus suboptimal surface utilization. However, neither model considers the
electrochemical activity or thermal behaviour inside the electrodes. On the other hand, detailed
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J. Electrochem. Sci. Eng. 4(1) (2014) 1-17
mathematical models have been formulated to predict transient local electrochemical and thermal
changes in a Li-ion cell in a rectilinear geometry [26–29] and a spiral-wound geometry [30,31],
both essentially 2D-collapsible geometries.
By virtue of the lack of a detailed resolution for modelling and simulation of coupled
electrochemistry, transport phenomena and heat generation for the 3D Li-ion cell, the aim of this
paper is twofold: First, to employ a thermal-electrochemical model for studying the behaviour of a
3D liquid electrolyte Li-ion cell applicable to various geometries; second, to apply this model to a
planar tessellated electrode geometry and conduct a reliability analysis to demonstrate the
redundancy and longevity that a 3D battery can attain. Our mathematical model will investigate
the transient conservation of charges, species and energy; it couples the electrochemical and
thermal behaviour through the heat generation arising from reversible, irreversible and ohmic
heating as well as through the temperature-dependent transport and electrochemical parameters.
Mathematical Formulation
The 3D battery has the advantage of having a larger areal energy capacity than the conventional 2D design, but also has a disadvantage of having non-uniform current density. This would
lead to the poor utilization of the electrode materials, resulting in lower cell efficiency, non-uniform heat dissipation etc. Studies have shown that a checkerboard cathode/anode array configuration, where each electrode is surrounded by four nearest neighbour opposite electrodes, provides a more uniform current output around every electrode compared to that of other arrays. Current uniformity in this 3D design would render it more useful in a wider variety of applications [6].
As a result, we have selected a 3D battery that consists of positive and negative electrodes
arranged in square planar tessellation as shown in Fig. 1 for our study. Each electrode is adjacently
bounded by four electrodes of opposite sign. Current collectors plates are present at either end of
the electrodes; one for the anode and another for the cathode.
For the individual electrodes, we consider two shapes of different extremes - circles and
squares. Square electrodes provide a cleaner tessellation in the array, shorter average distances
between electrodes and a higher packing efficiency. Circular electrodes are however much more
feasible to implement and representative of real-life manufacturing processes. Hence, we consider
both the square and circular electrode arrays in this paper, and compare the differences in
performance between these two extremes.
In order to ensure that the comparison between both square and circular arrays is fair, a few
restrictions have been imposed. The minimum distance between each electrode (wse), as well as
the thickness of both electrodes (wpe, wne) i.e. the diameter of the circular cross-section or the
edge length of the square cross-section, is kept constant in both arrays. The dimensions are
provided in Tables 1 and 2.
The electrochemical and thermal behaviour of a three-dimensional (3D) Li-ion cell consisting of
a graphite negative electrode (ne) and a manganese oxide spinel positive electrode (pe) as shown
in Fig. 1 is studied. The electrodes and the spaces between the electrodes are filled with an
electrolyte solution (el) of LiPF6 salt in 1:2 ethylene carbonate: dimethyl carbonate solvent. The
materials considered here are the same as that used for a conventional cell that is commercially
available with the assumption that these can be utilized to fabricate 3D batteries using the
conventional techniques.
As depicted in Fig. 1, there are two main scales involved in the modeling of a Li-ion cell: the
macro- and the micro-scale. In short, the transport of ions and electrons in the cell between the
doi: 10.5599/jese.2013.0040
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J. Electrochem. Sci. Eng. 4(1) (2014) 1-17
MODELING AND RELIABILITY ANALYSIS OF A 3D LI-ION BATTERY
electrodes is referred as the transport at the macroscale, which includes species transport in the
liquid electrolyte, electronic charge conduction in the solid phase and ionic charge conduction in
the liquid electrolyte; and the diffusion of ions in the active material present in the electrodes is
referred to as transport at the microscale, which includes diffusion of lithium in the active material
of the porous electrodes.
Figure 1. (a) Schematics of (a) 3D Li-ion battery, (b) section AA showing the various functional
layers in the battery with the roman numerals indicating the interfaces of these layers and the
boundaries, (c) agglomerate structure in the negative electrode (positive electrode also exhibits
similar structure), (d) diffusion of lithium in active material in the electrodes on the microscale,
(e) top view of the battery (xz-plane) with square cross-section, and (f) circular cross-section
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J. Electrochem. Sci. Eng. 4(1) (2014) 1-17
Table 1. Physical properties and design parameters of battery components
Parameter
cl0
Unit
mol m-3
cc (-)
-
ne
el
2.0 × 103
pe
cc (+)
-
Ref.
27
Cp
c s0
J kg-1 K-1
3.8 × 102
7.0 × 102
7.0 × 102
7.0 × 102
8.7 × 102
34,37
3.9 × 10
3
-
27
2.3 × 10
4
-
27
-
27
27
34
20
-
34
34
34,37
27
27
27
27
27
27
mol m
-3
max
s
mol m
-3
Dl
Ds
Ea,Di
Ea,Ds
Ea,σl
2 -1
c
-
m s
m2 s-1
kJ mol-1
-
kJ mol-1
-
-1
1.5 × 10
4
2.6 × 10
4
3.9 × 10
-14
7.5 × 10
10
-11
1.0 × 10
4
-
5 × 10⁻⁴
0.05 × 102
2 × 10⁻11
8.5 × 10⁻6
10 × 10⁻⁵
0.5
0.19
0.44
0.07
10 × 10⁻⁶
2.0 × 102
-
0.17
-
a, c
p
l
f
kJ mol
m
W m-1 K-1
mol2.5 m-0.5 s-1
m
m
-
10 × 10⁻⁶
3.8 × 102
-
5 × 10⁻⁴
0.05 × 102
2 × 10⁻11
12.5 × 10⁻6
10 × 10⁻⁵
0.5
0.14
0.36
0.03
20
0.01 × 102
-
θ i0
-
-
0.56
-
hi
k
k0
Rs
Wi

s
-3
kg m
S m-1
3
9.0 × 10
6.0 × 107
-13
3
1.9 × 10
1.0 × 102
1.2 × 10
-
3
4.1 × 10
3.8
3
3
2.7 × 10
3.8 × 107
27,34,37
34
Table 2. Other model parameters
Parameter
H
ht
iapp
L
Ta, Tref
W
wse
Unit
m
W m-2 K-1
A m-2
m
K
m
m
Value
5.7 × 10⁻⁴
5
7 × 10² (circular); 9 × 10² (square)
6.6 × 10⁻⁴
298.15
6.6 × 10⁻⁴
5.2 × 10⁻⁵
The model is based on the porous-electrode theory developed by Newman and Tiedemann
[32,33] and embodies the following main assumptions:
1. Isotropic material properties;
2. Uniform distribution of active materials of the same size in the electrodes;
3. The active material is assumed to be spherical; i.e., we only need to consider the radial direction at the microscale;
4. Side reactions are assumed negligible.
The mathematical formulation consists of the conservation equations of species and charge,
together with conservation of energy at macroscale [27,34]; the diffusion length or the polynomial
approximation approach is employed for the conservation of lithium inside the active material at
microscale. For the sake of brevity, the governing equations, initial conditions, and constitutive relations are provided in tables in the appendix and the details can be found in our earlier work [31].
doi: 10.5599/jese.2013.0040
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J. Electrochem. Sci. Eng. 4(1) (2014) 1-17
MODELING AND RELIABILITY ANALYSIS OF A 3D LI-ION BATTERY
The physical properties and design adjustable parameters pertaining to the geometry studied in
this work are given in Tables 1 and 2.
The current density is prescribed at the positive current collector at the boundary I (see Fig. 1b
for placement of roman numerals) and also Newton’s law of cooling is specified here. At the
interface between the current collector/electrode or the current collecting tab/current collector,
continuity of energy flux and solid-phase current is specified; insulation is specified for the ionic
flux and current. At the current collector/electrolyte, insulation is defined for the solid phase
current and continuity for the energy flux. At the boundaries IV and V, there is no flow of
ions/electrons as well as energy and hence insulation is specified here as well for solid phase
current and energy. At the electrode/electrolyte interfaces, continuity of energy flux and ionic flux
as well as ionic current is defined and since there is no flow of electrons across the interface,
insulation for solid phase current is defined. The current is collected from the negative current
collector at the boundary VII or otherwise this end is grounded and also Newton’s law of cooling is
specified here.
Numerics
The commercial finite-element solver, COMSOL Multiphysics 3.5a [35], was employed to solve
the 3D model. Linear elements were implemented for all dependent variables s, l, cl, cssurf , T and
csavg the direct solver UMFPACK was chosen as linear solver with a relative convergence tolerance
of 10−4, and solutions for all models were tested for mesh independence. All computations were
carried out on a workstation with dual-core processors (2.33 GHz) and a total of 64 GB random
access memory (RAM).
Charge and discharge currents, iapp, were applied at the respective boundaries with a smoothed
Heaviside function. For both 3D arrays, there were 3×104 elements and 1.6×105 degrees of
freedom (DoF) which required around 45 GB of memory for solution under 5 C discharge with a
solution time of around 1 hr. The reliability analysis was carried out by targeting one of the
electrodes – either positive or negative – as marked in our computational cell in Fig. 1f. We
assume that there will be no exchange current in the malfunctioning electrode as no reaction
occurs; to reflect this, the transfer current per unit volume, J, is set to zero in the simulation for
that electrode alone.
Results and Discussion
In this section, we begin by studying the behaviour during discharge of a 3D lithium-ion battery
with tessellated electrode geometry, for both the square and circular electrode arrays. A reliability
analysis is then carried out for the circular electrode array to study the behaviour of the battery
when one of the electrodes in the array malfunctions. Only the discharge process will be
illustrated as charging exhibits a similar behaviour.
Standard Discharge Behaviour
Discharge curves
First, we shall explore the global behaviour of the 3D battery in terms of potential during
discharge for different C-rates, as shown in Fig. 2. The drop in cell voltage during the discharge in
both the square and circular electrode arrays is similar. Both arrays exhibit a gentle and constant
decrease in potential for most of the discharge period except for the sharp drop towards the end
of discharge, similar to that of the 2D cell. Under all discharge rates, there is a sudden drop in the
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R. Hong Peng Liang at al.
J. Electrochem. Sci. Eng. 4(1) (2014) 1-17
potential from the initial value of 4.2 V during the initial period of discharge that corresponds to
ohmic losses. At 1 C-rate, there is a gradual drop in the potential from 3.9 V to 3 V until the end of
discharge at 3600 s when a sudden drop in the potential is seen as in Fig. 2. While a similar trend is
observed for discharge at 2 C-rate, the array experiences a much faster drop in potential at
5 C-rate due to a higher discharge current density.
Figure 2. Battery voltage during discharge at various discharge rates for square (continuous)
and circular (dashed) electrodes
Because electrodes in a 3D array are arranged in a parallel configuration, an array containing a
large number of electrodes will have a greater capacity compared to a single pair of electrodes as
compared to the 2D cell. Having more electrodes in an array would increase the total current
delivered but keeping the potential unchanged. The array capacity can also be increased by
elongating the electrodes into the plane, instead of increasing the capacity by making the
electrodes thicker as in 2D batteries. As such, power density is not sacrificed for an increase in the
array capacity in 3D batteries since the distance between electrodes remains the same. On the
other hand, array capacity is gained at the expense of power density in 2D cells as an increase in
capacity is attained by increasing the thickness of electrodes.
Electrochemical behaviour
During discharge, lithium ions deintercalate from the active material in the negative electrode
and enter the electrolyte; the reverse process happens in the positive electrode. Hence, the
concentration of lithium ions in the electrolyte increases in the negative electrode and decreases
in the positive electrode, as depicted in Fig. 3. The time constant for diffusion is around 100 s
( wi2 / Dleff ) after which the concentration profile reaches a pseudo-steady state. The lithium-ion
concentration reaches a maximum of 2100 mol m⁻³ at 1 C-rate and 2500 mol m⁻³ at 5 C-rate in the
cell, as well as a minimum of 1900 mol m⁻³ at 1 C-rate and 1700 mol m⁻³ at 5 C-rate. These
maximum and minimum concentration values are found in the negative and positive corner
electrodes respectively, since the corner electrodes are only surrounded by two nearest
neighbours: a negative corner electrode has fewer adjacent positive electrodes to consume fewer
doi: 10.5599/jese.2013.0040
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MODELING AND RELIABILITY ANALYSIS OF A 3D LI-ION BATTERY
lithium ions, while a positive corner electrode has fewer adjacent negative electrodes to produce
lithium ions.
Figure 3. Variation of concentration of lithium ions in the electrolyte along the xz-plane at
y=2.8 × 10⁻⁴ m at various times during discharge at 1 C and 5 C-rates for the circular electrodes
Moreover, there is variation in the lithium ion concentration in the electrolyte along the height
of the electrodes, as illustrated in Fig. 4a. Both arrays display similar behaviour, with the square
electrode array attaining a slightly higher concentration of 2105 mol m⁻³ in a negative corner
electrode compared to 2090 mol m⁻³ in the equivalent circular electrode. Extreme values are
observed in the areas nearer the current collector: negative electrodes have the highest lithium
ion concentrations near the negative current collector as consumption of lithium ions by the
positive electrode is lowest near the negative current collector; positive electrodes have the
lowest lithium ion concentrations near the positive current collector as production of lithium ions
in the negative electrode is lowest near the positive current collector.
Figure 4a. Concentration profile of lithium ions in the electrolyte at the end of discharge at 1 C-rate along
the xy-plane at z = 10⁻⁴ m (a, c) and at z = 2.5 × 10⁻⁴ m (b, d) for circular and square electrodes respectively
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R. Hong Peng Liang at al.
J. Electrochem. Sci. Eng. 4(1) (2014) 1-17
Figure 4b. Liquid phase potential profile in the electrolyte at the end of discharge at 1 C-rate along the xyplane at z=10⁻⁴ m (a, c) and at z=2.5 × 10⁻⁴ m (b, d) for circular and square electrodes respectively
The unequal distribution of lithium ions also results in a variation in the liquid phase potential in
the cell, as can be seen in Fig. 4b. Again, behaviour of both arrays are similar, with a maximum
potential drop of 12×10⁻³ V in the circular electrode array compared to 13×10⁻³ V in the square
electrode array. This potential drop, which can be attributed to ohmic losses and the concentration overpotential, gradually accentuates as the concentration gradient steepens during discharge. Extreme values of potential drop are observed nearest to the current collectors, because
of similar reasons that cause extreme values in lithium ion concentration. First, we shall explore
the global behaviour of the 3D battery in terms of potential during discharge for discharge curves.
Heat generation and thermal behaviour
The temperature of both circular and square arrays increases over time during discharge due to
heat generation, as shown in Fig. 5. For the square electrode array, the temperature increases by
12K, 20 K and 30 K above the ambient temperature for discharge rates of 1 C, 2 C and 5 C,
respectively.
Figure 5. Average battery temperature of the battery during discharge at various discharge
rates for square (continuous) and circular (dashed) electrodes
doi: 10.5599/jese.2013.0040
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MODELING AND RELIABILITY ANALYSIS OF A 3D LI-ION BATTERY
On the other hand, for the circular electrode array, the temperature increase is smaller, being
5 K, 8 K and 11 K for same discharge rates. Such a difference in array temperature over time is due
to the higher volume of the square electrodes as compared to the circular ones leading to more
heat generation in the square electrodes than the circular ones.
A comparison of the contribution from various layers towards heat generation is provided in
Figs. 6a-b. The negative electrode is the highest contributor, amounting to 60 % in both discharge
rates, due to its lower ionic conductivity and less porous nature. The positive electrode is the
second highest contributor. Heat generation in the current collector and electrolyte is purely by
ohmic heating and remains almost constant throughout the discharge.
a
b
Figure 6. Time history of total heat generation and heat generation in various layers during discharge
for square (continuous) and circular (dashed) electrodes at a – 1 C-rate, and b – 5 C-rate
Reliability Analysis
Due to the similarity in the behaviour of both the circular and square electrode arrays in the
reliability analysis, we will only consider the circular electrode array. The behaviour of
neighbouring electrodes is studied when either a target anode or a cathode malfunctions/fails.
Given the extreme discharge conditions of 5 C discharge for lithium-ion batteries, we shall discuss
the results for 5 C discharge rates as a worst-case scenario.
Discharge curves
The variation of cell voltage with time during discharge at 5 C-rate under both perturbed cases
is presented in Fig. 7. As expected, there is a decrease in the discharge time compared to the
normal case due to the loss in the energy capacity of the battery because of the malfunctioning of
the electrodes. When the positive electrode malfunctions, there is a decrease of 60 s in the
discharge time corresponding to a 10 % decrease in the energy capacity. Similarly, for the
malfunctioning negative electrode, there is a decrease of 110 s in the discharge time
corresponding to a 17 % decrease in the energy capacity. The negative electrode has higher
theoretical capacity than the positive electrode (defined as Ci in the constitutive relations) and
hence the capacity of the battery is reduced more when the negative electrode malfunctions
compared to the positive electrode malfunctioning. Thus, unlike the conventional parallel-plate
design, the 3D array is still able to safely generate power when an electrode malfunctions, though
with a lower energy capacity.
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R. Hong Peng Liang at al.
J. Electrochem. Sci. Eng. 4(1) (2014) 1-17
Figure 7. Battery voltage during discharge at 5 C-rate under normal (continuous) and perturbed cases
of malfunctioning either positive (dashed) or negative (dotted) electrodes as marked in Fig. 1
Electrochemical behaviour
When a positive electrode malfunctions, the concentration distribution of lithium ions in the
rest of the array away from the perturbed cell remains largely similar throughout high discharge
rates relative to that in a non-perturbed array, as shown by comparing Figs. 3b and 8a. However,
the concentration of lithium ions in the electrolyte in the malfunctioning positive electrode
increases continuously from the initial value of 2×10³ mol m⁻³ to 2.3×10³ mol m⁻³ at the end of
discharge, compared to a decrease to 1.8×10³ mol m⁻³ on average in the electrolyte in the other
positive electrodes. Because there is an inflow of ions from the adjacent negative electrodes that
act as source of lithium ions, but no reaction in the active material taking place to consume them,
lithium ions accumulate within the electrolyte in the malfunctioning positive electrode. This effect
is concentrated locally in and around the malfunctioning electrode as shown in Fig. 8a and is
insignificant towards the other electrodes in the array.
Figure 8. Variation of concentration of lithium ions in the electrolyte along the xz-plane at
y=2.8 × 10⁻⁴ m at various times during discharge at 5 C-rate under malfunctioning (a) positive
and (b) negative electrodes of circular cross-section
When a negative electrode malfunctions, the concentration distribution of lithium ions in the
rest of the array also remains largely similar throughout high discharge rates relative to that in a
non-perturbed array, as shown by comparing Figs. 3b and 8b. However, the concentration of
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MODELING AND RELIABILITY ANALYSIS OF A 3D LI-ION BATTERY
lithium ions in the electrolyte in the malfunctioning negative electrode decreases continuously
from the initial value of 2 x 103 mol m-3 to 1.8 x 103 mol m-3 at the end of discharge, compared to
an increase to 2.3 x 103 mol m-3 on average in the other negative electrodes. As the adjacent positive electrodes act as sink for lithium ions due to the reduction reaction, a concentration gradient
develops between these electrodes and the malfunctioning electrode. Lithium ions diffuse into the
positive electrodes from the electrolyte and the malfunctioning negative electrode does not give
out the lithium ions due to the absence of reaction in the active material, resulting in the depletion
of the ions within the electrolyte there. This effect is also concentrated locally in and around the
malfunctioning electrode as shown in Fig. 8b and is insignificant towards the rest of the array.
The cessation of function of any electrode would directly impact the electrochemical behaviour
on neighbouring electrodes to a significant degree, due to diffusion of lithium ions in and out of
the malfunctioning electrode which otherwise would not occur in a non-perturbed array.
However, this effect is negligible for electrodes further away during both the reaction phase and
the diffusion phase, due to the presence of many other functioning electrodes in an otherwise
intact array.
Heat generation and thermal behaviour
The rise in average temperature of the array in the perturbed cases in similar to that in the
standard discharge, in that the average temperature increases steadily at first before becoming
more gradual towards the end of discharge. However, there are some minor differences. When a
positive electrode malfunctions, the increase in temperature is smaller by 0 - 2 K compared to the
normal case during a 5 C discharge, and only 0 - 0.2 K during 1 C discharge rates, due to the
decrease in the number of heat sources. On the other hand, when an anode malfunctions, the
increase in temperature is smaller by 0 - 1 K compared to the normal case during a 5 C discharge,
and 0 - 0.2 K during 1 C discharge, due to the decreased heat generation in the negative electrodes
which is highest contributor to heat generation as seen before. Differences in thermal behavior
are negligible for electrodes further away from the malfunctioning electrode.
Conclusions
This paper presents a thermal-electrochemical coupled model for next-generation 3D Li-ion batteries applied to two different electrode geometries - square and circular. A reliability analysis was
also conducted to analyse the effect of a single malfunctioning electrode on the rest of the array.
In summary, the performance of the 3D cell during discharge under normal conditions was
similar for both the square and circular electrode arrays; potential, thermal behaviour and
electrochemical behaviour also did not show marked differences at any discharge rates under the
selected design parameters. Furthermore, the cell capacity can be increased by simply adding
more electrodes in the plane of the array or increasing the height of the electrodes, without
compromising on power density unlike in the conventional 2D design.
The performance of the 3D electrode array during perturbed conditions, in terms of the
changes in the potential and the concentration distribution, was only significant in and around the
malfunctioning electrode. A maximum change of around 17 % in the energy capacity and 10 % in
lithium ion concentration in the electrolyte in and around the malfunctioning electrode under a 5
C discharge was seen. Deviation in electrochemical behaviour is negligible more than one cell away
from the malfunctioning electrode. The model can also easily be extended to account for various
types of 3D designs and conditions.
12
R. Hong Peng Liang at al.
J. Electrochem. Sci. Eng. 4(1) (2014) 1-17
This design demonstrates a clear advantage in terms of reliability over the 2D battery, as the 3D
array does not stop functioning even if one of the electrodes fail, unlike the conventional 2D
parallel-plate design. This allows power to be continuously delivered in a safe manner until the
battery is eventually replaced, as there is only minor deviation in thermal behaviour of the cell. As
the array behaviour is likely to be significantly affected only when many electrodes malfunction,
actual implementation of 3D batteries with full-size arrays is viable. With good performance due to
the redundancy provided by the array, the 3D cell will be able to deliver reliability benefits which
are crucial in many modern applications. Further, the model can be extended to study the
transport in solid polymer electrolytes as well. Also, the model can be employed to study the
behaviour of the battery when there is short-circuiting of the electrodes which seems to be a
common problem in microbatteries.
Nomenclature
Cl
specific surface area for the faradaic reaction per unit
2
3
volume, m /m
-3
electrolyte concentration, mol m
avg
s
average concentration of Li in the active material, mol m
As
c
Cs
Cp
-3
cssurf
concentration of lithium in active material in the
-3
electrodes, mol m
-1 -1
specific heat capacity, J kg K
surface concentration of Li in the active material, mol m
Ea
H
ht
i0
is
J
k0
ls
n
q
Rs
activation energy for a variable, kJ mol
height of the battery, m
-2 -1
heat transfer coefficient, W m K
-2
exchange current density, A m
-2
solid phase current density, A m
-3
local charge transfer current per unit volume, A m
2.5
-0.5 -1
reaction rate constant, mol m s
diffusion length, m
normal vector
-2
conductive heat flux, W m
radius of active material, m
iapp
il
if
k
L
Nl
Q
R
r
diffusion coefficient of Li in the active material in the
2 -1
electrodes, m s
-1
Faraday’s constant, 96487 C mol
height of the functional layers in the battery, m
-2
applied current density, A m
-2
liquid phase current density, A m
-2
faradaic transfer current density, A m
-1 -1
thermal conductivity, W m K
length of the battery, m
-2 -1
species (lithium ion) flux, mol m s
-3
volumetric heat generation, W m
-1 -1
gas constant, J mol K
radial coordinate
t
time, s
t +0
transference number of cation
Dl diffusion coefficient of electrolyte, m2 s-1
T
Tref
Vi
Wi
Ds
-1
F
hi
-3
Ta, T0 ambient and initial temperature, K
U ref open circuit potential of the electrode, V
W width of the battery, m
temperature, K
reference temperature, 298.15 K
3
volume of the electrode i, m
thickness of the layer i, m
Greek
a, c anodic/cathodic transfer coefficient
f


s
s
volume fraction of the conductive filler additive in the
electrodes
overpotential, V
-3
density, kg m
electronic conductivity of solid matrix, S m
solid phase potential, V
-1
l
volume fraction of the electrolyte in the electrodes
p
volume fraction of the polymer in the electrodes

Bruggeman constant (= 1.5)
-1
ionic conductivity of electrolyte, S m
l
l
liquid phase potential, V

local state of charge of the electrodes
ne
negative electrode
el
electrolyte
eff
effective values
Subscripts
cc
current collector
pe positive electrode
l
liquid/ electrolyte
Superscripts
0
initial values
max maximum values
doi: 10.5599/jese.2013.0040
13
J. Electrochem. Sci. Eng. 4(1) (2014) 1-17
MODELING AND RELIABILITY ANALYSIS OF A 3D LI-ION BATTERY
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doi: 10.5599/jese.2013.0040
15
J. Electrochem. Sci. Eng. 4(1) (2014) 1-17
MODELING AND RELIABILITY ANALYSIS OF A 3D LI-ION BATTERY
Appendix A
Table A.1 Governing equations
Governing equation
 is = -J (pe,ne,cc)
is = -σs eff φs
il = J (pe,ne,el)
Flux
2RTσl eff
il = -σ φl +
(1 - t+0 )(lncl )
F
0
it
Nl = -Dleff cl + l +
F
eff
l
cl
J
+   Nl = (pe,ne,el)
t
F
i dc avg
3i
Ds surf avg
(cs - cs ) = - f , s = - f , (ne,pe)
ls
F dt
FRs
T
(ρC p )eff
+   q = Q (pe,ne,el,cc)
t
εl
-
q = -k eff T
Appendix B
Table B.1 Constitutive relations
J=
(ne, pe)
(el, cc)
if =

 α ηF 
 α ηF  
i0 exp  a  - exp  - c  
 RT 
 RT  

i0 =
Fk0 cl (csmax - cssurf )cssurf
η=
As =
Q=
θne , θpe =
Ci =
eff
Uref,
i =
eff
φs - φl -Uref,
i , i = ne, pe
3(1 - εl - ε f - εp )
Rs
Jη + JT
c
c
Uref, i
T
+ σseff (φs )2 + σleff (φl )2 +
Vi (1- εl - ε f - εp )ρC
i th , i = ne,pe
Uref, i + (T - Tref )
Uref, i
, i = ne, pe
σseff =
σleff =
σl εl
kieff =
ki (1- εl ) + kl εl ,i = ne, pe
(ρC p )i =
Dleff =
σl =
Θ(T ) =
2RTσleff
(1 - t+0 )(lncl ) φl , i = ne, pe
F
surf
s
max
s
T
σs (1 - εl - ε f - εp )
eff
16
 As i f

0
(ρC p )i (1- εl ) + (ρC p )l εl , i = ne, pe
Dl εl
-1.172  10-14 cl4 +1.3605  10-10 cl3 - 5.2245  10-7 cl2 + 6.7461  10-4 cl +1.0793  10-2
 Ea,Θ  1 1  
Θ(Tref )exp 
-   , Θ = Ds ,Dl ,σl


R
T
 ref T  

R. Hong Peng Liang at al.
J. Electrochem. Sci. Eng. 4(1) (2014) 1-17
φs0 =
Rs
5
Uref, pe (θpe0 ) - Uref, ne (θne0 )
φl0 =
-Uref, ne (θne0 )
Ecell =
φs I - φs VII
ls =
Uref, ne
T
=
344.1347exp(-32.9633θne + 8.3167)
2
- 0.852θne + 0.3622θne
+ 0.2698
1 + 749.0756exp(-34.7909θne + 8.8871)
=
 θ - 0.5169 
-4.1453+ 8.1471θpe -26.0645θ +12.766θ + 4.3127exp(0.5715θpe ) - 0.1842exp  - pe

 0.0462 
+1.2816sin(-4.9916θpe ) - 0.0904sin(-20.9669θpe -12.5788) + 0.0313sin(31.7663θpe -22.4295)
2
Uref, pe
T
2
pe
3
pe
Uref, ne =
-0.16 +1.32exp  -3θne  +10exp  -2000θne 
Uref, pe =


1

4.1983 + 0.0565tanh  -14.5546θpe + 8.6094  - 0.0275 
-1.9011
  0.9984 - θpe 0.4924




8
-0.1571exp  -0.0474θpe
 + 0.8102exp -40  θpe - 0.1339

Appendix C
I
Table C.1 Boundary conditions
n  is = -iapp , n  q = ht (T - Ta )
II
n  is II = n  is II , n  q II = n  q II , n  il = n  Nl = 0
III
n  is = 0, n  q III = n  q III
IV, V
n  is = 0 (IV), n  il = 0 (V), n  q = 0
VI
n  is = 0, n  il
VII
φs = 0, n  q = ht (T - Ta )
+
-
+
+
VI+
-
-
= n  il
VI-
, n  q VI = n  q VI , n  Nl
+
-
VI+
= n  Nl
VI-
Table C.2 Initial conditions
cssurf  csavg  cs0
cl = cl0
0 (ne,cc(-))
φs =  0
φs (pe,cc(+))
φl = φl0 (ne,pe,el)
T = T0
© 2014 by the authors; licensee IAPC, Zagreb, Croatia. This article is an open-access article
distributed under the terms and conditions of the Creative Commons Attribution license
(http://creativecommons.org/licenses/by/3.0/)
doi: 10.5599/jese.2013.0040
17
J. Electrochem. Sci. Eng. 4(1) (2014) 19-26; doi: 10.5599/jese.2013.0041
Open Access : : ISSN 1847-9286
www.jESE-online.org
Original scientific paper
Comparative voltammetric study and determination of
carbamate pesticide residues in soil at carbon nanotubes paste
electrodes
THOMMANDRU RAVEENDRANATH BABU, SARVAREDDY RAJASEKHAR REDDY,
PUCHAKAYALA SUJANA
Electroanalytical Lab., Department of Chemistry, N.B.K.R. Science and Arts College, Vidyanagar,
Nellore, AP, India

Corresponding Authors: E-mail: sarvareddymadhavi@gmail.com
Received: October 22, 2013; Revised: November 7, 2013; Published: January 25, 2014
Abstract
In this investigation, the persistence of carbamate pesticides in soil samples was investigated. A
simple and selective differential pulse adsorptive stripping voltammetry was selected for this
investigation. Carbon nanotubes paste electrodes were used as working electrodes for
differential pulse adsorptive stripping voltammetry and cyclic voltammetry. A symmetric study of
the various operational parameters that affect the stripping response was carried out by
differential pulse voltammetry. Peak currents were linear over the concentration range of 10-5 to
10-10 M with an accumulation potential of -0.6 V and a 70 s accumulation time with lower detection limits of 1.09x10-7 M, 1.07×10-7M, 1.09×10-7 M for chlorphropham, thiodicarb, aldicarb. The
relative standard deviation (n=10) and correlation coefficient values were 1.15 %, 0.988; 1.13 %,
0.978; and 1.14 %, 0.987, respectively. Universal buffer with pH range 2.0 - 6.0 was used as supporting electrolyte. The solutions with uniform concentration (10-5 M) were used in all determinations. Calculations were made by standard addition method.
Keywords
Thiodicarb; Aldicarb; Chlorpropham; Differential pulse adsorptive stripping voltammetry; Cyclic
voltammetry; CNTPE; Soil samples
Introduction
Pesticides are extensively and indiscriminately used in modern agricultural practices, resulting
in widespread distribution in the environment and posing serious health hazards to animals and
human beings. Besides inhalation from polluted environment, animals are also exposed to
pesticides through the utilisation of treated feeds and fodders. Thiodicarb (dimethyl N, N' –thiobis
doi: 10.5599/jese.2013.0041
19
J. Electrochem. Sci. Eng. 4(1) (2014) 19-26
CV STUDY OF CARBAMATE PESTICIDE IN SOIL
(methyl imino) carbonyloxy bisethanimido thioate) is a new carbamate compound with a broad
spectrum of activity that is being extensively used for crop protection. It is a class II category
compound (moderately toxic) as set forth by the United States Environmental Protection Agency
(USEPA) and World Health Organization (WHO). Various carbamate compounds have been
reported to cause biochemical changes in different species of animals [1-5]. Little information on
the effect of thiodicarb on biochemical profiles is available in dogs and rats [6-8]. However, no
detailed report is available regarding the effects of thiodicarb on various biochemical parameters
and blood enzymes in animals.
Chlorpropham (C10H12ClNO2)
Chlorpropham is a plant growth regulator used for the pre-emergence control of grass weeds in
alfalfa, Lima and snap beans, blueberries, cane berries, carrots, cranberries, ladino clover, garlic,
seed grass, onions, spinach, sugar beets, tomatoes, safflower, soybeans, gladioli and woody
nursery stock. It is also used to inhibit potato sprouting and for sucker control in tobacco. Parilla
et al. [9] reported SPE and HPLC/DAD methods to determine pesticide residues in water. Richard
[10] employed HPLC method to determine carbamate residues using post-column hydrolysis
electrochemical detection. Aulakh et al. [11] reported solid phase microextraction HPLC for the
analysis of pesticides. Tomomi et al. [12] developed a new analytical method for the determination
of nine pesticide residues including chlorpropham in fruits and vegetables using ESI-LC/MS/MS
with direct sample injection into a short column. Oosselton and Snelling [13] reported the use of
GLC, HPLC/DAD and TLC for the determination of 51 common pesticides including chlorpropham.
Thiodicarb (C10H18N4O4S3)
Thiodicarb is a non-systemic carbamate insecticide whose acetyl cholinesterase activity is
related to its main methomyl degradation product[14]. Xu and Li [15] determined thiodicarb by
reverse-phase high performance liquid chromatography.
Aldicarb (C7H14N2O2S)
Aldicarb is a carbamate insecticide which is the active substance in the pesticide Temik. It is
effective against thrips, aphids, spider mites, lygus, fleahoppers, and leafminers, but is primarily
used as a nematicide. Waliszewski and Szymczyński [16] reported a Simple method for the gaschromatographic determination of aldicarb, aldicarb sulphoxide and aldicarb sulphone in soil and
sugar beets. Mora et al. [17] determined the presence of the nematicide aldicarb and its
metabolites aldicarb sulphoxide and aldicarb sulphone in soils and potatoes by liquid
chromatography with photodiode array detection. Although there are reports in the literature for
several methods of determinations of pesticides, there are few focused on electrochemical
methods; hence, in this investigation, electrochemical determinations [18-20] were employed.
Experimental
Apparatus and electrodes
The electrochemical measurements were carried out with Metrohm model 101 potentiostat
and galvanostat. The three-electrode system consisted of carbon nanotubes paste electrode as the
working electrode, Ag/AgCl reference electrode and a platinum wire auxiliary electrode. The
electrodes joined the cell through holes in its Teflon cover. All of the potentials given in this work
were measured with respect to this reference system. Electrochemical experiments were carried
out in a voltammetric cell at room temperature. A magnetic stirrer was used during the
20
T. Raveendranath Babu at al.
J. Electrochem. Sci. Eng. 4(1) (2014) 19-26
accumulation step. The Elico Li-129 model glass calomel combined electrode was employed for
measuring pH values.
Preparation of carbon nanotubes paste electrode
The CNTPE was prepared by mixing multiwall CNTs powder (diameter 20-50 nm, either 1-5 mm
or 5-20 mm lengths) and Castrol oil in an agate mortar at a ratio of 50.0 % (w/w) each. A portion of
the resulting paste was packed firmly into the cavity (0.8 mm diameter) of a Teflon tube. The
electrical contact was established via a copper wire [21].
Reagents and solutions
All reagents used were of analytical reagent grade. Double distilled water was used throughout
the analysis. In the present investigation, universal buffers in the pH range 2.0 to 6.0 were used as
supporting electrolytes and were prepared using 0.2 M boric acid, 0.05 M citric acid and 0.1 M
trisodium orthophosphate solutions. Samples were obtained from RANKEM India, Ltd.
Result and discussion
All of the compounds exhibit well-defined voltammetric peaks at the same experimental
conditions but the reduction electrode potentials are somewhat different; this is attributed to the
difference in the nature of groups present in the compounds under investigation (Scheme 1).
Although all of the compounds possess electron-donating nitrogen on one or both sides of
carbonyl carbon, there are some differences in the environment of carbonyl carbon.
Scheme 1. Structures of the pesticides investigated in this work
In the case of chlorpropham, there is oxygen bonded with a propyl group on one side of the
carbonyl carbon and on the other side nitrogen with chlorobenzene. Because the aromatic ring is
closer to the electroactive group, it will experience less negative charge and undergo reduction at
somewhat lower electrode potentials when compared with the other two carbonyl groupcontaining pesticides. Two electrons are involved in reduction of one carbonyl group into the
hydroxyl group.
In the case of thiodicarb, there are two carbonyl groups with the same environments; in the
case of two carbonyl groups, there is oxygen bonded with electron-donating nitrogen on one side
and nitrogen bonded with electronegative sulphur and electron-donating alkyl groups on the other
side along with the other carbonyl group with the same environment. In the case of thiodicarb,
however, there is electron-donating nitrogen, alkyl groups with positive inductive effect; their
doi: 10.5599/jese.2013.0041
21
J. Electrochem. Sci. Eng. 4(1) (2014) 19-26
CV STUDY OF CARBAMATE PESTICIDE IN SOIL
impact on the electronic environment seems to be nil because of double bonds and
electronegative groups. In the case of thiodicarb, there is a well-defined peak due to 4 electron
reduction of two carbonyl groups.
In the case of aldicarb, there is only one carbonyl group on one side with nitrogen, while there
is electronegative oxygen bonded with nitrogen on the other side. Because of the electro rich
nitrogen being directly bonded with a carbonyl group, the environment around the electroactive
species seems to be more negative and reduction will take place at greater negative potentials
compared with the remaining two pesticides. Two electron reductions will take place.
Figure 1 shows DP-AdSV response for the samples (10-5M) under investigation over the pH
range 2.0-6.0 at CNTPE. The systematic studies of the various experimental and instrumental
parameters that affect the voltammetric response were carried out in order to establish the
optimum conditions. The pH of a solution is a critical factor affecting both the rate and equilibrium
state of the reduction process, as well as the rate of the electrode reaction. The influence of pH on
the voltammetric response was studied at CNTPE of the 10-5 M samples with pH between 2.0 and
6.0. The maximum peak currents were obtained with pH 4.0. Voltammograms obtained for
increasing values of the scan rate showed the existence of a linear dependence of the peak current
intensity on the scan rate between 10 to 60 mV s.-1 The peak currents were directly proportional
to the scan rate. The voltammetric behaviour of samples has been studied in the pH range from
2.0 to 6.0. A single well resolved peak was observed throughout the pH range and this single peak
is attributed to the reduction of corresponding groups. All the compounds under investigation
exhibit only one voltammetricpeak for each over the pH range 2.0 to 6.0. This wave / peak are
attributed to the simultaneous reduction of carbonyl group. Typical cyclic voltammograms are
shown in Fig. 2. No reduction peak is observed in basic medium (8  pH  12) for carbonyl groups
due to the precipitation. The diffusion controlled nature of electrode process is evidenced from
the linear plots of ip vs. V1/2 (Fig. 3).
Fig. 1.Stripping voltammograms of A - chlorpropham, B - thiodicar and C – aldicarb at CNTPE
Concentration: 10-5 M L-1, scan rate: 60 mV s-1, pH 4.0
22
T. Raveendranath Babu at al.
J. Electrochem. Sci. Eng. 4(1) (2014) 19-26
Fig. 2. Cyclic voltammograms of A - chlorpropham, B - thiodicar and C - aldicarb at CNTPE,
Concentration: 10-5 M L-1, scan rate: 60 mV s-1, pH 4.0
Fig. 3. Ip vs. V1/2 plots of A - chlorpropham, B - thiodicarb, C - aldicarb.
Concentration: 10-5 M L-1; Scan rate: 60 mV s-1, pH 4.0
Recovery experiments
Analysis
Based on the results obtained with differential pulse adsorptive stripping voltammetry and
cyclic voltammetry at CNTPE, differential pulse adsorptive stripping voltammetry and cyclic
voltammetry have been used for the quantitative determination of samples using both calibration
and standard addition methods. The investigated compounds were found to exhibit well resolved
peaks at pH 4.0, and the sharp well resolved peak was chosen for quantitative studies. Peak
currents are linear over the concentration range of 10-5 to 10-10 M with lower detection limits of
1.09×10-7 M for chlorpropham, 1.07×10-7 M for thiodicarb, and 1.09×10-7 M for aldicarb. The
relative standard deviation and correlation coefficients were found to be 1.15 %, 0.988; 1.13 %,
0.978; and 1.14 %, 0.987, respectively, for 10 replicates.
doi: 10.5599/jese.2013.0041
23
J. Electrochem. Sci. Eng. 4(1) (2014) 19-26
CV STUDY OF CARBAMATE PESTICIDE IN SOIL
Determination of pesticide samples from their standard solutions
To check the validity of the method, a standard solution (10-5 M) was prepared in dimethyl
formamide. 1 mL of the standard solution was transferred into a voltammetric cell and made up
with 9 mL of supporting electrolyte (pH 4.0), before being deoxygenated with nitrogen gas for
10 min, and then subjected to voltammetry. After obtaining voltammograms, a small increment of
the standard solution of samples was added to voltammetric cells and was deoxygenated for
10 min; voltammograms were recorded under similar conditions. In the same manner, 10 voltammograms were recorded for 10 standard additions. The optimum conditions for analytical determination were found to be at pH 4.0 and scan rate 60 mV s-1. The average recovery obtained for the
pesticide samples in soil samples ranged from 89.00 to 92.00 % for chlorpropham, from 97.50 to
99.33 % for thiodicarb and from 97.80 to 98.33 % for aldicarb for 10 replicates. The results are
shown in Table 1.
Table 1.Recoveries of chlorpropham, thiodicarb, aldicarb in standard solution of 1.0×10-5M
Amount added, µg mL-1
Amount found, µg mL-1
*Recovery, %
Standard deviation
Chlorpropham
3.0
2.79
93.00
0.024
Thiodicarb
3.0
2.98
99.33
0.034
Aldicarb
*Average of 10 replicates
3.0
2.95
98.33
0.028
Sample
Determination of pesticide samples in spiked soil samples
The soil under investigation was spiked with known amounts of formulations and dried on filter
paper at laboratory temperature. For extraction, 50 g of the dried soil was transferred into a
250 ml Erlenmeyer flask. These samples and blanks were extracted 2-5 times by acetone. The
extracts were then evaporated to dryness and the resulting residues were dissolved in DMF and
transferred to 50 ml voltammetric flasks. This solution was filtered through Whatman nylon
membrane filter paper and voltammograms of the filtrates were recorded by following the
previously mentioned procedure. The average recovery obtained for the sample in soil samples
ranged from 90.00 to 93.00 % for chlorpropham (bud nip), from 93.50 to 95.66 % for thiodicarb
(larvin) and from 92.70 to 95.66 % for aldicarb (aldicarb sulphone) for 10 replicates. The results are
presented in Table 2.
Table 2. Recoveries of chlorpropham, thiodicarb, aldicarb (formulations) in spiked soil samples
Sample
Amount added, µg mL-1
Amount found, µg mL-1
*Recovery, %
Standard deviation
Bud Nip
3.0
2.76
92.00
0.015
Larvin
3.0
2.87
95.66
0.024
Aldicarb sulphone
3.0
2.88
96.00
0.018
*Average of 10 replicates
Conclusion
In conclusion, the adopted method of differential pulse adsorptive stripping voltammetry is a
less tedious and economically low consumption method; hence, this can be used satisfactorily for
the determination of pesticide residues in soil. The obtained results also demonstrate the
24
T. Raveendranath Babu at al.
J. Electrochem. Sci. Eng. 4(1) (2014) 19-26
suitability of the developed DP-AdSV method for the determination of samples under investigation
in soil samples. The electrochemical reduction mechanism of the carbonyl group in all three
compounds was found to be irreversible. The nature of the electrode process for these
compounds is found to be diffusion controlled and involves adsorption on the electrode surface
without any kinetic complications. The variation of peak current with the pH of the supporting
electrolyte influences the diffusion coefficient values. The slight variations in diffusion coefficient
values with increasing pH may be attributed to a decrease in the availability of protons.
The heterogeneous forward rate constant values obtained for the reduction of these three
pesticides are found to decrease with an increase in the pH of the solution, as expected. From the
comparison of the forward rate constant values of the three compounds, it can be seen that they
reduce at different electrode potentials, which is attributed to the difference in the molecular
environment of the samples under investigation. Analytical procedures are described for the
quantitative determination of these compounds using DP-AdSV. In the present investigation,
standard addition and calibration methods were utilised for the determination of these pesticides
in soil samples. From the recoveries, it has been observed that the proposed method describes the
successful application of an electroanalytical technique for the analysis of these compounds. It
also demonstrates that DP-AdSV at a carbon nanotubes paste electrode could conveniently be
used for the quantitative determination of these pesticides in soil samples. The method shows a
good reproducibility and high accuracy compared with spectrophotometric, spectrofluorimetric
and chromatographic methods of analysis.
References
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[4] S. D. Moregaonkar, B. B .Deshpande, V. P Vadlmudi, N. M. Degloorkar, S. R. Rajurkar,
Indian. Vet. J. 70 (1993) 945-948.
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[7] H. B. Knaak, B. W .Wilson. ACS Symposium Series, 273 (1985) 63-79.
[8] N. N. Hamada, Rep. No. 210-216 from Hazleton Laboratories America Inc., Vienna, VA to
Union Carbide Agricultural Products Company Inc. Research Triangle Park, North Carolina,
1986
[9] P. Parrilla, J. L. M. Vidal, Anal. Lett. 30 (1997) 1719-1738.
[10] R. T. Krause, J. Chromatogr. A 442(1988) 333-343.
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[12] T. Goto, Y. Ito, S. Yamada, H. Matsumoto, H. Oka and. H. Nagase, Anal. Chim. Acta 555
(2006) 225-232.
[13] M. D. Osselton, R. D. Snelling J. Chromatogr. A 368 (1986) 265-271.
[14] G. Hoizey, F. Canas, L Binet, M. L. Kaltenbach, G. Jeunehomme, M. H. Bernard, D. Lamiable,
J. Forensic Sci. 53 (2008) 499-502.
[15] G. Xu, W. Zheng, Y. Li, S. Wang, J. Zhang, Y. Yan., Int. Biodeter. Biodegr. 62 (2008) 51–56.
[16] S. M. Waliszewski, G. A. Szymczyński, Fresen. J. Anal. Chem. 338 (1990) 75-76
[17] N. Unceta, A. Ugarte, A. Sanchez, A. Gómez-Caballero, M. A .Goicolea, R. J. Barrio, J.
Chromatogr. A 1061 (2004) 211-216
doi: 10.5599/jese.2013.0041
25
J. Electrochem. Sci. Eng. 4(1) (2014) 19-26
[18]
[19]
[20]
CV STUDY OF CARBAMATE PESTICIDE IN SOIL
S. Rajasekharreddy, K. Chandramohan and, NY. Sreedhar, Int. J. Sci. Eng. Res, 2(10) (2011)
1-4.
S. Rajasekhar Reddy, T. Raveendranath Babu, B. SreenivasuluInt, J. Res. Pharm. Life Sci. 1
(2013) 43-47.
S. Rajasekhar Reddy, T. Raveendra Nath Babu, Int. J. Nanosci.12 (2013) 130058.
© 2014 by the authors; licensee IAPC, Zagreb, Croatia. This article is an open-access article
distributed under the terms and conditions of the Creative Commons Attribution license
(http://creativecommons.org/licenses/by/3.0/)
26
J. Electrochem. Sci. Eng. 4(1) (2014) 27-35; doi: 10.5599/jese.2014.0042
Open Access : : ISSN 1847-9286
www.jESE-online.org
Original scientific paper
Synthesis of CuInSe2 thin films from electrodeposited Cu11In9
precursors by two-step annealing
TSUNG-WEI CHANG, SHAO-YU HU, WEN-HSI LEE
Department of Electrical Engineering, National Cheng Kung University, Tainan 701, Taiwan, R.O.C

Corresponding Authors: E-mail: leewen@mail.ncku.edu.tw
Received: February 12, 2013; Revised: November 22, 2013; Published: January 25, 2014
Abstract
In this study, copper indium selenide (CIS) films were synthesized from electrodeposited Cu-In-Se
precursors by two-step annealing. The agglomeration phenomenon of the electrodeposited In
layer usually occurred on the Cu surface. A thermal process was adopted to turn Cu-In precursors
into uniform Cu11In9 binary compounds. After deposition of the Se layer, annealing was
employed to form chalcopyrite CIS. However, synthesis of CIS from Cu11In9 requires sufficient
thermal energy. Annealing temperature and time were investigated to grow high quality CIS
film. Various electrodeposition conditions were investigated to achieve the proper atomic ratio
of CIS. The properties of the CIS films were characterized by scanning electron microscopy (SEM),
X-ray Diffraction (XRD), and Raman spectra.
Keywords
CuInSe2, CIS, Annealing, Electrodeposition
Introduction
The solar cell has emerged as a very important non-conventional energy source. Copper indium
selenide (CuInSe2) is a I–III–VI group semiconductor compound offering good possibilities for thinfilm photovoltaic (PV) applications because it has a energy gap of 1.02 eV [1–5]. Electrochemical
deposition is a low cost method of producing thin CIS films because it has several advantages for
large-area non-vacuum thin film production and little material waste. However, the crystallinity of
CIS film grown by single-step electrodeposition is inferior because its growing temperature is much
lower than that of the physical vapour deposition (PVD) method. The grains were small and loose.
The CIS film can also be synthesized from co-sputtered Cu11In9-Se precursors by the thermal
annealing process [6,7]. Large CIS grains can be grown due to the gas–liquid reaction during the
annealing process [8]. The Cu-In alloys are usually co-sputtered by PVD. The PVD technology is
doi: 10.5599/jese.2013.0042
27
J. Electrochem. Sci. Eng. 4(1) (2014) 27-35
SYNTHESIS OF CuInSe2 THIN FILMS FROM Cu11In9
excellent for good quality film growth but difficult to scale up because of the high manufacturing
costs.
In this study, Cu-In precursors were prepared by multi-step electrodeposition. However, the
agglomeration phenomenon of the electrodeposited In layer usually occurred on the Cu surface.
The surface was non-uniform and discontinuous. An annealing process was adopted to transform
Cu-In to Cu11In9 compound and create a uniform surface structure. After deposition of the Se layer
on the annealed Cu11In9, another annealing process is required to synthesize the CIS structure.
Various annealing temperatures and times were adopted to investigate the proper annealing
conditions and the mechanism of CIS synthesis. The deposition conditions were adjusted to
achieve a better atomic ratio. The properties of the CIS films were characterized by scanning
electron microscopy (SEM), X-ray Diffraction (XRD), and Raman spectra.
Experiment
The aqueous solution for the Cu deposition contained 0.75 M CuSO4, 4 mM H2SO4, and
0.5 mM HCl. The aqueous solution for the Se deposition contained 17 mM H2SeO3 and
0.5 mM HCl. The aqueous solution for the In deposition contained 50 mM InCl3 and 30 mM HCl.
The electrodepositions were carried out with AUTOLAB PGSTAT302, a conventional threeelectrode potentiostat, and the deposition conditions listed in Table 1. A thin slice of 99.99% pure
Pt electrode measuring 1 × 4 cm was employed as the counter electrode, and an Ag/AgCl
electrode served as the reference electrode. Glass substrates with sputtered Mo film were used as
the working electrodes. The electrodeposition area was a square measuring 1 x 1 cm. The
substrates were cleaned by ultrasonication in acetone, 99.5 % pure ethanol, and water before
sputtering and electrodeposition. A magnetic stirrer was used for the stirring procedure. The
rotation speed of the magnetic stirrer was set at 50 rpm.
Table 1. Electrodeposition and annealing condition of samples a - f.
Cu
In
Se
i / mA : / s
 / s (i = 5 mA)
i / mA
/ s
Tannealing / °C
 = 5 min)
Sample a
60 : 20 + 20 : 10
350
4
1450
550
Sample b
60 : 20 + 20 : 10
350
4
1450
600
Sample c
60 : 20 + 20 : 10
350
4
1450
650
Sample d
70 : 20 + 20 : 10
350
4
1450
650
Sample e
60 : 10 + 30 : 10
375
4
1450
650
Sample f
50 : 10 + 20 : 10
350
4
1450
650
The In deposition was carried out after the two-step growth of Cu. The Cu-In layers were
treated by rapid thermal annealing (RTA) at 500 °C for 5 min. The Se layer was deposited on the
Cu-In layer after annealing. The CIS film was synthesized by annealing the Cu-Se and In-Se
precursors. The deposition conditions and RTA listed in Table 1 were found to achieve better
proportions and structures.
The surface morphology and chemical composition of the films were characterized by SEM
(Philips XL-40FEG) and EDS, respectively. The Raman spectra were produced with a backscattering
configuration at room temperature with unpolarized light using a DILOR XY 800 spectrometer and
28
Ts-W Chang at al.
J. Electrochem. Sci. Eng. 4(1) (2014) 27-35
an Ar laser with a 514.5 nm wavelength as the light source. The phase composition and the
crystallographic structure were analysed by XRD using a Bruker D8 SSS multipurpose thin-film x-ray
diffractometer.
Results and discussion
In this study, CuInSe2 thin films were synthesized from electrodeposited Cu, In, and Se thin-film
precursors. However, the electrodeposition of the In layer on the copper surface with a current of
60 mA in 20 s + 20 mA in 10 s induced serious agglomeration phenomenon. Figure 1 shows the
SEM image of the deposited In on the Cu layer. It was deposited with a current density of
3-6 mA cm-2. The agglomeration phenomenon made it difficult for the In layer to cover the whole
surface. The grains of In were separated. Deposition with a high current density can lead to a
better distribution of In. However, it also leads to large over potential, which would cause bubbles
and a rough structure. A suitable value of 5 mA was employed for the deposition of In. After the
deposition of Se, the Cu-In-Se precursor was annealed by RTA to form the CIS structure. The XRD
results in Figure 2 show that the CIS structure can be synthesized at 450-550 °C. However, the SEM
images in Figure 3 show that the film has a rough surface and a non-uniform grain size. The CIS
structure came from the non-uniform In layer and the miscellaneous precursor type. The
precursors not only contain Cu, In and Se, but also some binary compounds, including Cu 11In9,
CuxSe and In2Se3, which were produced in the electrodeposition and annealing process. Different
precursors have different reactions and temperature requirements to form CIS, and other
reactions lead to a uniform structure [9].
Fig. 1. SEM images of deposited In on Cu surface with current densities
(a) 3 mA cm-2 (b) 4 mA cm-2 (c) 5 mA cm-2 (d) 6 mA cm-2 for 200s.
doi: 10.5599/jese.2014.0042
29
SYNTHESIS OF CuInSe2 THIN FILMS FROM Cu11In9
Intensity, a.u.
J. Electrochem. Sci. Eng. 4(1) (2014) 27-35
2 / °
Fig. 2. XRD of annealed CIS film synthesized from Cu-In-Se precursor with temperature.
Fig. 3. SEM images of annealed CIS film synthesized from bilayer electrodeposition of Cu-In-Se
precursors with temperature (a) 250 °C, (b) 350 °C, (c) 450 °C, (d) 550 °C.
30
Ts-W Chang at al.
J. Electrochem. Sci. Eng. 4(1) (2014) 27-35
In order to create a smooth In layer distribution and uniform CIS synthesis, a thermal pretreatment at 500 °C for 5 min was employed to improve the topography of the Cu-In layer.
Figure 4 shows the SEM image of the Cu-In thin film after annealing at 500 °C for 5 min. The film
re-grows continuously and covers the whole Cu surface. Figure 5 shows the XRD pattern of the
annealed Cu-In precursor. Most of the precursors were turned to Cu 11In9 and small amounts to
CuInSe2.
Intensity, a.u.
Fig. 4. SEM images of electrodeposited In layer on Cu surface (a) as-deposited film (b) annealed film.
2 / °
Fig.5. XRD pattern of annealed Cu/In precursors.
The Se layer was deposited on the annealed Cu-In surface at 4 mA cm-2 current density for
1200 s. All of the precursors were recrystallized by RTA at 600 °C for 3 min and observed by SEM
and EDS. Figure 6(a) shows the microstructure of the annealed CIS film at 600 °C for 3 min. The
grain size of the annealed CIS film synthesized from Cu11In9-Se precursors is much larger than that
of CIS film annealed by co-electrodeposition. During the thermal annealing, the Cu-In became
liquid phase and reacted with the gas phase Se. CIS grain growing and diffusion were easier in the
gas-liquid reaction. However, many voids were observed in the SEM image. This was because CIS
synthesis from the reaction of Cu11In9-Se precursors requires a higher annealing temperature.
doi: 10.5599/jese.2014.0042
31
J. Electrochem. Sci. Eng. 4(1) (2014) 27-35
SYNTHESIS OF CuInSe2 THIN FILMS FROM Cu11In9
Figure 6(b) shows the microstructure of the CIS film with an annealing temperature of 630 °C for
3 min. A higher synthesis temperature certainly reduces the voids in the film.
However, the EDS results shown in Table 2 indicate that the composition of the film is not
optimum for CIS. Se gas would easily dissipate during annealing. In Samples a, b, and c listed in
Table 1, the deposition times of Se was increased to 1450 s and the annealing temperature was
adjusted to find the proper value. The EDS results shown in Table 2 indicate that the atomic ratio
of Se increases to an appropriate value of 50 %.
Fig. 6. SEM images of CIS film after annealing at (a) 600 °C, (b) 630°C for 3min.
Table 2. The EDS analysis of atomic percent of CIS film after increasing
the deposition time for 1200 s and 1450 s of Se
at. % of Cu
at. % of In
at. % of Se
Cu/In ratio
Se deposition time, s
29.1
24.7
46.2
1.17
1200
26.6
23.2
50.2
1.14
1450
Figure 7 shows the SEM images of Samples a, b, and c. It is observed that increasing the
annealing temperature can increase the grain size of the CIS film. The voids on the surface were
also reduced with the higher temperature. A higher annealing temperature could provide
sufficient energy for the CIS film to diffuse and react more completely. The deposition condition
was adjusted in Samples d, e, and f to achieve a proper Cu-In ratio. The EDS results are shown in
Table 3. The Cu-In ratio of Sample f achieved nearly 1:1.
Fig. 7. SEM images of CIS film with the Se layer deposited on the annealed Cu/In surface at
4 mA cm-2 current density for 1200 s after annealing at (a) 600℃ (b) 630°C for 3min.
32
Ts-W Chang at al.
J. Electrochem. Sci. Eng. 4(1) (2014) 27-35
Table 3. The EDS analysis of atomic percent in samples d, e, and f.
at. % of Cu
at. % of In
at. % of Se
Cu/In ratio
Sample d
25.6
24.3
50.1
1.05
Sample e
25.4
22.8
51.8
1.11
Sample f
24.9
24.5
50.6
1.01
Figure 8 shows the SEM images of Sample f after annealing at 630 °C for 5 min and 10 min. The
grain of CIS film became large and dense, and the voids almost disappear in Sample f. The crosssection images of Sample f are shown in Figure 9. Large dense grains could be clearly observed and
the thickness of the CIS approached 2 μm.
Fig. 8. SEM images of sample f, annealed at 630 ℃ for (a) 5 min (b) 10 min.
Fig. 9. SEM images of cross-section of sample f, annealed at 630 °C for (a) 5 min, (b) 10 min.
Figure 10 shows the XRD patterns of the CIS films with various annealing conditions. The main
(112) peak confirmed the existence of chalcopyrite CIS. The (112) main peaks of the CIS films
annealed at 550 °C for 5 min and at 600 °C for 5 min contained some small peaks of impure phase.
However, the peaks were too close to be differentiated clearly by XRD, but the Raman analysis
found Cu1-xSex or InxSe.
A Raman spectrum was employed to analyse the film composition. Figure 11 shows the Raman
spectra of the CIS films with various annealing conditions. Cu2Se was found in the samples with the
lower annealing temperature or shorter annealing time. This is because Cu2Se was formed before
the synthesis of CIS. If the annealing does not provide sufficient energy or reaction time, the
precursors cannot completely transform to CIS. Figure 12 shows the XRD patterns of the CIS film
with the lower annealing temperature. Cu-Se and In-Se were found at 300 °C and CIS (112) was
found at 350 °C. This indicates that the precursors would turn into Cu-Se and In-Se binary
compounds before the synthesis of the chalcopyrite CIS [10].
doi: 10.5599/jese.2014.0042
33
SYNTHESIS OF CuInSe2 THIN FILMS FROM Cu11In9
Intensity, a.u.
Intensity, a.u.
J. Electrochem. Sci. Eng. 4(1) (2014) 27-35
2 / °
2 / °
Intensity, a.u.
Fig.10. XRD patterns of CIS films with conditions.
Wavenumber, cm-1
Intensity, a.u.
Fig.11. Raman spectra of CIS films obtained with conditions.
Wavenumber, cm-1
Fig.12. XRD patterns of CIS films after annealing at low temperature 250℃~350℃.
34
Ts-W Chang at al.
J. Electrochem. Sci. Eng. 4(1) (2014) 27-35
However, synthesized CIS from co-sputtered Cu11In9 can produce high quality film with large
grains. In this study, synthesis of the CIS from the electrodeposited Cu-In precursors was
investigated. A thermal process was adopted to eliminate the agglomeration phenomenon of
electrodeposited In and to form Cu11In9 compound. The electrodeposition conditions of Cu, In and
Se, were adjusted to achieve the preferred atomic proportion. However, the annealing
temperature of the synthesized CIS from Cu11In9 is critical. The XRD patterns and Raman spectra
show that the residue of the Cu2Se compound is due to an incomplete reaction at lower annealing
temperatures. Large dense grains could be grown at 650 °C for 5 min. Finally, we produced a high
quality CIS film with large grains from a cheap method of electrodeposition of Cu-In precursors.
Conclusions
Electrodeposition is a cheap and efficient method of producing CIS film. The crystallinity of the
co-electrodeposited film is inferior because of the low growing temperature. Synthesizing CIS from
co-sputtered Cu11In9 can produce high quality film with large grains. In this study, synthesizing CIS
from electrodeposited Cu-In precursors was investigated. A thermal process was adopted to
eliminate the agglomeration phenomenon of electrodeposited In to form Cu11In9 compound. The
electrodeposition conditions of Cu, In and Se, were adjusted to achieve the preferred atomic
proportion. However, the annealing temperature of synthesized CIS from Cu11In9 is critical. The
XRD patterns and Raman spectra show that the Cu2Se compound residue is due to an incomplete
reaction at lower annealing temperatures. Large dense grains could be grown at 650 °C for 5 min.
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© 2014 by the authors; licensee IAPC, Zagreb, Croatia. This article is an open-access article
distributed under the terms and conditions of the Creative Commons Attribution license
(http://creativecommons.org/licenses/by/3.0/)
doi: 10.5599/jese.2014.0042
35
J. Electrochem. Sci. Eng. 4(1) (2014) 37-44; doi: 10.5599/jese.2014.0043
Open Access : : ISSN 1847-9286
www.jESE-online.org
Original scientific paper
Determination of nevirapine in the presence of cucurbit(7)uril
with a gold electrode
ANA M. ESTEVA, ELÍAS BLANCO*,, JUAN J. PIÑA, ABEL I. BALBIN, CARMEN
QUINTANA*, PEDRO HERNÁNDEZ*
Departamento de Química Analítica, Facultad de Química, Universidad de La Habana, La Habana
10400, Cuba
*Departamento de Química Analítica y Análisis Instrumental, Facultad de Ciencias, Universidad
Autónoma de Madrid, Cantoblanco 28049, Madrid, Spain

Corresponding Author: E-mail: elias.blanco@uam.es; Tel.: +34-91-497-4172; Fax: +34-91-497-4931
Received: July 24, 2013; Revised: November 21, 2013; Published: January 25, 2014
Abstract
The electrochemical oxidation of nevirapine, an anti-HIV drug, at a gold electrode was
studied by voltammetric techniques. Nevirapine showed a signal that interfered with a
working electrode wave. This interference was solved by the use of cucurbit(7)uril
allowing nevirapine to be determined in tablets (80.4 % recovery, presence of stavudine
and lamivudine) and urine (98.4 %).
Keywords
Antiretroviral, Voltammetry, Tablets, Urine
Introduction
Nevirapine (NEV, Figure 1) is a non-nucleoside reverse transcriptase inhibitor (NNRTI) of HIV-1
that causes acquired immunodeficiency syndrome (AIDS). The drug directly bounds to and blocks
the activities of RNA and DNA polymerases, both dependent, which caused breakdown of the
enzyme catalytic site. NEV activity was not competitive with the reverse transcriptase enzyme or
with nucleoside triphosphates. Reverse transcriptase (RT) of HIV-2 and DNA polymerases of
eukaryotic cells (eg. human DNA polymerases alpha, beta, gamma and sigma) were not inhibited
by nevirapine. The in-vitro antiviral activity was determined in peripheral blood mononuclear cells
(PBMC), monocyte-derived macrophages and a lymphoblastoid cell line. The values of the 50 %
inhibitory concentrations (IC50) were in the range of 10 to 100 µM against laboratory and clinical
isolates of HIV-1. In cell cultures, nevirapine demonstrated additive to synergistic action against
doi: 10.5599/jese.2014.0043
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J. Electrochem. Sci. Eng. 4(1) (2014) 37-44
DETERMINATION OF NEVIRAPINE WITH A GOLD ELECTRODE
HIV-1 in combination regimens with zidovudine, didanosine, stavudine, lamivudine, saquinavir and
indinavir [1].
Figure 1. Nevirapine; 11-cyclopropyl–5,11–dihydro–4–methyl–6H dipyrido[3,2–b:2′,3′-e]-[1,4]diazepin–6–one.
Different analytical techniques were used to detect NEV, including high performance liquid
chromatography (HPLC) [2], matrix-assisted laser desorption/ionization-time of flight mass
spectrometry (MALDI-TOF) [3], and capillary electrophoresis [4]. These techniques require expensive equipment, costly reagents for sample preparation and analysis and quite some time.
Electroanalytical methods are an accurate and cheap alternative which offer very low detection
limits for electroactive molecules. Different drugs were determined by this technique achieving
very low detection limits [5]. Some articles have recently been published about the
electroanalytical determination of NEV by means of different working electrodes [6-8].
The family of compounds of cucurbit(n)urils (CB(n)) are polymeric macrocycles obtained by the
condensation reaction of glicoluryl and formaldehyde in acid conditions and have n units of glicoluryl bridged by methylene groups. They bind molecules by hydrophobic and ion-dipole
interactions (but not exclusively) due to the cavity portals delineated by a rim of carbonylic
oxygens. The hydrophobic cavity allowed the inclusion of different molecules depending on the
CB(n) homologue and the size of the guest [9,10].
We developed a method for the analysis of NEV using CB(7) and gold electrode. Low detection
limits were obtained. The method was applied to biological fluids (urine) and a pharmaceutical
formulation (which also contained lamivudine and stavudine) and it was demonstrated that the
methodology had fewer steps than other ones.
Experimental
Reagents
NEV was provided by the Center for State Control of Drugs (CECMED-Cuba). Aqueous solutions
of the analyte were prepared at a 2 mg mL-1 concentration in acid medium (pH < 3). Diluted
solutions were prepared in supporting electrolyte just before use. CB(7) was supplied by SigmaAldrich Chemical Co. All reagents were of analytical grade (> 98 %) and were provided by Scharlau.
Ultrapure water was produced by a Milli-Ro and Milli-Q system (Millipore, Waters). Solutions of
these compounds were stored at 4 °C and protected from light. Britton-Robinson buffer solutions
(BR, mixture of boric, acetic and phosphoric acids) were used as supporting electrolytes, prepared
at a final concentration of 0.04 M and the buffer pH was adjusted with 0.1 M NaOH.
NEV was determined in a tablet sample whose nominal content was 250 mg per tablet together
with 40 mg of stavudine and 150 mg of lamivudine. A tablet was dissolved in methanol and filtered
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A. M. Esteva at al.
J. Electrochem. Sci. Eng. 4(1) (2014) 37-44
through a cellulose membrane of 0.45 µm pore size to get a 2.5 mg mL-1 NEV solution which was
stored at 4 °C.
Apparatus
Electrochemical measurements were performed by means of a μAutolab III potentiostat made
by Eco-Chemie in a three electrodes cell: an Au working electrode (2.01 mm2 geometric area)
provided by BAS, a coiled platinum wire as counter electrode and an Ag/AgCl (3 M KCl) reference
electrode (all potentials in this paper were referred against it). The pH was controlled by means of
a Methrom 827 pH meter with combined glass and an Ag/AgCl/ (3 M KCl) electrode.
Procedure
Activation and regeneration of the gold electrode surface was carried out by successive
scanning in 0.1 M sulphuric acid between 0.0 V and 1.5 V at 100 mV s-1 by cyclic voltammetry (CV).
An ultrasonic bath was used to clean the electrode surface when required and prior to the
described activation procedure. Differential pulse voltammetry (DPV) was the chosen technique
for the analyte determination in solutions of a NEV:CB(7) ratio of 1:2, the measurements started at
0.4 V and the chosen scan rate and pulse amplitude were 25 mV s-1 and 25 mV, respectively.
Results and Discussion
Our studies were performed with NEV at a concentration of 100 µM (26.6 µg mL-1) by CV at gold
electrode in 0.04 M BR buffer at pH 2. The analyte showed irreversible redox behaviour and a
reduction wave was observed at 0.66 V. As it can be seen in Figure 2, a broad and intense signal at
1.14 V was seen in the anodic scan (green line) but close to the gold oxidation wave at 1.3 V (black
line). It shifted to potential values lower than 1.1 V between pH 2 and 6 until disappearance at
higher pH. Above that pH, NEV was not electroactive.
Figure 2. Cyclic voltammograms of NEV at 100 mV s-1 in 0.04 M BR buffer at pH 2. Black line,
supporting electrolyte; red line, 20 µM CB(7); green line, 100 µM NEV; blue line, 10 µM NEV;
cyan line, 10 µM NEV and 20 µM CB(7).
doi: 10.5599/jese.2014.0043
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DETERMINATION OF NEVIRAPINE WITH A GOLD ELECTRODE
An increase in the sweep rate (Vb) between 10 and 400 mV s-1 entailed a variation of the
intensity and potential of the signals when a 266 µg mL-1 analyte solution in 0.04 M BR at pH 2 was
analysed. When the logarithm of the anodic peak current was represented versus the logarithm of
the scan rate in Figure 3 (black points), a straight line was obtained with a 0.53 slope value (close
to 0.5) so the oxidation could happen after diffusion of the analyte to the electrode surface.
However, it was showed in Figure 2 (green line) that NEV was oxidized by means of at least two
processes and its shape was not a diffusion-like one so the 0.53 slope value was a chance. The
dependence between the logarithm of the cathodic peak current of the NEV oxidation product and
the logarithm of the scan rate was studied (Figure 3, red points) and a slope close to 1 was found
so the reduction of that product could be concomitant with an adsorption process. Nevertheless,
that wave was overlapped with the gold oxide reduction wave and both processes were
connected.
Figure 3. Effect of the change of the scan rate on the oxidation (black points and line)
and reduction peak currents (red points and line).
As before stated, the NEV oxidation wave was at a potential very close to the gold oxides
formation one so the measurements analysis could be complicated or even impossible if the
analyte concentrations of the sample solution were low, as in the case of a 10 µM NEV (blue line,
Figure 2). When CB(7) was added to solutions of this low NEV concentration (10 µM NEV and 20
µM CB(7), cyan line, Figure 2), the anodic signals were more separated, the NEV wave was
narrower and a huge increase in the peak current was observed when they were compared to the
signal of solutions of the same analyte concentration and no added CB(7) (blue line, Figure 2).
Voltammetric measurements of blank solutions of CB(7) did not show any signal but the same
waves observed when the cell just contained supporting electrolyte, as it can be seen in Figure 2,
red and black lines, respectively.
If a 1:2 NEV:CB(7) molar ratio was kept constant, the separation of NEV and gold waves in the
anodic scan observed at pH 2 in Figure 2 (cyan line) continued up to neutral pH. In these
conditions, the NEV cathodic signal was not observed at pH higher than 2. The peak potential (Ep)
depended on the medium pH so it can be concluded that the anodic reaction was coupled to an
acid-base one. In this case, this dependence followed a straight line whose equation was
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J. Electrochem. Sci. Eng. 4(1) (2014) 37-44
Ep / V = 1.19 - 0.021 pH (R2 = 0.998). As the line slope value (dEp/dpH) was close to 0.029 V per pH
unit, the number of exchanged protons was the half of the number of electrons according to the
Nernst equation.
The stoichiometric NEV:CB(7) ratio was studied by CV in 0.04 M BR buffer pH 2, at a constant
CB(7) concentration and changing NEV concentration, and vice versa. Current and potential values
were plotted and the slope change depending on the NEV:CB(7) ratio was indicative of successive
formation of NEV-CB(7) complexes of 1:2 stoichiometry.
As it is shown in Figure 4, the effect of the concentration (0.3-1.6 μg mL-1) on the signal was
studied at a 1:2 NEV:CB(7) ratio in 0.04 M BR pH 2 by DPV. Therefore, what it was done was to
augment the analyte concentration but also the macrocycle one in the measured solutions. The
peak current and the concentration were directly proportional up to 1 µg mL-1, data points that
were fitted to Ip / µA = -0.038 + 4.300c / µg mL-1, R2=0.999. For higher concentrations the analytical
signal was relatively constant probably due to surface saturation.
Figure 4. Effect of the concentration of NEV on the DPV measurements, at a constant
NEV:CB(7) ratio of 1:2 in 0.04 M BR pH 2 (see text). The voltammograms of the NEV
concentrations 0.267, 0.534, 0.801, 1.07 µg mL-1 are shown. The inset graph gives
the peak current vs. NEV concentration.
CV measurements of approximately 200 µg mL-1 stavudine and lamivudine solutions in
0.04 M BR were obtained at different pH. DPV measurements of these two interferences at pH 6
are shown in Figure 5 and it can be seen that the lamivudine reduction signal was at -0.2 V (red
line) and the stavudine one was at -0.1 V (black line). They both were well defined when CB(6) or
CB(7) were present in the solution. The signal could be a product of the possible formation of
inclusion complexes. These compounds did not show oxidation signals so did not interfere in NEV
determination by DPV when they were in the analysed sample.
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DETERMINATION OF NEVIRAPINE WITH A GOLD ELECTRODE
Figure 5. DPV measurements of 4 µM stavudine and lamivudine and with CB(7) (1:2) in pH 6 BR
buffer as electrolyte. Black line, stavudine; red line, lamivudine; green line, electrolyte.
Determination in tablet
A crushed tablet was left in contact with methanol for 24 hours, the suspension was filtered,
the resulting solution was transferred to a 100 mL volumetric flask and the volume was completed
with methanol. It contained 2.5 mg mL-1 of NEV and the working solutions were prepared from this
one. Voltammograms of sample solutions were recorded and, as it can be seen in Figure 6 and as
previously shown, the gold oxidation and NEV waves were overlapped if no CB(7) had been added
but they were separated if the macrocycle was present (1:2 NEV:CB(7) ratio). The results obtained
by means of the standard addition method showed that the content of NEV/tablet was 80.4% of
the nominal one (n = 4) in the presence of stavudine and lamivudine.
Figure 6. DPV measurements of solutions of the pharmaceutical sample in 0.04 M BR buffer pH
2. Black line, no CB(7) in solution; red line, with CB(7) (ration 1:2 NEV:CB(7)).
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A. M. Esteva at al.
J. Electrochem. Sci. Eng. 4(1) (2014) 37-44
Determination in urine
A previous treatment of liquid-liquid extraction was necessary given the complexity and
characteristics of the urine sample. 2 mL of urine of a healthy individuals were spiked with NEV to
reach a final concentration of 26 µg mL-1 and were subjected to liquid-liquid extraction with 10 mL
of diethyl ether. After shaking, the liquid was left for 3 min, the aqueous phase was discarded and
the organic one was evaporated. 10 mL of 0.04 M BR buffer pH 2 were used to dissolve the
residue, the solution was introduced in the electrochemical cell and DPV measurements of
increasing concentrations of NEV were performed to analyse the sample, voltammograms that are
shown in Figure 7. A recovery of 98.4 % (n = 3) was obtained for the spiked urine with 26 µg mL-1
NEV in presence of CB(7).
Figure 7. DPV measurements of NEV doped urine with successive additions of the drug in
presence of CB(7), maintaining the 1:2 ratio. Black line, 0 µg mL-1 NEV added; red line,
5.32 µg mL-1; green line, 10.6 µg mL-1.
Conclusions
An electroanalytical method was developed for the analysis of NEV in pharmaceutical
formulations in the presence of stavudine and lamivudine and in urine by means of a gold
electrode and DPV. NEV was electroactive between pH 2 and 6 and CV measurements showed that
NEV oxidation wave was very close to the gold oxides formation one but if CB(7) was added to a
NEV solution, both waves were separated and an increase in the analyte peak current was
observed. Measurements in 0.04 M BR buffer pH 2 were performed to get the stoichiometry of the
NEV-CB(7) complex behind this electrochemical behaviour and it was found that one NEV
molecule interacted with two CB(7) molecules, ratio which was kept constant in every calibration
or analyzed sample. The calibration of the response was performed and found the equation
Ip / µA = -0.038 + 4.300c / µg mL-1, R2=0.999. The analysis of tablets gave an 80.4 % recovery (n = 4)
just dissolving the sample in methanol. 2 mL of urine were doped with NEV at a concentration of
26 µg mL-1 and were subjected to liquid-liquid extraction due to the complex matrix and a 98.4 %
recovery (n = 3) was found.
doi: 10.5599/jese.2014.0043
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J. Electrochem. Sci. Eng. 4(1) (2014) 37-44
DETERMINATION OF NEVIRAPINE WITH A GOLD ELECTRODE
Acknowledgements: Authors thank to Spanish Agency for International Development Cooperation
(AECID, A/030784/10) and Comunidad de Madrid (S2009/PPQ-1642, AVANSENS).
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© 2014 by the authors; licensee IAPC, Zagreb, Croatia. This article is an open-access article
distributed under the terms and conditions of the Creative Commons Attribution license
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