Galvano static Charge-Discharge (GCD):
An electrode is kept at a constant current in an electrolyte using a process known as Galvanostatic. The capacity of the device can be determined, along with other performance parameters like the energy efficiency and rate capability, by measuring the voltage and current during both the charge and discharge phases.
The electrochemical technique known as
Galvanostatic charge-discharge (GCD) is used to examine the energy conversion
and storage capabilities of electrochemical devices like batteries and capacitors.
A device's performance can be evaluated under a variety of circumstances, such
as variable current densities or charge/discharge rates, by repeatedly
performing the charge and discharge cycles. The procedure involves recording
the current and voltage, and the curves that are produced reveal details about
the device's capacity, energy density, power density, and other characteristics
(Kaus, 2010 #43).
It is important to choose an appropriate current level that
can provide consistency and comparability of GCD data. In GCD studies, a
constant current charge is applied to the device initially until a specific
voltage or current limit is reached. Same continuous current. To investigate
the device's cyclic stability, the procedure might be carried out many than
once. The performance of batteries and Supercapacitors is frequently assessed
using GCD, which can deliver crucial details about the device's charging and
discharging behavior, including the charge/discharge duration, voltage
In GCD, the electrochemical system is subjected to a
continuous current that either charges or discharges it. Galvanostatic
Charge-Discharge (GCD) involves the application of a constant current to an
electrochemical system, which causes the system to either charge or discharge
(De Levie, 1964). The mechanism captures electrical energy as it is charging
and stores it as chemical energy. Anode and cathode, which are normally
separated by an electrolyte solution, make up the electrochemical system (T.
Liu, Pell, & Conway, 1997) .
It is most important and conventional technique used to test
different performance of electrochemical devices and cyclic life of devices.
GCD can also be used to check the stability of materials by charging and
discharging at constant current in fixed potential window. In GCD like cyclic
voltammetry potential are same and measure the charge discharge time (Nam, Kim,
& Kim, 2007). Charge and discharge cycle is continuing at same value of
current and reach at specific value of voltage. GCD is an effective method for
assessing the performance of energy storage systems under various circumstances
and for contrasting the performance of various systems (Andreas, Black, &
Oickle, 2014) .
Figure 3.10 Galvanostatic charge-discharges of nonporous
Supercapacitors
The capacitance (C) is written as.
C=Q/V
―V‖ is the voltage and ―Q‖ is the charge. GCD experimental
steps are as follow.
During experiment the value of current charge and discharge
remain constant. Rest the potential at open circuit potential. GCD discharge
consists of four steps.
- Constant power
- Constant current
- Constant capacitance rate
- Constant load
GCD charging takes under constant current and constant
capacitance rate mode can be conducted under single charge tests. y. It is a
useful tool for understanding the underlying electrochemical processes involved
and for optimizing the design and performance of electrochemical devices. The
charge and discharge current during Galvanostatic cycling of batteries are
frequently stated as a C-rate, which is determined by the battery capacity. A
measurement of the rate is the C-rate. It is a valuable
tool for comparing the performance of various devices or
materials, as well as for evaluating how well these devices function under a
variety of operating situations (M. A. Davis & H. A.
XRD pattern of ZnS nanostructure:
XRD stands for X-ray diffraction which is an experimental
technique that measures the diffraction pattern produced when X-rays diffracted
from sample when X-rays fall on crystalline sample.
The pattern obtained from scattered X-rays provides
information about position of atoms, bond lengths, angle, symmetry of crystal
and crustal structure. This information is helpful for deterring composition,
purity and material phase. XRD is commonly used in material science, chemistry,
mineralogy and physics (Liang, Xu, & Hark, 2010) .
The XRD pattern is obtained from 20º to 80º by using 2Ө
limit. The material on various substrates was characterized using X-ray
diffraction (XRD). It was unfortunate that only the peaks associated with the
substrates could be found. Al atom doping concentration creates disorder in the
lattice of ZnS. As we increase the concentration of dopant Al the defects
reported in ZnS is Schottky and in Zn Frenkel defect. The absence of any unexplained
peaks indicates the material's purity.
Figure 4.1 shows the XRD plot of ZnS doped with Al with
various applied potential. In this process we used nickel foam as a substrate.
ZnS is confirmed by strong intensities and sharp peak is found at approximately
28.63 degree with reflection plane of (111) as compared to other peaks. All
diffracted peaks show that the sample is Hexagonal and results are matched with
JPCDS Card no. 05-0566. While others peaks corresponding to angle 2𝜃
are (220), (311), (400) and (311) and found on graph are reduced. Our sample is
not completely matched with peaks of Zn because other peaks are founded due
sample doped with Al. As we increase the doping concentration of Al the
diffraction peaks shift towards higher diffraction angle. The d- spacing values
obtained from XRD pattern for peaks (111) and (220) observed for ZnS identified
by using JPCDS card. The both potential (-0.5v, -0.4) used for enhanced the
peaks results.
Al doped ZnS shows satisfied results with pureed form of
sample as reported in literature. It is found that the ionic radius of host Zn
ion is smaller as compared to dopant that’s why the value of lattice constant
slightly decreased. The average size of nanocrystalline of prominent peaks
(111) calculated from full width at half maximum (FWHM) by using Scherer
formula. The broadening of diffraction peaks seen in X- ray diffraction (XRD)
patterns can be related to the size of crystalline domains in a material using
the Debye-Scherer formula, which is an equation. We calculate crystalline size
of ZnS nanostructure of reference plane (111) by using Debye-Scherer formula.
D = 0.94λ/βcosɵ
Here D represents crystalline size, ɵ represent Bragg
diffraction angle of the peak (111), λ represent X-ray wavelength.
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