Cyclic voltammetry (CV)
This technique is extremely popular in chemical research because it can provide useful information about redox reactions provide fast information about electrochemical reaction and catalysts. Different scan rates are used to examine the CV curve Al doped ZnS the oxidation and reduction peaks are clearly shown in below figure.
CV curves are most important for energy storage devices
specially Supercapacitors. Now we explain importance of these devices as
follows. The redox potential, electron
transfer kinetics, and stability of a material, as well as other
electrochemical properties, are all shown by CV curves. Using this knowledge,
electrochemical systems such as batteries, fuel cells, and sensors can be
designed and optimized. The configuration and positioning of the CV peaks can
shed light on the electrochemical process's reaction mechanism and
intermediates. By using this knowledge, reaction conditions can be improved,
and the reaction's selectivity and efficiency can both be raised (J. Zhang
& Braunstein, 2006).
The characteristics of electrode surfaces, such as their
reactivity, stability, and adsorption behavior, can be investigated using CV
curves. Designing and improving electrode materials for diverse electrochemical
applications requires the use of this information. The electrochemical
characteristics of a variety of materials, including inorganic substances,
organic molecules, and biological systems, can be described using CV curves.
The creation of novel materials with customized electrochemical characteristics
for particular purposes depends on this information (Yan Wang, Allouache, &
Joubert, 2021).
The CV curve normally has two peaks: a cathodic peak for
reduction reactions and an anodic peak for oxidation reactions. Peak
positioning and shape reveal details about the species' and its mechanism's
redox behavior. The maximum current value recorded at the peak is known as the
peak current (ip). It is influenced by the amount of the electroactive species
present, the size of the electrode, and the rate of electron transfer (Ye Li et
al., 2017).
The potential value at which the highest current occurs is
known as the peak potential (Ep). It has to do with the species' redox
potential, the speed of electron transfer, and the composition of the electrode
material. The potential difference between the anodic and cathodic peaks is
known as the peak separation (E). The reversibility of the redox reaction and
the kinetics of the electron transfer mechanism are both covered. The
background current, which is the current that is present when there are no
electroactive species present, is mostly caused by the capacitive current,
which results Real-time electrochemical process monitoring using CV
can provide valuable insights into the kinetics and mechanisms of reactions.
This knowledge is essential for enhancing the environment for reactions and
raising the effectiveness of electrochemical processes. (Sarma, Ray, &
Misra, 2015)
When we increase scan rate anode peaks raise and fall in
cathodic peaks current densities are derived, which shows fast redox reaction
with low resistance. When scanning rate is more than before and redox peaks
shifts which shows due to internal resistance of internal diffusion and
increasing polarization. Increasing scan rate produce perfectly shapes of redox
peaks which indicates during cycling process polarization reduced. These peaks show
superior capability of ZnS nanoparticles. ZnS capacitance performance tests by
GCD and CV. In order to study the redox behavior, CV measurements were carried
out within a potential window between 0.0 and 1.0 V at scanning rates between
10 and 80 mV/ s. This revealed the typical characteristics of uniform ZnS nanosheets.
Below figure shows examine of CV curves at different scan rates of Al doped
ZnS. In figure we observe clearly oxidation and reduction peaks. The cathodic
peaks current densities fall and raise anodic peaks current densities when we increase
scan rate it was observed at low resistance and fast redox reaction. Increasing
scan rate shows clear shapes of redox peaks. We obtained different curves at
different scanning rates. From above it is clear that we used fixed value of optional
o.7 V and using different values of scanning rates 10 mV/s, 20 mV/s, 30 mV/s,
40mV/s, 50mV/s and 70 mV/s. In below graph the values of current are not fixed
but minor change in current taken with respect scan rate. As we increase scan
rate the value of current decrease.
Figure 4.5 The cyclic voltammetry graph
Redox peaks' shapes are kept in good form when scan rates
increase, demonstrating ZnS nanosheets' better rate capacity. The reversible
faradic reactions are completely explained by the non-rectangular CV curves,
which also show the electrode's pseudocapacitive nature
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