We also get a wave form cyclic voltammetry potential schematic diagram as shown below. An experiment using cyclic voltammetry (CV) produces a plot of the current (y-axis) vs. the applied voltage (x-axis), which is known as a cyclic voltammogram. It is made up of a number of peaks and valleys that are related to the various electrochemical processes taking place at the electrode surface.
Types of Voltammetry:
- Alternating current voltammetry
- Stripping voltammetry
- Rotated electrode voltammetry
- Ultramicroelectrodes
- Electrodes impedance spectroscopy
- Electrochemical impedance spectroscopy (EIS)
Powerful characterization methods like electrochemical
impedance spectroscopy (EIS) are frequently employed in industries as diverse
as energy, electro catalysis, and medicine. This technique is also much better
than old classical techniques because it can measure relation between applied
potential difference and current in frequency domain. EIS is an important
technique in the field of electrochemistry and important for recognizing
electrochemical reaction (M. Davis & H. Andreas, 2018).
EIS gained more attention in last decades due to lot of
application like it is more surface sensitive analysis of interfacial
properties. EIS is very powerful but complex technique. This technique also
used for detection of many issues in bio-science such as cancer effected cells,
DNA and detect pathogen.
Experimental Setup of EIS:
EIS consists of three electrodes which are mounted on stage.
These electrodes feature a reference electrode, a counter electrode made of
graphite or platinum, and a working electrode composed of basic materials. It
also consists of container which is made up of insulating material such as
plastic or glass. These insulating materials used to separate the portion of
electron transfer during testing. These electrodes are submerged inside in
container. These electrodes are connected to EIS frequency analyzer. For this purpose,
four leads are used two for current and two for voltage sense. After this complete
setup of EIS which is ready for testing (G. Wang et al., 2012).
Complex Impedance:
- Ohm’s law which is most important in electricity give relation between voltage, current and resistance as follow.
- E= IR R=E/I
- Here ―I‖ is current and ―Z‖ is impedance.
- For ideal circuit ohm’s law valid at all values of temperature and voltage.
It is Frequency Independent:
- Current and voltage are in phase in ideal resister.
- Electrochemical impedance measured current and AC potential of cell. It also used to measured small sinusoidal signal (Kullaiah Byrappa & Adschiri, 2007).
Plots of EIS:
The EIS uses two different types of plots Bode plot and the
Nyquist plot, which display the real and imaginary components of the cell
impedances respectively. Equivalent circuits and models can determine how each
individual structural element in a cell contributes to the overall impedance
(Kullaiah Byrappa & Adschiri, 2007) .
Bode plot:
The magnitude and phase of a system's frequency response are
shown on a graph called a Bode plot as a function of frequency. A Bode plot is
used in electrochemical impedance spectroscopy (EIS) to examine an
electrochemical system's impedance response across a variety of frequencies.
The Bode plot is actually the combination of two plots. The
phase shift is represented by the second ordinate, and the frequency is scaled
on the abscissa (x- axis). The logarithm of the impedance Z is one of the
ordinates (y-axis). The unique property of this plot is all information is
clearly visible. All components on graph are easily understandable. In EIS
resister and capacitor are parallel and visible in the forms of peaks in the
phase shift.
Nyquist plot:
Nyquist plots are frequently utilized in a range of
electrochemical applications, such as biosensors, fuel cells, batteries, and
corrosion research. They offer useful data for comprehending these systems'
behavior and raising their efficiency (Santhanagopalan & White, 2012).
- A Resister and Capacitor in Nyquist plot and bode plot
- The most important and simplest component of circuit is resister.
Commonly we consider this relation is valid for DC current.
In this scenario, both AC and DC current are subject to Ohm's Law
(Santhanagopalan & White, 2012) Another important element is capacitor.
Most common and simple type of capacitor is parallel plate capacitor which
consists of two parallel plate separated by very small distance. One plate is
positively charged and other is negatively charged. Basic operation of
capacitor is used to store energy.
V=E C=Q/E
Here ―C‖ is the capacitance of capacitor which is defined as
―ability of capacitor to store energy is called capacitance‖ (Santhanagopalan
& White, 2012) .
Figure 3.9 Schematic diagram of bode and Nyquist plot for
resister and capacitor.
