Arun Kumar

The main equation of capacitance is C=Q/V

in cyclic voltammetry : C= area/(m*V* scan rate)

m is mass of active material, scan rate unit is V/sec

In GCD: C= (I dt)/m(dV)

I is discharge current. dt discharge time..dV dicharge voltage

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Dear Arun Kumar

All these electrochemical techniques have their own importance.

Cyclic voltammetry: is an electrochemical technique that takes place at the electrode-electrolyte interface for qualitative information of electrochemical reactions. Cyclic voltammetry is used to understand the mechanism of redox reaction and electron transfer kinetics of an electroactive species in electrolytes.

CV is an electrochemical technique for measuring the current response that develops in the electrochemical cell during a linearly cycled potential sweep between the chosen potential window. This process is repeated multiple times during the scan and changes in the current value are measured by the device. This scan generates a duck-shaped plot that is called cyclic voltammogram.

Galvanostatic charge-discharge technique: is also known as chronopotentiometry. It is used for testing of supercapacitor performance parameters like specific capacitance, cyclic stability, and resistance. Thereafter energy density, power density and columbic efficiency are calculated. In GCD current is controlled and voltage is measured. The voltage (V) is generated by the current applied during the charging process.

Electrochemical impedance spectroscopy: In the frequency domain, impedance spectroscopy is a powerful method to evaluate the specific capacitance. The supercapacitor is fabricated by two identical electrodes separated by solid/liquid/gel electrolyte. The IS gives the relation between idealized equivale@nt circuit and real system which comprises the electrical component (inductor, capacitor, resistor) in the parallel and series combinations. Electrochemical impedance spectroscopy is an AC technique in which an applied potential E(t) is modulated over time with a small amplitude (|E0| ∼ 5−10 mV) at a controlled frequency (ω).

Well prefer EIS over CV

Today, most/all of these exp. methods should be implemented for the evaluation of a new electrode (cell, device), because their exp. errors have very different origin(s). The first two

a) exp. methods (1st_Cyclic voltammetry, the older method, and 2nd_GCD) measure/work, mainly, in Time domain, e.g. primary_Data(Time),

while the,

b) newer, 3rd_EIS exp. method measures primary_Data via (sets of) complex_Z(F), works, mainly, in Frequency domain, e.g. primary_Data(Frequency).

Also, the newer, 3rd_EIS exp. method accompanied with a good ECM (Equivalent Circuit Model) results in a better evaluation of the many ECM-parameters, having the most practical/technical interest, today.

Electrochemical Impedance spectroscopy provides more accurate and dynamic capacitance. Theoretical equation for capacitance from impedance data can be found in a recent article by Kant et al. as J. Power Sources, 473 (2020), 228467.

The main advantage of the EIS, over the other (older) methods, is the asset application of the parametric handling the set of the Vdc-value(s) under the unique cells' relaxation state(s).

So, planning the session of the appropriate fixed Vdc-magnitude, in order to tune with the decided critical condition, iWE,CE=0, we can exclude/minimize the ('noisy') interference from several kinetic phenomena[1] in calculating (fitting the Z-spectra) the capacitance value(s) of (new era) super-capacitors.

1. Co-existing, unfortunately, i_WE,CE is, commonly, very high, in the other (older) methods.