3.3.2 Low frequency – impedance spectroscopy (IS)
The low-frequency impedance spectroscopy was conducted as shown in
Figure 6.A high-frequency zone and a low-frequency region are
represented. A semicircle is typically used to represent the high
frequency area, reflecting both the charge-transfer processes at the
electrode-electrolyte interfaces and the bulk properties of the
electrolytes. A capacitive spike can be seen in the low frequency area,
which is a result of charges building up and double layers forming at
the electrolyte-electrode contact.
The specific capacitance that is measured at low-frequency through
impedance spectroscopy is obtained, as illustrated below
\(C=\ \frac{-1}{2\pi fZ"m}\) (5)
Where m is the mass of the active electrode material (carbon) at one
electrode (considered to be m = 1 mg), f is the frequency, and Z” is
the imaginary portion of the impedance at low frequencies. The specific
capacitance was subsequently determined to be 186 F/g, which is nearly
the same value as the value derived from CV data, using low frequency
calculations.