## 2 Impedance Spectroscopy
### Scopes of Application
#### 2.1.2 Is Applied in Forest and Agriculture Management
In both cases, the evaluation of the cell electrodes was done by EleIS (measurements were conducted for frequencies between 0 Hz and 10 kHz, with an AC voltage amplitude of 0.01 V and using a four-points configuration), and the observations were used to support the claim that the new materials were efficient for usage in supercapacitor and solar cell applications. Supercapacitors represent other emerging functional materials where IS usage is essential for developing and improving manufactured devices. Supercapacitors represent an emerging class of capacitors that store and deliver between 10 and 100 times more electrical energy from their bulks faster than usual capacitors. These materials are generally used in devices that require fast charge and discharge cycles, such as batteries, photovoltaic cells, smart windows, and wearable capacitors. A supercapacitor comprises two electrodes with a porous surface and a thin separator, with high electrical resistance between them. During an interaction with the electrolyte (usually a selective salt-containing solvent), the separator material must prevent contact between the electrodes but allow charge transfer in the system. One of the challenges involves the development of environmentally friendly devices with the potential to solve energy problems of global interest. In a recent work, a nickel-doped nano spinel magnesium ferrite (Ni-doped MgFe\({}_{2}\)O\({}_{4}\) samples)/1 M KOH electrolyte system was evaluated as a supercapacitor [89]. The Ni\({}_{0.35}\)Mg\({}_{0.65}\)Fe\({}_{2}\)O\({}_{4}\) combination exhibited an extraordinary specific capacitance of 119 F/g, maintaining approximately 95% cyclic stability after 5000 charge and discharge cycles. EIS was used to analyze the electrochemical properties of the device (using a three-electrode cell configuration, where Pt served as the counter electrode in addition to the working electrode and Hg/HgO reference electrode), and the obtained electric results were related to the nanometric size of the crystallites (in the range of 8-11 nm), and with the excellent diffusion capacity of the ions. Using the same electrolyte, another semiconductor configuration, zinc ferrite oxide (ZnFe\({}_{2}\)O\({}_{4}\)), exhibited an even higher specific capacitance of 131 F/g, with cyclic stability of 92% after 1000 cycles [90]; all EIS measurements were carried out using a three-electrode system with a working electrode, a saturated calomel reference electrode, and a platinum wire counter electrode in the frequency range of 0.01 Hz and 100 kHz. The emergent appeal for developing new sustainable and low-cost materials with improved performance has triggered the search for functional natural and/or recyclable materials for manufacturing supercapacitors. For example, [PERSON] et al. [91] developed a supercapacitor with eggshell membrane (ESM) electrodes coated with carbon nanotubes and an in-natura ESM separator in a 1 M KOH electrolyte. The device exhibited a constant current density of 10 mA\(\cdot\)cm\({}^{-2}\) and an excellent stability of approximately 99% after 2 \(\times\) 10\({}^{5}\) cycles. EleIS characterization in the 10 mHz to 100 kHz range was established as a signature of the hybrid electrodes' ion transfer and electrical conductivity for a typical coin-cell configuration (two-points measuring setup). In the same vein, [PERSON] et al. [92] studied the potential usage of recycled tetrapak packaging impregnated with silver nanoparticles/barium molybdate (Ag/BaMoO4) as a flexible and high-efficiency supercapacitor (capacitance of 443 F/g and 92% stability after 500 charge/discharge cycles). EleIS tests were carried out using an AC voltage with 30 mV of amplitude, in the frequency range of 10 Hz-100 kHz, under a typical capacitor configuration; results showed that the progressive introduction of nanoparticles significantly reduced the charge-transfer resistance, facilitating the diffusion of ions in the system.