Name: evaluating the electrochemical properties of supercapacitors using the three-electrode system
Uploaded: 2022-01-07T15:00:00
Description: Watch this Scientific Journal Video about Evaluating the Electrochemical Properties of Supercapacitors using the Three-Electrode System at JoVE.com

This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry &#38; Energy (MOTIE) of the Republic of Korea (No. 20214000000280), and the Chung-Ang University Graduate Research Scholarship 2021.

1. Fabrication of electrode and supercapacitor (Figure 1)
<ol>
	<li>Prepare the electrodes prior to the electrochemical analysis by combining 80 weight (wt)% of the electrode active material (0.8 g activated carbon), 10 wt% of the conductive material (0.1 g carbon black), and 10 wt% of the binder (0.1 g polytetrafluoroethylene (PTFE)).
	<ol>
		<li>Drop isopropanol (IPA; 0.1-0.2 mL) into the above-mentioned mixture, then spread the mixture thinly into a dou...

This study provides a protocol for various analyses using a three-electrode system with a potentiostat device. This system is widely used to evaluate the electrochemical performance of supercapacitors. A suitable sequence for each analysis (CV, GCD, and EIS) is important for obtaining optimized electrochemical data. Compared with the two-electrode system having a simple setup, the three-electrode system is specialized for analyzing supercapacitors at the material level15. However, the selection of...

Supercapacitors have attracted enormous attention as suitable power sources for a variety of applications such as microelectronic devices, electric vehicles (EVs), and stationary energy storage systems. In EV applications, supercapacitors can be used for rapid acceleration and can enable the storage of regenerative energy during the deceleration and braking processes. In renewable energy fields, such as solar power generation1 and wind power generation2, supercapacitors can be used as stationary energy storage systems3,4. Renewable energy generation is limited by the fluctuating and intermittent nature of these energy supplies; therefore, an energy storage system that can respond immediately during irregular power generation is required5. Supercapacitors, which store energy via mechanisms that differ from those of lithium-ion batteries, exhibit a high power density, stable cycle performance, and fast charging-discharging6. Depending on the storage mechanism, supercapacitors can be distinguished into double-layer capacitors (EDLCs) and pseudocapacitors7. EDLCs accumulate electrostatic charge at the electrode surface. Therefore, the capacitance is determined by the amount of charge, which is affected by the surface area and porous structure of the electrode materials. By contrast, pseudocapacitors, which consist of conducting polymers and metal oxide materials, store charge through a Faradaic reaction process. The various electrochemical properties of supercapacitors are related to the electrode materials, and developing new electrode materials is the main issue in improving the performance of supercapacitors8. Hence, evaluating the electrochemical properties of these new materials or systems is important in the progress of research and further applications in real life. In this regard, electrochemical evaluation using a three-electrode system is the most basic and widely utilized method in lab-scale research of energy storage systems9,10,11,12,13.
The three-electrode system is a simple and reliable approach for evaluating the electrochemical properties, such as the specific capacitance, resistance, conductivity, and cycle life of supercapacitors14. The system offers the benefit of enabling analysis of the electrochemical characteristics of single materials15, which is in contrast to the two-electrode system, where the characteristics can be studied through the analysis of the given material. The two-electrode system just gives information about the reaction between two electrodes. It is suitable for analyzing the electrochemical properties of the entire energy storage system. The potential of the electrode is not fixed. Therefore, it is not known at what voltage the reaction takes place. However, three-electrode system analyzes only one electrode with fixing potential which can perform a detailed analysis of the single electrode. Therefore, the system is targeted toward analyzing the specific performance at the material level. The three-electrode system consists of a working electrode (WE), reference electrode (RE), and counter electrode (CE)16,17. The WE is the target of research, assessment as it performs the electrochemical reaction of interest18 and is composed of a redox material that is of potential interest. In the case of EDLCs, utilizing high surface area materials is the main issue. Therefore, porous materials with a high surface area and micropores, such as porous carbon, graphene, and nanotubes, are preferred19,20. Activated carbon is the most common material for EDLCs because of its high specific area (&#62;1000 m2/g) and many micropores. Pseudocapacitors are fabricated with materials that can undergo a Faradaic reaction21. Metal oxides (RuOx, MnOx, etc.) and conducting polymers (PANI, PPy, etc.) are commonly used22. The RE and CE are used to analyze the electrochemical properties of the WE. The RE serves as a reference for measuring and controlling the potential of the system; the normal hydrogen electrode (NHE) and Ag/AgCl (saturated KCl) are generally chosen as the RE23. The CE is paired with the WE and completes the electrical circuit to allow charge transfer. For the CE, electrochemically inert materials are used, such as platinum (Pt) and gold (Au)24. All components of the three-electrode system are connected to a potentiostat device, which controls the potential of the entire circuit.
Cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) are typical analytical methods that use a three-electrode system. Various electrochemical characteristics of supercapacitors can be assessed using these methods. CV is the basic electrochemical method used to investigate the electrochemical behavior (electron transfer coefficient, reversible or irreversible, etc.) and capacitive properties of material during repeated redox processes14,24. The CV plot shows redox peaks related to the reduction and oxidation of the material. Through this information, researchers can evaluate the electrode performance and determine the potential where the material is reduced and oxidized. Furthermore, through CV analysis, it is possible to determine the amount of charge that material or electrode can store. The total charge is a function of the potential, and the capacitance can be easily calculated6,18. Capacitance is the main issue in supercapacitors. A higher capacitance represents the ability to store more charge. EDLCs give rise to rectangular CV patterns with linear lines so that the capacitance of the electrode can be calculated easily. Pseudocapacitors present redox peaks in rectangular plots. Based on this information, researchers can assess the electrochemical properties of materials using CV measurements18.
GCD is a commonly employed method for identifying the cycle stability of an electrode. For long-term use, the cycle stability should be verified at a constant current density. Each cycle consists of charge-discharge steps14. Researchers can determine the cycle stability through variations in the charge-discharge graph, specific capacitance retention, and Coulombic efficiency. EDLCs give rise to a linear pattern; thus, the specific capacitance of the electrode can be calculated easily using the slope of the discharge curve6. However, pseudocapacitors exhibit a nonlinear pattern. The discharge slope varies during the discharging process7. Furthermore, the internal resistance can be analyzed through the current-resistance (IR) drop, which is the potential drop owing to the resistance6,25.
EIS is a useful method for identifying the impedance of energy storage systems without destruction of the sample26. The impedance can be calculated by applying a sinusoidal voltage and determining the phase angle14. The impedance is also a function of the frequency. Therefore, the EIS spectrum is acquired over a range of frequencies. At high frequencies, kinetic factors such as the internal resistance and charge transfer are operative24,27. At low frequencies, the diffusion factor and Warburg impedance can be detected, which are related to mass transfer and thermodynamics24,27. EIS is a powerful tool for analyzing the kinetic and thermodynamic properties of a material at the same time28. This study describes the analysis protocols for evaluating the electrochemical performance of supercapacitors using a three-electrode system.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Activated carbon</td>
			<td>GS</td>
			<td></td>
			<td>Active material</td>
		</tr>
		<tr>
			<td>Ag/AgCl electrode</td>
			<td>BASi</td>
			<td>RE-5B</td>
			<td>Reference electrode</td>
		</tr>
		<tr>
			<td>Carbon black</td>
			<td>Hyundai</td>
			<td></td>
			<td>Conductive material</td>
		</tr>
		<tr>
			<td>Desicator</td>
			<td>Navimro</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Electrode pressing machine</td>
			<td>Rotech</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Extractor</td>
			<td>WonA Tech</td>
			<td></td>
			<td>Convert program (raw data to excel form)</td>
		</tr>
		<tr>
			<td>Isopropanol(IPA)</td>
			<td>Samchun</td>
			<td>I0346</td>
			<td>Solvent to melt the binder</td>
		</tr>
		<tr>
			<td>Polytetrafluoroethylene(PTFE)</td>
			<td>Hyundai</td>
			<td></td>
			<td>Binder</td>
		</tr>
		<tr>
			<td>Potentiostat</td>
			<td>WonA Tech</td>
			<td>Zive SP1</td>
			<td></td>
		</tr>
		<tr>
			<td>Pt electrode</td>
			<td>BASi</td>
			<td>MW-018122017</td>
			<td>Counter electrode</td>
		</tr>
		<tr>
			<td>Reaction flask</td>
			<td>Duran</td>
			<td></td>
			<td>Container for electrolyte</td>
		</tr>
		<tr>
			<td>SM6</td>
			<td>WonA Tech</td>
			<td></td>
			<td>Program of setting sequence and measuring electrochemical result</td>
		</tr>
		<tr>
			<td>Sulfuric acid</td>
			<td>Samshun</td>
			<td>S1423</td>
			<td>Electrolyte</td>
		</tr>
		<tr>
			<td>SUS mesh</td>
			<td>Navimro</td>
			<td></td>
			<td>Current collector</td>
		</tr>
		<tr>
			<td>Teflon cap</td>
			<td>WonA Tech</td>
			<td></td>
			<td>Cap of the electrolyte continer</td>
		</tr>
		<tr>
			<td>Zman</td>
			<td>WonA Tech</td>
			<td></td>
			<td>EIS program</td>
		</tr>
	</tbody>
</table>

evaluating the electrochemical properties of supercapacitors using the three-electrode system

The three-electrode system is a basic and general analytical platform for investigating the electrochemical performance and characteristics of energy storage systems at the material level. Supercapacitors are one of the most important emergent energy storage systems developed in the past decade. Here, the electrochemical performance of a supercapacitor was evaluated using a three-electrode system with a potentiostat device. The three-electrode system consisted of a working electrode (WE), reference electrode (RE), and counter electrode (CE). The WE is the electrode where the potential is controlled and the current is measured, and it is the target of research. The RE acts as a reference for measuring and controlling the potential of the system, and the CE is used to complete the closed circuit to enable electrochemical measurements. This system provides accurate analytical results for evaluating electrochemical parameters such as the specific capacitance, stability, and impedance through cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). Several experimental design protocols are proposed by controlling the parameter values of the sequence when using a three-electrode system with a potentiostat device to evaluate the electrochemical performance of supercapacitors. Through these protocols, the researcher can set up a three-electrode system to obtain reasonable electrochemical results for assessing the performance of supercapacitors.

The electrodes were manufactured according to protocol step 1 (Figure 1). Thin and homogeneous electrodes were attached to SUS mesh with a size of 1 cm2 and 0.1-0.2 mm thickness. After drying, the weight of the pure electrode was obtained. The electrode was immersed in a 2 M H2SO4 aqueous electrolyte, and the electrolyte was allowed to sufficiently permeate the electrode before the electrochemical analyses. The production sequence and system setting for the e...

Watch this Scientific Journal Video about Evaluating the Electrochemical Properties of Supercapacitors using the Three-Electrode System at JoVE.com

Evaluating the Electrochemical Properties of Supercapacitors using the Three-Electrode System

The protocol describes the evaluation of various electrochemical properties of supercapacitors using a three-electrode system with a potentiostat device.

The three-electrode system is a basic and general analytical platform for investigating the electrochemical performance and characteristics of energy ...

We present a detailed protocol for evaluating supercapacitors through a three-electrode system. The researcher can set up a three-electrode system to obtain good electrochemical research through these protocols. A three-electrode system is a reliable approach for evaluating the electrochemical properties, such as the specific capacitance resistance of supercapacitors.It offers the benefit of analyzing single materials level. In energy storage system, a negative material field, researchers can determine the electrochemical performance of synthesis materials and evaluate them through this protocol. Prepare the electrodes prior to the electrochemical analysis by combining 0.8 grams of activated carbon, 0.1 grams of carbon black, and 0.1 grams of binder.Drop 0.1 to 0.2 milliliters of isopropanol into this mixture. Then, spread the mixture thinly into a dough with a roller. Cut the stainless steel mesh to 1.5 centimeters in width and five centimeters in length and attach the electrode dough of thickness of 0.1 to 0.2 millimeter with an electrode pressing machine to the stainless steel mesh.Dry the assembled supercapacitor electrode in an oven at 80 degrees Celsius for about a day to evaporate the isopropanol. Weigh the stainless steel mesh to obtain the weight of the electrode and then immerse the mesh in the electrolyte of a two-molar sulfuric acid aqueous solution. Place the stainless steel mesh in a desiccator to remove air bubbles at the surface of the supercapacitor electrode.Run the potentiostat measurement program to set the measurement experiment sequence file. Click the Experiment button in the toolbar, go to Sequence File Editor, and select New or directly click the New Sequence button. Click the Add button to add a sequence step.In every step, set Control as SWEEP, Configuration as PSTAT, Mode as CYCLIC, and Range as AUTO. Set the reference for Initial, Middle, and Final as E reference and enter the respective values under Value. For setting the voltage scan rate, enter the respective values in Scan rate values.Set Quiet times as zero and Segments as the number 2N plus one where N is the number of cycles. Here, 21 was applied for 10 cycles. Copy step one and paste it from step two to step five by clicking Paste On.Change the Scan rate values.Set Cut Off Condition as Condition-1, set Item as Step End, and Go Next as Next. In the controlling Miscellaneous setting section, under the sampling tab, set Item as Times, OP as greater than or equal to, and Delta Value as 0.333333, 0.166666, 0.111111, 0.06667, and 0.0333 for each scan rate. This is the time interval for recording the data.Click Save as to save the CV analysis sequence file in any computer folder. After setting the measurement experiment sequence file and adding a sequence step, in step one, set Control as CONSTANT, Configuration as GSTAT, Mode as NORMAL, and Range as AUTO. Set the reference for current ampere as zero.When the mass of the electrode is 0.00235 grams, set the value as 0.0018618 ampere, which means the current density is 1 ampere per gram. Set Cut Off Condition for Condition-1, set Item as Voltage, OP as greater than or equal to, and Delta Value as 0.8 volts and Go Next as Next. In the controlling miscellaneous setting section, in the sampling tab, set Item as Times, OP as greater than or equal to, and Delta Value as 0.1.In step two, current is the negative value of step one. For setting Condition-1, set Item as Voltage, OP as less than or equal to, Delta Value as minus 0.2 volts, and Go Next as Next. In step three, set Control as LOOP, Configuration as CYCLE, and set List 1 in Condition-1 of Cut Off Condition as Loop Next, Go Next as step one, and set List 2 as Step End and Go Next as Next.Set the iteration value as 10, which is the number of repeating cycles. Step one, step two, and step three form a single loop. Copy and paste them after step four and change the value of current ampere to either of the calculated values for various current densities of 2, 3, 5, and 10 amperes per gram.Click Save As to save the GCD analysis sequence file in any computer folder Run the potentiostat measurement program to set the measurement experiment sequence file. Click the Experiment button in the toolbar and go to Sequence File Editor and New or click the New Sequence button. Click the Add button to add a sequence step.In step one, set Control as CONSTANT, Configuration as PSTAT, Mode as TIMER STOP, and Range as AUTO. Set the reference for voltage as E reference and value as 0.5 volts, which is half of the size of the voltage range. For Condition-1, set Item as Step Time, OP as greater than or equal to, Delta Value as three, and Go Next as Next.This is the process for stabilizing the potentiostat device. In step two, set Control as EIS, Configuration as PSTAT, Mode as LOG, and Range as AUTO. Set Speed of Initial as Normal, and Value of Initial and Middle as one megahertz, which is the high frequency value, and Final as one microhertz, which is the low frequency value.Set the reference for Bias as E reference and Value as 0.5 volts. To get a linear response result, set the Amplitude as one millivolt, set Density as 10, and Iteration as one. Click Save As to save the EIS analysis sequence file in any computer folder.Connect the three types of lines, the working electrode, the reference electrode silver in silver chloride, and the counter electrode, that is platinum wire, to the SUS mesh, respectively. Connect the fourth line, the working sensor, to the working electrode. Fill 100 milliliters of two-molar aqueous sulfuric acid electrolyte in a beaker.Cover the glass container with a cap and immerse the three electrodes in the electrolyte through a perforation in the cap. Position the electrodes to maintain the working electrode at a constant distance between the counter-electrode and the reference electrode. Operate the potentiostat device and run the measurement program to perform the CV, GCD, and EIS analyses.Run the measurement program and open the prepared sequence. Click Apply to CH to insert the potentiostat's channel sequence. Start the measurement by clicking the Start button.The well-developed rectangle-shaped graph in the scan rate range from 10 to 200 millivolt per second indicates EDLC characteristics and confirms that the supercapacitor operated well as an EDLC. When the scan rate was above 300 millivolts per second, the graph lost its rectangular shape, which means that the electrode lost the EDLC characteristics. The GCD graph of the electrode presented a symmetric linear profile in all current densities.This is also a characteristic property of EDLC. The AC working electrode showed 99.2%capacitance retention over 10, 000 cycles at a current density of 10 amperes per gram. In the Nyquist plot, part A corresponds to the equivalent series resistance.Part B presents a semi-circle, the diameter of which reflects the electrolyte resistance in the pores of the electrodes or charge transfer resistance. Furthermore, the sum of parts A and B is interpreted as the internal resistance. In part C, the 45-degrees angle line region indicates the iron transport limitation of the electrode structures in the electrolyte or iron transport limitation in the bulk electrolyte.The vertical line in part D is attributed to the dominant capacitive behavior of the electric double-layer formed at the electrode or electrolyte interface. The process of obtaining the exact weight of the electrode is most important. Accurate performance evaluation requires knowing the exact weight of each material, including electrodes.

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