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

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.