Method for high time resolution detection of double electron layer charging and discharging dynamics

Abstract

The application relates to a method for detecting double-electron layer charging and discharging dynamics with high time resolution, in particular to a method for detecting the dynamic behavior of double-electron layer structures on the surface of an electrolyte solution and a platinum plate electrode in a charging and discharging process with high time resolution. The method is composed of a function generator, an electrolytic cell, an oscilloscope and a multimeter. A pulse voltage is output by a power supply and applied to a platinum disc electrode immersed in an electrolyte solution. Current data flowing through the circuit are detected by a current meter, and the electrode voltage is detected by a voltage meter. The dynamic behavior of the double-electron layer between the electrode surface and the electrolyte solution is obtained through fitting calculation.

Description

Technical Field

[0001] This invention belongs to the field of electrochemistry, specifically a method for detecting the kinetics of double-electron-layer charging and discharging processes with high time resolution. Background Technology

[0002] When a charged electrode comes into contact with an electrolyte solution, an electric double layer (EDL) structure forms at the interface. Electrons or holes accumulate within the electrode, while ions with opposite charges accumulate in the solution near the electrode to form a capacitor. Since EDL capacitors are fundamental to future energy storage devices, the concept of EDL is crucial in electrochemistry. Therefore, understanding the charging kinetics of EDL is of great significance for enhancing our understanding of the performance and electrocatalytic mechanisms of double-layer supercapacitors. EDL was initially discovered by Helmholtz, and subsequently, the Gouy-Chapman theory introduced the concept of a diffusion layer. This theory uses the Poisson-Boltzmann (PB) equation to characterize ion distribution, which describes the equilibrium established between ion diffusion and electric field-driven motion. The Gouy-Chapman theory ingeniously explains the change in EDL capacitance with applied voltage. Stern further divides the EDL structure into two layers—the Stern layer composed of adsorbed material and the external diffusion layer. This model was later improved by Grahame, who divided the Stern layer into an inner Helmholtz layer and an outer Helmholtz layer composed of solvated material, in which ions or molecules adhering to the electrode may lose their solvated shell. To date, theoretical methods describing the structure and charge dynamics of EDLs continue to evolve, and many models and simulations focusing on the dynamics of the EDL charging process have emerged.

[0003] Since the ionic structure within the EDL is characterized using the Poisson-Nernst-Planck (PNP) equation, the motion of ions is described by the PNP equation. Numerous models and simulations focusing on EDL charging have emerged, utilizing analytical or numerical solutions to the PNP equation. However, experimental characterization of EDL charging dynamics remains limited. Previous work measuring EDL charging dynamics employed various techniques, such as transient current measurements, surface force balancing, and time-resolved X-ray diffraction. Nevertheless, the need for high-time-resolution measurements of EDL charging dynamics persists.

[0004] Therefore, there is an urgent need for a device that can measure the charging dynamics of EDL with a time resolution of 2 μs, to detect the influence of factors such as electrolyte solution concentration and applied voltage on the charging and discharging dynamics of the double electron layer. Summary of the Invention

[0005] This invention provides a method for detecting the kinetics of double-electron-layer (EDL) charging and discharging processes with high temporal resolution. A device capable of measuring EDL charging dynamics with a temporal resolution of 2 μs is constructed to detect the influence of factors such as electrolyte solution concentration and applied voltage on the kinetics of EDL charging and discharging. This method is applied to study the kinetic behavior of the EDL charging and discharging process between the electrode surface and the electrolyte solution.

[0006] The technical solution adopted by the present invention to achieve the above objectives is: a method for high time-resolution detection of double-electron-layer charge-discharge dynamics, comprising the following steps:

[0007] The test module outputs a pulse voltage signal to induce the EDL to switch between charging and non-charging states in order to measure the charging and discharging dynamics of the EDL.

[0008] The current flowing through the working electrode and the counter electrode is measured by the current detection module, and a time-resolved current is formed based on the change in current magnitude at different times.

[0009] The voltage detection module measures the voltage between the working electrode and the reference electrode, and between the working electrode and the counter electrode, to measure the potential of the anode and cathode.

[0010] Based on the measured time, the current and voltage are distinguished, and the dynamics of the double-electron-layer charging and discharging process are analyzed.

[0011] The rising and falling edges of the pulse voltage signal are less than 7ns.

[0012] Before use, the working electrode and the counter electrode are polished with nano-alumina powder particles, cleaned with distilled water and anhydrous ethanol, and then dried with nitrogen gas.

[0013] The analysis of the dynamics of the double-electron-layer charging and discharging process based on the measured time-resolved current and voltage includes the following steps:

[0014] The electrolytic cell is replaced by a known capacitor. The measured time-resolved current is fitted to obtain the calculated resistance and capacitance values. The calculated resistance and capacitance values ​​are then compared with the resistance and capacitance values ​​of the known capacitor to verify the reliability of the dynamic system of the double-electron-layer charging and discharging process.

[0015] The resistance and capacitance values ​​are calculated by fitting the measured time-resolved current, as detailed below:

[0016] The current is ρ(t)=∑ i A i exp-t / τ i A was obtained through fitting. i τ i ρ(t) is the current, A iτ represents the proportion corresponding to the i-th index. i Let be the i-th time constant, t be time, and exp be the exponent with base e.

[0017] The current density ρ0 = ∑A is obtained. i and time constant τ=(∑A i τ i ) / ρ0;

[0018] The resistance R is obtained by R = V / ρ0, and the capacitance value is finally calculated by C = ρ0τ / V; V represents the voltage applied between the anode and cathode.

[0019] A voltage is applied to the electrodes using a function generator to obtain current data and the fitting results of single-exponential and triple-exponential methods. This yields current data for sodium sulfate solutions of different concentrations under different voltages, along with the initial current, equilibrium time, resistance, and capacitance values ​​obtained after fitting. Furthermore, the changes in double-layer resistance with electrolyte concentration and applied voltage are obtained. By changing the type of electrolyte solution in the electrolytic cell, the influence of the types of cations and anions in the electrolyte on the EDL charging kinetics is investigated. Finally, by changing the distance between the two platinum disk electrodes, the changes in capacitance and resistance properties in the sodium sulfate solution are obtained.

[0020] A system for high time-resolution detection of double-electron-layer charge-discharge dynamics includes:

[0021] The test module includes a function generator, which is connected via a BNC wire. The positive terminal of the function generator is connected to the working electrode immersed in the electrolyte solution in the electrolytic cell, and the negative terminal is connected to the counter electrode. The function generator outputs a pulse voltage signal to induce the EDL to switch between charging and non-charging states in order to measure the charging and discharging dynamics of the EDL.

[0022] The voltage detection module includes a multimeter, wherein the voltage probe of the multimeter has its positive terminal clamped on the working electrode or the counter electrode, and its negative terminal clamped on the reference electrode, for measuring the voltage between the working electrode and the reference electrode, and the voltage between the counter electrode and the reference electrode.

[0023] The current detection module includes an oscilloscope, which is connected to the working electrode and the counter electrode in the electrolytic cell via current probes to record current data during the charging and discharging process.

[0024] The present invention has the following beneficial effects and advantages:

[0025] Current work on measuring EDL charging kinetics employs various techniques, such as transient current measurement, surface force balancing, time-resolved X-ray diffraction, and electrodynamic current methods. However, the need for high-time-resolution measurements of EDL charging kinetics remains. To address this gap, we have constructed a device capable of measuring EDL charging dynamics with a time resolution of 2 μs, enabling high-time-resolution detection of the double-electron-layer charging and discharging process kinetics to overcome the long response times of existing capacitance testing methods. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the test method.

[0027] Figure 2 The graph shows the current data detected by the device for the commercial capacitor in Example 1, as well as the capacitance and resistance results obtained after fitting and calculation.

[0028] Figure 3 The graph shows the current data of the 0.2M sodium sulfate solution at 0.6V in Example 2.

[0029] Figure 4 The graph shows the voltage data of the 0.2M sodium sulfate solution at 0.6V in Example 2.

[0030] Figure 5 The graph shows the current data of sodium sulfate solution under different voltages in Example 2, as well as the resistance and capacitance data obtained after fitting calculation.

[0031] Figure 6 This is a comparison chart of charging dynamics in Example 3.

[0032] Figure 7 The graph shows the changes in capacitance, resistance, and other properties in a 0.2M sodium sulfate solution in Example 4. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0034] This invention consists of three parts: a testing module, a voltage detection module, and a current detection module. The testing module comprises a function generator, an electrolytic cell, platinum disk electrodes, and a reference electrode. The current detection module includes an oscilloscope and a current probe; the voltage detection module includes a multimeter and a voltage probe.

[0035] In the test module: the function generator outputs a pulse voltage signal through a BNC line, with the positive terminal connected to the working electrode immersed in the electrolyte solution in the electrolytic cell, and the negative terminal connected to the counter electrode.

[0036] In the current detection module: when the function generator outputs a pulse voltage, the oscilloscope, through a current probe, is connected to both the working electrode and the counter electrode in the electrolytic cell to record the current data flowing through the circuit during charging and discharging. The current at both the working and counter electrodes is detected, which involves monitoring the current in the circuit. By changing the position of the ammeter in the circuit, the current near the two electrodes is monitored to ensure the accuracy of the current data. The current data reflects the change in current magnitude over different times, serving as the time-resolved current.

[0037] In the voltage detection module: when the function generator outputs a pulse voltage, a multimeter is connected to the working electrode / counter electrode and the reference electrode via voltage probes to record the voltage data of the working electrode / counter electrode during the charging and discharging process. The working electrode is the anode, and the counter electrode is the cathode.

[0038] The objective of this invention is achieved through the following solution.

[0039] 1. In the test module of the present invention, the function generator outputs a pulse voltage signal through a BNC line. The positive terminal is connected to the working electrode immersed in the electrolyte solution in the electrolytic cell, and the negative terminal is connected to the counter electrode. Before use, the working electrode needs to be polished with nano-alumina powder particles, cleaned with distilled water and anhydrous ethanol, and then dried with nitrogen.

[0040] 2. In the current detection module of the present invention, when the function generator outputs a pulse voltage, the oscilloscope is connected to the working electrode and the counter electrode in the electrolytic cell through a current probe, and the current data flowing through the circuit during the charging and discharging process is recorded respectively. The highest time accuracy of the oscilloscope is 8 ns, and the time resolution of the voltmeter is about 50 μs.

[0041] 3. In the voltage detection module of the present invention, when the function generator outputs a pulse voltage, a multimeter is connected to the working electrode / counter electrode and the reference electrode through a voltage probe to record the voltage data of the working electrode / counter electrode during the charging and discharging process.

[0042] 4. By applying the current ρ(t) = ∑ i A i exp-t / τ i By fitting the data, we can obtain the current density ρ0 = ∑A. i and time constant τ=(∑A i τ i Therefore, the resistance R is obtained by R = V / ρ0, and the capacitance value is finally calculated by C = ρ0τ / V.

[0043] Aqueous solutions of each electrolyte at concentrations of 0.00 M, 0.01 M, 0.03 M, 0.05 M, 0.1 M, 0.2 M, 0.3 M, and 0.4 M were prepared and poured into a quartz electrolytic cell. The electrochemical cell was rinsed with distilled water and ethanol and dried with pure nitrogen before use. Two identical platinum plate electrodes, each 3 mm in diameter (0.0707 cm²), were immersed in the electrolyte solution. The platinum electrodes were polished with alumina nanoparticle powder, rinsed with distilled water and ethanol, and dried with nitrogen before each measurement. The two electrodes were connected by a voltage pulse generator that provided a square voltage pulse to induce the EDL to switch between charging and non-charging states to measure the charge / discharge dynamics of the EDL. The rise and fall times of the square voltage were less than 7 ns, much faster than the charge / discharge dynamics. The time-resolved current flowing through the electrodes was measured using a current probe and oscilloscope without affecting the circuitry. The potentials at the anode and cathode were measured using a time-resolved voltmeter connected to an SCE reference electrode, which was also immersed in the solution. The internal impedance of the voltage pulse generator is set to 50Ω. See the experimental setup diagram. Figure 1 .

[0044] See Figure 1 After the equipment is connected, the function generator outputs a pulse voltage with a period of 0.4s (pulse 0.2s). The positive and negative terminals of the function generator are connected to the working and counter electrodes, respectively. An oscilloscope is connected to the working and counter electrodes via a current probe to record the current data of the double electron layer during charging and discharging. A multimeter uses a voltage probe to detect the voltage between the working / counter electrode and the Ag / AgCl reference electrode.

[0045] Example 1:

[0046] All reagents and materials required for the experiment were purchased from the market. To verify the feasibility of the experimental equipment, a commercially available capacitor was first selected to replace the electrolytic cell for validation. Figure 2 As shown, (a) and (b) are the normalized current data of commercial capacitors under different voltages. (d) and (e) are the normalized current data of different commercial capacitors under the same voltage. (c) shows the resistance values ​​of different capacitors under different voltages, and (f) shows the capacitance values ​​of different capacitors under different voltages. From this, we can see that the capacitance values ​​obtained by this device are consistent with the commercial capacitance values, thus confirming the reliability of the device.

[0047] Example 2:

[0048] Sodium sulfate solutions of varying concentrations, submerging the platinum disc electrodes, were placed in an electrolytic cell. A voltage of 0.05V-0.6V with a period of 0.4s (pulse 0.2s) was applied to the electrodes using a function generator. Figure 3(c) shows the current data of 0.2M sodium sulfate solution at 0.6V and the fitting results of single exponent and triple exponent. (a) shows the current data of the entire voltage cycle. (b) is a comparison chart of the current data during the charging and discharging processes. Figure 4 This provides voltage data for the anode, cathode, and solution. Figure 5 The figures show the current data of sodium sulfate solutions of different concentrations under different voltages, as well as the initial current, equilibrium time, resistance, and capacitance values ​​obtained after fitting. (a) and (e) are the current graphs of 0.2M sodium sulfate solution before and after normalization under different voltages; (b) and (f) are the current data of sodium sulfate solutions of different concentrations before and after normalization at 0.2V; and (c), (d), (g), and (h) are the initial current, resistance, time constant, and capacitance data of sodium sulfate solutions of different concentrations under different voltages, respectively. The figures show that the double-layer resistance does not change significantly with the electrolyte solution concentration or the applied voltage; the capacitance increases with increasing voltage but does not change significantly with the sodium sulfate solution concentration.

[0049] Example 3:

[0050] The effects of varying cation and anion types in the electrolyte solution on the charging kinetics of EDL were investigated by changing the type of electrolyte solution in the electrolytic cell. Figure 6 The charging dynamics in electrolyte solutions were compared. Figures (a) and (b) show the charge dynamics of sulfate and nitrate, respectively. (e) and (f) are normalized data from (a) and (b). Time constant and capacitance data are shown in figures (g) and (h). Initial current and total EDL are shown in figures (c) and (d), respectively. Applying a logarithmic scale to both reveals a linear relationship between resistance and concentration. Nitrate exhibits a higher resistance than sulfate, with a resistivity on the order of Li. + Na + >K + >H + It is consistent with the diffusion rate of ions.

[0051] Example 4:

[0052] The changes in properties such as capacitance and resistance in a 0.2M sodium sulfate solution were investigated by varying the distance between two platinum disk electrodes. Figure 7 As shown, (a) and (c) are the current data before and after normalization at different electrode distances, (b) shows the initial current and time constant, and (d) shows the capacitance and resistance. It can be seen from the figures that applying a 0.6V voltage for 0.4s (pulse 0.2s) through the function generator, increasing the distance between the electrodes leads to a decrease in the initial current, accompanied by a slightly slower charging time. Therefore, the total resistance increases slightly with increasing distance, while the capacitance remains unaffected.

Claims

1. A method for high time-resolution detection of double-electron-layer charge-discharge dynamics, characterized in that, Includes the following steps: The test module outputs a pulse voltage signal to induce the EDL to switch between charging and non-charging states in order to measure the charging and discharging dynamics of the EDL. The current flowing through the working electrode and the counter electrode is measured by the current detection module, and a time-resolved current is formed based on the change in current magnitude at different times. The voltage detection module measures the voltage between the working electrode and the reference electrode, and between the working electrode and the counter electrode, to measure the potential of the anode and cathode. Based on the measured time, the current and voltage are distinguished, and the dynamics of the double-electron-layer charging and discharging process are analyzed.

2. The method for high time-resolution detection of double-electron-layer charge-discharge dynamics according to claim 1, characterized in that, The rising and falling edges of the pulse voltage signal are less than 7ns.

3. The method for high time-resolution detection of double-electron-layer charge-discharge dynamics according to claim 1, characterized in that, Before use, the working electrode and the counter electrode are polished with nano-alumina powder particles, cleaned with distilled water and anhydrous ethanol, and then dried with nitrogen gas.

4. The method for high time-resolution detection of double-electron-layer charge-discharge dynamics according to claim 1, characterized in that, The analysis of the dynamics of the double-electron-layer charging and discharging process based on the measured time-resolved current and voltage includes the following steps: The electrolytic cell is replaced by a known capacitor. The measured time-resolved current is fitted to obtain the calculated resistance and capacitance values. The calculated resistance and capacitance values ​​are then compared with the resistance and capacitance values ​​of the known capacitor to verify the reliability of the dynamic system of the double-electron-layer charging and discharging process. The resistance and capacitance values ​​are calculated by fitting the measured time-resolved current, as detailed below: The current is ρ(t)=∑ i A i exp-t / τ i A was obtained through fitting. i τ i ρ(t) is the current, A i τ represents the proportion corresponding to the i-th index. i Let be the i-th time constant, t be time, and exp be the exponent with base e. The current density ρ0 = ∑A is obtained. i and time constant τ=(∑A i τ i ) / ρ0; The resistance R is obtained by R = V / ρ0, and the capacitance value is finally calculated by C = ρ0τ / V; V represents the voltage applied between the anode and cathode.

5. The method for high time-resolution detection of double-electron-layer charge-discharge dynamics according to claim 1, characterized in that, By applying voltage to the electrodes using a function generator, current data and the fitting results of single-exponential and triple-exponential methods are obtained. This yields current data for sodium sulfate solutions of different concentrations under different voltages, as well as the initial current, equilibrium time, resistance, and capacitance values ​​obtained after fitting. Consequently, the changes in double-electron-layer resistance with electrolyte solution concentration and the magnitude of applied voltage are obtained.

6. The method for high time-resolution detection of double-electron-layer charge-discharge dynamics according to claim 1, characterized in that, By changing the type of electrolyte solution in the electrolytic cell, the effects of the types of cations and anions in the electrolyte on the charging kinetics of EDL were obtained.

7. The method for high time-resolution detection of double-electron-layer charge-discharge dynamics according to claim 1, characterized in that, By changing the distance between two platinum disk electrodes, the changes in capacitance and resistance in sodium sulfate solution were obtained.

8. A system for high time-resolution detection of double-electron-layer charge-discharge dynamics, characterized in that, include: The test module includes a function generator, which is connected via a BNC wire. The positive terminal of the function generator is connected to the working electrode immersed in the electrolyte solution in the electrolytic cell, and the negative terminal is connected to the counter electrode. The function generator outputs a pulse voltage signal to induce the EDL to switch between charging and non-charging states in order to measure the charging and discharging dynamics of the EDL. The voltage detection module includes a multimeter, wherein the voltage probe of the multimeter has its positive terminal clamped on the working electrode or the counter electrode, and its negative terminal clamped on the reference electrode, for measuring the voltage between the working electrode and the reference electrode, and the voltage between the counter electrode and the reference electrode. The current detection module includes an oscilloscope, which is connected to the working electrode and the counter electrode in the electrolytic cell via current probes to record current data during the charging and discharging process.

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