Effective capacitance measurement method and system based on single-frequency impedance

Abstract

The invention belongs to the field of effective capacitance measurement, and discloses an effective capacitance measurement method and system based on single-frequency impedance, and the method comprises the steps: S1, placing a working electrode, a reference electrode and a counter electrode of an electrochemical system in an electrolyte solution; s2, applying a single-frequency alternating-current potential signal to the working electrode; s3, measuring the impedance of the working electrode at a specific frequency point; s4, calculating effective capacitance according to the impedance; and S5, evaluating the performance of the electrochemical system based on the effective capacitance. The method is simplified and efficient, single-frequency measurement is adopted to replace complex broadband scanning, the measurement time is remarkably shortened, the calculation burden is reduced, and the method is suitable for real-time monitoring and portable equipment. By analyzing the change of the effective capacitance along with the frequency, various electrochemical characteristics such as capacitance behavior, film resistance, ion transfer process, potential dependence and gas interference of the fixed connection layer can be effectively represented.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of effective capacitance measurement, and in particular to a single-frequency impedance-based effective capacitance measurement method and system. BACKGROUND

[0002] Electrochemical impedance spectroscopy (EIS) is a powerful non-steady-state electrochemical measurement technique, which obtains impedance information of an electrochemical system by applying a small-amplitude sinusoidal perturbation (alternating potential or alternating current) to the system and measuring its response signal. This technique can effectively characterize the interfacial processes (such as double-layer charging), charge transfer kinetics, and bulk material properties (such as membrane resistance, capacitance) of various electrochemical systems, including ion-selective electrodes (ISEs), and is therefore widely used in fields such as sensor characterization, corrosion research, battery analysis, and biosensing.

[0003] Conventional EIS measurements are usually performed by scanning over a very wide frequency range (e.g., from 1 MHz at high frequency to 10 mHz at low frequency). In the high-frequency region (1 MHz-10 kHz), the impedance spectrum usually presents a semicircle related to the electrode bulk resistance and geometric capacitance, which reflects the ion migration process in the solution and membrane bulk phase. As the frequency decreases to the medium-low frequency region (1 Hz-10 mHz), the impedance spectrum often presents a tilted straight line or another semicircle, which is closely related to the diffusion transfer process of ions / mass at the interface or in the membrane. In particular, at such an extremely low frequency of 10 mHz, the low-frequency capacitance (C LF =-1 / (2πfZ'') can be calculated from the impedance imaginary part Z'', which is generally considered a key parameter for evaluating the charge storage capability of solid-state ion-electron transfer layers (such as conductive polymers).

[0004] For solid-state ion-selective electrodes (SCISEs), their EIS responses are usually fitted and analyzed using a resistance-capacitance (RC) equivalent circuit model. In this model, the solid junction layer with charge storage capability (such as poly(3,4-ethylenedioxythiophene) PEDOT) is simplified as a capacitance (C PEDOT ), and the ion-selective membrane is mainly characterized as a resistance (R b ). This simplified model helps to understand the basic working principle of SCISEs.

[0005] Although broadband EIS can provide comprehensive system information, its measurement process is time-consuming, data processing is complex, and professional software is needed for equivalent circuit fitting, which is difficult to meet the demand for real-time, rapid and online monitoring of electrode performance, especially in practical applications or portable devices. Therefore, single-frequency impedance (or capacitance) measurement is proposed as a simplified alternative. This method only measures at one or a few characteristic frequencies that are most sensitive to the target parameters. For example, measuring capacitance at low frequencies (such as 1 Hz or lower) can directly reflect the double-layer capacitance or bulk-phase redox capacitance of the solid attachment layer (such as conductive polymer); while measuring impedance at high frequencies can track the changes in ion-selective membrane resistance. This method significantly reduces measurement time and computational resource consumption, making it very suitable for continuous performance tracking, stability evaluation, quality control of SCISEs and integration into compact sensing systems.

[0006] Existing studies have shown that EIS data is highly consistent with the results of other electrochemical techniques such as chronopotentiometry and cyclic voltammetry, and numerical simulation work has been done to gain a deeper understanding of the interface and bulk-phase kinetic processes in ISEs. These works have laid a solid foundation for evaluating electrode performance using impedance information. However, a key point often overlooked is that the double-layer capacitance of the electrode interface or the bulk capacitance of the solid attachment layer itself has significant frequency dispersion, i.e. its measured value is strongly dependent on the measurement frequency. Even at a frequency as low as 1 Hz, this decay follows a power law and can be observed. This means that it is crucial to choose a characteristic frequency that is stable and truly reflects the target process.

[0007] In summary, although broadband EIS is comprehensive but inefficient, the existing single-frequency measurement strategies focus on tracking a single parameter (such as only measuring low-frequency capacitance or high-frequency resistance), and lack a systematic approach that can quickly and comprehensively depict the dynamic response behavior of the entire electrode system at different time scales by measuring a unified parameter (such as effective capacitance ) at multiple discrete but key frequency points. In addition, how to effectively distinguish the contributions of the solid attachment layer, ion-selective membrane and environmental factors (such as ion strength, dissolved oxygen, applied potential) to the overall impedance performance of the electrode using this simplified measurement method is still a challenge for current technology.

[0008] Therefore, the purpose of the present application is to overcome the shortcomings of the prior art, and to provide a single-frequency effective capacitance measurement method that is simple to operate, fast to measure, rich in information and can be used for in-depth analysis of the performance of each component of SCISEs.

[0009] Electrochemical impedance spectroscopy (EIS) is a powerful technique for characterizing electrochemical systems, such as interfacial processes, charge transfer kinetics, and material properties in ion-selective electrodes (ISEs). Traditional EIS operates over a wide frequency range (e.g., 1 MHz to 10 mHz) by applying a sinusoidal signal (alternating potential or current) and sweeping the frequency to obtain an impedance spectrum. However, wide-frequency EIS measurements are time-consuming and computationally demanding, making them unsuitable for real-time monitoring and stability assessment.

[0010] For solid-state ion-selective electrodes (SCISEs), the EIS response is typically modeled using a resistance-capacitance (RC) equivalent circuit, where the solid junction is represented as a capacitance and the ion-selective membrane as a resistance. While wide-frequency EIS provides comprehensive information, single-frequency impedance or capacitance measurements offer a simplified and efficient alternative, particularly suitable for real-time monitoring and stability assessment of SCISEs. This single-frequency approach can reduce measurement time and computational burden, making it particularly suitable for continuous performance tracking, quality control, and integration into compact or portable sensing systems. There is a need for a simplified, accurate, and reliable readout strategy for assessing the performance of SCISEs, particularly the capacitance behavior and ion-electron transduction capabilities of their solid junctions. SUMMARY

[0011] The present invention aims to disclose an effective capacitance measurement method and system based on single-frequency impedance, which solves the technical problems presented in the background art.

[0012] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: The present invention provides an effective capacitance measurement method based on single-frequency impedance, comprising: S1, placing a working electrode, a reference electrode, and a counter electrode of an electrochemical system in an electrolyte solution; S2, applying a single-frequency alternating potential signal to the working electrode; S3, measuring the impedance of the working electrode at a specific frequency point; S4, calculating the effective capacitance based on the impedance; S5, evaluating the performance of the electrochemical system based on the effective capacitance.

[0013] Preferably, the direct current bias potential of the single-frequency alternating potential signal is 0 V, and the alternating excitation amplitude is 10 mV.

[0014] Preferably, the specific frequency point ranges from 1 MHz to 10 mHz.

[0015] Preferably, the effective capacitance is calculated by the formula: (f) = 1 / (2πf|Z(f)|) Alternatively, effective capacitance The calculation formula is: (f) = -1 / (2pif Z''(f)) where f is the frequency, |Z(f)| is the impedance modulus, and Z''(f) is the impedance imaginary part.

[0016] Preferably, the working electrode is a PEDOT modified glassy carbon electrode or K+-SCISEs based on a PEDOT immobilization layer and a valinomycin doped PVC membrane.

[0017] Preferably, at each frequency point, if the working electrode is a PEDOT modified glassy carbon electrode, the duration of the measurement is 1.8 minutes; if the working electrode is a K+-SCISEs, the duration of the measurement is 6 minutes.

[0018] Preferably, the performance evaluation of the electrochemical system includes at least any one of the following evaluation items: Evaluation item one: by plotting the log versus the log f graph, analyzing the trend between Ceffand f; Evaluation item two: by comparing the effective capacitance values at low frequencies under different PEDOT deposition charges, evaluating the influence of the PEDOT film thickness on the capacitance; Evaluation item three: by measuring in KCl solutions of different ionic strengths, evaluating the influence of the ionic strength on the effective capacitance, and / or by measuring in solutions with a constant ionic background but different KCl concentrations, evaluating the ion selectivity; Evaluation item four: by measuring under different applied direct current bias potentials, evaluating the influence of the potential on the PEDOT doping / dedoping behavior; Evaluation item five: by measuring in a non-gassed, purged, purged environment, evaluating the influence of dissolved gas interference on the effective capacitance.

[0019] Preferably, for K+-SCISEs, by comparing the log -log f relationship of spin-coated films and drop-coated films, evaluating the influence of film thickness and resistance on the effective capacitance frequency response.

[0020] Preferably, it also includes a long-term stability evaluation step: under open circuit potential, continuously monitoring the impedance and effective capacitance of K+-SCISEs at a fixed frequency, with a measurement time interval of 60 seconds and a total duration of greater than or equal to 10 hours, evaluating the long-term stability of the electrode by the capacitance drift and signal-to-noise ratio.

[0021] The application also provides a single-frequency impedance-based effective capacitance measurement system, comprising an application module, a measurement module, a calculation module and an evaluation module; The application module is used to apply a single-frequency alternating current potential signal to the working electrode after the working electrode, the reference electrode and the counter electrode of the electrochemical system are placed in the electrolyte solution; The measurement module is used to measure the impedance of the working electrode at a specific frequency point; The calculation module is used to calculate the effective capacitance according to the impedance; The evaluation module is used to evaluate the performance of the electrochemical system based on the effective capacitance.

[0022] Advantages: Compared with the prior art, the application has the following advantages: 1. Simplification and high efficiency: single-frequency measurement is used instead of complex wide-frequency scanning, which significantly shortens the measurement time, reduces the calculation burden, and is suitable for real-time monitoring and portable devices.

[0023] 2. Information-rich: by analyzing the effective capacitance With the change of frequency, the capacitance behavior of the solid contact layer, the membrane resistance, the ion transfer process, the potential dependence and the gas interference and other electrochemical characteristics can be effectively characterized.

[0024] 3. Precise and stable: using small amplitude alternating current excitation (ΔEac=10mV) helps to minimize electrode surface polarization, improve measurement stability and reliability. The method has high signal-to-noise ratio (SNR>20000) and small baseline drift (<2nF / min), which can realize accurate resolution of capacitance value.

[0025] 4. Strong universality: the method is suitable for different types of solid contact layer materials and ion-selective membranes, and can be used for SCISEs research and development, performance optimization and quality control.

[0026] 5. Easy to model: time-resolved single-frequency impedance or effective capacitance data helps to more accurately simulate the ion transfer process and support the development of equivalent circuit models that better match the physical and electrochemical characteristics of the system. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0028] Figure 1 The schematic diagram of the change of the PEDOT / GC electrode.

[0029] Figure 2 Impedance plot for PEDOT / GC electrode.

[0030] Figure 3 Impedance plot for PEDOT / GC electrode under different concentrations of electrolyte Impedance plot as a function of frequency.

[0031] Figure 4 Impedance plot for PEDOT / GC electrode under different applied potentials C ec Impedance plot as a function of frequency.

[0032] Figure 5 Impedance plot for equivalent circuit and ion transfer mechanism and effective capacitance change.

[0033] Figure 6 Impedance plot for long-term stability of impedance Z and effective capacitance DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0035] With reference to Figure 1 The present application provides a single-frequency impedance-based effective capacitance measurement method, comprising: S1, placing a working electrode, a reference electrode and a counter electrode of an electrochemical system in an electrolyte solution; S2, applying a single-frequency alternating potential signal to the working electrode; S3, measuring the impedance of the working electrode at a specific frequency point; S4, calculating the effective capacitance according to the impedance; S5, evaluating the performance of the electrochemical system based on the effective capacitance.

[0036] Preferably, the direct current bias potential (E) of the single-frequency alternating potential signal is 0 V (relative to the open circuit potential OCP), and the alternating excitation amplitude (ΔEac) is 10 mV (RMS).

[0037] Preferably, the specific frequency point ranges from 1 MHz to 10 mHz. The impedance of the working electrode is measured at at least one frequency point.

[0038] ​Preferably, the frequency points are selected in a manner of decreasing by a factor of ten, and the frequency points include 1 MHz, 100 kHz, 10 kHz, 1 kHz, 100 Hz, 10 Hz, 1 Hz, 0.1 Hz, 0.01 Hz.

[0039] Preferably, the effective capacitance is calculated by the formula: (f) = 1 / (2pif|Z(f)| or, the effective capacitance is calculated by the formula: (f) = -1 / (2pifZ''(f)) wherein f is the frequency, |Z(f)| is the impedance modulus, and Z''(f) is the impedance imaginary part.

[0040] Preferably, the working electrode is a PEDOT modified glassy carbon electrode (PEDOT / GC) or K+-SCISEs based on a PEDOT immobilization layer and a valinomycin doped PVC membrane.

[0041] Preferably, at each frequency point, if the working electrode is a PEDOT modified glassy carbon electrode, the duration of the measurement is 1.8 minutes; if the working electrode is K+-SCISEs, the duration of the measurement is 6 minutes.

[0042] Preferably, the performance evaluation of the electrochemical system includes at least any one of the following evaluation items: Evaluation item one: by plotting the log versus the logf, the trend between and f is analyzed.

[0043] For the PEDOT / GC electrode, in the frequency range of 1 MHz to 10 Hz (logf≈6 to 1), the log has a linear relationship with the logf, and the slope is close to -1; in the low frequency range of 1 Hz to 10 mHz (logf≈0 to -2), tends to be a stable platform, representing the redox capacitance of the PEDOT immobilization layer.

[0044] Evaluation item two: by comparing the effective capacitance values at low frequencies (such as 10 mHz) under different PEDOT deposition charges (such as 1 mC, 5 mC, 10 mC), the influence of the PEDOT film thickness on the capacitance is evaluated.

[0045] Evaluation item three: by measuring , evaluate the effect of ion strength on effective capacitance, and / or by measuring , evaluate the ion selectivity; Evaluation item four: by measuring , evaluate the effect of potential on PEDOT doping / dedoping behavior; Evaluation item five: by measuring , evaluate the effect of dissolved gas (e.g. ) interference on effective capacitance under non-gassed, purged, purged environment.

[0046] Preferably, for K+-SCISEs, by comparing the log -logf relationship of spin-coated films (thin films, resistance about hundreds of Ω) and drop-coated films (thick films, resistance about 100 kΩ to 1 MΩ), evaluate the effect of film thickness and resistance on effective capacitance frequency response.

[0047] The log -logf of spin-coated films has a slope of about -0.4 in the low frequency region (1 Hz to 10 mHz), while the log -logf of drop-coated films is linear in a wider frequency range (1 MHz to 10 mHz) with a slope of about -0.99.

[0048] Preferably, it also includes a long-term stability evaluation step: for K+-SCISEs, continuous impedance and effective capacitance monitoring at a fixed frequency under open circuit potential, measurement time interval is 60 seconds, total duration is greater than or equal to 10 hours, evaluate the long-term stability of the electrode by capacitance drift and signal-to-noise ratio.

[0049] The present application also provides a single-frequency impedance-based effective capacitance measurement system, including an application module, a measurement module, a calculation module and an evaluation module; The application module is used to apply a single-frequency alternating current potential signal to the working electrode of the electrochemical system after the working electrode, reference electrode and counter electrode of the electrochemical system are placed in the electrolyte solution; The measurement module is used to measure the impedance of the working electrode at a specific frequency point; The calculation module is used to calculate the effective capacitance according to the impedance; The evaluation module is used to evaluate the performance of the electrochemical system based on the effective capacitance.

[0050] The present application will provide further embodiments below.

[0051] Example 1: Single-frequency effective capacitance measurement of PEDOT / GC electrode.

[0052] 1. Electrode preparation: After polishing and cleaning, the glassy carbon electrode was subjected to constant current electro-polymerization in an aqueous solution containing 0.01 M EDOT and 0.1 M NaPSS, with a charge of 1 mC, 5 mC and 10 mC, respectively.

[0053] 2. Measurement conditions: A three-electrode system was used for the measurement in 0.1 M KCl solution. The reference electrode was Ag / AgCl / 3M KCl, and the counter electrode was a platinum rod. The applied direct current potential was 0 V (vs. OCP), and the alternating current excitation amplitude was 10 mV RMS.

[0054] 3. Measurement frequency: Single-frequency impedance measurements were performed at 1 MHz, 100 kHz, 10 kHz, 1 kHz, 100 Hz, 10 Hz, 1 Hz, 0.1 Hz, 0.01 Hz, etc. The measurement duration at each frequency point was 1.8 minutes.

[0055] 4. Data processing: Based on the measured impedance modulus |Z|, the effective capacitance at each frequency point was calculated according to the formula (f) = 1 / (2πf|Z(f)|). .

[0056] 5. Result analysis: As shown in the f graph, 1g, 1i of Figure 1 , the log shows a linear relationship with logf (slope ~-1) in the range of 1 MHz to 10 Hz, and a platform appears in the low-frequency region (1 Hz to 10 mHz), with stable capacitance values increasing with the increase of PEDOT deposition charge Figure 1 (inserted in g graph), indicating that PEDOT has reversible doping / dedoping behavior and good capacitance characteristics.

[0057] Figure 1 The a graph of Figure 1 shows the equivalent circuit and ion transfer mechanism diagram of the PEDOT / GC electrode in 0.1 M KCl solution. Figure 1 The b graph-c graph of Figure 1 shows the EIS graph (Nyquist graph) of the 1 mC PEDOT / GC electrode in 0.1 M KCl from 1 MHz to 10 mHz. Figure 1 The e graph of shows the Bode graph (logZ and phase angle vs. logf) of the 1 mC PEDOT / GC electrode. Figure 1Figure h of the drawings shows log vs. logf plot (error bars, n=3), inset is the low frequency capacitance vs. logf plot (error bars, n=3), inset is the low frequency capacitance Figure 1 Figure h of the drawings shows log vs. logf plot (error bars, n=3), inset is the low frequency capacitance Figure 1 Figure i of the drawings shows log vs. logf plot (error bars, n=3), inset is the low frequency capacitance

[0058] Figure 2 Figure a of the drawings shows impedance Z plot of 5mC PEDOT / GC electrode from 10mHz to 0.1kHz in 0.1M KCl. Figure 2 Figure b of the drawings shows effective capacitance plot of 5mC PEDOT / GC electrode in the corresponding frequency range.

[0059] Example 2: Effect of ionic strength on effective capacitance of PEDOT / GC electrode.

[0060] 1. Measurement condition: using 1mC PEDOT / GC electrode, measurements were carried out in 0.1M, 0.01M, 0.001M, 0.0001M KCl solutions (without background and with 0.1M NaCl background), frequency range 1MHz to 10mHz.

[0061] 2. Result analysis: as shown in Figure a of the drawings, 3c, without background electrolyte, as KCl concentration decreases, solution resistance increases, high frequency region capacitance response is similar, but low frequency region effective capacitance decreases due to increased diffusion resistance. With 0.1M NaCl background (Figure b of the drawings, 3d), capacitance response at different KCl concentrations is basically consistent, indicating that PEDOT has similar cation exchange ability for K+ and Na+. Figure 3 Figure 3 Figure 3

[0062] Figure 3 Figure a of the drawings shows impedance Z plot of 1mC PEDOT / GC electrode in different concentrations of KCl (0.1M to 0.0001M, without background electrolyte) vs. frequency. Figure b of the drawings shows impedance Z plot of 1mC PEDOT / GC electrode in different concentrations of KCl (0.1M to 0.0001M, with 0.1M NaCl background) vs. frequency. Figure 3 Figure b of the drawings shows impedance Z plot of 1mC PEDOT / GC electrode in different concentrations of KCl (0.1M to 0.0001M, with 0.1M NaCl background) vs. frequency. Figure b of the drawings shows impedance Z plot of 1mC PEDOT / GC electrode in different concentrations of KCl (0.1M to 0.0001M, with 0.1M NaCl background) vs. frequency. Figure 3 ​​​Fig. 1a-c show the Nyquist plots of the 1 mC PEDOT / GC electrode in 0.1 M KCl under different conditions: (a) without gas flow, (b) purging with N2, and (c) purging with O2. Figure 3 Fig. 2a-b show the log f plots of the 1 mC PEDOT / GC electrode in 0.1 M KCl under different conditions: (a) without gas flow, and (b) purging with N2. Fig. 3 shows the plots of C vs. f of the 1 mC PEDOT / GC electrode in 0.1 M KCl under different conditions: (a) without gas flow, (b) purging with N2, and (c) purging with O2.

[0063] Example 3: Effect of applied potential and gas interference on the effective capacitance of PEDOT / GC electrode.

[0064] 1. Measurement condition: using 1 mC PEDOT / GC electrode, in 0.1 M KCl, under the conditions of (a) without gas flow, (b) purging with N2, and (c) purging with O2, the measurements were carried out at the applied potentials of -0.2 V, 0 V, +0.2 V (vs. reference electrode) with 10 min intervals.

[0065] 2. Result analysis: as shown in Fig. 1a-d, the order of the low frequency effective capacitance is -0.2 V > 0 V > +0.2 V, which is consistent with the reduction (de-doping) and oxidation (doping) process of PEDOT. Figure 4

[0066] Figure 4 Fig. 1a-c show the Nyquist plots of the 1 mC PEDOT / GC electrode in 0.1 M KCl under different conditions: (a) without gas flow, (b) purging with N2, and (c) purging with O2. Fig. 2a-b show the log f plots of the 1 mC PEDOT / GC electrode in 0.1 M KCl under different conditions: (a) without gas flow, and (b) purging with N2. Figure 4 Fig. 3 shows the plots of C vs. f of the 1 mC PEDOT / GC electrode in 0.1 M KCl under different conditions: (a) without gas flow, (b) purging with N2, and (c) purging with O2. Figure 4 Fig. 4a-c show the log f plots of the 1 mC PEDOT / GC electrode in 0.1 M KCl under different conditions: (a) without gas flow, (b) purging with N2, and (c) purging with O2.

[0067] Example 4: Single frequency effective capacitance measurement of K+-SCISEs.

[0068] 1. Electrode preparation: on the prepared PEDOT / GC electrode, drop or spin coating K+ ion selective membrane solution (THF solution containing valinomycin, KTFPB, ETH500, DOS, PVC) to form drop-coated or spin-coated film.

[0069] 2. Measurement condition: same as Example 1, but the measurement time at each frequency point was extended to 6 min.

[0070] 3. Result analysis: as shown in Fig. 5f-j-k, for K+-SCISEs with spin-coated film (low resistance), the log f plots of the effective capacitance are shown in Fig. 5f-j-k. Figure 5 ​​​​​​​​-logf relationship in the low frequency region has a slope of -0.4; while for K+-SCISEs with drop-casted films (high resistance), the log -logf is linear over a wide frequency range with a slope of -0.99. The greater the film resistance, the lower the low frequency capacitance value and the steeper the frequency response slope. The log -logf remains well linear Figure 5 in the low frequency region (Figure a in the inset).

[0071] Figure 5 Figure a in the inset shows the equivalent circuit and ion transfer mechanism schematic of K+-SCISEs. Figure 5 Figures b-c in the inset show the EIS plots (Nyquist plots) of K+-SCISEs with 1 mCPEDOT solidified layer and spin-casted films in 0.1 M KCl from 1 MHz to 10 mHz. Figure 5 Figures d-e in the inset show the impedance Z plots of K+-SCISEs with 1 mCPEDOT and spin-casted films in 0.1 M KCl over different frequency ranges. Figure 5 Figure f in the inset shows the effective capacitance of K+-SCISEs with 1 mCPEDOT and spin-casted films calculated based on Z vs. logf. Figure 5 Figure g in the inset shows the impedance Z and log Z of K+-SCISEs with 1 mCPEDOT and spin-casted films vs. logf. Figure 5 Figures h-i in the inset show the Bode plots (log Z and phase angle vs. logf) of K+-SCISEs with spin-casted and drop-casted films. Figure 5 Figure j in the inset shows the of K+-SCISEs with 1 mCPEDOT and spin-casted films calculated based on Z and Z" vs. logf. Figure 6 Figure k in the inset shows the log vs. logf comparison of PEDOT / GC, K+-SCISEs with spin-casted and drop-casted films in 0.1 M KCl. Figure 6 Figure l in the inset shows the log vs. logf of SCISEs with K+-selective drop-casted films in different concentrations of KCl (0.1 M to 0.0001 M).

[0072] Example 5: Long-term stability monitoring of K+-SCISEs.

[0073] 1. Measurement conditions: For K+-SCISEs with a 5mC PEDOT bonding layer and spin-coated film, impedance and effective capacitance were continuously monitored for 10 hours at a fixed frequency of 1Hz in 0.1M KCl at open circuit potential, with a data acquisition interval of 60 seconds.

[0074] 2. Results Analysis: For example... ​ As shown, the effective capacitance has a certain drift (15.65nF / h), but the signal-to-noise ratio is high (SNR=1350), indicating that the measurement accuracy is high and the noise is low. The PEDOT bonding layer can achieve stable ion-electron transduction.

[0075] Table 1. Standard deviation (%) of 1 mC PEDOT, 5 mC PEDOT and 10 mC PEDOT in 0.1 M KCl solution, in the frequency range from 1 MHz to 10 mHz.

[0076] The single-frequency effective capacitance measurement method provided by this invention can simplify, quickly and accurately characterize the electrochemical performance of PEDOT-based bonding layers and SCISEs, providing an effective tool for electrode development, performance evaluation and real-time monitoring.

[0077] Table 2. Signal-to-noise ratio and baseline drift of 5mC PEDOT in the low-frequency range (100Hz to 10mHz)

[0078] ​ The impedance Z and effective capacitance of K+-SCISEs with a 5mC PEDOT bonded layer and spin-coated film are shown by continuous monitoring at 1Hz for 10 hours in 0.1M KCl. The long-term stability plot.

[0079] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for measuring effective capacitance based on single-frequency impedance, characterized in that, include: S1, place the working electrode, reference electrode, and counter electrode of the electrochemical system in an electrolyte solution; S2, apply a single-frequency AC potential signal to the working electrode; S3, Measure the impedance of the working electrode at a specific frequency point; S4, calculate the effective capacitance based on the impedance; S5 evaluates the performance of electrochemical systems based on effective capacitance.

2. The effective capacitance measurement method based on single-frequency impedance according to claim 1, characterized in that, The DC bias potential of the single-frequency AC potential signal is 0V, and the AC excitation amplitude is 10mV.

3. The effective capacitance measurement method based on single-frequency impedance according to claim 1, characterized in that, The specific frequency range is from 1MHz to 10mHz.

4. The effective capacitance measurement method based on single-frequency impedance according to claim 1, characterized in that, Effective capacitance The calculation formula is: (f)=1 / (2πf|Z(f)|) or, Effective capacitance The calculation formula is: (f)=–1 / (2πfZ''(f)) Where f is the frequency, |Z(f)| is the impedance magnitude, and Z''(f) is the imaginary part of the impedance.

5. The effective capacitance measurement method based on single-frequency impedance according to claim 1, characterized in that, The working electrode is a PEDOT-modified glassy carbon electrode or a K+-SCISE based on a PEDOT bonding layer and a valine-doped PVC film.

6. The effective capacitance measurement method based on single-frequency impedance according to claim 5, characterized in that, At each frequency point, if the working electrode is a PEDOT-modified glassy carbon electrode, the measurement duration is 1.8 minutes; if the working electrode is a K+-SCISEs, the measurement duration is 6 minutes.

7. The effective capacitance measurement method based on single-frequency impedance according to claim 4, characterized in that, Performance evaluation of an electrochemical system should include at least one of the following evaluation items: Evaluation Item 1: By plotting logs Compared to the logf relationship graph, the analysis The trend relationship between f and f; Evaluation Item 2: By comparing the effective capacitance values ​​at low frequencies under different PEDOT deposition charges, the influence of PEDOT film thickness on capacitance is evaluated. Evaluation Item 3: Measurement in KCl solutions of different ionic strengths To assess the effect of ionic strength on effective capacitance, and / or by measuring in solutions with different KCl concentrations containing a constant ionic background. To evaluate ion selectivity; Evaluation Item 4: Measurement under different applied DC bias potentials To evaluate the effect of potential on the doping / dedoping behavior of PEDOT; Assessment Item 5: Through non-ventilation, Blowing, Measurement under purging environment To assess the impact of dissolved gas interference on effective capacitance.

8. The effective capacitance measurement method based on single-frequency impedance according to claim 7, characterized in that, For K+-SCISEs, the logarithmic values ​​of spin-coated and drop-coated films were compared. -logf relationship, to evaluate the effect of film thickness and resistance on the effective capacitance frequency response.

9. The effective capacitance measurement method based on single-frequency impedance according to claim 1, characterized in that, It also includes a long-term stability assessment step: at open circuit potential, K+-SCISEs are continuously monitored for impedance and effective capacitance at a fixed frequency, with a measurement time interval of 60 seconds and a total duration of ≥10 hours, and the long-term stability of the electrodes is assessed by capacitance drift and signal-to-noise ratio.

10. An effective capacitance measurement system based on single-frequency impedance, characterized in that, It includes an application module, a measurement module, a calculation module, and an evaluation module; The application module is used to apply a single-frequency AC potential signal to the working electrode after the working electrode, reference electrode, and counter electrode of the electrochemical system are placed in an electrolyte solution; The measurement module is used to measure the impedance of the working electrode at a specific frequency point; The calculation module is used to calculate the effective capacitance based on the impedance; The evaluation module is used to evaluate the performance of electrochemical systems based on effective capacitance.

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