How to measure AC impedance?

Delahay systematically discussed the problem of using communication methods to scientifically research the kinetic model of the whole process of photocatalysis from the basic theory. H. Gerischer and W. The EIS (Electrochemical Impedance Spectroscopy, referred to as EIS) scientific research published by Mehl in 1955 on the reflection of hydrogen evolution will be the key early EIS scientific research on the irreversible electrode process. They discovered the characteristic impedance measured in this scientific research. There is inductive reactance in the spectrum, and the phase-frequency characteristics of the existing inductance components. H. Gerischer used the network analysis method of linear thermal components to measure the characteristic impedance spectrum of the electrical level system software with the AC current bridge. The equivalent circuit method was selected in it, and the Faraday characteristics of the electrode process have been discovered since then. Impedance can have different equivalent circuit modes. At the beginning of the 1960s, French physicist J. H. In the experiment, Sluyters maintained the application of the communication characteristic impedance spectroscopy method in the scientific research of the whole process of photocatalysis. In addition, Smith et al. studied the same problem from a different perspective, that is, in the steady state of DC, basically accumulate small amplitude AC current data signals, and observe the valley value of the current that does not respond. This method is called Communication voltammetry or communication polarography. The results obtained by the two methods are the same.
According to the definition of characteristic impedance, the input encouragement data signal of the measured system should be the amount of current, and the data signal without response in the photocatalytic measurement is the electrode potential. For the electrical level system software of the reversible electrode reaction, it is very convenient to select the current amount as the oscillation data signal to carry out the characteristic impedance measurement, because the potential difference of the reversible electrode reaction is at the equilibrium potential difference. For the irreversible electrode reaction, it is very complicated. The Faraday current intensity flowing through the electric level is much higher than the exchange current intensity of the electrode reaction. To maintain the necessary irreversibility level, it is necessary to maintain the necessary Faraday current intensity or maintain the electric level. The level system software is at the necessary unbalanced potential difference. It is very difficult to keep the electrical level system software in a certain potential difference section for a long time by manipulating the amount of current.
The communication AC characteristic impedance method means that the sine waveform oscillating data signal with a small amplitude value of different frequency is used in the electrical level system software. The electrical level characteristic impedance obtained from the relationship between the non-response of the electrical level system software and the oscillation data signal is inferred. The equivalent circuit of the power level can analyze the whole process and principle of the dynamic model included in the power level system software, and estimate the main parameters of the dynamic model of the power level system software from the parameter values of the relevant components in the equivalent circuit, such as the power level Electric double layer capacitors, resistors reflecting the whole process of charge transfer, main parameters of the whole process of external diffusion and convection heat transfer, etc.
Communication AC characteristic impedance measurement method
Communication AC characteristic impedance method is a very key method in photoelectric catalytic testing technology, and it is a key method for scientific research on the dynamic model and appearance of electrode process. Very recently, the detection precision of communication AC characteristic impedance has become higher and higher, and the characteristic impedance spectrum of UHF data signals also has excellent reproducibility. In addition to the development of electronic information technology, the automatic technology of characteristic impedance spectrum analysis The level is getting higher and higher, which enables people to better understand the structure of the electric double layer on the electric level surface, the transformation of the active coating, the cause of pitting, the development trend, the stop and the whole process of adsorption and desorption of specific chemical substances.

       (1) Communication and AC characteristic impedance: Communication and AC characteristic impedance is characteristic impedance. In electromagnetics, it refers to the composite characteristics of resistors and reactances displayed by electronic device components to communicate and exchange encouragement data signals; in photocatalysis, it is Refers to the composite characteristics of resistors and reactance exhibited by the communication and exchange encouragement data signals released by the electrical level to the system. The enterprise of characteristic impedance mode is Euro mother, and the enterprise of characteristic impedance argument (phase angle) is slope or degree.

       (2) Communication and AC characteristic impedance spectrum: In the whole process of measuring characteristic impedance, if the frequency of the communication and communication encouragement data signal is constantly changed, a series of characteristic impedance statistics that change with frequency can be measured. The combination of this type of frequency-dependent characteristic impedance statistical data is called the characteristic impedance frequency spectrum or the characteristic impedance spectrum. The characteristic impedance spectrum is the complex number of frequency, which can be expressed by the composition of amplitude-frequency characteristics and phase-frequency characteristics; it can also show the real and imaginary parts of characteristic impedance in the complex plane with frequency as a parameter. The wider the measurement frequency range, the more detailed the characteristic impedance spectrum information content can be obtained. The frequency range of RST5200 electrochemical workstation is 0.00001Hz～1MHz, which can perform characteristic impedance spectrum measurement very well.

       (3) Electrochemical Impedance Spectroscopy: Electrochemical Impedance Spectroscopy is the standard for this kind of photocatalytic test, and the selected technique is a small data signal communication AC steady-state measurement method. For parameters such as aqueous resistors, electric double-layer capacitors and Faraday resistors in the photocatalytic level management system, electrochemical impedance spectroscopy can be used to measure accurately; and temporary steps such as current step and potential difference step can be used to measure the parameters. When measuring in a state, the precision is somewhat lower. On the other hand, characteristics such as the entire process of external diffusion and convection heat transfer that must be measured for a long time cannot be maintained by the transient method, and this is indeed the long term of electrochemical impedance spectroscopy.

       (4) Diversity of electrochemical impedance spectroscopy measurement: In terms of the basic principle of measurement, there is no difference between measuring the characteristic impedance spectrum of the electrical level management system in photoelectric catalysis and measuring the characteristic impedance spectrum of electronic device components in electromagnetics. Generally, people expect to obtain the electrochemical impedance spectroscopy when the electrical level management system is in a certain situation. In order to maintain the electrical level management system, the electrode potential must be kept constant. It is generally believed that a 50mV change in electrode potential will destroy the current situation. Therefore, in the electrochemical impedance spectroscopy measurement, we must pay attention to two key links, namely: the reference point potential difference and the sinusoidal communication data signal strength.

       (5) The strength of sinusoidal communication and AC data signals: In order to prevent great harm to the photoelectric catalytic level management system and the expectation that it has a good line shape and no response, the strength of sinusoidal communication and AC data signals can generally be built in the middle of 2-20mV. .

      (6) Fully automatic debiasing: In the whole process of electrochemical impedance spectroscopy measurement, because the potential difference of the reference point may not be equivalent to the lead potential difference and its small discrete system effect, there will also be an electric current in the work. Direct current component. By removing this direct current component (bias current), the dynamic range of the communication AC data signal can be expanded, and the signal-to-noise ratio can be improved. The RST5200 electrochemical workstation can dynamically adjust the amount of debiasing current during the whole measurement process, so that the statistical data of characteristic impedance spectroscopy can be improved. The other is that in the notification bar of the program interface, the amount of electrical polarization current in the information work can be displayed in real time for the operator's reference. The left and right are the related indications of the communication characteristic impedance. Below, people will briefly describe the terms encountered in the whole process of the experiment setting, so that the user can better grasp the communication characteristic impedance method. Communication AC characteristic impedance measurement method
(1) Frequency band: In electrochemical impedance spectroscopy, describing frequency transitions in most ways can make the characteristic impedance spectrum look compact and without loss of characteristics. In most plane coordinates, people are more accustomed to using 10 as the base. Because of this, in the RST electrochemical workstation, the frequency range in which the frequency is converted 10 times is called a frequency band. For example: call the frequency range from 1 Hz to 10 Hz as frequency band 6; call the frequency range from 10 Hz to 100 Hz as frequency band 7, these. In each frequency band, 1~24 frequency bands can be included, depending on the settings of the operator. Generally, some frequency bands can be set for the frequency bands that must be mainly concerned, and some frequency bands can be set less for the frequency bands with too long operation time.

      (2) Frequency band: The characteristic impedance of photocatalysis is a connotation of frequency (for example, frequency is an independent variable in amplitude-frequency characteristics and phase-frequency characteristics; frequency is a parametric variable in characteristic impedance complex plane and admittance complex plane). In order to describe the characteristic impedance characteristics of the photoelectric catalytic management system more comprehensively, people must measure within a wide frequency range, usually more than a dozen frequencies. In the RST electrochemical workstation, this type of leaving measurement frequency is called a frequency band. After measurement, one set of measurement values will be obtained for each frequency point.

      (3) Cycle: In the RST electrochemical workstation, the waveform generated by the sinusoidal waveform for 1 detailed cycle time (position variable = 2?60 degrees) is called 1 cycle. In the steady-state measurement of communicating and communicating data signals, the longer the measurement time, the higher the signal-to-noise ratio. Therefore, if the frequency of a certain frequency band is set a little higher, the measurement statistics of this frequency band will be more accurate, or the relative measurement time will be longer and longer.

      (4) Start and stop frequency, stop frequency: In the whole process of electrochemical impedance spectroscopy measurement, people call the position measurement frequency the start and stop frequency; the measurement frequency is called the stop frequency. Tips: Because the frequency band with higher frequency requires shorter measurement time, if you set the start and end frequency to high frequency and the stop frequency to high frequency, the characteristic impedance can be seen relatively early in the whole measurement process Panorama of the spectrum. (5) Operation time: The operation time is closely related to the setting of main parameters such as the start and end frequency, the stop frequency, the total number of frequency bands, and the number of cycles of each frequency band. In the mobile phone software of the RST electrochemical workstation, when the main parameters are changed, the operating time will be measured and obtained immediately, which is beneficial to the operator to measure.

       (6) Reference point potential difference: In the RST electrochemical workstation, the AC potential (relative to the reference electrode) applied to the working level in the electrolytic cell is called the reference point potential difference. In electromagnetics, in order to facilitate signal analysis, the AC/DC power mixed data signal is often regarded as composed of a communication AC data signal and a DC data signal accumulated. From the time waveform perspective, the DC data signal can shift the communication AC waveform upward or downward, which is then called the reference point data signal. If it is described in terms of potential difference (working voltage), it is called the reference point potential difference (working voltage). Most of the photoelectrocatalytic characteristic impedance measurements are carried out under the standard of lead potential difference. At this time, the amount of current in the external circuit is zero, and there is no over-potential difference on the working electric level. When the communication and AC data signal added to the working power level is sufficient for an hour, such as 2mV～20mV, it is generally felt that this kind of equilibrium situation is not easy to be destroyed. Warm reminder, at this time, the reference point potential difference added to the working power level should be its lead potential difference.,because the lead potential difference of the photocatalytic system software.