An electrochemical potential step transient test method and system for high temperature and high pressure diffusion control

Abstract

The application discloses a kind of electrochemical potential step transient test method and system for high temperature and high pressure diffusion control.The system includes high temperature and high pressure reactor, integrated three-electrode test unit, multistage sealing assembly, safety control subsystem and data acquisition unit;Multistage sealing assembly adopts conical surface sealing-high temperature ceramic insulation-back end hydraulic compensation composite design, to ensure the sealing and insulation reliability under high temperature and high pressure;Integrated three-electrode test unit is modular probe structure.When testing, inject corrosion solution into the kettle and heat up to target working condition, apply potential step signal to excite diffusion-controlled transient current response, and analyze test curve based on Cottrell equation and porous medium diffusion model.The application can in situ quantitatively obtain diffusion coefficient, porosity and effective thickness and other key parameters under the condition of 120-250 DEG C, 2.7-350 bar, to provide data support for metal component corrosion risk assessment.

Description

Technical Field

[0001] This invention relates to an electrochemical potential step transient testing method and system for high-temperature and high-pressure diffusion control, belonging to the fields of electrochemical testing and materials corrosion science and technology. Background Technology

[0002] In industrial fields such as oil and gas extraction, geothermal power generation, and high-temperature chemical processing, metal components (such as stainless steel and pipeline steel) are often used in environments containing CO2, H2S, and Cl. - Extreme environments with high temperature and pressure (120~250℃, 2.7~350 bar) in corrosive media. Under these conditions, corrosion product deposits such as FeCO3, FeS, and Cr(OH)3 easily form on metal surfaces. The formation and growth of these deposits are often dominated by the diffusion process of reactants or products in the solution, directly affecting the corrosion risk and service life of materials, becoming a key issue restricting the safe and stable operation of industrial equipment.

[0003] In-situ, dynamic, and quantitative characterization of diffusion control steps in metal corrosion is a core research direction in materials corrosion science. The test results directly determine the reliability of corrosion prediction models and the effectiveness of protection schemes. As industrial equipment upgrades to higher temperature, higher pressure, and more corrosive operating conditions, stringent requirements are placed on the adaptability of testing technologies to operating conditions, process sensitivity, and parameter quantification.

[0004] Current testing technologies have significant bottlenecks: conventional electrochemical methods (such as electrochemical impedance spectroscopy (EIS) and potentiodynamic scanning) are difficult to implement under high temperature and high pressure conditions, and it is difficult to clearly distinguish between diffusion and charge transfer steps. They are not sensitive enough to transient diffusion processes and cannot accurately capture the kinetic characteristics of deposited film growth. Although non-in-situ sampling analysis can obtain the morphology and composition of corrosion products, it cannot reflect the in-situ, continuous interface corrosion and diffusion interaction process, and the data lacks timeliness and representativeness.

[0005] Meanwhile, the sealing and electrode stability issues under high temperature and high pressure environments have long remained unresolved: traditional sealing materials are prone to aging and failure, leading to media leakage; reference electrodes are susceptible to contamination or potential drift, making it impossible to maintain a stable reference; and the insulation reliability between the working electrode and the reaction vessel is also difficult to guarantee. These factors severely restrict the development and application of high temperature and high pressure electrochemical testing technology.

[0006] Therefore, there is an urgent need for an electrochemical potential step transient testing method and system for high-temperature and high-pressure diffusion control, in order to solve key problems such as in-situ dynamic characterization of diffusion processes under high temperature and high pressure, sealing reliability and long-term electrode stability, to achieve quantitative analysis of corrosion product deposition kinetics, and to meet the actual industrial testing needs. Summary of the Invention

[0007] The purpose of this invention is to provide an electrochemical potential step transient test method and system for high-temperature and high-pressure diffusion control, which aims to simulate real industrial corrosion environment, solve the technical problems of reliable sealing of working electrode, long-term stability of reference electrode and quantitative characterization of diffusion characteristics of corrosion product deposit layer under high temperature and high pressure, and realize in-situ and dynamic analysis of diffusion-controlled corrosion process.

[0008] The electrochemical potential step transient testing system for high-temperature and high-pressure diffusion control provided by the present invention includes a high-temperature and high-pressure reactor, an integrated three-electrode testing unit, a multi-stage sealing assembly, a safety control subsystem, and a data acquisition unit.

[0009] The high-temperature and high-pressure reactor is used to contain corrosive media to simulate high-temperature and high-pressure industrial corrosion conditions. The integrated three-electrode testing unit is a modular probe structure that can be inserted into the reaction vessel as a whole, and integrates a working electrode, an auxiliary electrode, and a high-temperature and high-pressure reference electrode. The multi-stage sealing assembly is used to achieve sealing and insulation between the working electrode and the reactor lid, and adopts a composite design of conical seal - high temperature ceramic insulation - rear hydraulic compensation; The safety control subsystem is used to monitor the temperature and pressure of the reactor in real time, and has over-temperature and over-pressure alarm and automatic interlocking pressure relief function to avoid safety risks under extreme working conditions. The data acquisition unit includes a potentiostat and a high-precision data logger, which are connected to the electrodes inside the reactor via a high-voltage through-chamber electrical connector. The control software enables the application of potential step signals, recording of transient current-time curves, and analysis and processing.

[0010] Preferably, the composite design structure of the conical seal-high temperature ceramic insulation-rear hydraulic compensation is as follows: The working electrode passes through a high-strength alloy sleeve with an inner conical surface. A flexible graphite gasket or mica gasket is filled between the two as a primary seal. A metal O-ring is used for the main seal between the outside of the sleeve and the vessel lid. A pressurized chamber is provided at the lead-out end of the working electrode outside the vessel. A micro hydraulic pump is used to make the pressure inside the chamber slightly higher than the pressure of the medium inside the vessel to form reverse pressure compensation.

[0011] Preferably, the metal O-ring is made of Inconel nickel alloy; the reverse pressure difference formed by the micro hydraulic pump driving the pressurized chamber is 0.1 to 0.5 bar higher than the medium pressure inside the high-temperature and high-pressure reactor.

[0012] Preferably, the working electrode is a metal or alloy rod to be tested, the auxiliary electrode is a platinum-iridium alloy wire, and the high-temperature and high-pressure reference electrode is an Ag / AgCl external pressure balanced electrode, which is connected to the corrosive medium through a capillary salt bridge. The front end of the capillary salt bridge is equipped with a porous ceramic diaphragm, and the rear end is connected in series with an external pressure balancing valve to ensure the long-term stability and anti-pollution capability of the potential under high temperature and high pressure.

[0013] Preferably, the high-pressure through-chamber electrical connector is a corrosion-resistant and sealed structure integrated into the lid of the high-temperature and high-pressure reactor, and its interface is provided with an Al2O3 or ZrO2 ceramic insulating bushing to ensure insulation reliability.

[0014] Preferably, the vessel body of the high-temperature and high-pressure reactor is made of Hastelloy or duplex stainless steel; the high-temperature and high-pressure reactor is suitable for reactors containing CO2, H2S and / or Cl with a pH value of 3-10. - It can withstand corrosive media and operate stably for more than 72 hours under conditions of 120-250℃ and 2.7-350 bar to simulate the service environment of materials.

[0015] Preferably, on the modular probe of the integrated three-electrode test unit, the test working surface of the working electrode has a pre-calibrated and fixed geometric area.

[0016] The present invention further provides an electrochemical potential step transient test method for high-temperature and high-pressure diffusion control, which, using the aforementioned test system, includes the following steps: Step S1: System setup and pre-stabilization: Install the integrated three-electrode test unit in the high-temperature and high-pressure reactor through a multi-stage sealing assembly, inject corrosive medium into the reactor, introduce target gas (such as CO2, H2S) to the set partial pressure, raise the temperature and pressure to the target operating condition, and wait for the open circuit potential of the working electrode to stabilize. Step S2: Application of diffusion-controlled potential step: A transient potential step from a stable open-circuit potential to a preset target potential is applied to the working electrode using a potentiostat. The selection of the target potential ensures that the electrode reaction is completely controlled by the diffusion step. Step S3: Transient current response recording: The current-time transient response curve of the working electrode after a potential step is synchronously recorded using a high-precision recorder at a sampling rate of not less than 100 Hz; Step S4: Analysis of diffusion parameters and deposited film characteristics: The current-time transient response curve is analyzed. When there is no significant deposited film on the working electrode surface, the initial stage of the curve is fitted based on the Cottrell equation to calculate the bulk diffusion coefficient of the reactants. When there is a porous deposited film on the working electrode surface, the effective diffusion coefficient, porosity, and effective thickness of the deposited layer are inverted by comparing the transient response curves of different film formation stages, using a porous medium diffusion model.

[0017] Preferably, the selection of the target potential is as follows: for the anodic dissolution reaction, a step to a positive potential that allows the reaction to reach the limiting diffusion current density; for the cathodic reduction reaction, a step to a negative potential that allows the reaction to reach the limiting diffusion current density.

[0018] Preferably, in step S4, when a porous deposited film exists on the surface of the working electrode, the inversion specifically includes: using the bulk diffusion coefficient measured when the electrode surface is clean as a benchmark, fitting the transient response curve after film formation using a nonlinear fitting method, based on the formula... Simultaneous inversion of the effective diffusion coefficient of the sedimentary layer Porosity and effective thickness ,in Tortuosity of the sedimentary layer; The method further includes: first applying a step potential in the first direction and holding it for a period of time, then applying a step potential in the opposite direction, and recording the complete transient current response under the two potential changes in order to analyze the structural evolution characteristics of the deposited layer under dynamic potential.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects: 1. Strong adaptability to operating conditions: For the first time, in-situ, dynamic electrochemical testing of diffusion-controlled corrosion processes under extreme operating conditions of 120~250℃ and 2.7~350 bar has been achieved. The system can run stably for ≥72 hours. The corrosive medium and operating parameters are completely matched to actual industrial conditions, and the representativeness and reliability of the test data are significantly improved.

[0020] 2. High test specificity and sensitivity: Through precise potential step design, the transient response of diffusion control is instantly excited, which can effectively eliminate interference from non-diffusion processes such as charge transfer and double-layer charging. It has extremely high sensitivity to capturing the dynamic characteristics of deposition film growth and is particularly suitable for the dynamic evolution study of corrosion product deposition films under high temperature and high pressure.

[0021] 3. Breakthrough in sealing and electrode stability: The innovative composite design of conical seal, high-temperature ceramic insulation and hydraulic compensation at the rear end (0.1~0.5 bar pressure difference) fundamentally solves the problem of leakage and insulation failure of metal electrodes under high temperature and high pressure; paired with Ag / AgCl reference electrode with "front-end porous ceramic diaphragm + rear-end pressure balance valve", it ensures long-term potential stability and anti-pollution ability.

[0022] 4. High degree of parameter quantification: Through single or series of transient tests, combined with the Cottrell equation and porous media diffusion model, key parameters such as bulk diffusion coefficient, effective diffusion coefficient of deposited layer, porosity, and effective thickness can be quantitatively obtained, providing core data support for the establishment of corrosion prediction models, corrosion risk assessment of metal components, and life prediction.

[0023] 5. Excellent system integration and safety: The test unit adopts a modular probe design, which is convenient for installation, calibration and maintenance, and greatly improves the repeatability of experiments; the system is equipped with a complete safety protection mechanism such as over-temperature and over-pressure audible and visual alarms and automatic interlocking pressure relief, taking into account both operational safety and long-term continuous testing requirements. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall high-temperature and high-pressure in-situ electrochemical testing system of the present invention.

[0025] Figure 2 This is a detailed cross-sectional view of the sealing assembly for a high-temperature, high-pressure metal working electrode.

[0026] Figure 3 This is a schematic diagram of the structure of an integrated three-electrode test unit (probe).

[0027] Figure 4 This is a schematic diagram of a typical potential step signal and its corresponding transient current response curve.

[0028] Figure 5 This is a schematic diagram of fitting and analyzing transient current data using the Cottrell equation. Detailed Implementation

[0029] To better understand the technical solution of the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] I. Testing System This invention relates to an electrochemical potential step transient testing system for high-temperature, high-pressure diffusion control. For example... Figure 1 As shown, the system includes a high-temperature and high-pressure reactor 1, a multi-stage sealing assembly 2, an integrated three-electrode testing unit 3 (probe), a safety control subsystem 4, and a data acquisition unit 5. The integrated three-electrode testing unit 3 is sealed and insulated from the high-temperature and high-pressure reactor 1 through the multi-stage sealing assembly 2. The safety control subsystem 4 is electrically connected to the high-temperature and high-pressure reactor 1, and the data acquisition unit 5 is electrically connected to the integrated three-electrode testing unit 3 through a high-pressure through-chamber electrical connector.

[0031] 1. High-temperature and high-pressure reactor like Figure 1 As shown, the high-temperature and high-pressure reactor 1 is used to contain CO2, H2S, and Cl. -Corrosive solutions of various media are used to simulate high-temperature and high-pressure industrial corrosion conditions. In this embodiment, the vessel body of the high-temperature and high-pressure reactor 1 is made of Hastelloy or duplex stainless steel, which has excellent resistance to acid corrosion and sulfide stress cracking. It can be adapted to corrosive media with pH values ​​of 3 to 10 and can operate stably for more than 72 hours under conditions of 120 to 250°C and 2.7 to 350 bar. Preferably, it is equipped with a standardized installation interface adapted to the integrated three-electrode testing unit 3, which facilitates the quick disassembly and calibration of the probe and effectively improves the reproducibility and efficiency of the experiment.

[0032] 2. Multi-stage sealing assembly 2 like Figure 2 As shown, the multi-stage sealing assembly 2 is used to achieve reliable sealing and high-voltage insulation between the working electrode 301 and the reactor lid. It adopts a composite design of "conical surface seal + high-temperature ceramic insulation + rear hydraulic compensation".

[0033] In this embodiment, the electrode body 201 (i.e., the extension of the working electrode 301) passes through a high-strength alloy sleeve 203 with an inner conical surface, and a flexible graphite gasket or mica gasket 205 is filled between them to form a primary seal. A metal O-ring 204 is used for the main seal between the outside of the sleeve 203 and the reactor lid. This O-ring is preferably made of Inconel alloy to withstand high temperature and high pressure environments. A pressurized chamber 202 is provided at the rear end of the electrode, and a micro hydraulic pump (not shown in the figure) is used to make the pressure in this chamber slightly higher than the pressure of the medium inside the reactor, forming reverse pressure compensation. Preferably, this reverse pressure difference is controlled within the range of 0.1 to 0.5 bar. All parts involving insulation between the electrode and metal components are completely covered with Al2O3 or ZrO2 ceramic insulators to ensure insulation reliability under extreme operating conditions.

[0034] 3. Integrated three-electrode test unit like Figure 1 and Figure 3 As shown, the integrated three-electrode test unit 3 is a modular probe structure that can be inserted into the reactor as a whole. It integrates a working electrode 301, an auxiliary electrode 303, and a high-temperature and high-pressure reference electrode 302.

[0035] In this embodiment, the working electrode 301 is a metal or alloy rod to be tested. The geometric area of ​​its test working surface is pre-calibrated and fixed, and the area error is preferably controlled within ≤±5% to ensure the accuracy of the Cottrell equation fitting. The auxiliary electrode 303 is preferably a platinum-iridium alloy wire, which has both excellent conductivity and chemical inertness. The high-temperature and high-pressure reference electrode 302 is preferably an Ag / AgCl external pressure balanced electrode, which is connected to the corrosive solution through a capillary salt bridge 304. Preferably, the capillary salt bridge 304 has a porous ceramic diaphragm 305 (pore size, for example, ≤2μm) at the front end and an external pressure balancing valve 306 connected in series at the rear end to jointly ensure the long-term stability of the reference electrode potential under high temperature and high pressure and effectively isolate the corrosive medium contamination. It should be noted that other reference electrodes suitable for high-temperature and high-pressure aqueous solutions (such as Pd / H2 electrodes) can also be selected according to the specific test medium.

[0036] 4. Safety control subsystem 4 and data acquisition unit 5 Safety control subsystem 4 includes temperature sensors, pressure sensors, over-temperature and over-pressure audible and visual alarm devices, and automatic interlocking pressure relief valves, which are used to monitor the working conditions in real time and ensure experimental safety.

[0037] like Figure 1 As shown, the data acquisition unit 5 includes a potentiostat 501 and a high-precision data logger 502. The potentiostat 501 is connected to the electrodes inside the reactor via a high-voltage through-chamber electrical connector. This connector is a corrosion-resistant, sealed structure integrated into the reactor lid, and its interface is equipped with a ceramic insulating bushing. The high-precision data logger 502 has a sampling rate of no less than 100 Hz and supports continuous acquisition for no less than 24 hours. Its supporting control software supports customizable potential step parameters (amplitude, hold time) and can realize synchronous data recording, storage, and automated fitting analysis based on the Cottrell equation.

[0038] II. Testing Methods The testing method using the above system provided by this invention will be described in detail below using "in-situ characterization of FeCO3 film growth in X65 pipeline steel in CO2 environment" as an example.

[0039] Step S1: System preparation and baseline testing (without membrane) Assemble the integrated three-electrode test unit 3. The working electrode 301 is made of X65 pipeline steel, and its working surface is pre-calibrated. Install the test unit in the reactor and ensure it is sealed. Inject a deoxygenated 3wt.% NaCl solution into the reactor 1, introduce CO2 gas, and raise the temperature and pressure to the target operating conditions (100℃, total pressure 30 bar). After the open circuit potential of the working electrode stabilizes for 24 hours, conduct the first potential step experiment: apply a step signal from the open circuit potential to -1.2 V (vs. Ag / AgCl) through the potentiostat 501 to make the hydrogen ion reduction reaction reach the limiting diffusion state. Record the transient current curve (corresponding to) at a sampling rate of 200 Hz. Figure 4 (Curve 8), and the bulk diffusion coefficient D of hydrogen ions was obtained by fitting the Cottrell equation, which served as the benchmark for the membrane-free state (corresponding to curve 8). Figure 5 (Middle line 9).

[0040] Step S2, In-situ Film Formation and Process Monitoring The potential of the working electrode 301 was controlled near the self-corrosion potential, allowing it to naturally corrode and form an FeCO3 film in a CO2 environment. The potential step experiment in step S1 was repeated on days 1, 3, and 7 after film formation (corresponding to...). Figure 4 (Signal 6), obtain the transient current curves for each film formation stage (corresponding to) Figure 4 (Middle curve 7).

[0041] Step S3: Data Analysis and Parameter Extraction Comparative analysis of the i(t) curves and i~t curves at each stage -1 / 2 Figure (as shown) Figure 5 As shown in the figure, the current response decreases significantly with increasing film formation time. Using the bulk diffusion coefficient D obtained in step S1 as a benchmark, a porous media diffusion model ( (where the tortuosity τ of the sedimentary layer is taken as an empirical value of 1.5 to 2.0), and nonlinear fitting is performed on the data of the 7th day (corresponding to...). Figure 5 (Linear 10), inverting the effective diffusion coefficient of the FeCO3 film. The equivalent thickness L is calculated, and the porosity ε is obtained.

[0042] Step S4: Experiment Termination and System Maintenance After the test, the pressure is slowly released at a rate not exceeding 0.5 bar / min via safety control subsystem 4, and the device is disassembled after cooling. Post-analysis (such as SEM, XRD, etc.) can be performed on the electrode surface to verify the inversion results. The sealing and vulnerable parts are replaced, and the system is cleaned in preparation for subsequent experiments.

[0043] The results of this embodiment show that the system of the present invention can clearly capture the dynamic process of FeCO3 membrane growth, and the inverted membrane parameters (such as the decrease in porosity) are consistent with the observed trend of microstructure, which verifies the effectiveness and reliability of the method.

[0044] To make the system of the present invention more versatile and practical, the following extended embodiments can also be adopted: The integrated three-electrode test unit 3 can be designed as a modular pluggable structure, which facilitates quick replacement of working electrodes 301 of different materials or reference electrodes 302 of different types to meet diverse material testing needs.

[0045] The flexible graphite gaskets, metal O-rings, and other vulnerable parts in the multi-stage sealing assembly 2 can be designed as standardized replaceable parts to reduce long-term maintenance costs.

[0046] Data acquisition unit 5 can integrate a wireless data transmission module to enable remote monitoring and data management under hazardous conditions, further improving operational safety.

Claims

1. An electrochemical potential step transient testing system for high-temperature and high-pressure diffusion control, comprising a high-temperature and high-pressure reactor, an integrated three-electrode testing unit, a multi-stage sealing assembly, a safety control subsystem, and a data acquisition unit; The high-temperature and high-pressure reactor is used to contain corrosive media to simulate high-temperature and high-pressure industrial corrosion conditions. The integrated three-electrode testing unit is a modular probe structure that can be inserted into the reaction vessel as a whole, and integrates a working electrode, an auxiliary electrode, and a high-temperature and high-pressure reference electrode. The multi-stage sealing assembly is used to achieve sealing and insulation between the working electrode and the reactor lid, and adopts a composite design of conical seal - high temperature ceramic insulation - rear hydraulic compensation; The safety control subsystem is used to monitor the temperature and pressure of the reactor in real time, and has over-temperature and over-pressure alarm and automatic interlocking pressure relief function. The data acquisition unit includes a potentiostat and a high-precision data logger, which are connected to the electrodes inside the reactor via a high-voltage through-chamber electrical connector. The control software enables the application of potential step signals, recording of transient current-time curves, and analysis and processing.

2. The electrochemical potential step transient testing system according to claim 1, characterized in that: The composite design structure of the conical seal-high temperature ceramic insulation-rear hydraulic compensation is as follows: The working electrode passes through a high-strength alloy sleeve with an inner conical surface. A flexible graphite gasket or mica gasket is filled between the two as a primary seal. A metal O-ring is used for the main seal between the outside of the sleeve and the vessel lid. A pressurized chamber is provided at the lead-out end of the working electrode outside the vessel. A micro hydraulic pump is used to make the pressure inside the chamber slightly higher than the pressure of the medium inside the vessel to form reverse pressure compensation.

3. The electrochemical potential step transient testing system according to claim 2, characterized in that: The metal O-ring is made of Inconel nickel alloy; the reverse pressure difference formed by the micro hydraulic pump driving the pressurized chamber is 0.1 to 0.5 bar higher than the pressure of the medium inside the high-temperature and high-pressure reactor.

4. The electrochemical potential step transient testing system according to any one of claims 1-3, characterized in that: The working electrode is a metal or alloy rod to be tested, the auxiliary electrode is a platinum-iridium alloy wire, and the high-temperature and high-pressure reference electrode is an Ag / AgCl external pressure balanced electrode.

5. The electrochemical potential step transient testing system according to any one of claims 1-4, characterized in that: The high-pressure through-chamber electrical connector is a corrosion-resistant and sealed structure integrated into the lid of the high-temperature and high-pressure reactor, and its interface is provided with an Al2O3 or ZrO2 ceramic insulating bushing.

6. The electrochemical potential step transient testing system according to any one of claims 1-5, characterized in that: The kettle body of the high-temperature and high-pressure reaction kettle is made of hastelloy or duplex stainless steel; the high-temperature and high-pressure reaction kettle is suitable for corrosive medium containing CO2, H2S and / or Cl - with pH value of 3-10, and can continuously and stably run for more than 72 hours under the working condition of 120-250 DEG C and 2.7-350 bar.

7. The electrochemical potential step transient testing system according to any one of claims 1-6, characterized in that: On the modular probe of the integrated three-electrode test unit, the test working surface of the working electrode has a pre-calibrated and fixed geometric area.

8. A method for testing electrochemical potential step transients for high-temperature, high-pressure diffusion control, using the testing system described in any one of claims 1-7, comprising the following steps: Step S1: System setup and pre-stabilization: Install the integrated three-electrode test unit in the high-temperature and high-pressure reactor through a multi-stage sealing assembly, inject corrosive medium into the reactor, introduce the target gas to the set partial pressure, raise the temperature and pressure to the target working condition, and wait for the open circuit potential of the working electrode to stabilize. Step S2: Application of diffusion-controlled potential step: A transient potential step from a stable open-circuit potential to a preset target potential is applied to the working electrode using a potentiostat. The selection of the target potential ensures that the electrode reaction is completely controlled by the diffusion step. Step S3: Transient current response recording: The current-time transient response curve of the working electrode after a potential step is synchronously recorded using a high-precision recorder at a sampling rate of not less than 100 Hz. Step S4: Analysis of diffusion parameters and deposited film characteristics: The current-time transient response curve is analyzed. When there is no significant deposited film on the working electrode surface, the initial stage of the curve is fitted based on the Cottrell equation to calculate the bulk diffusion coefficient of the reactants. When there is a porous deposited film on the working electrode surface, the effective diffusion coefficient, porosity, and effective thickness of the deposited layer are inverted by comparing the transient response curves of different film formation stages, using a porous medium diffusion model.

9. The test method according to claim 8, characterized in that: The selection of the target potential is specifically as follows: for the anodic dissolution reaction, a step to a positive potential that allows the reaction to reach the limiting diffusion current density; for the cathodic reduction reaction, a step to a negative potential that allows the reaction to reach the limiting diffusion current density.

10. The test method according to claim 8 or 9, characterized in that: In step S4, when a porous deposited film exists on the surface of the working electrode, the inversion specifically includes: using the bulk diffusion coefficient measured when the electrode surface is clean as a benchmark, fitting the transient response curve after film formation using a nonlinear fitting method, based on the formula... Simultaneous inversion of the effective diffusion coefficient of the sedimentary layer Porosity and effective thickness ,in Tortuosity of the sedimentary layer; The method further includes: first applying a step potential in the first direction and holding it for a period of time, then applying a step potential in the opposite direction, and recording the complete transient current response under the two potential changes in order to analyze the structural evolution characteristics of the deposited layer under dynamic potential.

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