Method for EIS characterization of powdery sample

Abstract

The invention discloses an EIS characterization method for a powdery sample. The method comprises the following steps: drying; grinding; weighing: preparing a sample solution, namely slowly pouring a sample weighed on weighing paper into a clean sample tube, and accurately transferring a certain amount of dispersing agent and binder by using a pipette; performing ultrasonic dispersion; selecting a glassy carbon electrode; selecting the glassy carbon electrode to be L-shaped according to the structure; polishing the glassy carbon electrode; dispensing: dispensing 2.4 mL of the electrode with the diameter of 3 mm and 10mL of the electrode with the diameter of 5 mm in order to ensure that the surface of the electrode is uniformly covered with a sample; coating drying; electrolyte preparation: proper electrolyte is selected and prepared according to experimental conditions; and design of a three-electrode system: adopting the three-electrode system for EIS characterization. The invention aims to provide a method for EIS characterization of a powdery sample, and solves the problem of reaction mechanism of the sample in the electrochemical reaction process.

Description

Technical Field

[0001] The invention belongs to the field of detection technology, and in particular relates to a method for EIS characterization of powdered samples. Background Art

[0002] Electrochemical Impedance Spectroscopy (EIS): An AC signal with a small amplitude and different frequencies is applied to the electrochemical system, and the ratio of the AC signal voltage to the current (this ratio is the impedance of the system) is measured as the frequency of the sine wave ω changes, or the phase angle Φ of the impedance changes as ω changes.

[0003] There are two commonly used electrochemical impedance spectroscopy, namely Nyquist diagram and Bode diagram. In photocatalytic research, Nyquist diagram is more common. In the Nyquist diagram, Z' (real part) and Z" (imaginary part) show the electron transfer resistance (Rct) on the electrode surface. Its value is the same as the diameter of the semicircular part and can be used to describe the characteristics of the interface between the electrode and the electrolyte. The Nyquist diagram consists of two parts. The semicircular part in the high-frequency area corresponds to the electron transport limitation process, and the linear part in the low-frequency area corresponds to the diffusion limitation process. By calculating the electron transfer resistance Rct on the electrode surface, some phenomena in the experimental processes such as photocatalysis and electrocatalysis can be explained.

[0004] In recent years, due to the rapid development of frequency response analyzers, the test accuracy of AC impedance has become higher and higher, and it is currently widely used in the field of electrochemistry. Electrochemical impedance spectroscopy is a very important method in electrochemical testing technology. It is an important means to analyze electrode process dynamics, double layer and diffusion, and study the mechanism of electrode materials, solid electrolytes, conductive polymers and corrosion protection. Summary of the invention

[0005] The purpose of the present invention is to provide a method for EIS characterization of powdered samples to solve the problem of reaction mechanism of samples during electrochemical reaction.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for EIS characterization of a powdered sample, comprising the following steps:

[0008] Drying: Put the powdered sample into a glass drying dish, put the glass drying dish into a vacuum drying oven, and dry it at a specified temperature until the mass of the sample no longer changes;

[0009] Grinding: Suitable for powder materials that are easy to agglomerate and some brittle materials; for many bulk and brittle materials, directly use a clean pestle and mortar to grind them; during the grinding process, use a medicine spoon to scrape the sample on the mortar wall and pestle head into the mortar;

[0010] Weighing: Use a high-precision electronic balance to weigh a certain mass of powder sample;

[0011] Sample solution preparation: slowly pour the sample weighed on the weighing paper into a clean sample tube, and use a pipette to accurately transfer a certain amount of dispersant and binder;

[0012] Ultrasonic dispersion: After the sample solution is prepared, the next step is to perform ultrasonic dispersion to ensure the uniformity of the material. For materials that are easy to disperse, simple water bath ultrasonic treatment is sufficient. To prevent solvent volatilization, the sample is sealed with sealing film and the ultrasonic treatment time exceeds 1 hour. For materials that are difficult to disperse, a handheld ultrasonic cell disruptor is used for treatment.

[0013] Selection of glassy carbon electrode: L-type glassy carbon electrode is selected according to its structure; L-type glassy carbon electrode is to place the electrodes parallel to each other; Using L-type glassy carbon electrode: Because it is placed opposite to the counter electrode, it can better capture the directional migration of reactant ions in the electrolyte, and this directional migration helps to improve the efficiency and rate of the reaction; The gas generated by the L-type glassy carbon electrode escapes upward under the pressure in the electrolyte, which is conducive to the desorption of gas;

[0014] Polishing of glassy carbon electrode: Use wet lens paper to gently wipe the electrode surface to remove dirt and ensure that the electrode surface is smooth; then sprinkle a small amount of 0.3 micron polishing powder on the polishing disc, add a small amount of deionized water, and stir it slightly with the insulating part of the glassy carbon electrode to form a polishing slurry; hold the glassy carbon electrode vertically, and use your elbow to apply force evenly to move the electrode slowly in the polishing slurry, with a circular or "8" shape; polish for 2-3 minutes, ensuring that the electrode surface is pressed on the polishing disc and cannot be skewed to maintain the flatness of the electrode surface; rinse the electrode surface with deionized water, then place the polished electrode head vertically in a small beaker containing a small amount of deionized water, place it in an ultrasonic water bath, and ultrasonically clean it for 2-3 minutes and repeat three times to ensure that there is no residual polishing slurry on the electrode surface; finally, blow dry the electrode or let it dry at room temperature;

[0015] Drip coating: The process aims to ensure that the electrode surface is evenly covered with the sample. For a 3mm diameter electrode, 2.4mL is dripped, and for a 5mm diameter electrode, 10mL is dripped.

[0016] Coating drying: Coating drying can be achieved by natural air drying, low temperature drying or light baking, the specific method depends on the volatility of the solvent;

[0017] Preparation of electrolyte: Select and configure the appropriate electrolyte according to the experimental conditions to prepare for the next test. Note that the same electrolyte should be selected for the same set of experiments;

[0018] Design of three-electrode system: EIS characterization adopts a three-electrode system, with a platinum sheet or carbon rod as the counter electrode, a saturated calomel electrode or Ag / AgCl as the reference electrode, and a glassy carbon electrode as the working electrode; note that the same three-electrode system should be selected for the same set of experiments.

[0019] Furthermore, the amount of the binder should be moderate. Using an excessive amount of binder may shield the active sites of the catalyst, while too little binder may cause the electrode to fall off.

[0020] Furthermore, the dispersant is an anhydrous ethanol dispersant.

[0021] Furthermore, the grinding disc is made of suede.

[0022] Furthermore, the polishing powder contains Al2O3.

[0023] Further, when the coating is dry, the volatile ethanol is simply dried, but care is taken to avoid overheating or close heat sources that may damage the sample and electrode.

[0024] Furthermore, ITO glass is not used as the working electrode.

[0025] Compared with the prior art, the beneficial technical effects of the present invention are:

[0026] The purpose of the present invention is to provide a method for EIS characterization of powdered samples, solve the problem of reaction mechanism of samples in the electrochemical reaction process, and realize EIS characterization of powdered samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described below in conjunction with the accompanying drawings.

[0028] Figure 1 This is the impedance test parameter setting page for CHI 760E electrochemical workstation;

[0029] Figure 2 This is the page for saving impedance test data results of CHI 760E electrochemical workstation. DETAILED DESCRIPTION

[0030] The present invention is further described in detail below in conjunction with embodiments:

[0031] This embodiment provides a sample preparation and testing method for EIS characterization of a powdered sample.

[0032] Specifically, for the powdered FeOOH sample obtained by the hydrothermal synthesis method, in order to explore its electrocatalytic water splitting activity, it is necessary to perform EIS characterization analysis on it.

[0033] Specifically, this embodiment uses the domestically produced Chenhua CHI 760E electrochemical workstation as an example to perform EIS testing.

[0034] The specific sample preparation and testing process is as follows:

[0035] 1. The powdered FeOOH sample was completely dried in a vacuum oven and then ground into an agate mortar.

[0036] 2. Use an electronic balance to weigh 5 mg of the ground FeOOH sample, then transfer it to a pre-prepared small sample tube in time, add 250 mL of anhydrous ethanol dispersant and 250 mL of deionized water, and then add 20 uL of nafion reagent (binder).

[0037] 3. Place the sample tube on the sample rack, then put it into the ultrasonic disperser to disperse the powder sample in the solution into a suspension. During the ultrasonic process, avoid excessive ultrasonic time to avoid excessively high sample temperature.

[0038] 4. Sprinkle a small amount of 0.3 micron polishing powder on the suede, and add a small amount of deionized water to the polishing powder. Use a glass rod to mix the polishing powder and deionized water, then hold the lower half of the glassy carbon electrode vertically and start polishing the electrode until the conductive part of the glassy carbon electrode is smooth and shiny.

[0039] 5. Use a pipette to transfer the sample suspension and carefully spread it on the conductive part of the glassy carbon electrode. Allow it to air dry naturally to become the working electrode for EIS testing.

[0040] 6. Prepare 1M KOH solution, use a measuring cylinder to measure 50mL into the electrochemical test device, use a platinum sheet as the counter electrode, a saturated calomel electrode as the reference electrode, and a glassy carbon electrode as the working electrode. Assemble the three-electrode system as required, with the red electrode clamp for the counter electrode, the white electrode clamp for the reference electrode, and the green electrode clamp for the working electrode. Note that the bottom of the working electrode should avoid contact with the device wall or the counter electrode and reference electrode.

[0041] 7. Press the power button on the electrochemical workstation and open the CHI 760E test software on the computer. Click Setup-Hardware Test to connect the electrochemical workstation to the test software. When you hear a sound from the workstation, it means that the connection is complete.

[0042] 8. Set the open circuit voltage: Click Setup-Technique Selection-OCPT (Open Circuit Potential-Time)-OK. When the workstation is running smoothly (i.e. the measured value is a line parallel to the X-axis with very small fluctuations), record the open circuit voltage scanned in the lower left corner of the software. This will be used when entering parameters later.

[0043] 9. Click Setup-Technique Selection-IMP(ACImpedance)-OK, and then set the parameters. The parameter setting page is as follows: Figure 1 As shown. Enter the electrochemical impedance parameters page, and fill in the open circuit voltage value in Init (V) according to the open circuit voltage obtained in the previous step. The frequency range of the CHI 760E electrochemical workstation is 0.01-100000Hz. The smaller the low frequency setting value, the longer the test time. In this embodiment, the High Frequency (frequency at high frequency) is set to 100000Hz, and the Low Frequency (frequency at low frequency) is set to 0.1Hz. Use the default values ​​for Amplitude (amplitude) and Quiet Time (quiet time), click OK, and prepare for the electrochemical impedance test.

[0044] 10. Click (icon Represents running the test, represents pause, ■ represents termination), run the experiment, the AC impedance test page appears, and the remaining time of the experiment is displayed in the upper right corner. The scanned data should be kept continuous as much as possible.

[0045] 11. Data conversion: Click Graphics-Graph Options, enter the Graphics Options dialog box, and select Nyquist: Z”-Z’. Figure 2 At this time, the computer will automatically convert the experimental data. After the computer automatically converts the data, the files are saved in *.bin and *.txt formats, waiting for the next step of data processing and analysis.

[0046] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for EIS characterization of powdered samples, characterized in that: The steps include: Drying: Put the powdered sample into a glass drying dish, put the glass drying dish into a vacuum drying oven, and dry it at a specified temperature until the mass of the sample no longer changes; Grinding: Suitable for powder materials that are easy to agglomerate and some brittle materials; for many bulk and brittle materials, directly use a clean pestle and mortar to grind them; during the grinding process, use a medicine spoon to scrape the sample on the mortar wall and pestle head into the mortar; Weighing: Use a high-precision electronic balance to weigh a certain mass of powder sample; Sample solution preparation: slowly pour the sample weighed on the weighing paper into a clean sample tube, and use a pipette to accurately transfer a certain amount of dispersant and binder; Ultrasonic dispersion: After the sample solution is prepared, the next step is to perform ultrasonic dispersion to ensure the uniformity of the material. For materials that are easy to disperse, simple water bath ultrasonic treatment is sufficient. To prevent solvent volatilization, the sample is sealed with sealing film and the ultrasonic treatment time exceeds 1 hour. For materials that are difficult to disperse, a handheld ultrasonic cell disruptor is used for treatment. Selection of glassy carbon electrode: L-type glassy carbon electrode is selected according to its structure; L-type glassy carbon electrode is to place the electrodes parallel to each other; Using L-type glassy carbon electrode: Because it is placed opposite to the counter electrode, it can better capture the directional migration of reactant ions in the electrolyte, and this directional migration helps to improve the efficiency and rate of the reaction; The gas generated by the L-type glassy carbon electrode escapes upward under the pressure in the electrolyte, which is conducive to the desorption of gas; Polishing of glassy carbon electrode: Use wet lens paper to gently wipe the electrode surface to remove dirt and ensure that the electrode surface is smooth; then sprinkle a small amount of 0.3 micron polishing powder on the polishing disc, add a small amount of deionized water, and stir it slightly with the insulating part of the glassy carbon electrode to form a polishing slurry; hold the glassy carbon electrode vertically, and use your elbow to apply force evenly to move the electrode slowly in the polishing slurry in a circular or "8" shape; polish for 2-3 minutes, ensuring that the electrode surface is pressed on the polishing disc and cannot be skewed to maintain the flatness of the electrode surface; rinse the electrode surface with deionized water, then place the polished electrode head vertically in a small beaker containing a small amount of deionized water, place it in an ultrasonic water bath, and ultrasonically clean it for 2-3 minutes and repeat three times to ensure that there is no residual polishing slurry on the electrode surface; finally, blow dry the electrode or let it dry at room temperature; Drip coating: The process aims to ensure that the electrode surface is evenly covered with the sample. For a 3mm diameter electrode, 2.4mL is dripped, and for a 5mm diameter electrode, 10mL is dripped. Coating drying: Coating drying can be achieved by natural air drying, low temperature drying or light baking, the specific method depends on the volatility of the solvent; Preparation of electrolyte: Select and configure the appropriate electrolyte according to the experimental conditions to prepare for the next test. Note that the same electrolyte should be selected for the same set of experiments; Design of three-electrode system: EIS characterization adopts a three-electrode system, with a platinum sheet or carbon rod as the counter electrode, a saturated calomel electrode or Ag / AgCl as the reference electrode, and a glassy carbon electrode as the working electrode; note that the same three-electrode system should be selected for the same set of experiments.

2. The method for EIS characterization of powdered samples according to claim 1, characterized in that: The amount of the binder should be moderate. Using too much binder may shield the active sites of the catalyst, while too little binder may cause the electrode to fall off.

3. The method for EIS characterization of a powdered sample according to claim 1, characterized in that: The dispersant is an anhydrous ethanol dispersant.

4. The method for EIS characterization of a powdered sample according to claim 1, characterized in that: The grinding disc is made of suede.

5. The method for EIS characterization of powdered samples according to claim 1, characterized in that: Polishing powder is not Al2O3.

6. The method for EIS characterization of powdered samples according to claim 1, characterized in that: When the coating is dry, simply allow the volatile ethanol to dry, but be careful to avoid overheating or close heat sources that may damage the sample and electrode.

7. The method for EIS characterization of a powdered sample according to claim 1, characterized in that: ITO glass is not used as the working electrode.

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