Built-in reference electrode, preparation method thereof and fuel cell

Abstract

The invention belongs to the field of cell testing, and particularly relates to a built-in reference electrode, a preparation method thereof and a fuel cell. The built-in reference electrode comprises a reference electrode and an insulating layer arranged on the outer side of the reference electrode; the parts, extending out of the insulating layer, of the two ends of the reference electrode are respectively an internal electrode and an external electrode; a catalyst coating is arranged at the end part of the internal electrode; according to the built-in reference electrode designed by the invention, the built-in reference electrode in the battery is realized through a catalyst coated on the reference electrode, a wrapped insulating layer and a proper insertion position, and the built-in reference electrode is different from the traditional method that the reference electrode needs to be led out for external measurement.

Description

Technical Field

[0001] The invention belongs to the field of battery testing, and in particular relates to a built-in reference electrode and a preparation method thereof, and a fuel cell. Background Art

[0002] Issues such as single-chip consistency, fault warning, and lifespan prediction in proton exchange membrane fuel cells continue to hinder their large-scale development and application. To address these issues, we must delve into the electrochemical process at the microscopic level under real fuel cell operating conditions. By designing novel electrode testing systems to examine the voltage loss and electrochemical microenvironment across fuel cell components and interfaces under operating conditions, we can improve fuel cell testing technology.

[0003] The current method for determining fuel cell voltage is to extend a lead from each of the two bipolar plates of a single cell. The voltage difference between the two leads is the voltage of the single-point cell, which is also known as the relative potential. However, when evaluating the electrochemical performance of fuel cell components, such as catalysts, carbon paper, and bipolar plates, a three-electrode test system is used to measure the absolute potential in a specific solution system. The two cannot be directly correlated during fuel cell operation.

[0004] To accurately determine the cathode and anode potentials of a fuel cell during operation, a stable reference electrode must be introduced into the fuel cell structure to measure the potential difference between the reference electrode and the cathode and anode. Existing solutions include extending a reference electrode outside the fuel cell body through a salt bridge and buffer solution to measure the potential difference between the reference electrode and the cathode and anode. Another approach involves modifying the bipolar plate by creating a small flow channel adjacent to the existing bipolar plate flow channel, allowing hydrogen to flow through the channel and allowing the reference electrode to be used for measurement.

[0005] However, these solutions change the original test structure of the fuel cell and are more complicated to assemble. In the fuel cell stack, due to the thin thickness of the bipolar plates and proton exchange membranes, it is difficult to perform secondary processing after processing and forming. The introduced reference electrode cannot be integrated with the existing fuel cell system, and it is impossible to achieve synchronous online monitoring of the potential during the operation of the fuel cell stack composed of multiple single cells. Summary of the Invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a built-in reference electrode, a preparation method thereof, and a fuel cell.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A built-in reference electrode comprises a reference electrode and an insulating layer arranged outside the reference electrode; the portions of the reference electrode extending out of the insulating layer at both ends are the internal electrode and the external electrode respectively; the end portion of the internal electrode is provided with a catalyst coating; the catalyst coating is a hydrogen oxidation catalyst.

[0009] The hydrogen oxidation catalyst is one of a platinum-carbon catalyst, a ruthenium-carbon catalyst, or an iridium-carbon catalyst, or a mixture thereof.

[0010] The reference electrode is a platinum metal electrode or a platinum alloy electrode, and is in the shape of a wire, a mesh or a sheet. Preferably, the reference electrode is in the shape of a wire; and the internal electrode is in the shape of a mesh or a sheet.

[0011] The present invention also includes a method for preparing the built-in reference electrode, comprising the following steps: 1) coating the outer side of the reference electrode with a polytetrafluoroethylene emulsion to obtain an insulating layer; 2) coating the end portion of the internal electrode of the reference cell with a catalyst slurry to obtain a catalyst coating; the order of steps 1) and 2) is not particular;

[0012] Preferably, the catalyst slurry comprises a hydrogen oxidation catalyst, water, isopropanol and Nafion, the concentration of the hydrogen oxidation catalyst is 2 mg / mL, and the volume ratio of the other three liquid solvents is water: isopropanol: Nafion is 4:3:0.004.

[0013] The present invention also includes a fuel cell, comprising an anode plate, a cathode plate, and a plurality of single cells arranged between the anode plate and the cathode plate; each of the single cells is composed of a bipolar plate, a cathode carbon paper, a membrane electrode, an anode carbon paper, and a bipolar plate arranged in sequence; the built-in reference electrode is arranged between the membrane electrode and the anode carbon paper.

[0014] The membrane electrode comprises a membrane electrode frame and a membrane electrode catalyst arranged in the membrane electrode frame; the internal electrode of the reference electrode is connected to the membrane electrode catalyst; the insulating layer of the built-in reference electrode is in contact with the membrane electrode frame.

[0015] The anode plate and cathode plate respectively include an end plate and a current collector.

[0016] The external electrode of the reference electrode is connected to the measuring device; the two bipolar plates adjacent to the membrane electrode are respectively connected to the measuring device as the working electrode and the counter electrode.

[0017] The thickness of the reference electrode is 20-100 μm.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The built-in reference electrode designed by the present invention realizes the built-in reference electrode inside the battery through the catalyst coated on the reference electrode, the wrapped insulating layer and the appropriate insertion position, which is different from the traditional method that requires the reference electrode to be led out for external measurement. The fuel cell with the built-in reference electrode realizes the synchronous measurement of the cathode potential (cathode polarization), the anode potential (anode polarization) and the battery polarization, which is different from the traditional method that requires the separate measurement of the anode and cathode polarization, eliminating the experimental error. At the same time, during the test process, even if the fuel cell stack is in an operating state, online monitoring can be achieved without affecting the operation of the fuel cell. The electrochemical workstation can also be used to synchronously measure the electrochemical impedance of the cathode, anode and the whole, enriching the characterization test means of the fuel cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the overall structure of a fuel cell reference electrode according to an embodiment of the present invention;

[0021] Figure 2 A schematic diagram of the partial structure of a fuel cell reference electrode according to an embodiment of the present invention;

[0022] Figure 3 Schematic diagram of a reference electrode in a fuel cell reference electrode according to an embodiment of the present invention;

[0023] Figure 4 This is a diagram of the polarization curves of the anode, cathode, and the entire battery measured using the fuel cell reference electrode described in an embodiment of the present invention. DETAILED DESCRIPTION

[0024] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and the best embodiments.

[0025] Figure 1-3 A built-in reference electrode 6 is shown, comprising a reference electrode 61 and an insulating layer 62 arranged on the outside of the reference electrode; the portions of the reference electrode extending out of the insulating layer at both ends are the internal electrode and the external electrode, respectively; the end portion of the internal electrode is provided with a catalyst coating; the catalyst coating is a hydrogen oxidation catalyst, including a platinum-carbon catalyst, a ruthenium-carbon catalyst, an iridium-carbon catalyst, etc.

[0026] The reference electrode is a platinum metal electrode or a platinum alloy electrode, and is in the shape of a wire, a mesh or a sheet. Preferably, the reference electrode is in the shape of a wire; the internal electrode is in the shape of a mesh or a sheet, and the mesh or sheet shape is more conducive to contact with the fuel cell.

[0027] The preparation method of the built-in reference electrode includes the following steps: 1) coating the outer side of the reference electrode with polytetrafluoroethylene emulsion to obtain an insulating layer; specifically, a diluted polytetrafluoroethylene emulsion can be applied to the surface of the reference electrode with a brush; 2) coating the end portion of the internal electrode of the reference cell with a catalyst slurry to obtain a catalyst coating; the catalyst slurry is formed by mixing a platinum carbon catalyst, water, isopropanol and Nafion solution, wherein the concentration of the hydrogen oxidation catalyst is 2 mg / mL, and the volume ratio of the other three liquid solvents is water: isopropanol: Nafion of 4:3:0.004; a small amount of the above-configured catalyst slurry is dripped onto the end portion of the electrode by an immersion method and dried naturally in an environment.

[0028] Figure 1-3 A fuel cell is shown, comprising an anode plate, a cathode plate, and multiple single cells disposed between the anode and cathode plates. The anode and cathode plates each include an end plate 1 and a current collector 2. Each single cell comprises a bipolar plate 3, cathode carbon paper, a membrane electrode 5, anode carbon paper, and a bipolar plate 3, arranged in this order. Both the cathode and anode carbon paper are made of carbon paper 4. A built-in reference electrode 6 is disposed between the membrane electrode and the anode carbon paper.

[0029] The membrane electrode 5 ( Figure 2 (shown) includes a membrane electrode frame 52 and a membrane electrode catalyst 51 arranged in the membrane electrode frame; the internal electrode of the reference electrode is connected to the membrane electrode catalyst 51; the insulating layer 62 of the built-in reference electrode is in contact with the membrane electrode frame 52. The electrode portion 61 can be made of platinum wire or platinum alloy wire, etc., and the part of the electrode portion 61 that contacts the membrane electrode catalyst portion 51, that is, the internal electrode portion, can be replaced with a platinum mesh, a platinum alloy mesh, a platinum sheet, a platinum alloy sheet, etc. The internal electrode and the membrane electrode catalyst 51 are in full contact and are conductive during the operation of the fuel cell; the membrane electrode frame portion 52 does not participate in the electrochemical reaction involved in the operation of the fuel cell, and isolates the direct electron transfer between the two adjacent carbon papers 4. Therefore, it is necessary to wrap the insulating layer 62 where the built-in reference electrode 6 as a whole contacts the membrane electrode frame portion 52 to prevent the inserted reference electrode from contacting the adjacent carbon paper 4 or bipolar plate 3, causing a short circuit.

[0030] The end of the internal electrode of the reference electrode that contacts the membrane electrode catalyst portion 51 is coated with a catalyst coating. Due to the influence of anode polarization, the phase potential of the electrolyte membrane on the anode side should be lower than the anode solid phase potential. The introduction of the internal reference electrode allows for relatively accurate measurement of this process. Furthermore, the end of the internal electrode is coated with a catalyst coating, and the hydrogen concentration is relatively saturated, indicating that a hydrogen oxidation reaction is occurring. This reaction itself serves as a standard hydrogen electrode to determine the zero point of the electrode potential. Therefore, the internal reference electrode is suitable as a reference electrode for testing in a three-electrode system.

[0031] The insulating layer 62 of the reference electrode is a polytetrafluoroethylene layer. A polytetrafluoroethylene dilution solution can be applied to the surface of the electrode part 61 with a brush to isolate the contact between the membrane electrode frame parts 52 on both sides and the bipolar plate 4, avoiding the risk of short circuit.

[0032] The thickness of the reference electrode is 20-100μm. The thickness of the bipolar plate 3 is about 500 microns, the thickness of the carbon paper 4 is about 150 microns, and the thickness of the membrane electrode 5 is about 10 microns. The thickness of the introduced built-in reference electrode 6 as a whole is about 100 microns, and a higher processing method can reduce it to 20 microns, which is much smaller than the thickness of the bipolar plate 3 and the carbon paper 4, and is fully suitable for the overall assembly structure. By implementing this solution, the number of single cells, the number of reference electrodes 6, and the insertion position of the reference electrode 6 as a whole can be increased or decreased according to the test requirements of the fuel cell stack to be tested. Compared with the traditional fuel cell stack structure solution, it neither changes the structure of the fuel cell stack nor affects the normal operation of the fuel cell stack.

[0033] The external electrode of the reference electrode is connected to the measuring device; the two bipolar plates adjacent to the membrane electrode are respectively connected to the measuring device as the working electrode and the counter electrode.

[0034] In traditional fuel cell stacks, voltage is collected at the current collecting plate 2 and bipolar plate 3. The voltage difference between the current collecting plates 2 on both sides is measured as the total voltage of the fuel cell stack, and the voltage difference between two adjacent bipolar plates 3 is measured as the cell voltage of the single cell between them. The present invention proposes a reference electrode design for online monitoring of the electrode potential of single cells in a fuel cell stack. This design introduces an additional reference electrode into the fuel cell, creating a three-electrode measurement system. During testing, the built-in reference electrode 6 is connected as a reference electrode. Two adjacent bipolar plates 3 serve as both the working electrode and the counter electrode, enabling simultaneous measurement of the anode and cathode. Theoretically, the polarization curve of a battery should be equal to the potential difference between the cathode and the reference electrode, and the potential difference between the anode and the reference electrode. Simultaneous measurement of these three values ​​can eliminate measurement errors at different times and under different conditions, enabling tests including, but not limited to, linear voltammetry, cyclic voltammetry, and AC impedance testing.

[0035] The reference electrode 61, with a portion of its length exposed outside the dimensions of the fuel cell, serves as an external reference electrode for connection to an external voltage measurement device, including but not limited to a voltmeter, data acquisition module, electronic load, or electrochemical workstation. The two bipolar plates adjacent to the membrane electrode being measured serve as the working and counter electrodes for connection to the external voltage measurement device. When measuring anodic polarization, the anode plate serves as the working electrode, and the cathode plate as the counter electrode. When measuring cathodic polarization, the cathode plate serves as the working electrode, and the anode plate as the counter electrode. When measuring cell polarization, the voltage difference between the cathode and cathode plates is directly measured.

[0036] The fuel cell is operated under normal load. When the battery performance reaches stability, the polarization curve test is performed on the battery. The dwell time of each current value is set to 300s, and the average value from 40 seconds before the current step to 10 seconds before the current step is taken. During this process, the current, battery voltage, anode voltage relative to reference electrode 6, and cathode voltage relative to reference electrode 6 are recorded.

[0037] Figure 4 The graphs show the changes in the cell voltage, the anode voltage relative to the reference electrode 6, and the cathode voltage relative to the reference electrode 6 as the current density gradually increases. The results show that the cell voltage is essentially equal to the difference between the anode voltage relative to the reference electrode 6 and the cathode voltage relative to the reference electrode 6. The obtained cell polarization, cathode polarization, and anode polarization curves also conform to the experimental rules.

[0038] The experimental results show that the reference electrode design provided in this application for the synchronous online monitoring of the anode and cathode potentials of single cells in a fuel cell stack can place a stable, reliable and accurate reference electrode inside the fuel cell, and realize the synchronous online monitoring of the electrode potential without affecting the operation of the fuel cell.

[0039] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A built-in reference electrode, characterized in that It includes a reference electrode and an insulating layer arranged on the outside of the reference electrode; the parts of the reference electrode extending out of the insulating layer at both ends are the internal electrode and the external electrode respectively; the end part of the internal electrode is provided with a catalyst coating; the catalyst coating is a hydrogen oxidation catalyst.

2. The built-in reference electrode according to claim 1, characterized in that The hydrogen oxidation catalyst is one of a platinum-carbon catalyst, a ruthenium-carbon catalyst, or an iridium-carbon catalyst, or a mixture thereof.

3. The built-in reference electrode according to claim 1, characterized in that The reference electrode is a platinum metal electrode or a platinum alloy electrode, and is in the shape of a wire, a mesh or a sheet. Preferably, the reference electrode is in the shape of a wire; and the internal electrode is in the shape of a mesh or a sheet.

4. A method for preparing the built-in reference electrode according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: 1) coating the outer side of the reference electrode with polytetrafluoroethylene emulsion to obtain an insulating layer; 2) applying a catalyst slurry to the end portion of the internal electrode of the reference cell to obtain a catalyst coating; steps 1) and 2) are not performed in any particular order; Preferably, the catalyst slurry comprises a hydrogen oxidation catalyst, water, isopropanol and Nafion, the concentration of the hydrogen oxidation catalyst is 2 mg / mL, and the volume ratio of the other three liquid solvents is water: isopropanol: Nafion is 4:3:0.

004.

5. A fuel cell, characterized in that: It comprises an anode plate, a cathode plate and a plurality of single cells arranged between the anode plate and the cathode plate; each of the single cells is composed of a bipolar plate, a cathode carbon paper, a membrane electrode, an anode carbon paper and a bipolar plate arranged in sequence; the built-in reference electrode according to any one of claims 1 to 3 is arranged between the membrane electrode and the anode carbon paper.

6. The fuel cell according to claim 5, characterized in that The membrane electrode comprises a membrane electrode frame and a membrane electrode catalyst arranged in the membrane electrode frame; the internal electrode of the reference electrode is connected to the membrane electrode catalyst; the insulating layer of the built-in reference electrode is in contact with the membrane electrode frame.

7. The fuel cell according to claim 5, characterized in that The anode plate and cathode plate respectively include an end plate and a current collector.

8. The fuel cell according to claim 5, characterized in that The external electrode of the reference electrode is connected to the measuring device; the two bipolar plates adjacent to the membrane electrode are respectively connected to the measuring device as the working electrode and the counter electrode.

9. The fuel cell according to claim 8, characterized in that The thickness of the reference electrode is 20-100 μm.

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