Method for manufacturing catalyst materials for electrodes of electrochemical cells

Abstract

The present invention relates to a method for producing a catalyst material for an electrode of an electrochemical cell, the method comprising the step of doping a carbon material with nitrogen atoms by contacting the carbon material with urea at a temperature in the temperature range of 550°C to 900°C, or by contacting the carbon material with cyanamide at a temperature in the temperature range of 700°C to 900°C, or by contacting an oxidized carbon material with cyanamide at a temperature in the temperature range of 550°C to 650°C, or by contacting the oxidized carbon material with melamine at a temperature in the temperature range of 550°C to 650°C.

Description

[Technical Field]

[0001] This invention relates to a method for producing catalyst materials for electrodes in electrochemical cells.

[0002] As energy carriers, electrochemical cells such as fuel cells and electrolytic cells are increasingly being used. One of the typical problems with electrochemical cells is the large power loss over time. This is particularly pronounced in low-temperature fuel cells with small amounts of catalyst, and is due to the non-uniform distribution of ionomers. To achieve a uniform distribution of ionomers, attempts have been made to incorporate nitrogen atoms into the carbon skeleton of the catalyst carbon carrier. For this purpose, carbon materials have been reacted with gaseous NH3 (see, for example, Sebastian Ott et al.: “Ionomer distribution control in porous carbon-supported catalyst layers for high-power and low Pt-loaded proton exchange membrane fuel cells”, Nature Materials, Januar 2020, doi.org / 10.1038 / s41563-019-0487-0, or F. Jaouen et al.: “Non-Noble Electrocatalysts for O2Reduction: How Does Heat Treatment Affect Their Activity and Structure? Part I. Model for Carbon Black Gasification by NH3: Parametric Calibration and Electrochemical Validation”, J. Phys. Chem. C 2007, 111, 5963-5970, 1. December, 2006). However, electrodes fabricated using carbon materials reacted with NH3 have been found to be insufficient in terms of performance.

[0003] Therefore, based on this prior art, the object of the present invention is to present a method for producing a catalyst material for electrodes of an electrochemical cell that can achieve consistently high performance in the electrochemical cell.

[0004] This problem is solved by the method described in claim 1. Dependent claims describe advantageous developments and embodiments of the present invention.

[0005] Accordingly, this problem is solved by a method that includes the step of doping a carbon material with nitrogen atoms. Here, doping can be carried out in various ways, namely, on the one hand, the carbon material 7 50℃~ 85 By contacting urea at a temperature in the 0°C range, is acid This can be achieved by contacting a carbonized material with cyanamide at a temperature in the range of 550°C to 650°C, or by contacting an oxided carbon material with melamine at a temperature in the range of 550°C to 650°C.

[0006] In order to achieve maximum power density in the electrochemical cell and maintain a stable state over the long term, it is important to adhere to the specified temperature range for various dopants. .acid Doping of carbonized materials with cyanamide is particularly advantageous when carried out at a temperature of approximately 600°C, and doping with melamine is also particularly advantageous when carried out at a temperature of approximately 600°C. This can further improve the power density of the electrochemical cell.

[0007] When using melamine or cyanamide as a nitrogen dopant at a doping temperature of 600°C, it is also necessary to oxidize the carbon material before doping.

[0008] The nitrogen-doped carbon materials produced in this way serve as high-performance supports for catalysts commonly used in electrochemical cells. By doping carbon materials with nitrogen atoms, the nitrogen atoms are directly incorporated into the carbon skeleton. An NHx group is formed, which is positively charged during the production of the catalyst material or electrode. This allows the ionomers used in the production of electrodes to react under strong Coulomb interactions with most negatively charged groups (particularly SO3 groups), resulting in a very uniform distribution of the ionomers, thereby enabling the achievement of persistently high power densities.

[0009] The nitrogen atom-doped carbon material produced by the method according to the present invention is used in the manufacture of electrode catalysts for electrochemical cells. In this case, the catalyst is used, for example, as a catalyst ink that is directly applied to a film, thereby forming an electrode. In this way, the catalyst is directly coated onto the film.

[0010] According to one advantageous developmental model, doping of carbon materials with nitrogen atoms is carried out in a tubular furnace. This is because, in this case, the doping reaction can be controlled particularly well, and resources can be saved.

[0011] More advantageously, doping of carbon materials with nitrogen atoms is carried out for 1.5 to 12 hours, particularly 2 to 7 hours, and especially 2 to 4 hours. If the doping time is too short, less than 1.5 hours, nitrogen doping may be insufficient, and if the doping time is too long, not only is the reaction time prolonged and economically disadvantageous, but it may also cause the carbon material to decompose. To overcome the above drawbacks, a doping time of 2 to 4 hours, particularly about 2.5 hours, is especially preferable.

[0012] Due to their excellent conductivity and high-temperature stability, carbon materials are preferably selected from carbon black, graphite, and graphitized carbon. An example of a carbon material is available under the trade name Ketjenblack. Furthermore, suitable carbon black is available in 200m 2Low specific surface area of ​​less than / g carbon, or 250-600m² 2 A moderate specific surface area of ​​carbon, or 600 m². 2 It has a high specific surface area, exceeding that of carbon. Suitable graphitized carbon is 200m 2 Low specific surface area of ​​less than / g carbon, or 250-600m² 2 A moderate specific surface area of ​​carbon, or 600 m². 2 It has a high specific surface area of ​​over 1g carbon. Here, the specific surface area is determined by the gas adsorption isotherm using the BET method.

[0013] To remove any reaction residue from the doping reaction that may occur, a step of washing the doped carbon material with water may be advantageously provided. Furthermore, the washed doped carbon material may be dried before further processing or storage.

[0014] To further improve the power density of electrodes manufactured using doped carbon materials in electrochemical cells , When anamide is used for doping, it is provided that the carbon material is oxidized before doping with nitrogen atoms.

[0015] mosquito The oxidation of carboxymethylcellulose materials occurs at 550°C to 650°C, not only when doping with melamine, but also when doping with cyanamide. ,mosquito This is carried out by reacting the ion material with a 70 wt% HNO3 aqueous solution under reflux. So The reaction time is advantageously between 15 minutes and 3 hours, and especially between 30 minutes and 60 minutes.

[0016] In order to improve the catalytic properties of the catalyst material for the electrodes of an electrochemical cell, it is preferable to add a catalytically active metal such as platinum and / or a platinum-containing alloy to the carbon material doped with nitrogen atoms. By the method according to the invention, since the pore structure of the mesopores and micropores of the carbon material remains almost completely intact, the catalytically active metal can be very easily impregnated, and this catalytically active metal adheres permanently and stably to the carbon material, thereby further improving the output density of the electrochemical cell.

[0017] For the above reasons, it is also advantageous that the content of platinum or a platinum-containing alloy relative to the total weight of the carbon material doped with nitrogen atoms is 5 to 50% by weight.

[0018] In order to provide a particularly good bond with the ionomer, the doping of the carbon material with nitrogen atoms is preferably carried out such that the carbon material is doped with 0.4 to 2% by weight, particularly 0.8 to 1.5% by weight, of nitrogen.

[0019] Particularly preferably, the electrode is formed as a cathode, and even more preferably, it is formed as the cathode of a fuel cell.

[0020] Further details, features and advantages of the present invention will become apparent from the following description and drawings.

Brief Description of the Drawings

[0021] [Figure 1] It is a graph showing the output density of an electrochemical cell using a carbon material doped with various dopants at 600 °C. [Figure 2] It is a graph showing the output density of an electrochemical cell using a carbon material doped with various dopants at 800 °C. [Figure 3] It is a graph showing the output density of an electrochemical cell using an oxidized carbon material doped with various dopants at 600 °C.

[0022] Specifically, the graph in FIG. 1 is A / cm2 The output density i of the electrochemical cell measured in units is shown with respect to the voltage in volts. The temperature of the cell was 90 °C and the pressure was 170 kPa a,c Unless otherwise explicitly stated, any percentage value means percentage by weight (% (wt%)).

[0023] The cell was prepared as follows: 1. Preparation of the catalyst First, commercially available Ketjenblack EC-300J (manufacturer: Akzo Nobel) and 100 ml of a 70 wt% aqueous HNO3 solution were stirred under reflux for 0.5 hours, and reflux was caused using an oil bath heated to 70 °C. After the reaction time, the oxidized carbon was filtered and washed with hot water to remove all the remaining acid. Then, the oxidized carbon was dried in an oven.

[0024] Next, the oxidized carbon (see the following table for details) was mixed with various nitrogen sources (i.e., melamine, urea, or cyanamide). The ratio of carbon to the nitrogen source is also shown in the following table.

[0025] Next, this mixture was heated in a tubular furnace under a constant nitrogen flow rate at each of the indicated temperatures (T set °C reference) at a heating rate of 400 K / h and held for 2.5 hours.

[0026] Next, using the doped oxidized carbon, platinum was deposited on each carbon by the polyol method to produce the catalyst. The polyol method involves mixing 300 mg of functionalized carbon, 200 ml of ethylene glycol, 100 ml of deionized water, and 1.35 ml of a 0.25 mol / L concentrated H2PtCl6 aqueous solution. The resulting dispersion was first stirred under reflux at 25 °C for 18 hours and then at 120 °C for 2 hours. After the reaction was completed, the catalyst was filtered and washed with hot water to remove the reaction residue and trace amounts of chloride. Then, the obtained catalyst powder was dried in a vacuum oven.

[0027] The summary of the experiments conducted is shown in the following table:

Table 1

[0028] 2. Cell manufacturing All of the fabricated membrane electrode assemblies were manufactured using the decal transfer method. For this purpose, a catalyst ink was prepared by mixing the catalyst powder prepared as described above with water, followed by 1-propanol and at least one aqueous ionomer dispersion (725EW 3M dry powder dispersed in 40% H2O / 60% 1-propanol, resulting in an 18 wt% ionomer solution). This catalyst ink was then coated onto PTFE using a Meyer bar. The coated decal was then dried.

[0029] For both electrodes, the ionomer / carbon weight ratio (I / C) was set to 0.65. For the cathode catalyst, a catalyst with modified nitrogen (melamine, urea, cyanamide) was used, consisting of a carbon support with 20% Pt deposited. The total nitrogen weight percentage of the carbon ranged from 0.8% to 1.2%.

[0030] All anode electrodes contained 30% by weight of Pt on graphitized Ketjenblack (TEC10EA30E, commercially available from Tanaka Kikinzoku Kogyo Co., Ltd.).

[0031] The amount of Pt loaded in the cathode electrode is 0.11 mg pt / cm 2 The nominal film thickness when using 20 wt% Pt / modified carbon (= N-doped carbon) was approximately 14 μm. When using 30 wt% Pt / C (unmodified carbon = non-N-doped carbon), the loading amount for each anode was approximately 0.1 mg. pt / cm 2 That was the case.

[0032] A 10 μm thick film (Gore MX20.10) was placed between the anode decal and cathode decal manufactured as described above, hot-pressed at 155°C for 3 minutes, and then subjected to a pressure of 0.24 kN / cm². 2 Applying force, 5cm 2We manufactured an MEA of the following size. Next, we laminated the MEA between two gaskets (200 x 200 mm, 25 μm PEN film, CMC 61325 coated with a heat-activated adhesive (approximately 15 μm thick), CMC Klebetechnik, Germany) and laid it 5 cm 2 An active MEA surface measuring (50 × 10 mm) was obtained.

[0033] All tests were conducted using a single-cell test station with improved single-cell hardware (Tandem Technologies Ltd.) featuring 14 serpentine channels, including a graphite channel composite flow field. The cell contact pressure was set to 9 bar, and the compressibility of the gas diffusion layer (SGL29BC on both the anode and cathode electrodes) was set to 20% using incompressible glass fiber PTFE seals (Fiberflon).

[0034] The polarization curves in Figures 1 to 3 were recorded at a cell temperature of 90°C and a relative humidity (RH) of 30%RH.

[0035] The flow rates were kept constant at 1000 nccm of H2 on the anode side and 2000 nccm of air on the cathode side, and the outlet pressure was set to 170 kPa on both sides. Because the amount of water produced was very small and the reaction gas was in excess, the inlet humidity (RH) and outlet humidity (RH) were kept equal, taking into account a pressure loss of approximately 1 kPa at the active surface of the MEA.

[0036] Figure 1 shows a graph illustrating the power density of electrochemical cells using carbon materials doped with various dopants at 600°C.

[0037] Curve 1 shows the test results of an electrochemical cell using urea-doped carbon material at a temperature of 600°C.

[0038] Curve 2 shows the test results of an electrochemical cell using melamine-doped carbon material at a temperature of 600°C.

[0039] Curve 3 shows the test results of an electrochemical cell using NH3-doped carbon material at a temperature of 600°C.

[0040] Curve 4 shows the test results for an electrochemical cell using the same carbon material as the electrochemical cell described above, but without nitrogen doping.

[0041] Curve 5 shows the test results of an electrochemical cell using cyanamide-doped carbon material at a temperature of 600°C.

[0042] From the graph in Figure 1, it can be inferred that using urea-doped carbon material at 600°C results in significantly better and therefore higher power density than using any other doped carbon material, particularly the NH3-doped carbon material used as a comparative example.

[0043] Figure 2 shows A / cm 2 This graph plots the power density i of an electrochemical cell, measured in units of volts, against a voltage in volts. The electrochemical cell was manufactured and measured in the same manner as shown in Figure 1.

[0044] Curve 1 shows the test results of an electrochemical cell using cyanamide-doped carbon material at a temperature of 800°C.

[0045] Curve 2 shows the test results of an electrochemical cell using urea-doped carbon material at a temperature of 800°C.

[0046] Curve 3 shows the test results of an electrochemical cell using NH3-doped carbon material at a temperature of 800°C.

[0047] Curve 4 shows the test results of an electrochemical cell using melamine-doped carbon material at a temperature of 800°C.

[0048] Curve 5 shows the test results for an electrochemical cell that uses the same carbon material as the electrochemical cell described above, but without nitrogen doping.

[0049] From the graph in Figure 2, it can be inferred that using carbon materials doped with urea and cyanamide at 800°C results in significantly better and therefore higher power densities than any other doped carbon material, particularly the NH3-doped carbon material used as a comparative example. Furthermore, all doped carbon materials showed a favorable improvement in power density compared to undoped carbon materials.

[0050] Figure 3 shows A / cm 2 This graph plots the power density i of an electrochemical cell, measured in units of volts, against a voltage in volts. The electrochemical cell was manufactured and measured in the same manner as shown in Figure 1, except that the carbon material was oxidized under reflux in a 70 wt% HNO3 aqueous solution for 30 minutes before doping, and the oxidized carbon material was washed before doping to remove residue of the oxidizing reagent.

[0051] Curve 1 shows the test results of an electrochemical cell using cyanamide-doped carbon oxide material at a temperature of 600°C.

[0052] Curve 2 shows the test results of an electrochemical cell using melamine-doped carbon oxide material at a temperature of 600°C.

[0053] Curve 3 shows the test results of an electrochemical cell using NH3-doped carbon oxide material at a temperature of 600°C.

[0054] Curve 4, at a temperature of 600°C urea The test results of an electrochemical cell using a carbon oxide material doped with [specific compound] are shown.

[0055] Curve 5 shows the test results for an electrochemical cell using the same carbon oxide material as the electrochemical cell described above, but without nitrogen doping.

[0056] From the graph in Figure 3, it can be inferred that using cyanamide or melamine-doped carbon oxide materials at 600°C results in significantly better, and therefore higher, power densities compared to any other doped carbon oxide material, particularly the NH3-doped carbon material used as a comparative example. Furthermore, all doped carbon oxide materials showed a favorable improvement in power density compared to oxidized but undoped carbon materials.

Claims

1. A method for producing a catalyst material for electrodes of an electrochemical cell, wherein the method is: - By contacting the carbon material with urea at a temperature in the range of 750°C to 850°C, - By contacting a carbon oxide material with cyanamide at a temperature in the range of 550°C to 650°C, or - By bringing the carbon oxide material into contact with melamine at a temperature range of 550°C to 650°C The process includes the step of doping a carbon material or an oxidized carbon material with nitrogen atoms. The method further includes adding platinum or a platinum-containing alloy to the nitrogen atom-doped carbon material or carbon oxide material, The carbon material or carbon oxide material is doped with nitrogen atoms for 2 to 4 hours. The carbon material is selected from carbon black, graphite, and graphitized carbon. The aforementioned oxidized carbon material is a carbon material selected from carbon black, graphite, and graphitized carbon, which is subjected to reflux in a 70% by weight HNO ３ A method obtained by reacting with an aqueous solution.

2. The method according to claim 1, wherein the doping of the carbon material or oxidized carbon material with nitrogen atoms is performed in a tubular furnace.

3. The method according to claim 1 or 2, further comprising the step of washing a doped carbon material or a doped carbon oxide material with water.

4. The method according to any one of claims 1 to 3, wherein the content of platinum or a platinum-containing alloy in the nitrogen atom-doped carbon material or carbon oxide material is 5 to 50% by weight.

5. The method according to any one of claims 1 to 4, wherein the doping of the carbon material or carbon oxide material with nitrogen atoms is carried out by doping the carbon material or carbon oxide material with 0.4% to 2% by weight of nitrogen.

6. A method for producing a catalyst material for the cathode of an electrochemical cell, according to any one of claims 1 to 5.

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