Preparation method and application of bifunctional heterojunction catalyst for AEM electrolyzed water

Abstract

The invention discloses a preparation method of a bifunctional heterojunction catalyst for AEM electrolyzed water. The method comprises the following steps: step 1, mixing multi-walled carbon nanotubes, deionized water, absolute ethyl alcohol and inorganic acid; step 2, putting the mixed solution in the step 1 into an ultrasonic machine to form a porous structure and more active adsorption sites; step 3, carrying out freeze drying treatment on the mixed solution treated in the step 2; step 4, mixing the dried multi-walled carbon nanotubes with acetylacetone salt, and uniformly grinding the mixed powder; and step 5, putting the powder obtained in the step 4 into a tubular furnace, and carrying out heat treatment in the atmosphere of H2 / Ar to obtain the PtFeCoNiMoZr / ZrO heterojunction catalyst. The catalyst has a remarkable catalytic effect on HER and OER reactions, and meanwhile, stable electrolysis which stably runs for 200 hours in an AEM electrolytic cell under the current density of 1200 mA / cm < 2 > is successfully realized.

Description

Technical Field

[0001] This invention relates to a method for preparing a bifunctional catalyst, specifically a method for preparing a bifunctional heterojunction catalyst for AEM water electrolysis and its application in an AEM electrolyzer. Background Technology

[0002] Anion exchange membrane electrolysis (AEMWE) technology has become one of the most popular and promising mainstream hydrogen production technologies due to its combination of the high efficiency of proton exchange membrane (PEM) electrolysis and the low cost of alkaline electrolysis (ALK). However, the high energy consumption problem has seriously restricted the commercialization process of AEMWE.

[0003] In the AEM hydrogen production system, the electrolyzer voltage (cell voltage) is the core indicator determining the overall energy consumption of water electrolysis. The formula for calculating the cell voltage is as follows:

[0004]

[0005] in, The theoretical decomposition voltage of water is 1.23 V; The total resistance of the electrolytic cell is given in Ω·cm. 2 , Let A be the electrolysis current; , These are the overpotentials for the oxygen evolution reaction (OER) at the anode and the hydrogen evolution reaction (HER) at the cathode, respectively.

[0006] As can be seen from the above formulas, the overpotentials of HER and OER are key factors affecting the energy consumption of AEM hydrogen production. Since the electrode is the site of electrochemical reactions, its catalytic activity influences the polarization of these reactions. Therefore, developing highly catalytically active and stable electrodes to reduce electrode reaction polarization and thus lower the cell voltage of the electrolyzer is an important way to reduce the energy consumption of AEM hydrogen production.

[0007] Platinum (Pt)-based high-entropy alloys possess excellent electrocatalytic performance due to their multiple active sites, high-entropy effect, and slow diffusion effect. CN117070782B discloses a Pt-based high-entropy alloy catalyst, but it only catalyzes the HER reaction, requiring the design of a catalyst for the OER reaction, and the catalyst preparation process is complex. CN120758919A discloses a Pt-based catalyst, which, although showing increased activity with the same Pt ​​dosage, is also only effective for the HER reaction. CN119121311A and CN115928133B disclose bifunctional catalysts, but they do not resolve the contradiction between long-term stability and excellent electrochemical activity, and the catalyst preparation cost is high.

[0008] In summary, existing water electrolysis catalysts for hydrogen production have at least the following problems:

[0009] 1. Most catalysts are designed for one-sided electrochemical reactions (HER or OER), with only a small number of catalysts possessing two-sided catalytic capabilities;

[0010] 2. The long-term stability and excellent electrochemical performance of the catalyst cannot be simultaneously achieved;

[0011] 3. The catalyst preparation process is complex and expensive;

[0012] Therefore, research on developing bifunctional water electrolysis catalysts that combine high stability, high catalytic activity, and low cost is particularly important. Summary of the Invention

[0013] This invention provides a method for preparing a bifunctional heterojunction catalyst for AEM water electrolysis and its application. A two-step heating method is used to form a PtFeCoNiMoZr high-entropy alloy solid solution. ZrO2 is precipitated in a furnace using a high-temperature solid-state method, with controlled temperature and gas atmosphere, successfully preparing a PtFeCoNiMoZr / ZrO heterojunction catalyst. This catalyst exhibits significant catalytic effects for HER and OER reactions and successfully achieves a catalyst efficiency of 1200 mA / cm² in an AEM electrolyzer. 2 Stable electrolysis that operates stably for 200 hours at a given current density.

[0014] The objective of this invention is achieved through the following technical solution:

[0015] A method for preparing a bifunctional heterojunction catalyst for AEM water electrolysis, such as Figure 1 As shown, it includes the following steps:

[0016] Step 1: Mix multi-walled carbon nanotubes, deionized water, anhydrous ethanol, and inorganic acid. Place the mixed solution in a centrifuge and disperse by centrifugation. The volume ratio of the multi-walled carbon nanotubes, deionized water, anhydrous ethanol, and inorganic acid is 1:0.5±0.2:0.1±0.01:0.1±0.01, preferably 1:0.5:0.1:0.1. The inorganic acid is sulfuric acid or hydrochloric acid. The centrifugation speed is 5000~10000 rpm / min, and the time is 5~10 min.

[0017] Step 2: Place the mixed solution from Step 1 into an ultrasonic machine and sonicate it to etch the surface of the multi-walled carbon nanotubes with inorganic acid, forming a porous structure and more active adsorption sites. The ultrasonic treatment time is 30-60 min.

[0018] Step 3: Freeze-dry the mixed solution processed in Step 2 to further deepen the pore structure and active adsorption sites on the surface of multi-walled carbon nanotubes. The freeze-drying temperature is -20~-35℃, preferably -30℃, and the time is 1~4 h, preferably 2 h.

[0019] Step 4: Mix the dried multi-walled carbon nanotubes with acetylacetone salt, and grind the mixed powder evenly. The mass ratio of the multi-walled carbon nanotubes to acetylacetone salt is 3:3~5, preferably 3:4. The acetylacetone salt is a mixture of platinum acetylacetone, iron acetylacetone, cobalt acetylacetone, nickel acetylacetone, molybdenum acetylacetone, and zirconium acetylacetone. The molar ratio of platinum acetylacetone, iron acetylacetone, cobalt acetylacetone, nickel acetylacetone, molybdenum acetylacetone, and zirconium acetylacetone is 1:1:1:1:1:1.

[0020] Step 5: Place the powder obtained in Step 4 into a tube furnace and heat it to 500-700℃, preferably 600℃, at a heating rate of 5-10℃ / min in an H2 / Ar atmosphere (5-10% H2 / 90-95% Ar) for the first stage of heat treatment. Then, heat it to 1000-1200℃, preferably 1100℃, at a heating rate of 5-20℃ / min for the second stage of heat treatment. Cool the furnace to obtain the PtFeCoNiMoZr / ZrO heterojunction catalyst.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. Based on the multi-active-site characteristics of high-entropy alloys, this invention selects zirconium oxide, which has high stability, low cost and is easy to synthesize, to form a heterojunction with it. Through a simple and easy-to-implement high-temperature solid-state method, a bifunctional heterojunction water electrolysis catalyst with both high stability and high catalytic activity was successfully prepared.

[0023] 2. This catalyst is a bifunctional catalyst, exhibiting excellent catalytic performance for both OER and HER reactions: For the HER reaction, this catalyst achieves excellent catalytic performance at 10 mA / cm². 2 and 100 mA / cm 2 At current densities, there are only 25 mV and 74 mV overpotentials; for the OER response, at 10 mA / cm², the overpotentials are only 25 mV and 74 mV. 2 At current density, the overpotential is only 242 mV, significantly lower than that of commercial IrO2 catalysts (320 mV); when this heterojunction catalyst is applied to AEM hydrogen production, at 1200 mA / cm², the overpotential is only 242 mV, significantly lower than that of commercial IrO2 catalysts (320 mV); 2At a current density of only 2.26 V, the cell voltage remains stable after 200 h of stable operation, indicating that the bifunctional heterojunction catalyst has both excellent electrocatalytic activity and long-term stability in the electrolyzer.

[0024] 3. This catalyst resolves the contradiction between long-term stability and high catalytic activity in existing catalysts, achieving both high catalytic activity and long-term stability.

[0025] 4. The catalyst is inexpensive, has a simple preparation process, and is easy to operate. Attached Figure Description

[0026] Figure 1 Flowchart for the preparation of PtFeCoNiMoZr / ZrO heterojunction catalyst;

[0027] Figure 2 TEM image of the PtFeCoNiMoZr / ZrO heterojunction catalyst prepared in Example 1;

[0028] Figure 3 TEM and EDS images of the PtFeCoNiMoZr / ZrO heterojunction catalyst prepared in Example 1;

[0029] Figure 4 XRD pattern and high-resolution image of the PtFeCoNiMoZr / ZrO heterojunction catalyst prepared in Example 1;

[0030] Figure 5 The overpotential comparison diagram is shown for the PtFeCoNiMoZr / ZrO heterojunction catalyst prepared in Example 1.

[0031] Figure 6 LSV curves of the PtFeCoNiMoZr / ZrO heterojunction catalyst prepared in Example 1 and a commercial catalyst;

[0032] Figure 7 The PtFeCoNiMoZr / ZrO heterojunction catalyst prepared in Example 1 was applied to the cell pressure diagram in an AEM electrolyzer. Detailed Implementation

[0033] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0034] Example 1:

[0035] Multi-walled carbon nanotubes, deionized water, anhydrous ethanol, and sulfuric acid were mixed in a volume ratio of 1:0.5:0.1:0.1, ultrasonically dispersed, freeze-dried, and then mixed with acetylacetone salt (mass ratio of 3:4). After grinding evenly, the mixture was heated to 600℃ at a heating rate of 10℃ in an atmosphere of H2:Ar = 5:95 and held for 2 hours. Then, the temperature was increased to 1100℃ at a heating rate of 20℃ and held for 2 hours. The mixture was then cooled in the furnace to prepare the PtFeCoNiMoZr / ZrO heterojunction catalyst.

[0036] Example 2:

[0037] Multi-walled carbon nanotubes, deionized water, anhydrous ethanol, and sulfuric acid were mixed in a volume ratio of 1:0.5:0.1:0.1, ultrasonically dispersed, freeze-dried, and then mixed with acetylacetone salt (mass ratio of 3:4). After grinding evenly, the mixture was heated to 600℃ at a heating rate of 10℃ in an atmosphere of H2:Ar = 10:90 and held for 2 hours. Then, the temperature was increased to 1100℃ at a heating rate of 10℃ and held for 2 hours. The mixture was then cooled in the furnace to prepare the PtFeCoNiMoZr / ZrO heterojunction catalyst.

[0038] Comparative Example 2:

[0039] The difference between this comparative example and Example 1 is that sulfuric acid was not mixed with multi-walled carbon nanotubes.

[0040] Comparative Example 3:

[0041] The difference between this comparative example and Example 1 is that multi-walled carbon nanotubes, deionized water, anhydrous ethanol, and sulfuric acid are mixed in a volume ratio of 1:0.5:0.1:0.15.

[0042]

[0043] As can be seen from Table 1, when multi-walled carbon nanotubes, deionized water, anhydrous ethanol, and sulfuric acid are mixed in a mass ratio of 1:0.5:0.1:0.1, the catalyst has the lowest overpotential of 2.38V, which is significantly lower than the catalysts prepared without sulfuric acid and with a mass ratio of 0.15. Therefore, the preferred ratio of sulfuric acid to other raw materials is 1:0.5:0.1:0.1.

[0044] Comparative Example 4:

[0045] The difference between this comparative example and Example 1 is that: after the mixed powder is ground evenly, it is heated to 600°C in an Ar atmosphere at a heating rate of 10°C and held for 2 hours, then heated to 1100°C at a heating rate of 20°C and held for 2 hours, and then cooled in the furnace.

[0046] Comparative Example 5:

[0047] The difference between this comparative example and Example 1 is that: after the mixed powder is ground evenly, it is heated to 600°C at a heating rate of 10°C in an atmosphere of Ar and CO, held for 2 hours, and then heated to 1100°C at a heating rate of 20°C for 2 hours, and then cooled in the furnace.

[0048]

[0049] As shown in Table 2, after heat treatment in Ar and H2 atmospheres, the catalyst overpotential is 2.38V, which is the lowest, indicating the best catalytic activity. In contrast, the catalyst overpotential is highest in Ar atmosphere alone. In Ar and CO atmospheres, the catalyst overpotential is 2.57V, which is lower than that of commercial catalysts (3.32V), indicating that CO has a certain reduction effect, but the reduction effect is not as good as that of H2. Therefore, the heat treatment atmosphere of Ar and H2 is preferred.

[0050] Comparative Example 6:

[0051] The difference between this comparative example and Example 2 is that the muffle furnace is first heated to 500°C and held for 2 hours, then heated to 1100°C and heated for 2 hours, and then cooled inside the furnace.

[0052] Comparative Example 7:

[0053] The difference between this comparative example and Example 2 is that the muffle furnace is first heated to 700°C and held for 2 hours, then heated to 1100°C and heated for 2 hours, and then cooled inside the furnace.

[0054]

[0055] As shown in Table 2, after heat treatment at 600℃, the catalyst overpotential is 2.38V, which is the lowest, indicating the best catalytic activity. However, after heat treatment at 500℃, the temperature is insufficient to promote the formation of a solid solution in the high-entropy alloy, resulting in limited oxide precipitation and the formation of a heterojunction catalyst, low electrochemical activity, and a catalyst overpotential as high as 2.95V. After heat treatment at 700℃, the excessive temperature causes excessive solid solution of the high-entropy alloy, which is not conducive to the precipitation of oxides in the subsequent stage, and the activity of the prepared catalyst is also limited, with a catalyst overpotential as high as 2.71V. Therefore, the preferred temperature for the first stage heat treatment in the muffle furnace is 600℃.

[0056] Transmission electron microscopy (TEM) image of the PtFeCoNiMoZr / ZrO heterojunction catalyst prepared in Example 1 is shown below. Figure 2 (a) and Figure 2 As shown in (b), the catalyst has two forms: one is small alloy particles (high entropy alloy) densely distributed on multi-walled carbon nanotubes, and the other is a larger heterojunction.

[0057] Figure 3(a) Figure 3 (b) The morphology of the heterojunction is clearly shown, and the interface between the two phases is clearly displayed. Figure 3 (d)~ Figure 3 (h) shows that Pt, Fe, Co, Ni and Mo exhibit a co-localized distribution. It is worth noting that Zr and O exhibit an overlapping distribution.

[0058] Figure 4 (a) shows the XRD pattern of the catalyst. The peak at 2Θ=26° corresponds to multi-walled carbon nanotubes (PDF#97-003-1170), and the peaks at 2Θ=42.047°, 48.944°, 71.724°, and 86.779° correspond to Pt-based high-entropy alloys (PDF#04-006-6730). It is worth noting that in Figure 4 (b) In the high-resolution image shown, 2Θ = 42.047° (d = 2.1472 Å, (111)) is consistent with the result in the XRD, proving that a Pt-based high-entropy alloy was indeed formed. The peaks of 2Θ = 30.236°, 34.625°, and 35.267° correspond to ZrO2 (PDF#04-005-4504), and 2Θ = 34.625° (d = 2.5885 Å, (002)) corresponds to the result in the XRD, confirming the formation of ZrO2.

[0059] Figure 5 The overpotential performance of AEMWE is shown, and it can be seen that at 1200 mA / cm 2 At the specified current density, the prepared catalyst requires only an overpotential of 2.38 V, while the device consisting of PtC as the cathode and RuO2 as the anode requires an overpotential of 3.32 V.

[0060] Figure 6 The LSV curves of the PtFeCoNiMoZr / ZrO heterojunction catalyst and the commercial catalyst are shown. As can be seen from the figure, the onset potential of the PtFeCoNiMoZr / ZrO heterojunction catalyst (~1.2 V) is significantly lower than that of the commercial catalyst (~1.5 V). At the same voltage, the current density of the PtFeCoNiMoZr / ZrO heterojunction catalyst is significantly higher than that of the commercial catalyst. Therefore, the PtFeCoNiMoZr / ZrO heterojunction catalyst exhibits a lower onset potential and a higher current density, indicating that its catalytic activity is significantly better than that of PtC / RuO2.

[0061] The stability of AEMWE was tested using the chronopotential method. Figure 7 It can be seen that at 1200 mA / cm 2When operating at a constant current density for 200 h, the voltage remained essentially unchanged, demonstrating excellent electrocatalytic performance.

Claims

1. A method for preparing a bifunctional heterojunction catalyst for AEM water electrolysis, characterized in that... The method includes the following steps: Step 1: Mix multi-walled carbon nanotubes, deionized water, anhydrous ethanol, and inorganic acid. Place the mixed solution in a centrifuge and centrifuge to disperse it. The volume ratio of multi-walled carbon nanotubes, deionized water, anhydrous ethanol, and inorganic acid is 1:0.5±0.2:0.1±0.01:0.1±0.

01. Step 2: Place the mixed solution from Step 1 into an ultrasonic machine and sonicate it to etch the surface of the multi-walled carbon nanotubes with inorganic acid, forming a porous structure and more active adsorption sites. Step 3: Freeze-dry the mixed solution processed in Step 2 to further enhance the pore structure and active adsorption sites on the surface of multi-walled carbon nanotubes. Step 4: Mix the dried multi-walled carbon nanotubes with acetylacetone salt, and grind the mixed powder evenly, wherein the mass ratio of the multi-walled carbon nanotubes to acetylacetone salt is 3:3~5. Step 5: Place the powder obtained in Step 4 into a tube furnace and heat it to 500-700℃ at a heating rate of 5-10℃ / min in an H2 / Ar atmosphere, and hold it for 1-3 hours for the first stage of heat treatment; then heat it to 1000-1200℃ at a heating rate of 5-20℃ / min, and heat it for 1-3 hours for the second stage of heat treatment; cool it in the furnace to prepare the PtFeCoNiMoZr / ZrO heterojunction catalyst.

2. The method for preparing a bifunctional heterojunction catalyst for AEM water electrolysis according to claim 1, characterized in that... In step 1, the inorganic acid is sulfuric acid or hydrochloric acid, and the centrifugal dispersion speed is 5000~10000 rpm / min, and the time is 5~10min.

3. The method for preparing a bifunctional heterojunction catalyst for AEM water electrolysis according to claim 1, characterized in that... In step 1, the volume ratio of multi-walled carbon nanotubes, deionized water, anhydrous ethanol, and inorganic acid is 1:0.5:0.1:0.

1.

4. The method for preparing a bifunctional heterojunction catalyst for AEM water electrolysis according to claim 1, characterized in that... In step 2, the ultrasonic treatment time is 30-60 minutes.

5. The method for preparing a bifunctional heterojunction catalyst for AEM water electrolysis according to claim 1, characterized in that... In step 3, the freeze-drying process is carried out at a temperature of -20 to -35°C for 1 to 4 hours.

6. The method for preparing a bifunctional heterojunction catalyst for AEM water electrolysis according to claim 5, characterized in that... The freeze-drying process was carried out at a temperature of -30°C for 2 hours.

7. The method for preparing a bifunctional heterojunction catalyst for AEM water electrolysis according to claim 1, characterized in that... In step 4, the acetylacetone salt is a mixture of platinum acetylacetone, iron acetylacetone, cobalt acetylacetone, nickel acetylacetone, molybdenum acetylacetone, and zirconium acetylacetone, with a molar ratio of 1:1:1:1:1:1 and a mass ratio of multi-walled carbon nanotubes to the acetylacetone salt of 3:

4.

8. The method for preparing a bifunctional heterojunction catalyst for AEM water electrolysis according to claim 1, characterized in that... In step 5, the volume content of H2 in the H2 / Ar atmosphere is 5-10%, and the volume content of Ar is 90-95%.

9. The method for preparing a bifunctional heterojunction catalyst for AEM water electrolysis according to claim 1, characterized in that... In step 5, the temperature of the first stage heat treatment is 600℃, and the temperature of the second stage heat treatment is 1100℃.

10. The application of a bifunctional heterojunction catalyst prepared by the method of any one of claims 1-9 in an AEM electrolyzer.

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