A kind of heteroatom doped carrier type bifunctional oxygen electrode catalyst and preparation method and application

Abstract

The application discloses a kind of heteroatom doped carrier type bifunctional oxygen electrode catalyst and preparation method and application, select high conductivity, high stability nitrogen, tungsten heteroatom doped titanium oxide carrier, load PtIr alloy nanoparticles as bifunctional oxygen electrode catalyst, can greatly improve the dispersion of noble metal active component and surface active site density, so as to improve the utilization rate of noble metal and catalytic activity and life and reduce cost.

Description

Technical fields:

[0001] This invention relates to the field of electrocatalytic nanomaterials technology, specifically to a heteroatom-doped support-type bifunctional oxygen electrode catalyst, its preparation method, and its application. Background technology:

[0002] Hydrogen energy, as a green, low-carbon, and widely applicable secondary energy source, helps accelerate the decarbonization of the transportation sector, aligning with my country's carbon emission reduction strategy. Integrated Regenerative Fuel Cells (URFCs) combine fuel cells (FCs) with water electrolysis (WE) technology, offering advantages such as low-temperature start-up, zero pollution, high energy efficiency, and high power density. The fuel cell produces water through fuel H2 and oxidant O2; water electrolysis then produces the necessary fuel H2 and oxidant O2 for fuel cell operation, enabling the fuel cell to be "regenerated" through WE technology. In enclosed or sealed environments such as islands and spacecraft, URFCs, as a typical "closed-environment renewable energy technology," can meet basic life resource needs such as O2 and H2O, as well as emergency energy needs such as electricity and heat, playing a role in life support, energy assistance, and emergency response.

[0003] The membrane electrode assembly (MEA) is a core component of URFC, with both fuel cell (FC) and energy storage (WE) functions performed by the same MEA. Compared to single-function fuel cells and water electrolysis, URFC's power generation-storage technology not only requires catalysts to be inexpensive and stable, but also demands greater dual catalytic functionality. For the hydrogen electrode in URFC, commercially available Pt-based catalysts exhibit excellent catalytic performance for both H2 oxidation (HOR) and H2 evolution (HER). However, in the oxygen electrode, the active sites required for O2 reduction (ORR) and O2 evolution (OER) are not consistent. Catalyst materials with optimal ORR activity are difficult to simultaneously provide optimal OER activity. Therefore, the preparation of efficient and stable oxygen electrode catalysts with dual ORR and OER functions is a key research focus for URFC.

[0004] Current research indicates that Pt / IrOx, formed by mixing platinum black and iridium oxide, is the most widely used catalyst in URFC. However, due to the direct loading of Pt onto IrOx, the amount of precious metals used is high, resulting in a high cost for URFC. Secondly, URFC has a high potential (>1.5V) in WE mode, and the high temperature, high humidity, and acidic environment place high demands on the support. Commonly used carbon supports are not suitable for use in oxygen electrodes, and the interaction between carbon and catalyst particles is weak or almost non-existent, which can cause catalyst particles to detach, migrate, or aggregate under operating conditions, leading to deactivation. Therefore, the development of low-cost, long-life bifunctional catalysts determines the performance of URFC and is a key technology affecting the power supply performance and stability of URFC. Summary of the Invention:

[0005] The purpose of this invention is to provide a heteroatom-doped supported bifunctional oxygen electrode catalyst, its preparation method, and its application, which solves the problems of high cost, insufficient efficiency, and instability of existing bifunctional oxygen electrode catalysts.

[0006] This invention is achieved through the following technical solutions:

[0007] A heteroatom-doped support-type bifunctional oxygen electrode catalyst comprises PtIr alloy nanoparticles uniformly loaded on a nitrogen- and tungsten-doped titanium oxide support. The catalyst support is anatase phase, and based on the total molar percentage of the support (100%), the molar ratio of N in the support is 1%–10%, the molar ratio of W is 5%–30%, and the remainder is titanium oxide. Based on the total mass percentage of the PtIr alloy nanoparticles (100%), the mass percentage of Pt is 50%–90%, and the remainder is Ir.

[0008] Preferably, the size of the platinum-iridium alloy nanoparticles is 2–10 nm.

[0009] Preferably, the W molar ratio in the carrier is 15-25%.

[0010] Preferably, the Pt mass percentage in the PtIr alloy nanoparticles is 75%.

[0011] The method for preparing the heteroatom-doped supported bifunctional oxygen electrode catalyst includes the following steps:

[0012] (1) Ammonium metatungstate, tetrabutyl titanate, water and inhibitor are mixed to form a solution, heated at 75-85℃ for 12 hours under stirring, and then placed in a reaction vessel at 155-165℃ for 8-12 hours. After centrifugation and drying, doped NW-TiOx support is obtained; the inhibitor is an acid solution.

[0013] (2) Mix the platinum compound and iridium compound in a certain proportion, dissolve them in water with the NW-TiOx support, and heat at 55-65℃.

[0014] An alkaline solution was added dropwise under heating and stirring to form a precursor solution, which was then heated to 100°C, washed and dried to obtain the catalyst precursor.

[0015] (3) The catalyst precursor is calcined in air at 300-500℃ for 3-5 hours, and then a reducing gas is introduced to continue calcining for 7-9 hours. The obtained product is washed and dried to obtain the target catalyst PtIr / NW-TiOx.

[0016] Preferably, the acid in step (1) is selected from one or more of acetic acid, hydrochloric acid, and nitric acid.

[0017] Preferably, the platinum compound and iridium compound in step (2) have good solubility in acidic solution, and the platinum compound is selected from one or more of chloroplatinic acid, platinum chloride, and platinum acetylacetonate; the iridium compound is selected from one or more of chloroiridium acid, iridium chloride, and iridium acetylacetonate.

[0018] The reducing gas in step (3) is selected from any one of hydrogen, hydrogen / argon, or hydrogen / nitrogen mixture.

[0019] This invention also protects the application of heteroatom-doped supported bifunctional oxygen electrode catalysts in electrocatalysts, used as cathode oxygen reduction (ORR) catalysts for fuel cells, anode oxygen evolution (OER) catalysts for water electrolysis, and URFC bifunctional oxygen electrode catalysts, for the preparation of cathode membrane electrodes for fuel cells, anode membrane electrodes for water electrolysis, and oxygen electrodes for regenerative fuel cells.

[0020] The beneficial effects of this invention are as follows:

[0021] (1) In this invention, titanium oxide is doped with nitrogen and tungsten atoms in situ to form a heteroatom-doped support, which can effectively improve the conductivity of titanium oxide and thus improve the conductivity of the catalyst. Furthermore, due to the presence of the highly conductive support, the consumption of precious metals is greatly reduced, effectively reducing the cost of MEA and URFC.

[0022] (2) Due to the oxygen vacancy defects and heteroatom doping of the doped support, the metal-support interaction between the highly conductive support and PtIr nanoparticles can change the local charge distribution of the catalyst, which not only improves the catalytic activity of the PtIr active component, but also effectively fixes the PtIr nanoparticles, improves the stability of the active component, and thus improves the lifetime of MEA.

[0023] (3) The PtIr alloy nanoparticles in this invention are small in size and uniformly distributed on the carrier surface, which effectively improves the utilization rate of precious metals and the active area.

[0024] In summary, this invention uses a highly conductive and stable nitrogen- and tungsten heteroatom-doped titanium oxide support to support PtIr alloy nanoparticles as a bifunctional oxygen electrode catalyst. This can greatly improve the dispersion of the noble metal active components and the density of surface active sites, thereby improving the utilization rate, catalytic activity and lifespan of the noble metal and reducing costs. Attached image description:

[0025] Figure 1 Images of the NW-TiOx support prepared in Example 1 are shown, where Figure a is a TEM image of the NW-TiOx prepared in Example 1, Figure b is a high-resolution HR-TEM image, and Figure c shows the interatomic distance in Figure b. Figure 1 It can be seen that the interplanar spacing of NW-TiOx is 3.2. Spacing between anatase (101) crystal planes The proximity of the crystal planes, possibly due to doping with heteroatoms N and W, may have reduced the interplanar spacing.

[0026] Figure 2 This is a TEM image of the target catalyst PtIr / NW-TiOx prepared in Example 1. Due to the incorporation of Ir atoms into the Pt lattice or the strong metal-support interaction (MSI), the interplanar spacing of PtIr increases to [value missing]. Slightly higher than the interplanar spacing of Pt(100)

[0027] Figure 3 The ORR and OER performance tests of Example 1, Comparative Example 1, and Comparative Example 2 are shown in Figure a. Figure a shows the ORR performance test, and Figure b shows the OER performance test. As can be seen from the figures, the bifunctional oxygen electrode PtIr / NW-TiOx catalyst of the present invention has ORR performance close to that of the most widely used commercial Pt / C catalyst, and OER performance far exceeds that of the most widely used commercial IrOx catalyst.

[0028] Figure 4 This is a TEM image of the heteroatom-doped support-type bifunctional oxygen electrode catalyst prepared in Example 2.

[0029] Figure 5 This is a TEM image of the heteroatom-doped support-type bifunctional oxygen electrode catalyst prepared in Example 3. Detailed implementation method:

[0030] The following is a further description of the invention, but not a limitation thereof.

[0031] Example 1: Preparation of heteroatom-doped supported bifunctional oxygen electrode catalyst

[0032] (1) Mix 2.46g ammonium metatungstate, 10.21g tetrabutyl titanate and 100mL of 1M acetic acid solution, wherein the molar ratio of tungsten to titanium is 25%, and heat at 80°C for 12 hours with stirring.

[0033] (2) The solution from step (1) was transferred to a hydration reactor. The heating rate was 5℃ / min, the reaction temperature was 160℃, and the reaction time was 12 hours. After centrifugation and drying, nitrogen- and tungsten-doped titanium oxide support NW-TiOx was obtained. Figure 1 As shown.

[0034] (3) Grind the carrier obtained in step (2), weigh 0.06 g and add it to 6 mL of deionized water, then add 1 mL of chloroiridium acid solution with a concentration of 5 mg / mL; 3 mL of chloroplatinic acid solution with a concentration of 5 mg / mL; sonicate the sample, and then heat it at 60℃.

[0035] The mixture was stirred and reacted for 12 hours.

[0036] (4) Add NaOH solution dropwise to the mixed solution from step (3) until OH... - The catalyst precursor was obtained by heating the catalyst to 100°C with a molar ratio of 5 to the noble metal PtIr, stirring, washing and drying.

[0037] (5) The catalyst precursor from step (4) was calcined at 400°C in air for 4 hours, and then calcined for another 8 hours by introducing hydrogen / argon reducing gas. The resulting product was ground, washed, and dried to obtain the target catalyst PtIr / NW-TiOx, as shown below. Figure 2 As shown.

[0038] (6) The PtIr / NW-TiOx obtained in step (6) was mixed with ethanol, water, and Nafion solution to prepare catalyst ink. ORR and OER activities were tested using a three-electrode system. Using 0.5M H2SO4 as the electrolyte solution, a glassy carbon electrode coated with catalyst ink as the working electrode, an Ag / AgCl electrode as the reference electrode, and a Pt wire as the auxiliary electrode, the activity of the material was tested using a linear sweep method. The results are as follows: Figure 3 As shown.

[0039] Example 2:

[0040] The operation steps of Example 1 were repeated, except that the amount of ammonium metatungstate added in step (1) was changed so that the molar ratio of tungsten to titanium was 15%. The final catalyst is as follows. Figure 4 As shown.

[0041] Example 3:

[0042] Repeat the steps of Example 1, except that the amounts of chloroplatinic acid and chloroacetic acid in step (3) are changed to 2 mL each, while the concentration remains constant. The final catalyst is as follows: Figure 5 As shown.

[0043] Comparative Example 1:

[0044] Commercial IrOx and 40% Pt / C catalyst, weighing the same weight as the catalyst in Example 1, were mixed with ethanol, water, and Nafion solution to prepare catalyst ink. ORR and OER activities were tested using a three-electrode system. Using 0.5M H₂SO₄ as the electrolyte solution, a glassy carbon electrode coated with catalyst ink as the working electrode, an Ag / AgCl electrode as the reference electrode, and a Pt wire as the auxiliary electrode, the activity of the material was tested using a linear sweep method. The results are as follows: Figure 3 As shown.

[0045] Finally, it should be noted that the above are merely preferred embodiments of the present invention. Those skilled in the art can still modify the technical solutions described in the foregoing embodiments, make equivalent substitutions for some technical features, or improve some operational steps. Any modifications, substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A heteroatom-doped supported oxygen electrode catalyst with dual functions of O2 reduction and O2 evolution, characterized in that, The catalyst is composed of PtIr alloy nanoparticles uniformly loaded on a nitrogen- and tungsten-doped titanium oxide support. The catalyst support is anatase phase, and based on the total molar percentage of the support (100%), the molar ratio of N is 1% to 10%, the molar ratio of W is 5% to 30%, and the remainder is titanium oxide. Based on the total mass percentage of the PtIr alloy nanoparticles (100%), the mass percentage of Pt is 50% to 90%, and the remainder is Ir. The size of the platinum-iridium alloy nanoparticles is 2 to 10 nm.

2. The heteroatom-doped supported oxygen electrode catalyst with dual functions of O2 reduction and O2 evolution according to claim 1, characterized in that, The molar ratio of W in the carrier is 15-25%.

3. The heteroatom-doped supported oxygen electrode catalyst with dual functions of O2 reduction and O2 evolution according to claim 1, characterized in that, The Pt mass percentage in the PtIr alloy nanoparticles is 75%.

4. The method for preparing the heteroatom-doped supported oxygen electrode catalyst with dual functions of O2 reduction and O2 evolution as described in claim 1, characterized in that, The method includes the following steps: (1) Ammonium metatungstate, tetrabutyl titanate, water and inhibitor are mixed to form a solution, heated at 75-85℃ for 12 hours under stirring, and then placed in a reaction vessel at 155-165℃ for 8-12 hours. After centrifugation and drying, doped NW-TiOx support is obtained; the inhibitor is an acid solution. (2) The platinum compound and iridium compound are mixed in proportion and dissolved in water with the NW-TiOx support. An alkaline solution is added dropwise under heating and stirring at 55-65℃ to form a precursor solution. Then the solution is heated to 100℃, washed and dried to obtain the catalyst precursor. (3) The catalyst precursor is calcined in air at 300~500 °C for 3-5 hours, and then a reducing gas is introduced to continue calcining for 7-9 hours. The resulting product is washed and dried to obtain the target catalyst.

5. The preparation method according to claim 4, characterized in that, The acid solution in step (1) is selected from one or more of acetic acid, hydrochloric acid, and nitric acid.

6. The preparation method according to claim 4, characterized in that, Step (2) The platinum compound is selected from one or more of chloroplatinic acid, platinum chloride, and platinum acetylacetonate; the iridium compound is selected from one or more of chloroiridium acid, iridium chloride, and iridium acetylacetonate.

7. The preparation method according to claim 4, characterized in that, The reducing gas in step (3) is selected from any one of hydrogen, hydrogen / argon, or hydrogen / nitrogen mixture.

8. The application of the heteroatom-doped supported oxygen electrode catalyst with dual functions of O2 reduction and O2 evolution as described in claim 1 in electrocatalysts, characterized in that, It is used as a catalyst for oxygen reduction at the cathode of fuel cells, a catalyst for oxygen evolution at the anode of water electrolysis, and a bifunctional oxygen electrode catalyst for URFC. It is used to prepare cathode membrane electrodes, anode membrane electrodes for water electrolysis, and oxygen electrodes for renewable fuel cells.

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