Direct sodium borohydride fuel cell anode catalyst and preparation and application thereof

Abstract

The invention discloses a direct sodium borohydride fuel cell anode catalyst which is characterized in that a nano carbon material is used as a carrier of an active component, and the active component is distributed on the surface of the nano carbon material to form a three-dimensional supported microstructure; and the active component is alloy nanoparticles composed of Pt, Au and Pd. The invention also discloses a preparation method of the catalyst, which comprises the following steps: taking a nano carbon material as a carbon heat carrier, mixing the carbon heat carrier with metal precursors of Pt, Au and Pd, loading the mixture on a conductive substrate, and preparing the catalyst through a carbon heat shock method. And when the conductive substrate is foamed nickel or carbon cloth, the catalyst is formed on the foamed nickel in situ and can be directly used as an anode of the direct sodium borohydride fuel cell. According to the invention, the synergistic catalysis of Pt, Au and Pd is realized by utilizing an electron transfer structure in multi-element metals of Pt, Au and Pd, and the dispersion effect of the nano carbon carrier is cooperated, so that the catalytic selectivity and catalytic performance of the catalyst are improved, and the coulombic efficiency is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the field of fuel cells and relates to a direct sodium borohydride fuel cell anode catalyst and a preparation method thereof. Background Art

[0002] With the rapid development of modern science and technology, global energy demand and environmental carrying capacity have almost reached their limits. Traditional fossil energy systems can no longer meet the requirements of sustainable development. At the same time, environmental problems such as global warming and extreme climates are frequent. There is an urgent need to develop new energy technologies to achieve green and low-carbon development. Direct sodium borohydride fuel cells (DBFCs) are energy conversion devices that convert chemical energy stored in sodium borohydride fuel and oxidant into electrical energy. They have a high theoretical energy density (5.67Ah g -1 ), high energy conversion efficiency (91%), convenient fuel transportation and storage, and pollution-free products have attracted widespread attention from researchers. However, the application-oriented DBFC technology still faces challenges such as low anode reaction coulomb number and coulomb efficiency due to NaBH4 hydrolysis and NaBH4 permeation, as well as low fuel utilization. Developing anode catalysts with high catalytic selectivity is a key issue in addressing NaBH4 hydrolysis and promoting the practical application of DBFC technology.

[0003] The oxidation reaction of sodium borohydride (BOR) is an 8-electron reaction, that is, a BH4 - Completely oxidized to BO2 - Produces 8 electrons. In actual batteries, BH4 oxidized on the surface of the anode catalyst - The number of electrons converted is typically less than 8, and the actual reaction pathway varies with the anode catalyst, electrode potential, fuel concentration, and temperature. Studies on the anodic oxidation mechanism of NaBH4 have shown that the key factor influencing the BOR coulomb number is the anode catalyst used. Specifically, the electrochemical reaction pathways of NaBH4 on different anode catalyst surfaces vary. For example, the theoretical coulomb number of BOR electrons on Pd is 6, while on Ni it is 4. However, during the actual reaction, the number of electrons transferred is lower than the theoretical number due to variations in fuel concentration and temperature. The decrease in the anodic reaction coulomb number not only reduces the fuel energy density but also reduces the fuel output power and utilization rate. This is because the incomplete oxidation of NaBH4 generates hydrogen in situ, and the hydrolysis reaction of NaBH4 also produces hydrogen. This hydrogen generation not only reduces fuel utilization but also hinders the mass transfer of NaBH4 in the fuel, exacerbating anodic polarization. Studies have shown that by designing electrocatalysts and adjusting the anode structure, the hydrogen produced by the incomplete oxidation reaction and hydrolysis reaction of NaBH4 can be oxidized, thereby improving the anode reaction coulomb number and coulomb efficiency (the ratio of the actual energy released by the fuel to the theoretical energy) in actual batteries.

[0004] It is reported that different metals have different degrees of excellence in different properties. The noble metal catalysts used as anodes in direct sodium borohydride fuel cells mainly include Pt, Pd, Au, Ag, etc. Pt and Pd have good activity in borohydride oxidation reaction and have a good activity in BH4 - Borohydride has excellent adsorption capacity and generally has high power density. The hydrolysis reaction of borohydride on Au and Ag surfaces is somewhat inhibited, but its slow electrode kinetics result in low power density. The development of anode catalysts with high Coulombic efficiency, high fuel utilization, and high power density is crucial. Summary of the Invention

[0005] The present invention aims to address the low fuel utilization and Coulombic efficiency of direct sodium borohydride fuel cells (DBH2) anodes. It provides a highly efficient three-dimensional supported anode catalyst for the sodium borohydride oxidation reaction, as well as its preparation method and application. Compared with traditional catalysts, this catalyst significantly improves Coulombic efficiency, simplifies synthesis methods, and significantly enhances catalytic selectivity and battery power generation performance.

[0006] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions.

[0007] The present invention first provides a three-dimensional supported direct sodium borohydride fuel cell anode catalyst. The catalyst uses a nanocarbon material as a carrier for the active component. The nanocarbon material forms a spherical carrier, and the active component is evenly distributed on the surface of the nanocarbon material to form a three-dimensional supported microstructure. The active component is an alloy nanoparticle composed of Pt, Au, and Pd. The nanocarbon material is selected from one or more of carbon nanoparticles, carbon nanotubes, and superconducting carbon black.

[0008] Furthermore, in the anode catalyst, the mass ratio of the total amount of the active components Pt, Au, and Pd to the nano-carbon material is 1:10-1:20.

[0009] Furthermore, in the active components, the molar ratio of Pt, Au and Pd is 2:1:1-1:2:2, wherein 1:1:1 is most preferred. The anode catalyst with this ratio has the best coulombic efficiency and power generation performance when applied to DBFC.

[0010] Furthermore, the particle size of the anode catalyst is less than 10 nm, with an average particle size of about 3.5 nm. The PtAuPd alloy is evenly distributed on the surface of the spherical carrier composed of carbon nanoparticles, resulting in a high electrochemically active surface area (ECSA). For example, the electrochemically active surface area of ​​the PtAuPd / C catalyst prepared in Example 2 of the present invention reaches 118 cm 2 .

[0011] The present invention also provides a method for preparing the aforementioned three-dimensional supported direct sodium borohydride fuel cell anode catalyst. This method uses a nanocarbon material as a carbon heat carrier, mixed with metal precursors of Pt, Au, and Pd, and supported on a conductive substrate. The three-dimensional supported direct sodium borohydride fuel cell anode catalyst, namely PtAuPd / C, is prepared by a carbon thermal shock method. This synthesis method is simple to operate and can control the appropriate composition of the catalyst by designing the combination of metal components.

[0012] Furthermore, the nano-carbon material can be selected from one or more of carbon nanoparticles, carbon nanotubes, superconducting carbon black, and the like.

[0013] Furthermore, the conductive substrate can be carbon cloth or nickel foam, etc. When nickel foam is used as the conductive substrate, the catalyst is in situ formed on the nickel foam current collector. The prepared catalyst PtAuPd / C is in situ loaded on the nickel foam current collector and can be directly used as the anode of a direct sodium borohydride fuel cell, simplifying the battery assembly process.

[0014] The preparation method of the catalyst provided by the present invention specifically comprises the following steps:

[0015] (1) Chloroplatinic acid, chloroauric acid and palladium chloride are dissolved in anhydrous ethanol, mixed to obtain a metal precursor salt solution, and then the metal precursor salt solution is mixed with the nanocarbon material to form a slurry.

[0016] The molar ratio of chloroplatinic acid, chloroauric acid and palladium chloride is 2:1:1-1:2:2, with 1:1:1 being the most preferred. The mass ratio of the metal to the nanocarbon material in the metal precursor salt solution is 1:10-1:20.

[0017] (2) Add Nafion solution to the slurry, stir evenly, and then apply it to the surface of the conductive substrate, and dry it naturally. The concentration of the Nafion solution is 5wt%; the conductive substrate is foamed nickel or carbon cloth.

[0018] (3) The conductive substrate loaded with the precursor prepared in step (2) is connected to a copper electrode, and a capacitor is externally connected. The capacitor is charged by a direct power supply, and the electrical energy is converted into thermal shock by the capacitor discharge. The metal salts of platinum, gold, and palladium on the conductive substrate are thermally decomposed to form alloy nanoparticles, thereby forming the three-dimensional supported direct sodium borohydride fuel cell anode catalyst PtAuPd / C on the conductive substrate. The capacitor discharge voltage is set to 19-25V; the thermal decomposition temperature formed by the thermal shock is 450-600°C or 700-800°C. Different thermal decomposition temperatures are used depending on the conductive substrate. For example, the thermal decomposition temperature of the nickel foam conductive substrate is controlled to be 450-600°C, while the thermal decomposition temperature of the carbon cloth conductive substrate is controlled to be 700-800°C.

[0019] The present invention also provides two methods for applying the anode catalyst prepared by the above-mentioned preparation method in a direct sodium borohydride fuel cell. One method comprises: the above-mentioned conductive substrate is carbon cloth. After step (3), the prepared anode catalyst is shaken off the carbon cloth, mixed with a binder to form an electrode slurry, applied to a current collector, and dried to form an electrode. The electrode is then used as the anode of the direct sodium borohydride fuel cell. Furthermore, the nanocarbon material is superconductive carbon black, such as the superconductive carbon black BP2000 used in Example 2.

[0020] Another application method of the anode catalyst prepared by the above preparation method in a direct sodium borohydride fuel cell: the above conductive substrate is nickel foam, and the nickel foam also serves as the current collector of the anode in the direct sodium borohydride fuel cell. After step (3), the catalyst has been in situ formed on the nickel foam current collector, and the prepared catalyst PtAuPd / C is in situ loaded on the nickel foam current collector and directly used as the anode of the direct sodium borohydride fuel cell. This application method simplifies the battery assembly process. The catalyst PtAuPd / C in situ loaded on the nickel foam current collector prepared in Example 1 of the present invention is used, wherein the carbon heat carrier nano-carbon material uses carbon nanoparticles.

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

[0022] (1) The catalyst of the present invention can be formed in situ on a current collector and directly applied as an anode to a direct sodium borohydride fuel cell, thereby simplifying the catalyst and electrode preparation process.

[0023] (2) The present invention uses a carbon thermal shock method to uniformly disperse alloy nanoparticles on the surface of nanocarbon material particles to form nanoactive components, thereby obtaining a large specific surface area and significantly improving the catalytic active area and electronic conductivity of the catalyst.

[0024] (3) The present invention utilizes the electron transfer structure within the multi-metal Pt, Au, and Pd to achieve synergistic catalysis. Its catalytic effect is superior to that of PtAu / C and PtPd / C alloy catalysts. The dispersion effect of the nanocarbon carrier is also synergistic, which improves the catalytic selectivity and catalytic performance of the catalyst. The selectivity of the sodium borohydride oxidation reaction is close to that of a 6-electron reaction, which significantly improves the Coulombic efficiency, the fuel utilization rate is as high as 71.3%, and the maximum power density of the fuel cell reaches 206mW cm -2 .

[0025] (3) The preparation method of the three-dimensional supported catalyst of the present invention is simple and efficient, and provides an effective way to develop high coulombic efficiency direct sodium borohydride fuel cell anode catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the X-ray diffraction pattern of the PtAuPd / C catalyst prepared in Example 1-2 of the present invention.

[0027] Figure 2 This is a TEM image of the catalyst PtAuPd / C prepared in Example 2 of the present invention, where the inset shows the particle size distribution.

[0028] Figure 3 This is the EDS image of the catalyst PtAuPd / C prepared in Example 2 of the present invention.

[0029] Figure 4 The CV curves and C values ​​of the catalyst prepared in Example 2 of the present invention at different scan rates are shown in FIG. dl Fit the curve.

[0030] Figure 5 CV curves of borohydride oxidation reaction of the catalysts prepared in Example 2 of the present invention and Comparative Examples 1-5 in 1M NaOH+0.1MNaBH4 solution.

[0031] Figure 6 Graphs showing the hydrogen production rate and the number of transferred electrons for the catalysts prepared in Example 2 and Comparative Examples 1-5 of the present invention.

[0032] Figure 7 Statistical graphs of DBFC cell performance and maximum power density of the catalysts of Example 1 of the present invention and Comparative Examples 1-5 at 60°C.

[0033] Figure 8 The catalyst prepared in Example 2 of the present invention and the commercial Pt / C catalyst in Comparative Example 6 were heated at room temperature, 20 g of fuel and a discharge current of 50 mA·cm -2 Battery Coulombic efficiency test and statistical chart. DETAILED DESCRIPTION

[0034] In order to explain the technical content of the present invention in detail, the following is a further clear, detailed and complete description in conjunction with the embodiments. The examples listed are only for further explanation of the present invention and are not intended to limit the present invention.

[0035] Example 1

[0036] In this embodiment, the conductive substrate is made of nickel foam, and the carbon heat carrier nanocarbon material is made of carbon nanoparticles. The specific surface area of ​​the carbon nanoparticles is 1000-1500m 2 / g, a three-dimensional supported PtAuPd / C catalyst formed in situ on nickel foam was prepared. The specific preparation method is as follows:

[0037] Step (1): Add chloroplatinic acid and chloroauric acid to an appropriate amount of anhydrous ethanol to prepare a 0.1M metal salt solution, and add palladium chloride to an appropriate amount of anhydrous ethanol to prepare a 0.01M metal salt solution. 100 μL of Pt and Au salt solutions and 1000 μL of Pd salt solution are respectively added to a 50mL beaker and 25mL of anhydrous ethanol is added and ultrasonicated for 10 minutes, wherein the molar ratio of Pt, Au and Pd is 1:1:1 to obtain a metal precursor salt solution, and then the metal precursor salt solution is mixed with carbon nanoparticles, and the mass ratio of metal to carbon nanoparticles in the metal precursor salt solution is 4.97:80; stir on a magnetic stirrer for 2 hours.

[0038] Step (2): Add 30 μL of 5 wt% Nafion solution to the mixed viscous solution and stir for 10 minutes. Then, apply the slurry to the surface of nickel foam and dry it naturally. The final precursor loading is 5 mg / cm 2 .

[0039] Step (3): The nickel foam loaded with the precursor prepared in step (2) is connected to a copper electrode via a copper fixture, and a capacitor is charged using a direct power supply and discharged through the capacitor, with the capacitor discharge voltage set to approximately 25 V. The electrical energy is converted into thermal shock, and the metal salts of platinum, gold, and palladium on the nickel foam decompose to form alloy nanoparticles, the pyrolysis temperature of which is 450-600°C. The in-situ carbon thermal shock yields a three-dimensional supported PtAuPd / C catalyst, which can be directly used as the anode of a sodium borohydride fuel cell.

[0040] Example 2

[0041] In this embodiment, the conductive substrate is made of carbon cloth, and the carbon heat carrier nanocarbon material is superconductive carbon black BP2000 to prepare a PtAuPd / C catalyst. The specific preparation method is as follows.

[0042] Step (1): Add chloroplatinic acid and chloroauric acid to an appropriate amount of anhydrous ethanol to prepare a 0.1M metal salt solution, and add palladium chloride to an appropriate amount of anhydrous ethanol to prepare a 0.01M metal salt solution. 100 μL of Pt and Au salt solutions and 1000 μL of Pd salt solution were respectively added to a 50mL beaker and added with 25mL of anhydrous ethanol and ultrasonicated for 10 minutes to form a metal precursor salt solution. 80 mg of superconductive carbon black BP2000 was weighed and added to the beaker and ultrasonicated for 10 minutes to mix the metal precursor salt solution and BP2000 evenly. The mass ratio of all metals in the metal precursor to BP2000 was 4.97:80. The beaker was stirred on a magnetic stirrer for 2 hours.

[0043] Step (2): Add 30 μL of 5 wt% Nafion solution and stir for 10 minutes to form an electrode slurry. Apply the electrode slurry to a 4 cm × 5 cm carbon cloth, coating both sides alternately. Then place in a cool place to dry.

[0044] Step (3): Cut the dried carbon cloth into rectangular strips of 1 cm × 1.5 cm and fix them to the copper fixture of the transient carbon thermal shock system and expose them to air. The two ends of the carbon cloth are in full contact with the copper fixture so that current can flow through the carbon cloth. The heat exposure conditions are controlled by applying electric pulses. When the current flows through the carbon cloth, heat is generated, thereby heating the sample for rapid heat treatment, achieving the purpose of rapid temperature rise and promoting rapid reduction of metal cations. Subsequently, rapid cooling is achieved through efficient heat dissipation, thereby suppressing atomic phase separation and obtaining smaller and more uniformly dispersed alloy nanoparticles. After fixing the carbon cloth, adjust the voltage to about 19 V and sinter at a temperature of 700-800 ° C. Then remove the strip, cut the two ends to make it a square strip of about 1 cm × 1 cm, and shake off the sample on it to obtain the PtAuPd / C catalyst.

[0045] Example 3

[0046] In this embodiment, the mass ratio of PtAuPd metal to carbon nanoparticles in the metal precursor salt solution is 1:10; the metal salt in the metal precursor salt solution is added to satisfy the molar ratio of Pt, Au, and Pd of 2:1:1. Other conditions are the same as those in Example 1.

[0047] Example 4

[0048] In this embodiment, the mass ratio of PtAuPd metal to carbon nanoparticles in the metal precursor salt solution is 1:20; the metal salt in the metal precursor salt solution is added to satisfy the molar ratio of Pt, Au, and Pd of 1:2:2. Other conditions are the same as those in Example 1.

[0049] Application Example 1

[0050] In this application example, the PtAuPd / C catalyst prepared in situ on nickel foam as a current collector in Example 1 was directly used as the anode of a direct sodium borohydride fuel cell. Furthermore, in this application example, Co(OH)2-PPY-BP was used as the cathode, N117 was used as the proton exchange membrane, and a sodium borohydride solution composed of 5 wt.% NaBH4, 10 wt.% NaOH, and 85% deionized water was used as the fuel to form a direct sodium borohydride fuel cell.

[0051] Application Example 2

[0052] In this application example, the PtAuPd / C catalyst prepared in Example 2 was shaken off the carbon cloth and collected. Approximately 5 mg of the prepared PtAuPd / C catalyst was weighed, added to 35 μL of a 5 wt% Nafion solution, and ground thoroughly in a mortar with an appropriate amount of anhydrous ethanol until it was ink-like. The mixture was then coated onto a 1 cm × 1 cm nickel foam to form an electrode. This electrode served as the anode of a direct sodium borohydride fuel cell, with a cathode of Co(OH)2-PPY-BP and a proton exchange membrane of N117. A sodium borohydride solution composed of 5 wt.% NaBH4, 10 wt.% NaOH, and 85% deionized water was used as the fuel.

[0053] Comparative Example 1

[0054] The specific preparation method of PtAu / C catalyst is as follows:

[0055] Step (1): dissolving chloroplatinic acid and chloroauric acid in anhydrous ethanol, mixing them in a molar ratio of 1:1 to obtain a metal salt precursor solution, and then uniformly mixing the noble metal in the metal precursor salt solution with the carbon nanoparticles.

[0056] Step (2) is consistent with step (2) of Example 1.

[0057] Step (3) is consistent with step (3) of Example 1.

[0058] Comparative Example 2

[0059] The specific preparation method of PtPd / C catalyst is as follows:

[0060] Step (1): dissolving chloroplatinic acid and palladium chloride in anhydrous ethanol, mixing them in a molar ratio of 1:1 to obtain a metal salt precursor solution, and then uniformly mixing the noble metal in the metal precursor salt solution with carbon nanoparticles.

[0061] Step (2) is consistent with step (2) of Example 1.

[0062] Step (3) is consistent with step (3) of Example 1.

[0063] Comparative Example 3

[0064] The specific preparation method of Pt / C catalyst is as follows:

[0065] Step (1): dissolving chloroplatinic acid in anhydrous ethanol, mixing them in a molar ratio of 1:1 to obtain a metal salt precursor solution, and then uniformly mixing the noble metal in the metal precursor salt solution with the carbon nanoparticles.

[0066] Step (2) is consistent with step (2) of Example 1.

[0067] Step (3) is consistent with step (3) of Example 1.

[0068] Comparative Example 4

[0069] The specific preparation method of carbon-supported Au / C catalyst is as follows:

[0070] Step (1): dissolving chloroauric acid in anhydrous ethanol, mixing them in a molar ratio of 1:1 to obtain a metal salt precursor solution, and then uniformly mixing the noble metal in the metal precursor salt solution with the carbon nanoparticles.

[0071] Step (2) is consistent with step (2) of Example 1.

[0072] Step (3) is consistent with step (3) of Example 1.

[0073] Comparative Example 5

[0074] The specific preparation method of carbon-supported Pd / C catalyst is as follows:

[0075] Step (1): dissolving palladium chloride in anhydrous ethanol, mixing them in a molar ratio of 1:1 to obtain a metal salt precursor solution, and then uniformly mixing the noble metal in the metal precursor salt solution with carbon nanoparticles.

[0076] Step (2) is consistent with step (2) of Example 1.

[0077] Step (3) is consistent with step (3) of Example 1.

[0078] Comparative Example 6

[0079] Commercial Pt / C catalyst.

[0080] Various tests and analyses were performed on the catalysts of the examples and comparative examples, as detailed below.

[0081] (1) Catalyst XRD and micromorphology analysis

[0082] The crystal phase of the PtAuPd / C catalyst prepared in each embodiment was analyzed by XRD. The XRD test results of the catalysts in each embodiment showed that Pt, Au and Pd in ​​the catalyst formed an alloy phase. Figure 1 The XRD patterns of the PtAuPd / C catalysts prepared in Examples 1 and 2 are shown. The diffraction peaks in the figures indicate the formation of a PtAuPd alloy. A relatively strong Ni peak appears in the XRD pattern of Example 1, which is due to the nickel foam of the current collector.

[0083] The particle size and element distribution of the PtAuPd / C catalysts prepared in each embodiment were analyzed by TEM and EDS. The test results show that the PtAuPd / C catalyst prepared by the instantaneous carbon thermal method of the present invention has a small particle size of <10nm and an average particle size of less than 4nm; and the three metal elements Pt, Au, and Pd are evenly distributed. Figure 2 and attached Figure 3 , are TEM images and EDS images of the PtAuPd / C catalyst prepared in Example 2, respectively. Figure 2 The illustration in the figure is the particle size distribution diagram of the PtAuPd / C catalyst of Example 2. Figure 2 It can be seen from the figure that the catalyst particle size of Example 2 is less than 10 nm, and the average particle size is 3.84 nm. Figure 3 It can be clearly seen that the three elements Pt, Au, and Pd are evenly dispersed in the carbon heat carrier nanocarbon material; the small particle size and uniform distribution of the active components make the catalyst have a larger specific surface area, which is beneficial to increase the contact area between the catalyst and the reactants, as well as the synergistic effect between the active components, thereby increasing the reaction rate.

[0084] (2) CV curve, electrochemical active area and other test analysis

[0085] 4 mg of a PtAuPd / C catalyst prepared using carbon cloth as a carbon heat carrier, such as the catalyst prepared in Example 2, was weighed; 775 μL of anhydrous ethanol and 25 μL of a 5 wt% Nafion solution were added to form a slurry. The slurry was ultrasonicated in an ice-water bath for 10 minutes to prepare a catalyst ink. 6 μL of the slurry was then drop-coated on a treated rotating disk electrode. After the ink on the electrode dried, the ink was drop-coated again. A total of four drop-coatings were performed to achieve a loading of 600 μg cm -2 . After the drop coating is completed, it is dried at room temperature to obtain a working electrode. Then the test is carried out on a CHI 730e electrochemical workstation. The test temperature is room temperature. The test system is a standard three-electrode system, in which the Hg / HgO electrode is the reference electrode, the glassy carbon rod is the counter electrode, and the rotating disk electrode coated with a catalyst is the working electrode. The test is carried out in an electrolyte saturated with argon. When testing ECSA (electrochemically active area), the electrolyte is 1M NaOH solution, the test scan range is 0.9~1.1V (vs. RHE), and the scan rates are 10, 20, 40, 60, and 80mV·s, respectively. -1 , the result is Figure 4 When performing cyclic voltammetry (CV) tests, the electrolyte was 1M NaOH + 0.1M NaBH4, the test scan range was 0.2 to 1.3 V (vs. RHE), and the scan rate was 50 mV·s -1 , the result is Figure 5 shown.

[0086] Figure 4 (a) shows the CV curves of the PtAuPd / C catalyst prepared in Example 2 at different scan rates. Figure 4 The curve in (a) can be obtained by fitting Figure 4 (b) The average double-layer capacitance of the PtAuPd / C catalyst of Example 2 is 24.13 mF·cm -2 The electrochemical active area of ​​the PtAuPd / C catalyst of Example 2 is 118 cm 2 . Figure 5 The CV curves of borohydride oxidation reaction of the samples prepared in Example 2 and Comparative Examples 1-5 in 1M NaOH+0.1M NaBH solution are shown. Compared with the comparative examples, the maximum current density that Example 2 can achieve is 212 mA cm -2 , which has been significantly improved compared with the comparative examples. This should be due to the synergistic effect between the three nano-alloy active components of Pt, Au and Pd, which enable them to exhibit the best borohydride oxidation performance.

[0087] (3) Hydrogen production test

[0088] Hydrogen production test: Weigh 5 mg of PtAuPd / C catalyst prepared with carbon cloth as carbon heat carrier (as in Example 2), add 35 μL of 5 wt% Nafion solution and an appropriate amount of anhydrous ethanol, grind it in a mortar until it is ink-like, and then apply it on a 1 cm × 1 cm nickel foam. The test system is a standard three-electrode system, in which the Hg / HgO electrode is the reference electrode, the nickel foam is the counter electrode, and the nickel foam coated with the catalyst is the working electrode. By testing at different currents for the same time and recording the hydrogen production volume, the hydrogen production rate (such as Figure 6 (a) in Figure ), and thus the number of transferred electrons of each catalyst was calculated ( Figure 6 As can be seen from the figure, compared with the comparative examples, the catalyst of the embodiment has the highest number of transferred electrons, such as Figure 6 The number of transferred electrons of PtAuPd / C in Example 2 in (b) is 5.7, which means that the selectivity of the sodium borohydride oxidation reaction is close to a 6-electron reaction, indicating that the catalyst of the present invention can significantly improve the coulombic efficiency and fuel utilization rate.

[0089] (4) Battery test

[0090] The present invention conducted a battery test on a direct sodium borohydride fuel cell assembled with the catalysts prepared in each embodiment and comparative example. The assembly method is the same as that in Application Example 1 and Application Example 2. Test conditions: fuel flow rate is 25-30 mL·min -1 , humidified high-purity oxygen was used as the oxidant, with a flow rate of 100 mL min -1, temperature was 60℃; the battery performance of the catalyst was evaluated using a PFX-2011 battery tester. The power generation performance of the single cell was analyzed by recording the voltage at different currents and drawing current density-voltage curves and current density-power density curves. In addition, at room temperature, with 20g of fuel and a constant current of 50mA, the coulombic efficiency of the electrocatalytic sodium borohydride oxidation reaction of each catalyst was analyzed by drawing voltage-time curves. Figure 7 The results of the battery performance tests of the catalysts of Example 1 and Comparative Examples 1-6 applied to direct sodium borohydride fuel cells are shown. The battery test of Example 1 is the test of Application Example 1 (a battery assembled with the catalyst of Example 1). Figure 7 (a) shows the DBFC battery performance and maximum power density statistics of Example 1 and Comparative Examples 1-6 at 60°C. Figure 7 It can be clearly seen in (b) that the catalyst of Example 1 has a maximum power density of 206 mW·cm -2 .

[0091] The coulombic efficiency of the PtAuPd / C catalyst of Example 2 and the commercial Pt / C catalyst of Comparative Example 6 in a direct sodium borohydride fuel cell was determined by plotting a voltage-time curve at a constant current of 50 mA and 20 g of the catalyst. Figure 8 Figure (a) shows the Coulomb efficiency test diagram of the two. Through calculation, as shown in Figure 8 The calculation results in Figure (b) clearly show that the PtAuPd / C catalyst of Example 2 achieves a Coulombic efficiency of 71.3%, significantly higher than the 61.8% of commercial Pt / C. This demonstrates that the PtAuPd / C catalyst prepared by the method of the present invention has a high Coulombic efficiency, enabling efficient fuel utilization.

[0092] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications derived therefrom remain within the scope of protection of the present invention.

Claims

1. A direct sodium borohydride fuel cell anode catalyst, characterized in that: The anode catalyst uses nanocarbon material as a carrier of the active component, the nanocarbon material constitutes a spherical carrier, and the active component is evenly distributed on the surface of the nanocarbon material to form a three-dimensional loaded microstructure; wherein the active component is an alloy nanoparticle composed of Pt, Au, and Pd; the nanocarbon material is selected from one or more of carbon nanoparticles, carbon nanotubes, and superconducting carbon black.

2. A direct sodium borohydride fuel cell anode catalyst according to claim 1, characterized in that: In the anode catalyst, the mass ratio of the total amount of the active components Pt, Au, and Pd to the nano-carbon material is 1:10-1:20; and the molar ratio of Pt, Au, and Pd in ​​the active components is 2:1:1-1:2:

2.

3. The direct sodium borohydride fuel cell anode catalyst according to claim 1, characterized in that: The particle size of the anode catalyst is less than 10 nm.

4. The method for preparing a direct sodium borohydride fuel cell anode catalyst according to any one of claims 1 to 3, characterized in that: The nanocarbon material is used as a carbon heat carrier, which is mixed with a metal precursor formed by metal salts of Pt, Au, and Pd and loaded on a conductive substrate. The direct sodium borohydride fuel cell anode catalyst, namely PtAuPd / C, is prepared by a carbon thermal shock method.

5. The method for preparing a direct sodium borohydride fuel cell anode catalyst according to claim 4, characterized in that: The following steps are involved: (1) dissolving chloroplatinic acid, chloroauric acid and palladium chloride in anhydrous ethanol, mixing to obtain a metal precursor salt solution, and then mixing the metal precursor salt solution with a nano-carbon material to form a slurry; (2) adding Nafion solution dropwise to the slurry and stirring evenly, then coating the mixture on the surface of the conductive substrate and allowing it to dry naturally; (3) connecting the precursor-loaded conductive substrate prepared in step (2) above to a copper electrode, externally connecting a capacitor, charging the capacitor with a direct power supply, discharging through the capacitor, converting electrical energy into thermal shock, and thermally decomposing the metal salts of platinum, gold, and palladium on the conductive substrate to form alloy nanoparticles, thereby forming the direct sodium borohydride fuel cell anode catalyst PtAuPd / C on the conductive substrate; Wherein, the conductive substrate is carbon cloth or nickel foam; when nickel foam is used as the conductive substrate, the catalyst is in situ formed on the nickel foam current collector, and the prepared catalyst PtAuPd / C is in situ loaded on the nickel foam current collector and can be directly used as the anode of a direct sodium borohydride fuel cell.

6. The method for preparing a direct sodium borohydride fuel cell anode catalyst according to claim 5, characterized in that: In step (1), the molar ratio of chloroplatinic acid, chloroauric acid and palladium chloride is 2:1:1-1:2:2; the mass ratio of the metal to the nanocarbon material in the metal precursor salt solution is 1:10-1:

20.

7. The method for preparing a direct sodium borohydride fuel cell anode catalyst according to claim 5, characterized in that: In step (3), the capacitor discharge voltage is set to 19-25V; the thermal decomposition temperature formed by thermal shock is 450-600°C or 700-800°C, and different thermal decomposition temperatures are adopted according to different conductive substrates; when nickel foam is the conductive substrate, the thermal decomposition temperature is controlled to be 450-600°C; when carbon cloth is the conductive substrate, the thermal decomposition temperature is controlled to be 700-800°C.

8. Use of the anode catalyst prepared by the preparation method according to any one of claims 4 to 7, characterized in that: The conductive substrate is carbon cloth. After step (3), the prepared anode catalyst is shaken off the carbon cloth, mixed with a binder to form an electrode slurry, applied to a current collector and dried to form an electrode, which is used as the anode of a direct sodium borohydride fuel cell.

9. Use of the anode catalyst prepared by the preparation method according to any one of claims 4 to 7, characterized in that: The conductive substrate is nickel foam, which also serves as the current collector of the anode in a direct sodium borohydride fuel cell. After step (3), the catalyst has been in situ formed on the nickel foam current collector. The prepared catalyst PtAuPd / C is in situ loaded on the nickel foam current collector and directly used as the anode of the direct sodium borohydride fuel cell.

10. Use of the anode catalyst according to any one of claims 8 or 9, characterized in that: The catalyst has a selectivity of 5.7 for the sodium borohydride oxidation reaction, close to a 6-electron reaction; the fuel utilization rate is as high as 71.3%, and the maximum power density of the fuel cell reaches 206 mW cm -2 .

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