Amorphous metal phosphide / crystal metal element composite hydrazine oxidation catalyst, its preparation method and application

Abstract

The application discloses an amorphous metal phosphide / crystal metal element composite hydrazine oxidation catalyst and a preparation method and application thereof. The catalyst comprises a metal phosphide amorphous phase and a metal element crystal phase, and the metal element crystal phase is embedded in the metal phosphide amorphous phase in the form of dispersed nanoparticles. In the application, a carrier material is used as a cathode, a metal electrode is used as an anode, and is added into a solution containing a phosphide and a buffer, and then electro-deposition is carried out to obtain the amorphous metal phosphide / crystal metal element composite hydrazine oxidation catalyst. The preparation method of the application has the advantages of low cost, convenience and easy mass production. The prepared catalyst has high intrinsic catalytic activity, rich active sites and good conductivity, can efficiently and stably catalyze the electrochemical oxidation reaction of hydrazine under alkaline conditions, has a Faraday efficiency of 100%, and is superior to existing DHzFC anode electrocatalysts.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of fuel cell materials, and particularly relates to an amorphous metal phosphide / crystalline metal element composite hydrazine oxidation catalyst and a preparation method and application thereof. BACKGROUND

[0002] Fuel cells are a very promising clean energy conversion technology. In the search for advanced and reliable energy systems, direct hydrazine fuel cells (DHZFC) are considered as commercially viable power sources for vehicular and portable applications due to their many good properties and thus have attracted extensive attention from academia and industry. They have high energy density (5.42 Wh·g –1 ) and high theoretical cell voltage (1.56 V), and excellent stability at room temperature.

[0003] At the same time, the products produced are environmentally friendly (N2 and H2O), and the most prominent advantage is that direct hydrazine fuel cells do not need to use noble metals as electrocatalyst materials, which is very important for practical application. In addition, a promising detoxification technology has been developed to solve the toxicity of hydrazine monohydrate, which involves converting hydrazine monohydrate into solid hydrazone through an aldol reaction, and regenerating hydrazine monohydrate through hydrolysis of hydrazone.

[0004] The development of DHZFC as a commercially viable power generation device requires advanced anode catalysts to selectively promote the 4-electron pathway (N2H4+4OH – →N2+4H2O+4e – ) of hydrazine electro-oxidation reaction (HzOR). For decades, many non-noble metal, alloy or metal compound has been identified as an active HzOR catalyst, and its catalytic performance is even better than that of noble metal catalyst. Based on research findings, the performance of the catalyst can be improved mainly by two strategies: one is to use nanostructure engineering strategies to increase the number of active sites of the catalyst, and also to improve the mass transfer characteristics; the other is to use the generation of structural defects or the combination of electron conductive phases to enhance the charge transfer in the electrochemical reaction. Based on the comprehensive use of the above methods, several representative anode catalysts for direct hydrazine fuel cells have been developed, which exhibit high catalytic activity for the electrochemical oxidation of hydrazine at near room temperature. However, the catalytic performance of the existing anode catalysts still cannot meet the needs of commercial application of direct hydrazine fuel cells, and the lack of advanced and efficient anode electrocatalysts has become a key problem in the development of direct hydrazine fuel cell technology. Therefore, these strategies need to be used comprehensively to simultaneously improve the intrinsic catalytic performance, active site density and accessibility, and electronic conductivity of the anode electrocatalyst.

[0005] Transition metal phosphides have been widely studied as electrode materials in lithium-ion batteries, water electrolysis, supercapacitors and other fields due to their low price, good chemical stability, excellent electrical conductivity and other advantages. However, there are few studies on nanostructured transition metal phosphide electrocatalysts in the field of hydrazine fuel cell anode catalysts, and most of them are powder catalysts. It should be particularly pointed out that when powder electrocatalysts are used as electrodes, they need to be coated with a binder. This operation often causes the shielding of active sites, resulting in a decrease in catalytic activity due to the shedding of the active phase of the catalyst during the catalytic reaction. Meanwhile, the investigation of the published literature found that recent studies on transition metal phosphide catalysts have mostly focused on single-phase materials. At present, the catalytic mechanism of alkaline HzOR is still unclear. However, it is most likely that this involves N2H4 and OH - The reaction of the reactants requires complex catalysts to act on more than one site or function. In this case, heterojunction catalysts should provide more freedom to build multifunctional sites and achieve synergistic effects between them. In addition, it is noted that most of the reported transition metal phosphide catalysts are of crystalline nature, and amorphous phosphides are rarely studied for their HzOR performance. It is well known that disordered atomic arrangements can have a significant impact on electronic structure and bonding properties, which can enable amorphous materials to have unique catalytic properties. In this sense, amorphization can provide an exciting opportunity to address activity and selectivity by designing surface properties, and to advance the practicalization process of direct hydrazine fuel cells. SUMMARY

[0006] To solve the problems in the prior art, the purpose of the present application is to provide an amorphous metal phosphide / crystalline metal element composite hydrazine oxidation catalyst, a preparation method and application thereof. The method has the advantages of easy availability of raw materials, simple operation, easy mass production, and the prepared hydrazine oxidation catalyst has high intrinsic activity, rich active sites and good electrical conductivity, can efficiently and stably catalyze the electrochemical oxidation reaction of hydrazine under alkaline conditions, and the comprehensive catalytic performance is better than that of most existing DHzFC anode electrocatalysts.

[0007] The purpose of the present application is achieved by the following technical solutions:

[0008] An amorphous metal phosphide / crystalline metal element composite hydrazine oxidation catalyst, the catalyst comprising a metal phosphide amorphous phase and a metal element crystalline phase, the metal element crystalline phase being embedded in the metal phosphide amorphous phase in the form of dispersed nanoparticles.

[0009] Preferably, the metal phosphide is a transition metal phosphide; the metal element is a transition metal element; and the transition metal is at least one of Fe, Co, Ni, Cu and Zn.

[0010] Preferably, the amorphous metal phosphide phase exists in the form of nanoparticles, and the size of the nanoparticles is 20-50 nm.

[0011] Further preferably, the size of the particles of the amorphous metal phosphide phase is 20-30 nm.

[0012] Preferably, the metal element exists in the form of crystals, and the size of the particles is 2-3 nm.

[0013] The preparation method of the above-mentioned amorphous metal phosphide / crystal metal element composite hydrazine oxidation catalyst comprises the following steps:

[0014] The carrier material is used as the cathode, the metal electrode is used as the anode, and the solution containing the phosphide and the buffer is added, and then electro-deposition is performed (electro-deposition method using a two-electrode system). The metal ions are obtained by self-corrosion of the anode material, the phosphine gas is formed by decomposition of the phosphide in the solution, the metal ions flow to the cathode under the action of the electric field, and the amorphous metal phosphide base is formed by the phosphine gas in the solution under the action of the electric current. The metal ions can also be reduced to the crystal metal element and deposited on the amorphous metal phosphide base at the cathode under the same potential, thereby obtaining the amorphous metal phosphide / crystal metal element composite hydrazine oxidation catalyst.

[0015] Preferably, the carrier material is selected from foam metal, metal mesh, ion exchange resin, molecular sieve, and carbon cloth; more preferably, the carrier material is foam nickel (NF), foam cobalt (CF), foam copper (CF), or carbon cloth (CC).

[0016] Preferably, the phosphide capable of releasing phosphine gas is sodium hypophosphite.

[0017] Preferably, the buffer is ammonium fluoride.

[0018] Preferably, the metal electrode is selected from foam metal and metal mesh; and the metal is at least one of Fe, Co, Ni, Cu, and Zn.

[0019] Preferably, the electro-deposition reaction is performed for 0.5-2 h at a temperature of 20-60°C and a voltage of 2-4 V.

[0020] Further preferably, the electro-deposition voltage is 4 V.

[0021] Preferably, the concentration of the phosphide is 0.25-1.5 M.

[0022] Further preferably, the concentration of the phosphide is 0.5-1.25 M.

[0023] Preferably, the concentration of the buffer is 0.25-1.0 M.

[0024] Preferably, the molar ratio of the phosphide to the buffer is 4:1 to 4;

[0025] More preferably, the molar ratio of the phosphide to the buffer is 4:1 to 3;

[0026] Preferably, the solvent of the solution containing phosphide and buffer is water.

[0027] The above-mentioned amorphous metal phosphide / crystalline metal elemental composite hydrazine oxidation catalyst is used in the preparation of hydrazine fuel cells.

[0028] The principle of this invention is as follows: Current research on metal phosphide catalysts mostly focuses on single-phase materials, and the catalytic mechanism of alkaline HzOR remains unclear. However, it is most likely that this involves N₂H₄ and OH⁻. - The reaction of reactants requires complex catalysts to act on more than one site or function simultaneously. In this case, heterojunction catalysts should provide more degrees of freedom to construct multifunctional sites and achieve synergistic effects among them. The catalyst provided by this invention simultaneously prepares a composite heterojunction of amorphous and crystalline phases and provides a simple and easy preparation method to realize it. An electrodeposition method with a dual-electrode system is used to deposit a metal phosphide with an amorphous structure and a crystalline metal element on the surface of a support material. Under the action of current, the anode support material undergoes self-corrosion to form metal ions. The phosphide in the solution decomposes to release phosphine gas as a phosphorus source, which is co-deposited on the support surface with the metal ions. At the same potential, metal ions can also be deposited independently on the support surface, forming a heterojunction structure of amorphous metal phosphide and crystalline metal element. This heterojunction structure can provide different functional sites to achieve synergistic effects, improving the catalytic activity and stability of the catalyst. Furthermore, the addition of phosphorus enhances the reaction selectivity of the catalyst. In summary, the hydrazine oxidation catalyst provided by this invention has high catalytic activity, excellent stability, and nearly 100% selectivity for the electro-oxidation of four-electron hydrazine.

[0029] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0030] (1) The key difference between the present application and the traditional method is that the heterojunction with amorphous structure and crystal structure can be synthesized in one step, and the activity, stability and selectivity are optimized. By controlling the parameters of electrodeposition and the concentration of phosphide and buffer in the solution, a series of catalysts with different amorphous / crystal ratios can be synthesized. The addition of phosphorus source will inhibit the deposition of metal ions alone, and the co-deposition of phosphorus source and metal ions will occur. When the phosphorus content is greater than a certain degree, the amorphous structure will be formed. In the local area where the phosphorus source is absent, the metal ions will deposit alone to form a crystal structure dispersed in the matrix of amorphous metal phosphide. This heterojunction structure can provide multiple functional sites for the catalytic oxidation of hydrazine, ensuring the catalytic activity of the catalyst, and also enhancing the stability and selectivity of the catalyst.

[0031] (2) The preparation method of the present application has low raw material cost, is convenient to prepare, easy to mass-produce and pollution-free.

[0032] (3) The catalyst of the present application has high intrinsic catalytic activity, rich active sites and good conductivity, can efficiently and stably catalyze the electrochemical oxidation reaction of hydrazine under alkaline conditions, has a Faraday efficiency of 100%, and the comprehensive catalytic performance is better than most existing DHzFC anode electrocatalysts. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The a-Ni obtained in Example 1 of the present application x Scanning electron microscope morphology diagram of P / Ni / NF.

[0034] Figure 2 The a-Ni obtained in Example 1 of the present application x P / Ni / NF and reference sample a-Ni x X-ray diffraction diagram of P / NF, Ni / NF, Ni3P / Ni / NF.

[0035] Figure 3 The a-Ni obtained in Example 1 of the present application x Transmission electron microscope morphology diagram (a), selected area electron diffraction diagram (inset in a) and high-resolution electron microscope photograph diagram (b) of P / Ni / NF.

[0036] Figure 4 The a-Ni obtained in Example 1 of the present application x Transmission electron microscope morphology diagram (a) and high-resolution electron microscope photograph diagram (b) of P / NF.

[0037] Figure 5 The a-Ni obtained in Example 1 of the present application x X-ray photoelectron spectroscopy diagram of P / Ni / NF and reference sample Ni / NF: (a) Ni 2p spectrum; (b) P 2p spectrum.

[0038] Figure 6 a-Ni obtained in Example 1 of the present application x P / Ni / NF and a-Ni x P / NF, Ni / NF, Ni3P / Ni / NF catalysts in hydrazine anode oxidation reaction polarization curve comparison chart containing 0.5M hydrazine monohydrate and 1.0M sodium hydroxide solution.

[0039] Figure 7 a-Ni obtained in Example 1 of the present application x P / Ni / NF and a-Ni x P / NF, Ni / NF, Ni3P / Ni / NF sample at open circuit potential capacitance current density and potential scan speed relationship chart (a) and impedance spectrum test results at the initial potential (b).

[0040] Figure 8 a-Ni obtained in Example 1 of the present application x P / Ni / NF catalyst and reference sample cycle durability test results chart.

[0041] Figure 9 a-Ni obtained in Example 1 of the present application x P / Ni / NF catalyst and reference sample constant current durability test results chart (chronoamperometry method).

[0042] Figure 10 a-Ni obtained in Example 1 of the present application x P / Ni / NF catalyst after 100 hours of durability test scanning electron microscope morphology chart (a, b) and X-ray diffraction chart before and after reaction (c).

[0043] Figure 11 a-Ni obtained in Example 1 of the present application x P / Ni / NF catalyst X-ray photoelectron spectroscopy chart before and after stability.

[0044] Figure 12 a-Ni obtained in Example 1 of the present application x P / Ni / NF catalyst and reference sample reaction selectivity.

[0045] Figure 13 a-Ni obtained in Example 1 of the present application x P / Ni / NF catalyst as an anode electrocatalyst DHZFC polarization curve and power density curve.

[0046] Figure 14 a-Ni obtained in Example 2 of the present application xXRD patterns of P / Ni / CC (a) and reference sample Ni / CC (b).

[0047] Figure 15 a-Ni obtained in Example 2 of the present application x TEM morphology (a) and HRTEM image (b) of P / Ni / CC.

[0048] Figure 16 a-Ni obtained in Example 2 of the present application x Comparison of hydrazine oxidation reaction polarization curves of P / Ni / CC and reference sample Ni / CC.

[0049] Figure 17 a-Ni obtained in Example 2 of the present application x Durability test results of P / Ni / CC catalyst (chronoamperometry).

[0050] Figure 18 a-Co obtained in Example 3 of the present application x Comparison of hydrazine oxidation reaction polarization curves of P / Co / CF and Co / CF catalysts.

[0051] Figure 19 a-Co obtained in Example 3 of the present application x Durability test results of P / Co / CF catalyst (chronoamperometry).

[0052] Figure 20 a-Cu obtained in Example 4 of the present application x Comparison of hydrazine oxidation reaction polarization curves of P / Cu / cF and Cu / cF catalysts.

[0053] Figure 21 a-Cu obtained in Example 4 of the present application x Durability test results of P / Cu / cF catalyst (chronoamperometry).

[0054] Figure 22 XRD patterns of the series of catalysts obtained in Example 5 of the present application.

[0055] Figure 23 Comparison of hydrazine oxidation reaction polarization curves of the series of catalysts obtained in Example 5 of the present application.

[0056] Figure 24 XRD patterns of the series of catalysts obtained in Example 6 of the present application.

[0057] Figure 25 Comparison of hydrazine oxidation reaction polarization curves of the series of catalysts obtained in Example 6 of the present application.

[0058] Figure 26 This is a comparison of the polarization curves of the hydrazine oxidation reaction of the series of catalysts obtained in Example 7 of the present invention. Detailed Implementation

[0059] The present invention will be specifically described below with reference to the embodiments, but the implementation and protection scope of the present invention are not limited to the following embodiments.

[0060] Example 1

[0061] Using nickel foam as a carrier, its thickness is 1.60 mm and its areal density is ~650 g / m³. 2 The pore size is 0.20–0.80 mm. Nickel foam (1×3 cm) 2 The NF was ultrasonically cleaned sequentially with ethanol, hydrochloric acid solution (3M), and deionized water for 10 minutes each. NaH₂PO₂ (1.0M) and NH₄F (0.5M) were dissolved in 60 mL of deionized water. After thorough stirring, the solution was poured into an electrolytic cell. The cleaned NF was used as both the anode and cathode in the electrolytic cell containing the electrolyte. After applying a constant potential of 4V at room temperature for one hour, α-Ni was obtained. x P / Ni / NF.

[0062] Preparation of the Ni / NF sample: The only difference from the above preparation method is that the solution does not contain NaH2PO2.

[0063] Comparison sample a-Ni x Preparation of P / NF: The difference from the above preparation method is that the solute concentration of the solution is NaH2PO2 (1.0M) and NH4F (1.0M), and the electrodeposition temperature is 60℃.

[0064] Preparation of comparison sample Ni3P / Ni / NF: a-Ni x The P / Ni / NF sample was heated at 400℃ for 2 hours under an argon atmosphere to precipitate amorphous metal phosphide Ni. x P is converted into crystalline Ni3P.

[0065] Phase / structure / elemental chemical state characterization of catalysts:

[0066] (1) The a-Ni obtained in this embodiment x The scanning electron microscope (SEM) morphology and X-ray diffraction (XRD) patterns of P / Ni / NF are shown below. Figure 1 and Figure 2 As shown. By Figure 1 As can be seen, after electrodeposition, a large number of spherical particles grew on the surface of the nickel foam, and the size of the spherical particles at the edges was significantly larger than that in the central area. Figure 2 The 'a' in the equation can be seen as: a-Ni xThe P / Ni / NF structure exhibits amorphous diffraction peaks, with the peak positions corresponding to the (111) crystal plane of Ni, indicating the presence of nanocrystalline Ni. Meanwhile, a-Ni... x Peak position and shape of P / NF samples and α-Ni x The P / Ni / NF ratio is similar, but the peak intensity is significantly reduced, indicating that the amount of nanocrystalline Ni in the sample has been greatly reduced, and it can be approximated as amorphous Ni. x The Ni3P / Ni / NF sample is a single-phase Ni, which was confirmed in subsequent HRTEM results. The XRD results of the Ni3P / Ni / NF sample show a two-phase mixture of crystalline Ni3P and crystalline Ni. The XRD results of the Ni / NF sample show a single-phase crystalline Ni.

[0067] (2) a-Ni obtained in this embodiment x Transmission electron microscopy (TEM) morphology (a), selected area electron diffraction (inset), and high-resolution electron microscopy (HREM) image (b) of P / Ni / NF are shown below. Figure 3 As shown. Transmission electron microscopy observation ( Figure 3 a) further confirms a-Ni x The micron-sized particles in the P / Ni / NF sample are actually aggregates of nanoparticles with sizes ranging from 10 to 30 nm. Selected area electron diffraction patterns show a combination of sharp rings and diffuse halos, indicating the coexistence of nanocrystalline and amorphous phases. In the high-resolution electron microscope image in Figure (b), numerous irregularly shaped and varying-sized crystalline nanoparticles are scattered within an amorphous matrix, exhibiting a disordered atomic arrangement. Based on the interplanar spacing of the lattice fringes, these nanoparticles can be well classified as nanocrystalline Ni. In a-Ni... x Transmission electron microscopy morphology of P / NF ( Figure 4 a and b) in the figure indicate that only a very small amount of nanocrystalline Ni exists in the sample.

[0068] (3) The a-Ni obtained in this embodiment x The X-ray photoelectron spectrum of P / Ni / NF is as follows: Figure 5 As shown: (a) Ni 2p spectrum; (b) P 2p spectrum. Figure 5 It can be seen that the Ni element in the sample exists. 0 and Ni 2+ The signal, while the P element exists. 0 And P-O signals; compared with the Ni / NF binding energy, the Ni of the target sample was observed to be... 0 2p 1 / 2 The peak exhibits a positive shift of 0.4 eV. Meanwhile, compared to the original red phosphorus binding energy, the target sample's P... 0 2p 3 / 2 A negative shift of 0.5 eV. These results indicate that electrons transfer from Ni to P, confirming the Ni... x The formation of P. The remaining Ni. 2+and P-O signals are attributed to partial oxidation of the surface of the catalyst sample.

[0069] The target catalyst a-Ni obtained in this example x Electrocatalytic performance test of P / Ni / NF and reference samples:

[0070] (1) The a-Ni obtained in this example x P / Ni / NF and Ni / NF, a-Ni x The anodic polarization curves of hydrazine oxidation reaction of P / NF, Ni3P / Ni / NF catalysts in the solution containing 0.5M hydrazine monohydrate and 1.0M sodium hydroxide are shown in Figure 6 The results show that the a-Ni x P / Ni / NF catalyst has excellent electrocatalytic activity for hydrazine oxidation reaction, and can reach a current density of 1215mA / cm 2 when the potential is 0.3V relative to the reversible hydrogen electrode in the solution containing 0.5M hydrazine monohydrate and 1.0M sodium hydroxide.

[0071] (2) The a-Ni obtained in this example x P / Ni / NF and Ni / NF, a-Ni x The relationship curves of the capacitance current density and the potential scan rate of P / NF, Ni3P / Ni / NF samples at the open circuit potential and the impedance spectrum test results at the initial potential are shown in Figure 7 It can be seen from a in Figure 7 that the a-Ni x P / Ni / NF has the highest double-layer capacitance, i.e. the electrochemical specific surface area, which is higher than that of a-Ni x P / NF, Ni3P / Ni / NF and Ni / NF catalysts. At the same time, the a-Ni x P / Ni / NF has the smallest electrochemical impedance (b in Figure 7 ), which is smaller than that of a-Ni x P / NF, Ni3P / Ni / NF and Ni / NF catalysts, which indicates that the amorphous / crystalline heterophase junction structure is more conducive to fast mass transfer and increases the active site density.

[0072] (3) The a-Ni obtained in this example x The cycle durability test results of the P / Ni / NF catalyst and the reference samples are shown in Figure 8 After 1000 cycles of CV cycles, the activity remains 90.5%, which is higher than that of the reference samples. Figure 9 The galvanostatic durability test chart of the a-Ni x P / Ni / NF catalyst and the reference samples shows that the current density of the P / Ni / NF catalyst is 10mA / cm 2The catalyst activity did not show obvious decline, indicating that the catalyst had good durability.

[0073] (4) The a-Ni x P / Ni / NF catalyst after 100 hours of durability test, the phase / microstructure / surface chemical state results are shown in Figure 10 and 11 . The results show that the morphology, phase structure and surface chemical state of the catalyst do not change obviously, indicating that the catalyst has good structural stability.

[0074] (5) The a-Ni x P / Ni / NF catalyst and the reference sample were tested for reaction selectivity as shown in Figure 12 , which shows that the target catalyst has no non-faradic decomposition and has 100% faradic efficiency.

[0075] The target catalyst a-Ni x P / Ni / NF obtained in this example was tested for DHzFC performance.

[0076] The a-Ni x P / Ni / NF catalyst was used as an anode catalyst, commercial Pt / C was used as a cathode catalyst, and an aqueous solution containing 3.0M N2H4·H2O and 1.0M NaOH was used as fuel to assemble a DHzFC. The self-made DHzFC showed an open circuit voltage of 0.94V, and its maximum power density reached 133mW cm -2 ( Figure 13 ).

[0077] Example 2

[0078] Carbon cloth (CC, 1×3cm2) was used as the carrier, and was ultrasonically cleaned with hydrochloric acid (1M), anhydrous ethanol and deionized water for 20 minutes each. Then the carbon cloth was incubated in concentrated nitric acid (0.5M) at 90°C for 4 hours, and was cleaned with deionized water and anhydrous ethanol. At this time, NF was used as the anode, carbon cloth was used as the cathode, and the electrolyte was a mixed solution of NaH2PO2(1.0M) and NH4F(0.5M) dissolved in 60mL deionized water. After applying a constant potential of 4V for one hour, a-Ni x P / Ni / CC was obtained.

[0079] Preparation of the reference sample Ni / CC: Preparation of the reference sample Ni / NF: The only difference from the above preparation method is that the solution does not contain NaH2PO2.

[0080] The target catalyst a-Ni x P / Ni / CC and the reference sample Ni / CC were tested for electrocatalytic performance.

[0081] Phase / structure characterization of the catalyst:

[0082] XRD results show that ( Figure 14 The target catalyst is amorphous Ni. x P and crystalline Ni; the reference sample is crystalline Ni.

[0083] Transmission electron microscopy observation ( Figure 15 a) indicates that the target sample is composed of particles of 20–50 nm; according to high-resolution electron microscopy observation ( Figure 15 In b), nanocrystalline Ni of varying sizes are distributed in an amorphous matrix.

[0084] Electrocatalytic performance testing of catalysts:

[0085] (1) The a-Ni obtained in this embodiment x A comparison of the polarization curves of the hydrazine oxidation reaction of P / Ni / CC and Ni / CC catalysts is shown in the figure below. Figure 16 As shown. Test results indicate that a-Ni x The P / Ni / CC catalyst exhibits excellent electrocatalytic activity for the oxidation of hydrazine, achieving a current density of 1080 mA / cm² in a solution containing 0.5 M hydrazine monohydrate and 1.0 M sodium hydroxide, relative to a reversible hydrogen electrode potential of 0.30 V. 2 .

[0086] (2) a-Ni obtained in this embodiment x The durability test results of the P / Ni / CC catalyst (chronopotential method) are shown in the figure below. Figure 17 As shown. Test results indicate that after 100 hours of constant current (10mA / cm²), 2 The catalyst activity showed almost no decline when measured by current density, indicating good catalyst durability.

[0087] Example 3

[0088] Using cobalt foam (CF) as a carrier, the thickness is 1.80 mm and the areal density is 650 g / m³. 2 The pore size is 0.20–0.80 mm. Cobalt foam (1×3 cm⁻¹) 2 The CF4 was first ultrasonically cleaned with ethanol for 10 minutes, then activated with 1M hydrochloric acid solution for 5 minutes, and finally ultrasonically cleaned with deionized water for 10 minutes. NaH2PO2 (1.0M) and NH4F (0.5M) were dissolved in 60 mL of deionized water. After thorough stirring, the solution was poured into an electrolytic cell. The cleaned CF4 was used as both the anode and cathode in the electrolytic cell containing the electrolyte. After applying a constant potential of 4V for one hour, α-Co was obtained. x P / Co / CF.

[0089] Preparation of comparative sample Co / CF: the only difference from the above preparation method is that the solution does not contain NaH2PO2.

[0090] The catalyst a-Co x P / Co / CF, Co / CF obtained in this example

[0091] (1) The a-Co x P / Co / CF and Co / CF catalysts obtained in this example Figure 18 The test results show that the a-Co x P / Co / CF catalyst has excellent electrocatalytic activity for hydrazine oxidation reaction, and the current density is 1094 mA / cm 2 at 0.30 V relative to the reversible hydrogen electrode potential in a solution containing 0.5 M hydrazine monohydrate and 1.0 M sodium hydroxide.

[0092] (2) The a-Co x P / Co / CF catalyst obtained in this example Figure 19 The test results show that the catalyst activity almost does not decay after 100 hours of constant current (10 mA / cm 2 current density) measurement, indicating good durability of the catalyst.

[0093] Example 4

[0094] Foamed copper (cF) was used as the carrier. The foamed copper (1 x 3 cm 2 ) was first cleaned with ethanol for 10 minutes, then activated with 1 M hydrochloric acid solution for 5 minutes, and finally cleaned with deionized water for 10 minutes. NaH2PO2(1.0 M) and NH4F (0.5 M) were dissolved in 60 mL of deionized water solution. After the solution was stirred uniformly, it was poured into an electrolytic cell, and the cleaned cF was placed in the electrolytic cell containing the electrolyte as an anode and a cathode, respectively. A constant potential of 4 V was applied for one hour to obtain a-Cu x P / Cu / cF.

[0095] Preparation of comparative sample Cu / cF: the only difference from the above preparation method is that the solution does not contain NaH2PO2.

[0096] The catalyst a-Cu x P / Cu / cF, Cu / cF obtained in this example

[0097] (1) The a-Cu x P / Cu / cF and Cu / cF catalysts obtained in this example Figure 20 The test results show that the a-Cux P / Cu / cF catalyst has excellent electrocatalytic activity for hydrazine oxidation reaction, which is 1180 mA / cm 2 .

[0098] (2) The a-Cu x P / Cu / cF catalyst durability test results chart (chronoamperometry) as shown in Figure 21 . Test results show that the catalyst activity is almost no recession after 100 hours of constant current (10 mA / cm 2 current density) measurement, indicating good durability of the catalyst.

[0099] Example 5

[0100] This example is similar to Example 1, the difference is to change the electrolyte concentration.

[0101] The thickness of the foam nickel carrier is 1.60 mm, the surface density is ~ 650 g / m 2 , and the pore size is 0.20-0.80 mm. The foam nickel (1x3 cm 2 ) is sequentially cleaned with ethanol, hydrochloric acid solution (3M) and deionized water for 10 minutes. NaH2PO2 (0.5-1.25M), NH4F (0.25-0.75M) is dissolved in 60 mL deionized water solution according to the ratio of 2:1. After the solution is stirred evenly, pour it into the electrolytic cell, and the cleaned NF is put into the electrolytic cell containing the electrolyte as the anode and cathode, respectively. After applying a constant potential of 4V for one hour, a series of catalysts are obtained.

[0102] Phase characterization of the catalyst: According to the XRD results Figure 22 ), it is shown that the catalysts obtained at different concentrations have similar phases, which are amorphous Ni x P and nanocrystalline Ni mixed phase.

[0103] Electrocatalytic performance test of the catalyst obtained in this example:

[0104] The comparison chart of hydrazine oxidation reaction polarization curves of the catalyst obtained in this example is shown in Figure 23 . Test results show that the 1.0M NaH2PO2 / 0.5M NH4F catalyst has the most excellent electrocatalytic activity for hydrazine oxidation reaction, which is 1215 mA / cm 2 . The catalytic performance is 1215 mA / cm 2(1.0M NaH2PO2 / 0.5M NH4F), 1059 mA / cm 2 (0.75M NaH2PO2 / 0.375M NH4F), 1036 mA / cm 2 (0.5M NaH2PO2 / 0.25M NH4F), 1021 mA / cm 2 (1.25M NaH2PO2 / 0.62M NH4F).

[0105] Example 6

[0106] This example is similar to Example 1, except that the concentration of electrolyte is changed.

[0107] The foam nickel was used as the carrier, with a thickness of 1.60 mm, a surface density of ~650 g / m 2 , and a pore size of 0.20-0.80 mm. The foam nickel (1 x 3 cm 2 ) was cleaned with ethanol, hydrochloric acid solution (3M) and deionized water by ultrasonic for 10 minutes. NaH2PO2 was fixed at a concentration of 1.0M, and different concentrations of NH4F (0.25-1.0M) were dissolved in 60 mL deionized water solution. After the solution was stirred uniformly, it was poured into the electrolytic cell, and the cleaned NF was placed in the electrolytic cell as the anode and cathode, respectively. A constant potential of 4V was applied for one hour to obtain a series of catalysts.

[0108] Phase characterization of the catalyst: The XRD results Figure 24 indicate that the catalysts obtained at different concentrations have similar phases, which are amorphous Ni x P mixed with nanocrystalline Ni.

[0109] Electrocatalytic performance test of the catalyst obtained in this example:

[0110] The comparison chart of hydrazine oxidation reaction polarization curves of the catalyst obtained in this example is shown in Figure 25 . The test results show that the 1.0M NaH2PO2 / 0.5M NH4F catalyst has the most excellent electrocatalytic activity for hydrazine oxidation reaction, and the current density is 1215 mA / cm 2 when the potential is 0.30V relative to the reversible hydrogen electrode potential in a solution containing 0.5M hydrazine monohydrate and 1.0M sodium hydroxide. The catalytic performance is 1215 mA / cm 2 (1.0M NaH2PO2 / 0.5M NH4F), 1052 mA / cm 2 (1.0M NaH2PO2 / 0.25M NH4F), 983 mA / cm 2 (1.0M NaH2PO2 / 0.75M NH4F), 780 mA / cm2 (1.0M NaH2PO2 / 1.0M NH4F).

[0111] Example 7

[0112] This embodiment is similar to Embodiment 1, except that the electrodeposition time is changed.

[0113] Using nickel foam as a carrier, its thickness is 1.60 mm and its areal density is ~650 g / m³. 2 The pore size is 0.20–0.80 mm. Nickel foam (1×3 cm) 2 The catalyst was sequentially ultrasonically cleaned with ethanol, hydrochloric acid solution (3M), and deionized water for 10 minutes each. NaH₂PO₂ (1.0M) and NH₄F (0.5M) were dissolved in 60 mL of deionized water. After thorough stirring, the solution was poured into an electrolytic cell. The cleaned NF was used as both the anode and cathode in the electrolytic cell containing the electrolyte. A constant potential of 4V was applied for 30 / 60 / 90 / 120 minutes to obtain a series of catalysts.

[0114] Electrocatalytic performance testing of the catalyst obtained in this embodiment:

[0115] The polarization curves of the hydrazine oxidation reaction of the catalyst obtained in this embodiment are compared as follows: Figure 26 As shown in the figure. Test results indicate that the catalyst with an electrodeposition time of 60 minutes exhibits the best electrocatalytic activity for hydrazine oxidation, achieving a current density of 1215 mA / cm² in a solution containing 0.5 M hydrazine monohydrate and 1.0 M sodium hydroxide, relative to a reversible hydrogen electrode potential of 0.30 V. 2 The catalysts obtained from the other two different electrolyte concentrations also showed relatively superior performance. Their catalytic performance was 1215 mA / cm², respectively. 2 (60 minutes), 1076 mA / cm 2 (90 minutes), 966 mA / cm 2 (30 minutes), 821 mA / cm 2 (120 minutes)

[0116] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An amorphous metal phosphide / crystalline metal elemental composite hydrazine oxidation catalyst characterized by, The catalyst comprises a metal phosphide amorphous phase and a metal elemental crystal phase, the metal elemental crystal phase is embedded in the metal phosphide amorphous phase in the form of dispersed nanoparticles, the nanoparticle size of the metal elemental crystal phase is 2-3 nm, the metal phosphide amorphous phase exists in the form of nanoparticles, and the nanoparticle size is 20-50 nm; the preparation method of the catalyst comprises the following steps: taking a carrier material as a cathode, a metal electrode as an anode, and adding into a solution containing a phosphide and a buffer agent to perform electrodeposition, wherein the voltage of electrodeposition is 2-4 V, the time of electrodeposition is 0.5-2 h, and the temperature of electrodeposition is 20-60 ℃, the phosphide is sodium hypophosphite, the concentration is 0.25-1.5 M, the buffer agent is ammonium fluoride, the concentration is 0.25-1.0 M, and the molar ratio of the phosphide to the buffer agent is 4:1-4; and the catalyst is applied to preparation of a hydrazine fuel cell.

2. The amorphous metal phosphide / crystalline metal element composite hydrazine oxidation catalyst according to claim 1, characterized by, The metal phosphide is a transition metal phosphide; the metal elemental is a transition metal elemental; and the transition metal refers to at least one of Fe, Co, Ni, Cu and Zn.

3. The amorphous metal phosphide / crystalline metal element composite hydrazine oxidation catalyst according to claim 1, characterized by, The carrier material is selected from a foam metal, a metal mesh, an ion exchange resin, a molecular sieve and a carbon cloth.

4. The amorphous metal phosphide / crystalline metal element composite hydrazine oxidation catalyst according to claim 1, characterized by, The metal electrode is selected from a foam metal and a metal mesh, and the metal is at least one of Fe, Co, Ni, Cu and Zn.

5. A method for preparing the amorphous metal phosphide / crystalline metal element composite hydrazine oxidation catalyst according to claim 1, characterized by, The method comprises the following steps: taking a carrier material as a cathode, a metal electrode as an anode, and adding into a solution containing a phosphide and a buffer agent to perform electrodeposition, so as to obtain an amorphous metal phosphide / crystal metal elemental composite hydrazine oxidation catalyst.

6. The production method according to claim 5, wherein The voltage of electrodeposition is 2-4 V, the time of electrodeposition is 0.5-2 h, and the temperature of electrodeposition is 20-60 ℃.

7. The preparation method according to claim 5, characterized in that, The phosphide is sodium hypophosphite, the concentration is 0.25-1.5 M, the buffer agent is ammonium fluoride, the concentration is 0.25-1.0 M, and the molar ratio of the phosphide to the buffer agent is 4:1-4.

8. Application of the amorphous metal phosphide / crystal metal elemental composite hydrazine oxidation catalyst in claim 1 to preparation of a hydrazine fuel cell.

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