Preparation method of palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst and catalytic application of palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst in methanol fuel cell

Abstract

The invention provides a preparation method of a palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst and catalytic application of the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst in a methanol fuel cell, and relates to the field of electrode catalysts.The preparation method comprises the steps that firstly, titanium aluminum carbide MAX phase powder is subjected to LiF / HCl liquid phase selective etching, and a two-dimensional titanium carbide nanosheet is obtained; then adding the titanium carbide dispersion liquid into ionic liquid for ice-water bath ultrasonic treatment, then adding palladium salt powder for stirring and mixing, then adding an ascorbic acid solution for continuous stirring, then carrying out an oil bath reaction, carrying out alternate centrifugal washing treatment on a product through ethanol and deionized water, and then carrying out freeze drying to obtain the titanium carbide / palladium oxide composite material. The palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst is obtained. The ionic liquid modified titanium carbide nanosheet is used as a template, the crystal palladium nanocluster is deposited on the surface of the ionic liquid modified titanium carbide nanosheet, and the prepared catalyst has the advantages of multilayer sheet structure, high catalytic activity and high toxicity resistance, and can be applied to the field of catalysis of methanol fuel cells.

Description

Technical Field

[0001] The present invention relates to the field of preparation of electrode catalysts, and particularly to a preparation method of a palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst and its catalytic application in a methanol fuel cell. Background Art

[0002] The growth of industrialization has led to an increase in global energy demand. With the continuous use of fossil fuels, serious environmental problems exist globally. Therefore, it is urgent to develop new energy sources and design new energy conversion devices. As an environmentally friendly green energy source, fuel cells have many advantages such as high energy conversion efficiency, low pollution, and low noise. Direct methanol fuel cells (DMFCs) have attracted considerable attention due to their large energy density, excellent energy conversion efficiency, portability, and low emissions. However, the intrinsic kinetics of the anodic oxidation reaction of organic small molecules in direct methanol fuel cells is generally slow, which requires noble metal catalysts such as platinum (Pt) to catalyze the reaction. However, the high price and easy poisoning characteristics of platinum have greatly limited its large-scale commercial application. Therefore, the research and preparation of low-cost, highly catalytically active, and stable platinum substitute electrocatalysts contribute to the rapid development of direct formic acid fuel cells.

[0003] Among the elements in the same group, palladium (Pd) is considered a good substitute for Pt and has good catalytic activity and durability under alkaline conditions. To improve the catalytic performance of single-metal Pd, researchers usually use surface structure regulation methods such as loading to improve the catalytic ability of single-metal Pd. Currently, the most widely studied carbon carrier materials (such as graphene, carbon nanotubes, and carbon black) can significantly improve the catalytic performance of the catalyst while reducing the amount of noble metal used. However, the carbon atoms in the carbon carrier are chemically inert, and the electronic interaction with the palladium component is weak; on the other hand, the corrosion of the carbon carrier during the catalytic process will cause the detachment and aggregation of palladium atoms, making it difficult to maintain long-term stable operation.

[0004] Ti3C2T x materials have become an important choice for carrier materials due to their large specific surface area, excellent electrical conductivity, and rich surface functional groups. Ti3C2T x is not very stable under air and aqueous solution conditions. At the same time, due to the existence of van der Waals forces and hydrogen bond interactions between adjacent nanosheets, re-stacking and aggregation are likely to occur during the catalyst synthesis and catalytic process, affecting the catalytic activity. Ionic liquids (ILs) have advantages such as high ionic conductivity, good thermal stability, and chemical stability, and are considered ideal electrode modification materials. Adding ionic liquids (ILs) to enhance two-dimensional Ti3C2T xThe conductivity and thermal stability of the nanosheets are expected to better improve the catalytic performance of the modified electrode anode catalyst by utilizing the synergistic effect between the two, thereby significantly enhancing its catalytic activity.

[0005] So far, some studies have used ionic liquid-functionalized carbon nanotubes as catalysts and ionic liquids as electrolytes for electrocatalytic reactions (Li T, Wang Y, Chen T, et al. Ionic liquid in-situ functionalized carbon nanotube film as self-supported metal-free electrocatalysts for oxygen evolution[J]. Chemical Engineering Journal, 2024, 484: 149767.; Liu X, Mariani A, Diemant T, et al. Reinforcing the Electrode / Electrolyte Interphases of Lithium Metal Batteries Employing Locally Concentrated Ionic Liquid Electrolytes[J]. Advanced Materials, 2024, 36(1): 2309062.). However, there has been no report on using ionic liquid-modified titanium carbide nanosheets as carriers and loading palladium nanoparticles on them as catalysts for methanol oxidation.

[0006] Chinese Patent CN118407086A discloses a preparation method and application of an ionic liquid-functionalized copper-based catalytic material. In this method, copper salt is added to an ionic liquid aqueous solution, heated and dissolved, sodium hydroxide solution is added dropwise with stirring, and then ascorbic acid solution is added dropwise with stirring. The solid is separated from the reaction solution and dried to obtain cuprous oxide loaded with ionic liquid. The addition of ionic liquid can regulate the morphology and particle size of cuprous oxide, and the ionic liquid is loaded on the surface of cuprous oxide. The ionic liquid has certain advantages in CO2 capture and conversion, which improves the electrocatalytic performance. However, there is still room for improvement in the electrocatalytic performance of the catalyst of this invention, and it may face problems such as insufficient activity, poor selectivity, and difficulty in large-scale production in the field of methanol oxidation.

[0007] Therefore, how to design and synthesize an ionic liquid-modified palladium-loaded titanium carbide composite catalyst, on the one hand, reduce the stacking of titanium carbide nanosheets in the composite system to prevent the aggregation of palladium nanoparticles and thus increase the catalytic active sites, and on the other hand, adjust the electronic state of palladium and enhance the interaction between the metal and the support, so as to improve the utilization efficiency of palladium and effectively play its unique advantages in the field of electrocatalysis is the focus and difficulty of the current work. Summary of the Invention

[0008] In order to solve the above-mentioned defects and deficiencies in the prior art, the present invention provides a preparation method of a palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst and its catalytic application in a methanol fuel cell. The method uses ionic liquid-modified titanium carbide nanosheets as a support, deposits crystalline palladium nanoclusters on its surface, and the prepared composite electrode catalyst enhances the stability and conductivity of the two-dimensional titanium carbide layered structure by using ionic liquid, maintains the characteristics of large specific surface area and abundant surface functional groups of titanium carbide nanosheets, and at the same time has the advantages of two-dimensional layered structure, high catalytic activity and high anti-toxicity, and can be applied in the catalytic field of methanol fuel cells.

[0009] The technical solution of the present invention is specifically as follows: A preparation method of a palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst, the preparation steps are as follows: S1. Prepare a titanium carbide nanosheet dispersion; S2. Add an ionic liquid to the solution in step S1, perform ultrasonic treatment in an ice-water bath, and mix evenly to obtain an ionic liquid-modified titanium carbide nanosheet solution. The addition amount of the ionic liquid to the titanium carbide nanosheets is 100-500:1 by mass ratio; S3. Add palladium acetylacetonate to the solution in step S2, stir evenly in an ice-water bath to obtain a binary complex solution of palladium acetylacetonate / ionic liquid-modified titanium carbide nanosheets. The addition amount of palladium element in the palladium acetylacetonate to the titanium carbide nanosheets is 0.25:1 by mass ratio; S4. Add an ascorbic acid solution to the solution in step S3, stir and mix evenly, and perform ultrasonic treatment in an ice-water bath. The addition amount of the ascorbic acid to the titanium carbide nanosheets is 1.1-4.4:1 by mass ratio; S5. Perform an oil bath reaction on the binary complex solution in step S4 to obtain a product. The oil bath reaction conditions are: place it in an oil bath at a temperature of 60-100 °C for 1-3 h, and then alternately centrifuge and wash with ethanol and deionized water, and freeze-dry to obtain a palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst.

[0010] In the present invention, titanium carbide nanosheets modified with ionic liquid are used as carriers. Two-dimensional titanium carbide is generated by chemical etching. Ultrasonic exfoliation is used to obtain monolayer or few-layer titanium carbide nanosheets from the two-dimensional titanium carbide sheets. Then, ionic liquid is added. Through the electrostatic attraction and hydrogen bonding interactions between the titanium carbide nanosheets and the ionic liquid, ionic liquid-modified titanium carbide nanosheets are finally formed. The anions in the ionic liquid can be adsorbed on the edges of the positively charged titanium carbide nanosheets through electrostatic interactions to encapsulate them, effectively reducing their oxidation tendency and improving the stability of the titanium carbide carrier. The cations in the ionic liquid can be modified onto the surface of the titanium carbide nanosheets, reducing the stacking and aggregation between the titanium carbide nanosheets. In addition, the ionic liquid cations can act as surfactants and templating agents to further regulate the morphology and structure of the supported noble metal palladium, facilitating the formation of palladium nanoclusters with uniform grain morphology and size. Then, palladium acetylacetonate and ascorbic acid solution are added. The ascorbic acid solution reduces palladium acetylacetonate to generate palladium metal nanostructures. The titanium carbide nanosheets can provide a large specific surface area and contain a large number of oxygen-containing functional groups as nucleation sites for palladium. The formed catalyst has many active sites, a large electrochemically active area, good electrical conductivity, and fast ion transfer ability, thus obtaining better electrocatalytic performance.

[0011] Further, in step S2, the mass ratio of the addition amount of the ionic liquid to the titanium carbide nanosheets is 300:1.

[0012] Further, in step S2, the ionic liquid is a 1-butyl-3-methylimidazolium tetrafluoroborate solution with a concentration of 5.4 mol / L.

[0013] Further, in step S2, the mixing condition is: ultrasonic treatment at 0 - 10 °C for 10 - 30 min.

[0014] Further, in step S3, the mixing condition is: stirring at 0 - 40 °C for 0.5 - 1 h.

[0015] Further, in step S4, the mass ratio of the addition amount of ascorbic acid to the titanium carbide nanosheets is 2.2:1.

[0016] Further, in step S5, the oil bath reaction condition is: oil bath reaction at 80 °C for 2 h.

[0017] Still further, in step S5, alternate centrifugal washing with ethanol and deionized water is performed 3 - 5 times, the centrifugal speed is 6000 - 10000 rpm, and the drying pressure during freeze-drying is 0 - 200 Pa.

[0018] In the above preparation method, the specific steps for preparing titanium carbide nanosheets in step S1 are as follows: P1, adding lithium fluoride to hydrochloric acid to synthesize hydrofluoric acid in situ to etch titanium aluminide; P2. The suspension is washed by centrifugation until the pH value is 6.5-7.5, and the obtained multilayer titanium carbide nanosheets are sonicated in an ice-water bath under the condition of passing argon gas. The suspension after sonication is centrifuged and screened to separate layers, and the centrifugal supernatant is freeze-dried to obtain single-layer or few-layer titanium carbide nanosheets.

[0019] A mixed solution of lithium fluoride and hydrochloric acid is used to etch the aluminum atomic layer in aluminum titanium carbide, and then ultrasonic peeling is used to generate a two-dimensional single-layer or few-layer carbon nitride nanosheet. During the etching process, the Al atomic layer is replaced by electronegative functional groups such as -OH, -F and -O. These electronegative functional groups on the surface can become nucleation sites for precious metal nanostructures and further stabilize nanocrystals, preventing the main catalyst from agglomerating during the catalytic process and causing a decrease in activity.

[0020] Furthermore, in step P1, the etching water bath reaction conditions are: placing in a water bath at a temperature of 40° C. for 36 hours, and the molar concentration of HCl is 9 M.

[0021] Furthermore, in step P2, the ultrasonic stripping time is 0.5-6 h, and the centrifugal speeds are 3500 and 5000 rpm respectively.

[0022] Another object of the present invention is to provide a palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst prepared by the above-mentioned preparation method.

[0023] Another object of the present invention is to provide the use of the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst for catalytic oxidation of methanol in a methanol fuel cell.

[0024] Compared with the prior art, the beneficial technical effects achieved by the present invention are: 1. The present invention prepares electrode catalysts by loading palladium nanoclusters on titanium carbide nanosheets modified with ionic liquids. The high catalytic activity of the palladium nanoclusters and the supporting effect of the titanium carbide nanosheets cooperate with each other to form a catalyst with uniform morphology and high dispersion. The catalyst has abundant catalytic active sites, excellent electrical conductivity, high utilization rate of precious metals, helps to enhance electrochemical activity, and has good anti-poisoning ability and catalytic stability.

[0025] 2. Ionic liquids can simultaneously stabilize the titanium carbide carrier and regulate the palladium morphology and structure, making it possible to easily prepare titanium carbide-supported palladium composite catalysts that are both low-cost and highly active, providing a new way to promote the practical application of direct methanol fuel cells.

[0026] 3. The preparation method of the catalyst of the present invention is simple and controllable, has good repeatability and low cost, and is conducive to large-scale industrial production. Brief Description of the Drawings

[0027] Figure 1 are the X-ray diffraction (XRD) pattern (Figure a) and Raman spectrum (Figure b) of the electrode catalyst prepared in Example 1 of the present invention.

[0028] Figure 2 is the field emission scanning electron microscope image (FE-SEM) of the electrode catalyst prepared in Example 1 of the present invention.

[0029] Figure 3 is the transmission electron microscope image (TEM) of the electrode catalyst prepared in Example 1 of the present invention.

[0030] Figure 4 is the cyclic voltammogram curves of the electrode catalyst (Pd / IL-Ti3C2T x ), palladium / titanium carbide nanosheets (Pd / Ti3C2T x ), palladium / graphene (Pd / RGO), palladium / carbon nanotubes (Pd / CNT) and palladium / carbon black (Pd / C) materials prepared in Example 1 of the present invention in 1 mol / L NaOH solution ( Figure 4 a) and the cyclic voltammogram curves in a mixed solution of 1 mol / L NaOH and 0.5 mol / L CH3OH ( Figure 4 b).

[0031] Figure 5 is the constant potential oxidation test data graph of the electrode catalyst (Pd / IL-Ti3C2T x ), palladium / titanium carbide nanosheets (Pd / Ti3C2T x ), palladium / graphene (Pd / RGO), palladium / carbon nanotubes (Pd / CNT) and palladium / carbon black (Pd / C) materials prepared in Example 1 of the present invention.

[0032] Figure 6 is the alternating current impedance spectra ( x ) of the electrode catalyst (Pd / IL-Ti3C2T Figure 6 a-b), palladium / graphene (Pd / RGO), palladium / carbon nanotubes (Pd / CNT) and palladium / carbon black (Pd / C) materials prepared in Example 1 of the present invention. Detailed Description of the Invention

[0033] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0034] Example 1 Palladium / Ionic Liquid-Ti3C2T x The preparation of the nanosheet composite electrode catalyst is as follows: S1. Prepare Ti3C2T x nanosheets; S2. Add 5 mL of ionic liquid to the Ti3C2T x nanosheets in step S1, ultrasonically treat in an ice-water bath for 10 min, and mix well to obtain an ionic liquid-modified Ti3C2T x nanosheet solution; the addition amount of the ionic liquid to the titanium carbide nanosheets is 300:1 by mass ratio; S3. Add 14.31 mg of palladium acetylacetonate to the solution in step S2. The addition amount of palladium element in palladium acetylacetonate to the Ti3C2T x nanosheets is 0.25:1 by mass ratio. Stir at 25 °C for 0.5 h and mix well to obtain a palladium acetylacetonate / ionic liquid-modified Ti3C2T x nanosheet binary composite solution; S4. Add 44 mg of ascorbic acid to the solution in step S3. Stir at 25 °C for 0.5 h to mix evenly. The addition amount of ascorbic acid to the titanium carbide nanosheets is 2.2:1 by mass ratio; S5. Place the binary composite solution in step S4 in an oil bath at 80 °C for 2 h to obtain the product, and then alternately centrifuge and wash 5 times with ethanol and deionized water, and freeze-dry. The drying pressure is 25 Pa, and the palladium / ionic liquid-Ti3C2T x nanosheet composite electrode catalyst is obtained.

[0035] There have been many reports in the prior art on the influence of the etching and ultrasonic dispersion conditions of titanium carbide on its dispersion degree, and this application of the present invention will not be elaborated. Preferably, the etching reaction time at room temperature in step P1 is 36 h, and the hydrochloric acid concentration is 9 mol / L; in step P2, centrifugal water washing is carried out at a rotation speed of 5000 rpm, and ultrasonic peeling at room temperature for 3 h is used as the preparation condition of this application. The following examples and comparative examples all use this condition.

[0036] Example 2 The preparation of the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst in Example 2 is different from that in Example 1 in that in step S2, the addition amount of the ionic liquid to the titanium carbide nanosheets is 100:1 by mass ratio.

[0037] Example 3 Preparation of the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst in Example 3, which is different from Example 1 in that in step S2, the mass ratio of the addition amount of the ionic liquid to the titanium carbide nanosheet is 500:1.

[0038] Example 4 Preparation of the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst in Example 4, which is different from Example 1 in that in step S4, the mass ratio of the addition amount of ascorbic acid to the titanium carbide nanosheet is 1.1:1.

[0039] Example 5 Preparation of the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst in Example 5, which is different from Example 1 in that in step S4, the mass ratio of the addition amount of ascorbic acid to the titanium carbide nanosheet is 4.4:1.

[0040] Example 6 Preparation of the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst in Example 6, which is different from Example 1 in that in step S5, the composite solution is placed in an oil bath at 60 °C for 2 h.

[0041] Example 7 Preparation of the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst in Example 7, which is different from Example 1 in that in step S5, the composite solution is placed in an oil bath at 100 °C for 3 h.

[0042] Example 8 Preparation of the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst in Example 8, which is different from Example 1 in that in step S5, the time for the oil bath reaction of the composite solution is 1 h.

[0043] Example 9 Preparation of the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst in Example 9, which is different from Example 1 in that in step S5, the time for the oil bath reaction of the composite solution is 3 h.

[0044] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that in step S2, the mass ratio of the addition amount of the ionic liquid to the titanium carbide nanosheet is 30:1.

[0045] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that in step S2, the mass ratio of the addition amount of the ionic liquid to the titanium carbide nanosheet is 1800:1.

[0046] Comparative Example 3 Comparative Example 3 is different from Example 1 in that in step S2, the mass ratio of the addition amount of the ionic liquid to the titanium carbide nanosheets is 0:1.

[0047] The following is the testing and performance characterization of the obtained catalyst.

[0048] Taking the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst prepared in Example 1 as an example for performance characterization.

[0049] (1) X-ray powder diffraction pattern and Zeta potential curve analysis Figure 1 The X-ray powder diffraction pattern and Zeta potential curve of the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst are shown. From Figure 1 the XRD pattern in a, the characteristic peaks of metallic palladium and titanium carbide can be clearly seen, indicating that these two components are contained in the composite product. Figure 1 b is the Zeta potential curve of the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst, indicating that the stability of the ionic liquid-titanium carbide colloid dispersion system obtained after the ionic liquid binds to the negatively charged titanium carbide nanosheets is greatly improved, and the excessive re-aggregation or re-accumulation of titanium carbide nanosheets can be avoided to a large extent.

[0050] (2) Field emission scanning electron microscope analysis Figure 2 The field emission scanning electron microscope image of the electrode catalyst is shown. From Figure 2 a, it can be seen that the catalyst has an obvious two-dimensional layered structure, and the titanium carbide nanosheets exist in the form of two-dimensional thin sheets. Among them, Figure 2 b is the local enlarged view, from which it can be seen that the surface structure of the titanium carbide nanosheets becomes rougher, and a large number of irregularly shaped Pd nanoclusters are evenly attached to its surface, forming a good dispersion.

[0051] (3) Transmission electron microscope image analysis Figure 3 The transmission electron microscope image of the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst is shown. Figure 3 a and 3b further prove that the palladium clusters are more evenly distributed on the two-dimensional pomelo peel-derived carbon; it shows that there is a strong metal-support interaction between Pd and the titanium carbide nanosheets, and the structural stability of the noble metal Pd can be increased under the support of the two-dimensional support titanium carbide. Figure 3The lattice fringes of the palladium nanostructure can be clearly seen. The measurement results show that the lattice fringe spacings at two locations are 0.195 nm and 0.225 nm respectively, corresponding to the (200) crystal plane and (111) crystal plane of Pd, respectively, which verifies again that the noble metal Pd is successfully loaded on the two-dimensional layered titanium carbide structure. In addition, the field emission scanning electron microscope photos of the catalyst and its elemental analysis show that the composite catalyst contains elements such as Pd, Ti, C, O, N, F, and B ( Figure 3 d-k), and the elements are evenly distributed on the titanium carbide nanosheets, thus proving that the modification with a small amount of ionic liquid not only enhances the structural stability of the two-dimensional Ti3C2T x nanosheets, but also makes the Pd nanoclusters more firmly loaded on the two-dimensional titanium carbide support material, which will be beneficial to improving the utilization rate of the noble metal Pd and thus reducing the cost consumption in the actual use process.

[0052] The above results show that the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst of the present invention has a two-dimensional layered structure, and the loading of palladium provides more binding sites. Therefore, its specific surface area is larger, and the palladium metal nanoclusters can be evenly distributed on the two-dimensional sheet structure, having higher catalytic performance and electrochemical activity.

[0053] (4) Catalytic activity test The electrochemical tests of the samples were all carried out on a CHI760E electrochemical workstation. The test system was a conventional three-electrode system, in which a saturated calomel electrode was used as the reference electrode, a platinum wire was used as the counter electrode, and a glassy carbon electrode was used as the working electrode.

[0054] The preparation process of the working electrode is as follows: Weigh 2 mg of catalyst powder and disperse it in a mixed solution of 0.475 mL of deionized water, 0.475 mL of ethanol, and 0.05 mL of Nafion (Dupont membrane solution), and ultrasonicate for 30 min; Take 0.005 mL of the dispersion of the above catalyst sample and drop it on the surface of the glassy carbon electrode, and dry it at room temperature for 0.5 h before testing. The electrochemically active surface area (ECSA) and the catalytic activity (CV) of methanol oxidation of the catalyst were both measured by cyclic voltammetry. The electrolytes were 0.5 mol / L NaOH solution and a mixed solution of 0.5 mol / L NaOH and 1 mol / L CH3OH, respectively, and the scanning rate was 20 mV . s -1 . The stability and methanol tolerance of the catalyst were evaluated by potentiostatic oxidation method. The conductivity of the catalyst was studied by electrochemical impedance spectroscopy, and the frequency range was from 10 5 ~0.02 Hz, and the amplitude was 10 mV.

[0055] By calculation Figure 4The area of the a curve in the hydrogen adsorption region indicates that the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst has the highest electrochemically active surface area of 138.7 m 2 g -1 . By testing the catalytic performance of the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst for methanol oxidation, as shown in Figure 4 b, the forward current density of this catalyst is 1651.2 mA mg -1 . A large electrochemically active area indicates that there are more active sites on the catalyst surface participating in the reaction, while a high forward current density indicates a fast reaction rate per unit area, strong overall catalytic activity, low electron transfer resistance, and is conducive to the progress of the electrochemical reaction.

[0056] To further illustrate the catalytic activity of this catalyst, cyclic voltammetry tests for methanol oxidation were also carried out on titanium carbide nanosheets (Ti3C2T x ), graphene (GO), carbon nanotubes (CNT), and carbon black (C), and the obtained data were compared. It can be seen from Figure 5 that the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst has significantly higher electrochemically active surface area and forward peak current density than the other four comparison samples, indicating its highest catalytic activity.

[0057] The electrochemical stability test of the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst was carried out using the potentiostatic oxidation method. It can be seen from Figure 6 that within the test time of 5000 s, the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst has always maintained the lowest current decay rate and the highest oxidation current density, indicating good catalytic durability. The electrochemical activity of the catalyst is closely related to its conductivity. AC impedance tests were carried out on all catalysts. As shown in Figure 6 a and Figure 6 b, the AC impedance curves of different catalysts all contain a semicircle pattern, and the semicircle diameters presented by the ionic liquid-modified titanium carbide-supported palladium electrode catalyst are all smaller than those of other catalysts, indicating that the ionic liquid-modified titanium carbide-supported palladium electrode catalyst has the smallest charge transfer resistance. Therefore, this catalyst can exhibit better catalytic activity.

[0058] The electrode catalysts of Examples 1-9 and Comparative Examples 1-3 were tested for methanol oxidation reaction, and the results are shown in Table 1.

[0059] Table 1 Performance indicators of the catalysts prepared in Examples 1-9 and Comparative Examples 1-3 for methanol oxidation reaction

[0060] As can be seen from Table 1, the catalysts prepared in Examples 1-9 all have high catalytic activity and stable catalytic activity. With the increase in the addition amount of ionic liquid in the solution, the active surface area, mass activity, and apparent activity of the catalyst all increase. However, if the addition amount of ionic liquid is too high, too low, or not added (see Comparative Examples 1-3), the performance of the catalyst will be significantly reduced compared to Example 1. Excessive modification with ionic liquid may lead to the formation of "soft agglomerates" between Ti3C2T x nanosheets, reducing the effective active area and destroying the conductive network. When the amount of ionic liquid is too small, it cannot fully modify the surface of Ti3C2T x nanosheets, resulting in the surface being unable to be effectively protected, making it difficult to form sufficient conductive channels and affecting the electron transfer efficiency, thus affecting the catalytic activity. If no ionic liquid is added, the proportion of titanium atoms exposed on the surface of Ti3C2T x nanosheets is relatively high. Its high chemical activity makes it easy to be oxidized in air and aqueous solution conditions, resulting in a significant reduction in conductivity and electrochemical activity. Therefore, the ratio of the addition of ionic liquid and titanium carbide nanosheets and the addition of ionic liquid are very important. An appropriate ratio of ionic liquid and titanium carbide nanosheets can improve the catalytic activity and is also conducive to the rapid transmission of the electrolyte during the reaction process, thereby effectively improving the catalytic performance.

[0061] Through preliminary pre-experiments, it was found that too high an amount of ascorbic acid would result in too high a dispersion degree of titanium carbide, which is not conducive to the dispersion of palladium nanostructures. Too high temperature and time would reduce the uniformity of the dispersion of nanostructures, with some palladium atoms stacking together to become ineffective catalysts, reducing the utilization rate. While too low an amount of ascorbic acid, too low temperature and time would all cause incomplete reduction of the precursor, also resulting in a decrease in catalytic activity. Through a large number of experiments in this application, the ratios of the components of the present invention were determined. Only when the components are in the above-mentioned ratio contents can a catalyst for direct methanol fuel cells with good catalytic performance be obtained.

[0062] As described above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for preparing a palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst, characterized in that: The preparation steps are as follows: S1, preparing a titanium carbide nanosheet dispersion; S2, adding ionic liquid to the solution of step S1, performing ultrasonication in an ice-water bath, and mixing thoroughly to obtain an ionic liquid-modified titanium carbide nanosheet solution, wherein the mass ratio of the ionic liquid to the titanium carbide nanosheet is 100-500:1; S3, adding palladium acetylacetonate to the solution of step S2, stirring evenly in an ice water bath to obtain a palladium acetylacetonate / ionic liquid modified titanium carbide nanosheet binary composite solution, wherein the mass ratio of palladium element in the palladium acetylacetonate to titanium carbide nanosheet is 0.25:1; S4, adding ascorbic acid solution to the solution of step S3, stirring and mixing evenly, and ultrasonicating in an ice-water bath, wherein the mass ratio of ascorbic acid to titanium carbide nanosheets is 1.1-4.4:1; S5. The binary complex solution of step S4 is subjected to an oil bath reaction to obtain a product. The oil bath reaction conditions are: placing the product in an oil bath at a temperature of 60-100° C. for 1-3 h, then washing the product by alternating centrifugation with ethanol and deionized water, and freeze-drying the product to obtain a palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst.

2. The method for preparing the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst according to claim 1, characterized in that: In the step S2, the mass ratio of the added amount of the ionic liquid to the titanium carbide nanosheets is 300:

1.

3. The method for preparing the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst according to claim 1, characterized in that: The ionic liquid is a 1-butyl-3-methylimidazolium tetrafluoroborate solution with a concentration of 5.4 mol / L.

4. The method for preparing the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst according to claim 1, characterized in that: The ice-water bath ultrasonication in step S2 and the ice-water bath stirring time in step S3 are both 10 to 30 min.

5. The method for preparing the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst according to claim 1, characterized in that: In the step S4, the added amount of ascorbic acid and titanium carbide nanosheets is 2.2:1 in a mass ratio.

6. The method for preparing the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst according to claim 1, characterized in that: In step S5, the oil bath reaction conditions are: placing the reaction in the oil bath at 80° C. for 2 h.

7. The method for preparing the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst according to any one of claims 1 to 6, characterized in that: The specific steps of preparing titanium carbide nanosheets in step S1 are as follows: P1, adding lithium fluoride to hydrochloric acid to synthesize hydrofluoric acid in situ to etch titanium aluminide; P2. The suspension is washed by centrifugation until the pH value is 6.5-7.5, and the obtained multilayer titanium carbide nanosheets are sonicated in an ice-water bath under the condition of passing argon gas. The suspension after sonication is centrifuged and screened to separate layers, and the centrifugal supernatant is freeze-dried to obtain single-layer or few-layer titanium carbide nanosheets.

8. The method for preparing the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst according to claim 7, characterized in that: In step P1, the etching water bath reaction conditions are: placing in a water bath at 40° C. for 36 h, and the molar concentration of HCl is 9 M.

9. A palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst, characterized in that: The method is described in claims 1 to 6.

10. Use of the palladium / ionic liquid-titanium carbide nanosheet composite electrode catalyst as claimed in claim 9 for catalytic oxidation of methanol in a methanol fuel cell.

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