CN112691687B - WC-C palladium-loaded composite material and preparation method and application thereof - Google Patents

WC-C palladium-loaded composite material and preparation method and application thereof Download PDF

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CN112691687B
CN112691687B CN202011367084.4A CN202011367084A CN112691687B CN 112691687 B CN112691687 B CN 112691687B CN 202011367084 A CN202011367084 A CN 202011367084A CN 112691687 B CN112691687 B CN 112691687B
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陈赵扬
彭荣贵
褚有群
李灵童
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Zhejiang University of Technology ZJUT
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Abstract

The invention discloses a WC-C palladium-loaded composite material and a preparation method and application thereof. The preparation method comprises the following steps: carrying out oxidation modification treatment on the activated carbon by using nitric acid; (2) Ultrasonically dispersing the activated carbon treated by nitric acid in absolute ethyl alcohol to form a mixed solution, and then adding WCl 6 Then stirring in water bath, cooling, washing, carrying out solid-liquid separation, and drying to obtain a solid; (3) Preparing an iron trichloride aqueous solution, adding urea to obtain a mixed solution, adding the solid obtained in the step (2) into the mixed solution, stirring for reaction, performing solid-liquid separation, and drying to obtain a solid; (4) Carrying out reduction carbonization on the solid by adopting a temperature programming-gas-solid reaction method under a hydrogen-rich atmosphere, and cooling to obtain Fe-WC-C particles after carbonization is finished; (5) And (3) putting the Fe-WC-C particles into a palladium chloride solution for a displacement reaction, performing solid-liquid separation, and drying to obtain the WC-C palladium-loaded composite material. The invention provides application of the WC-C palladium-loaded composite material as an electrocatalyst in an ethanol fuel cell.

Description

WC-C palladium-loaded composite material and preparation method and application thereof
(I) technical field
The invention relates to a WC-C palladium-loaded composite material, a preparation method thereof and application of the WC-C palladium-loaded composite material as an electrocatalyst in an ethanol fuel cell.
(II) background of the invention
The composite material is a material with new performance formed by two or more materials with different properties through a physical or chemical method on a macroscopic scale. The materials mutually make up for the deficiencies in performance to generate a synergistic effect, so that the comprehensive performance of the composite material is superior to that of the original composition material to meet various different requirements.
Tungsten carbide (WC), a metal carbide, has platinum-like catalytic activity and is therefore used in many applications in recent years for catalysts and catalyst substrates. Numerous studies indicate that tungsten carbide can be widely applied to numerous fields of electrocatalysis, particularly as a substrate, and can better embody the synergistic effect with the active metals of noble metal series, thereby improving the comprehensive performance of the composite material. The palladium metal can perform good electrocatalytic oxidation on small molecular compounds such as methanol, ethanol and the like, and has good potential value for improving the material performance through the compounding of palladium and WC. How to prepare the tungsten carbide palladium-loaded material with a special structure by utilizing a process technology with a more regulated space is a very valuable product research hotspot.
The composition of tungsten carbide and palladium must solve the following two difficulties: the first is the agglomeration problem of tungsten carbide, which is easy to cause the agglomeration problem of particles at the high temperature of the carbonization process; the second is how the palladium particles are supported on the tungsten carbide, whether a stable combined structure can be formed, otherwise, even if the palladium particles can be combined reluctantly, the palladium particles and the tungsten carbide are simply superposed, the influence of the electronic structure is almost negligible, and the functional embodiment of the composite material is not mentioned.
Combining the concept of composite materials, the combination of WC with a stable structure and highly dispersed and stably combined palladium nanoparticles is hopeful to make up the WC and the highly dispersed and stably combined palladium nanoparticles, so that the performance can be further improved. Therefore, such research is very popular among researchers of materials, especially researchers of related engineering applications. However, a preparation method that can control both the particle size of the WC substrate and the distribution pattern of the surface palladium in a synergistic manner remains challenging. However, in the existing reports, the palladium-carrying material is usually prepared by a liquid-phase sodium borohydride reduction method (reference: electrochimica acta,2017,247, 674-684), while the liquid-phase sodium borohydride reduction method suffers from too many influence factors, such as the concentration, pH value and addition speed and sequence of sodium borohydride can influence the morphology and particle size of metal palladium, and particularly in large-scale preparation, the aggregation phenomenon of palladium is difficult to solve, so that the difficulty of cost control and process standardization control is caused, the large-scale preparation is difficult, and the problem of meeting the material preparation is also solved.
Therefore, the composite catalyst with simple preparation conditions and stable, dispersed and controllable palladium is a key and important way for remarkably improving the catalytic activity of the composite nano-catalyst. Furthermore, if the dispersion of palladium can be effectively controlled, the preparation steps are reduced, and the production time, the energy consumption and the production cost generated by the production time and the energy consumption can be greatly reduced.
Reports on the preparation of the WC-C palladium-supported composite material by a colloid-assisted method are never found so far.
Disclosure of the invention
The invention aims to solve the first technical problem of providing a colloid-assisted preparation method of a WC-C palladium-loaded composite material, wherein the composite material prepared by the method has stable combination of all components and good thermal stability, and WC-C palladium-loaded composite material particles can be regulated and controlled in a nanometer to micrometer level so as to adapt to different application environments.
The invention aims to solve the second technical problem of providing a WC-C palladium-loaded composite material.
The third technical problem to be solved by the invention is to provide the application of the WC-C palladium-loaded composite material as an electrocatalyst in an ethanol fuel cell.
The technical solution of the present invention is specifically explained below.
In a first aspect, the invention provides a preparation method of a WC-C palladium-loaded composite material, which comprises the following steps:
(1) Carrying out oxidation modification treatment on the activated carbon by using nitric acid;
(2) Ultrasonically dispersing the activated carbon treated by nitric acid in absolute ethyl alcohol to form a mixed solution, and adding a certain amount of WCl into the mixed solution 6 Then stirring in water bath; stirring in water bath, cooling, washing, performing solid-liquid separation, and drying to obtain a solid;
(3) Preparing ferric trichloride aqueous solution, and adding a certain amount of urea into the solution to obtain mixed solution, wherein the molar ratio of the added urea to the ferric trichloride is 3-6: 1; putting the solid obtained in the step (2) into the mixed solution according to the mass ratio of the tungsten element to the iron element of 1: 0.1-0.25, stirring for 4-10 hours at the temperature of 60-90 ℃, and after stirring, performing solid-liquid separation and drying to obtain a solid;
(4) Carrying out reduction carbonization on the solid obtained in the step (3) by adopting a temperature programming-gas-solid reaction method under a hydrogen-rich atmosphere, and cooling to obtain Fe-WC-C particles after carbonization is finished;
(5) And (3) putting Fe-WC-C particles into a certain amount of palladium chloride solution according to the required palladium loading capacity for displacement reaction, and then carrying out solid-liquid separation on the solid obtained by the displacement reaction and drying to obtain the WC-C palladium-loaded composite material.
In the step (1) of the invention, the composite material is prepared by using activated carbon as a carrier, the activated carbon can be a commercial product, the particle size of the activated carbon can be selected according to the application occasion, and in the specific embodiment of the invention, nano-scale activated carbon is used. According to the method, in the step (1), the active carbon is subjected to oxidation modification treatment by using nitric acid, so that the number of oxygen-containing functional groups on the surface of the active carbon is increased, and the adsorption capacity of the active carbon on metal ions is improved. The specific operation steps of the oxidation modification treatment of the activated carbon by the nitric acid can refer to the reports of the prior literature (such as references: [ rock and mineral test, no. 4 of No. 33, p528-534 of 2014), [ Guangzhou chemical industry, no. 5 of No. 47 of 2019, p 7274-7277), for example, the following steps are adopted: firstly, washing commercially available activated carbon with deionized water and drying; and then carrying out nitric acid modification, wherein the nitric acid modification adopts an impregnation method, the mass fraction of a preferred nitric acid solution is 20-60%, the ratio of the mass of the activated carbon to the dosage of the nitric acid solution is 1 g: 5-15 mL, oscillating for 12-24 h at room temperature-50 ℃, and filtering, washing and drying to obtain the activated carbon after the nitric acid treatment for later use.
In the step (2) of the invention, the activated carbon is fully dispersed in the absolute ethyl alcohol by ultrasonic treatment, and the ultrasonic treatment time is properly prolonged, which is favorable for obtaining a mixed solution with more uniform dispersion, and the ultrasonic treatment time is preferably 10-30 minutes. Then adding a certain amount of WCl into the mixed solution 6 And stirred in a water bath, added with WCl 6 The mass ratio of the activated carbon to the activated carbon is controlled to be 1:0.5 to 3; the water bath stirring conditions are as follows: stirring in a water bath at 70-90 ℃ for 12-24 hours, and preferably stirring for 14-20 hours.
In the step (3), the material compounding is realized by utilizing the ferric hydroxide colloid generated by the hydrolysis of the urea in the mixed solution, specifically, three chemical reactions are performed in the mixed solution, firstly, the urea is subjected to the hydrolysis reaction at the temperature of 60-90 ℃ to generate ammonia gas, then, the ammonia gas is combined with water in the solution to generate ammonia water, and is ionized to generate a large number of hydroxide ions, and finally, the iron ions are combined with the hydroxide ions to generate the ferric hydroxide colloid which is attached to the solid in the solution, so that the material compounding is realized. The settings of urea content, temperature and time are all very critical. The experimental result shows that the urea content needs to be set to be 3-6: 1, wherein the preferable molar ratio is 4-5: 1. The temperature directly determines the rate of hydrolysis of urea and thus affects the rate of formation of ferric hydroxide colloid. When the temperature is lower than 60 ℃, the urea in the solution does not undergo hydrolysis reaction, when the temperature reaches above 60 ℃, the higher the temperature is, the faster the urea is hydrolyzed, but when the temperature is higher than 95 ℃, the temperature of the solution is close to the boiling point of water, so that bubbles are generated and even boiling affects the compounding of the colloid and the material, preferably, the temperature is 75-85 ℃, and the stirring time is 6-8 hours.
In step (4) of the invention, the solid obtained in step (3) is carbonized in a tube furnace under a hydrogen-rich atmosphere to prepare the iron/tungsten carbide/carbon composite material (Fe-WC-C). The hydrogen-rich atmosphere is as follows: h with the volume ratio of 1: 1-4 2 And CO mixed gas, the total gas flow is 80-160 ml/min; preferred hydrogen-rich atmospheres are: h with volume ratio of 1:4 2 And CO mixed gas, and the total gas flow is 100ml/min. Preferred carbonization conditions are: heating to 750-850 ℃ at a programmed heating rate of 3-7 ℃/min and keeping for 3-6 hours.
In the step (5) of the invention, palladium replacement is carried out on the iron/tungsten carbide/carbon composite material particles in the palladium-containing compound solution to realize palladium loading, wherein the palladium content in the composite material is controlled by the feeding ratio of the iron/tungsten carbide/carbon composite material particles and the palladium chloride solution. The invention preferably selects the palladium-containing compound solution as palladium chloride solution with the concentration of 3-10 mmol/L; feeding the palladium chloride solution according to the mass of Pd which is 5-20% of the mass of the prepared palladium/tungsten carbide/carbon composite material; the substitution temperature is preferably from room temperature to 50 ℃ and the substitution time is preferably from 5 to 12 hours. After the replacement reaction is finished, the composite material may also contain iron elements, and the existence of the iron elements does not reduce the electrocatalytic performance of the composite material, so that the iron elements do not need to be removed generally. If the iron element needs to be removed, the solid obtained after the replacement reaction is put into 10 to 20 percent hydrochloric acid solution for acid cleaning treatment to remove the iron element, and the acid cleaning time is 1 to 3 hours.
In a second aspect, the invention provides a WC-C palladium-supported composite material prepared according to the above preparation method.
In a third aspect, the invention provides the application of the WC-C palladium-supported composite material (Pd-WC-C) as an electrocatalyst in an ethanol fuel cell. The results show that the WC-C palladium-supported composite material can obviously improve the catalytic conversion efficiency compared with commercial Pd/C.
Compared with the prior art, the invention has the beneficial effects that:
(1) The preparation method has the advantages that: the invention utilizes the hydrolysis of urea in the mixed solution to generate stable ferric hydroxide colloid which is attached and distributed with WCl 6 The activated carbon obtains WC-C by one step through carbonization, realizes the uniform distribution of Fe element on the surface of the carrier, and further realizes the good dispersibility of palladium on the surface of the carrier through a displacement reaction by utilizing the activity of Fe. Pd in the WC-C palladium-loaded (Pd-WC-C) composite material is obtained by replacing Fe in situ, so that a plurality of steps in the conventional Pd-loaded method and consumption of raw materials such as a reducing agent are omitted, the steps are simple, and the cost is effectively reduced; the Pd carrying amount of the composite material can be easily regulated and controlled through the introduction amount of Fe and the addition amount of a palladium chloride solution in the later period, and the operation is simple and convenient.
(2) The structural performance of the WC-C palladium-loaded composite material has the advantages that: due to the adoption of in-situ load change, the combination of all components of the WC-C palladium-loaded composite material is stable, and the effective components are not easy to fall off, so that the utilization rate of Pd is improved, and the catalytic activity is improved; the composite material takes the activated carbon as a carrier, so that the stability of the catalyst is improved, and the coexistence of WC and Pd further enhances the catalytic activity of the palladium-supported catalyst; the particle size of the composite material particles can be controlled by the particle size of the activated carbon carrier, and can be regulated and controlled in a nanometer to micrometer level so as to adapt to different application environments.
(3) The WC-C palladium-loaded composite material has the advantages of being used as an electrocatalyst in an ethanol fuel cell: compared with the common commercial Pd/C catalyst, the performance of the WC-C palladium-loaded composite material as the electrocatalyst on the ethanol oxidation performance of the anode reaction of the ethanol fuel cell is greatly improved.
Description of the drawings
FIG. 1 is an X-ray diffraction pattern (XRD) of a WC-C palladium on palladium composite material prepared according to example 1 of the invention.
FIG. 2 is a graph of the catalytic activity of WC-C palladium-loaded composites prepared in examples 1 and 5 of the present invention and commercial Pd/C (5% palladium loading) versus ethanol. Commercial Pd/C (5% palladium loading) used for the tests was purchased from Aladdin reagents (Shanghai) Co., ltd; the counter electrode used for the test is a platinum electrode, and the reference electrode is a saturated calomel electrode; the solution at the time of the test was a mixed aqueous solution of ethanol (0.5M) and potassium hydroxide (0.5M) at a sweep rate of 50mV/s.
FIG. 3 is a graph of the catalytic activity of the WC-C palladium-loaded composite material prepared in the comparative example of the invention and commercial Pd/C (5% palladium loading) versus ethanol, the test conditions being consistent with those of FIG. 2.
(V) specific embodiment:
the invention will be further described in the following examples, which are given in conjunction with the appended drawings, without limiting the scope of the invention thereto:
the activated carbon used in the examples was purchased from Cabot corporation, usa and was available as VXC-72R, having a particle size of about 30nm.
Example 1:
soaking the cleaned and dried active carbon in a nitric acid solution with the mass fraction of 20%, wherein the ratio of the mass of the active carbon to the volume of the nitric acid solution is 1 g: 10mL, soaking for 12 hours at room temperature, filtering, washing and drying for later use; ultrasonically dispersing the activated carbon subjected to nitric acid oxidation treatment in absolute ethyl alcohol to form a mixed solution, wherein the ultrasonic treatment time is 10 minutes; adding WCl to the mixed solution 6 ，WCl 6 And (2) activatingThe mass ratio of the charcoal is controlled to be 1.5, the mixture is stirred for 14 hours in a water bath at 70 ℃, and solid-liquid separation is carried out after multiple times of washing to obtain solid A.
Preparing ferric trichloride solution according to the tungsten/iron mass ratio of 1: 0.1, and adding urea into the solution, wherein the molar ratio of the added urea to the ferric trichloride is 4: 1; and (3) putting the solid A into the solution, stirring for 6 hours in a water bath at 75 ℃, after the water bath stirring is finished, carrying out solid-liquid separation, and then putting the solid A into an oven to be dried to obtain a solid B.
Carbonizing the solid B in a tube furnace in the following atmosphere: the volume ratio is 1: 4H 2 And CO mixed gas, and the total gas flow is 100ml/min. The carbonization temperature is as follows: raising the temperature to 750 ℃ at the stage temperature programming rate of 7 ℃/min, keeping the temperature for 3 hours, and obtaining Fe-WC-C particles after cooling. And soaking the obtained particles in a palladium chloride solution of 3mmol/L at room temperature, feeding the palladium chloride solution according to the mass of Pd which is 5 percent of the mass of the prepared target composite material, keeping the mixture at the room temperature for 5 hours, filtering, and drying to obtain the WC-C palladium-loaded composite material. FIG. 1 is an X-ray diffraction pattern (XRD) of the WC-C palladium-supported composite material prepared.
The prepared WC-C palladium-loaded composite material is used for preparing an electrocatalyst, and the specific steps comprise:
(1) Pretreatment of the working electrode: firstly, using Al as working electrode (glassy carbon electrode) 2 O 3 Polishing the powder to a mirror surface and then cleaning; then the glassy carbon electrode is placed at 0.2mol/L KCl +1mmol/L K 3 Fe(CN) 6 Activating in the solution, and carrying out cyclic voltammetry scanning in a potential range of-0.1-0.5V at a scanning speed of 50mV/s, wherein when the peak potential difference of the obtained cyclic voltammetry curve is about 70mV, the electrode can be used;
(2) Preparation of a working electrode: weighing 3mgWC-C palladium-loaded composite material, placing the composite material into a sample tube, adding 160 mu L ethanol and 40 mu L5% Nafion to prepare emulsion, performing ultrasonic dispersion for 30min to obtain uniform catalyst slurry, sucking 5 mu L catalyst slurry by using a micro-pipetting gun, dripping the catalyst slurry onto the surface of a glassy carbon electrode, and drying at 50 ℃ to obtain the working electrode.
(3) The counter electrode adopted in the test is a platinum electrode, and the reference electrode is a saturated calomel electrode; the solution at the time of the test was a mixed aqueous solution of ethanol (0.5M) and potassium hydroxide (0.5M) at a sweep rate of 50mV/s, and the results are shown in FIG. 2.
(4) Working electrodes were prepared and tested as described above with commercial Pd/C (5% palladium loading, available from Aladdin reagent, inc.; shanghai) as a comparison, and the results are shown in FIG. 2.
Example 2:
similar to the process of example 1, the washed and dried activated carbon is soaked in a nitric acid solution with the mass fraction of 60%, the ratio of the mass of the activated carbon to the volume of the nitric acid solution is 1 g: 10mL, and after soaking for 24 hours at 50 ℃, the activated carbon is filtered, washed and dried for later use. Ultrasonically dispersing the activated carbon subjected to nitric acid oxidation treatment in absolute ethyl alcohol to form a mixed solution, wherein the ultrasonic treatment time is 30 minutes. WCl is added into the mixed solution 6 ，WCl 6 And the mass ratio of the activated carbon to the activated carbon is controlled to be 1.
The remaining steps were the same as in example 1 to obtain a WC-C supported palladium composite material.
Example 3:
in analogy to the procedure of example 1, the procedure of example 1 was followed to obtain solid A. Preparing ferric trichloride solution according to the tungsten/iron mass ratio of 1: 0.25, and adding urea into the solution, wherein the molar ratio of the added urea to the ferric trichloride is 5: 1; and (3) putting the solid A into the solution, stirring for 8 hours in a water bath at 85 ℃, separating solid from liquid after stirring in the water bath, and drying in an oven to obtain a solid B.
The remaining steps were the same as in example 1 to obtain a WC — C palladium-supported composite material.
Example 4:
analogously to the procedure of example 1, solid B was obtained according to the procedure of example 1 and was carbonized in a tube furnace in the following atmosphere: the volume ratio is 1: 4H 2 And CO mixed gas, and the total gas flow is 100ml/min. The carbonization temperature is as follows: heating to 850 ℃ at the stage temperature programming rate of 3 ℃/min, keeping for 6 hours, and cooling to obtain Fe-WC-C particles.
And soaking the obtained particles in 10mmol/L palladium chloride solution at room temperature, feeding the palladium chloride solution according to the mass of Pd which is 5 percent of the mass of the prepared target composite material, keeping the mixture at 50 ℃ for 12 hours, filtering, and drying to obtain the WC-C palladium-loaded composite material.
Example 5:
soaking the cleaned and dried activated carbon in a nitric acid solution with the mass fraction of 60%, wherein the ratio of the mass of the activated carbon to the volume of the nitric acid solution is 1g to 10m L, soaking for 24 hours at room temperature, filtering, washing and drying for later use. Ultrasonically dispersing the activated carbon subjected to nitric acid oxidation treatment in absolute ethyl alcohol to form a mixed solution, wherein the ultrasonic treatment time is 30 minutes. WCl is added to the mixed solution 6 ，WCl 6 And the mass ratio of the active carbon to the active carbon is controlled to be 1, the mixture is stirred for 20 hours in a water bath at 70 ℃, and solid-liquid separation is carried out after multiple times of washing to obtain a solid A.
Preparing ferric trichloride solution according to the tungsten/iron mass ratio of 1: 0.25, and adding urea into the solution, wherein the molar ratio of the added urea to the ferric trichloride is 4.5: 1; and (3) putting the solid A into the solution, stirring for 8 hours in a water bath at the temperature of 80 ℃, after the water bath stirring is finished, carrying out solid-liquid separation, and then placing the solid A into an oven to be dried to obtain a solid B.
Carbonizing the solid B in a tube furnace in the following atmosphere: the volume ratio is 1: 4H 2 And CO mixed gas, and the total gas flow is 100ml/min. The carbonization temperature is as follows: heating to 800 ℃ at the stage temperature programming rate of 5 ℃/min, keeping for 6 hours, and cooling to obtain Fe-WC-C particles. And soaking the obtained particles in a palladium chloride solution of 5mmol/L at room temperature, feeding the palladium chloride solution according to the mass of Pd which is 5 percent of the mass of the prepared target composite material, keeping the palladium chloride solution at 50 ℃ for 12 hours, filtering, and drying to obtain the WC-C palladium-loaded composite material.
Performance testing was performed according to the electrocatalyst preparation and application method of example 1, and the results are shown in FIG. 2.
Comparative example 1
In analogy to the procedure of example 1, the procedure of example 1 was followed to obtain solid A. Preparing ferric trichloride solution according to the tungsten/iron mass ratio of 1: 0.25, and adding urea into the solution, wherein the molar ratio of the added urea to the ferric trichloride is 5: 1; and (3) putting the solid A into the solution, stirring for 8 hours in a water bath at 50 ℃, after the water bath stirring is finished, carrying out solid-liquid separation, and then placing the solid A into an oven to be dried to obtain a solid B.
The remaining steps were the same as in example 1 to obtain a WC-C supported palladium composite material.
Comparative example 2
In analogy to the procedure of example 1, the procedure of example 1 was followed to obtain solid A. Preparing ferric trichloride solution according to the tungsten/iron mass ratio of 1: 0.25, adding urea into the solution, wherein the molar ratio of the added urea to the ferric trichloride is 9: 1; and (3) putting the solid A into the solution, stirring for 6 hours in a water bath at 75 ℃, after the water bath stirring is finished, carrying out solid-liquid separation, and then putting the solid A into an oven to be dried to obtain a solid B.
The remaining steps were the same as in example 1 to obtain a WC-C supported palladium composite material.
Comparative example 3
In analogy to the procedure of example 1, the procedure of example 1 was followed to obtain solid a. Preparing ferric trichloride solution according to the tungsten/iron mass ratio of 1: 0.25, and adding urea into the solution, wherein the molar ratio of the added urea to the ferric trichloride is 2: 1; and (3) putting the solid A into the solution, stirring for 8 hours in a water bath at 85 ℃, performing solid-liquid separation after the water bath stirring is finished, and drying in an oven to obtain a solid B.
The remaining steps were the same as in example 1 to obtain a WC-C supported palladium composite material.
Comparative example 4
In analogy to the procedure of example 1, the procedure of example 1 was followed to obtain solid A. Preparing ferric trichloride solution according to the tungsten/iron mass ratio of 1: 0.25, and adding urea into the solution, wherein the molar ratio of the added urea to the ferric trichloride is 5: 1; and (3) putting the solid A into the solution, stirring for 3 hours in a water bath at 75 ℃, after the water bath stirring is finished, carrying out solid-liquid separation, and then placing the solid A into an oven to be dried to obtain a solid B.
The remaining steps were the same as in example 1 to obtain a WC-C supported palladium composite material.

Claims (9)

1. A preparation method of a WC-C palladium-loaded composite material comprises the following steps:
(1) Carrying out oxidation modification treatment on the activated carbon by using nitric acid;
(2) Ultrasonically dispersing the activated carbon treated by nitric acid in absolute ethyl alcohol to form mixed solution, and adding a certain amount of WCl into the mixed solution 6 Then stirring in water bath; stirring in a water bath, cooling, washing, carrying out solid-liquid separation, and drying to obtain a solid;
(3) Preparing a ferric trichloride aqueous solution, adding a certain amount of urea into the solution to obtain a mixed solution, wherein the molar ratio of the added urea to the ferric trichloride is 3-6: 1; putting the solid obtained in the step (2) into the mixed solution according to the mass ratio of the tungsten element to the iron element of 1: 0.1-0.25, stirring for 4-10 hours at the temperature of 60-90 ℃, and after stirring, carrying out solid-liquid separation and drying to obtain a solid;
(4) Carrying out reduction carbonization on the solid obtained in the step (3) by adopting a temperature programming-gas-solid reaction method under a hydrogen-rich atmosphere, and cooling to obtain Fe-WC-C particles after carbonization is finished; the hydrogen-rich atmosphere is H with the volume ratio of 1:1 to 4 2 And CO mixed gas;
(5) And (2) putting the Fe-WC-C particles into a certain amount of palladium chloride solution according to the required palladium loading capacity for displacement reaction, and then carrying out solid-liquid separation on the solid obtained by the displacement reaction and drying to obtain the WC-C palladium-loaded composite material.
2. The method of claim 1, wherein: in the step (1), the oxidation modification treatment comprises the following steps: firstly, washing commercially available activated carbon with deionized water and drying; and then carrying out nitric acid modification, wherein the nitric acid modification adopts an immersion method, the mass fraction of a nitric acid solution is 20-60%, the ratio of the mass of the activated carbon to the using amount of the nitric acid solution is 1 g: 5-15 mL, oscillating for 12-24 h at room temperature-50 ℃, and filtering, washing and drying to obtain the activated carbon treated by the nitric acid for later use.
3. The method of claim 1, wherein: in the step (2), the ultrasonic treatment time is 10 to 30 minutes, and WCl is added 6 The mass ratio of the active carbon is controlled as1:0.5 to 3; the water bath stirring conditions are as follows: stirring the mixture in a water bath at the temperature of 70 to 90 ℃ for 12 to 24 hours.
4. The method of claim 3, wherein: in the step (2), the stirring time is 14 to 20 hours.
5. The method of claim 1, wherein: in the step (3), the molar ratio of urea to ferric trichloride is 4-5: 1, the reaction temperature is 75-85 ℃, and the stirring time is 6-8 hours.
6. The method of claim 1, wherein: in the step (4), the hydrogen-rich atmosphere is: h with the volume ratio of 1:1 to 4 2 Mixing the gas with CO, wherein the total gas flow is 80-160 ml/min; the carbonization conditions are as follows: heating to 750-850 ℃ at a programmed heating rate of 3-7 ℃/min and keeping for 3-6 hours.
7. The method of claim 1, wherein: in the step (5), the palladium compound solution is a palladium chloride solution with the concentration of 3 to 10 mmol/L; feeding the palladium chloride solution according to the mass of Pd, wherein the mass of the palladium chloride solution is 5-20% of that of the prepared palladium/tungsten carbide/carbon composite material; the replacement temperature is room temperature to 50 ℃, and the replacement time is 5 to 12 hours.
8. The WC-C palladium-supported composite material prepared by the preparation method according to claim 1.
9. Use of the WC-C supported palladium composite of claim 8 as an electrocatalyst in an ethanol fuel cell.
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