Composite catalyst and its preparation method and application

Abstract

The present invention relates to the field of fuel cell technology, and more particularly to a composite catalyst, its preparation method, and its application. The present invention provides a composite catalyst comprising a composite support and a precious metal supported on the surface of the composite support; the composite support comprises graphene and tin dioxide coated on the graphene surface; and the precious metal comprises Pt and / or Pd. This composite catalyst addresses the problem of ethanol electrooxidation performance degradation during cycling in direct ethanol fuel cells.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a composite catalyst and a preparation method and application thereof. Background Art

[0002] With the emergence and growing tensions between global energy and environmental challenges, fuel cell technology has garnered increasing attention. Direct ethanol fuel cells (DEFCs) use ethanol as fuel, offering advantages such as widespread availability, low corrosiveness, low permeability, and high energy density. Furthermore, the products produced by ethanol combustion are essential for ethanol synthesis in nature. Therefore, ethanol has attracted widespread attention as a clean energy source. To date, platinum remains the best-performing anode catalyst for DEFCs. However, platinum's high cost and susceptibility to poisoning have severely hindered the development of DEFC catalysts. Therefore, the development of inexpensive, highly active, and stable anode catalysts has become a key trend in DEFC research.

[0003] The electrooxidation of ethanol occurs primarily through two pathways. The C1 pathway involves the complete oxidation of ethanol to carbon dioxide, transferring 12 electrons. The C2 pathway involves the oxidation of ethanol to acetic acid, in which ethanol is not completely oxidized, transferring only 4 electrons. To promote C-C bond breakage during ethanol electrooxidation, improve the selectivity of the C1 pathway, and prevent catalyst poisoning, researchers often combine platinum with other metals or metal oxides and support them on high-surface-area supports to enhance ethanol electrooxidation activity. Currently, the conventional approach involves supporting precious metals on the surface of graphene to catalyze the electrooxidation of ethanol. However, this method suffers from capacity degradation during cycling in direct ethanol fuel cells. Summary of the Invention

[0004] The object of the present invention is to provide a composite catalyst and a preparation method and application thereof, wherein the composite catalyst solves the problem that ethanol electrooxidation in a direct ethanol fuel cell is easily attenuated during the cycle.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a composite catalyst comprising a composite carrier and a noble metal supported on the surface of the composite carrier;

[0007] The composite carrier includes graphene and tin dioxide coated on the surface of the graphene;

[0008] The noble metal includes Pt and / or Pd.

[0009] Preferably, the mass percentage of the noble metal in the composite catalyst is 1 to 20%;

[0010] The molar ratio of the noble metal to the tin atoms in tin dioxide is (0.1-2):1.

[0011] The present invention also provides a method for preparing the composite catalyst described in the above technical solution, comprising the following steps:

[0012] mixing graphene with concentrated nitric acid for pretreatment to obtain pretreated graphene;

[0013] Mixing an ammonia solution and a tin tetrachloride solution, mixing the mixture with the pretreated graphene, and then performing rotary evaporation and calcination in sequence to obtain a composite carrier;

[0014] Mixing an ethylene glycol solution of sodium citrate, a noble metal precursor and the composite support, and performing a hydrothermal reaction to obtain the composite catalyst;

[0015] The noble metal precursor is a platinum precursor and / or a palladium precursor.

[0016] Preferably, the pretreatment process is: heating the concentrated nitric acid and mixing the obtained concentrated nitric acid vapor with the graphene for pretreatment;

[0017] The heating temperature is 100-150° C. and the heating time is 6-12 hours;

[0018] After the pretreatment is completed, the process further includes allowing the patient to stand for 20 to 32 hours.

[0019] Preferably, the concentration of the ammonia solution is 0.3 to 0.6 mol / L;

[0020] The concentration of the tin tetrachloride solution is 0.05-0.2 mol / L;

[0021] The volume ratio of the ammonia solution to the tin tetrachloride solution is (0.1-10):1.

[0022] Preferably, the temperature of the rotary evaporation is 60-90° C., the rotation speed is 100-180 r / min, and the time is 30-90 min.

[0023] Preferably, the calcination temperature is 300-1000° C. and the calcination time is 1.5-4 hours.

[0024] Preferably, the mass ratio of sodium citrate, noble metal precursor and composite support in the ethylene glycol solution of sodium citrate is (0.1-2):(0.01-1):1;

[0025] The concentration of the noble metal precursor in the reaction solution of the hydrothermal reaction is 0.08 to 0.18 mol / L.

[0026] Preferably, the temperature of the hydrothermal reaction is 120-200°C and the time is 8-15h;

[0027] The pH value of the reaction solution before the hydrothermal reaction is 8-11, and the pH value of the product solution after the hydrothermal reaction is 3-5.

[0028] The present invention also provides the use of the composite catalyst described in the above technical solution or the composite catalyst prepared by the preparation method described in the above technical solution in the electrocatalytic oxidation of ethanol.

[0029] The present invention provides a composite catalyst, comprising a composite carrier and a noble metal loaded on the surface of the composite carrier; the composite carrier comprises graphene and tin dioxide coated on the surface of the graphene; the noble metal comprises Pt and / or Pd. The composite catalyst described in the present invention uses tin dioxide as a co-catalyst for the precious metal, and the precious metal is loaded at a position adjacent to the tin dioxide on the composite carrier. The tin dioxide can be effectively used to activate water molecules in the electrolyte to form oxygen-containing species, and then the toxic species adsorbed on the precious metal are directly oxidized and removed, thereby improving the efficiency of ethanol oxidation, the selectivity of carbon dioxide in the product, and the anti-poisoning ability of the catalyst. Compared with the catalyst obtained by directly loading the precious metal on the surface of graphene, the composite catalyst described in the present invention has higher ethanol electrooxidation efficiency and cycle stability when used to catalyze ethanol electrooxidation; the graphene has a large specific surface area, which can effectively improve the dispersion of the precious metal and reduce the amount of precious metal used. During the catalytic reaction, a solid-gas-liquid three-phase interface is formed on the surface, and the gas and liquid are well transferred through the three-dimensional network structure constructed by the graphene in the catalytic layer; therefore, the composite catalyst has a low amount of precious metal, strong anti-poisoning ability, good catalytic stability and high carbon dioxide selectivity, and can be applied to the anode of direct ethanol fuel cells;

[0030] The present invention also provides a method for preparing the composite catalyst described in the above technical solution, comprising the following steps: mixing graphene with concentrated nitric acid and pre-treating it to obtain pre-treated graphene; mixing an aqueous ammonia solution and a tin tetrachloride solution, mixing the mixture with the pre-treated graphene, and then sequentially performing rotary evaporation and calcining to obtain a composite support; mixing an ethylene glycol solution of sodium citrate, a noble metal precursor, and the composite support, and performing a hydrothermal reaction to obtain the composite catalyst; the noble metal precursor is a platinum precursor and / or a palladium precursor. The composite support described in the present invention is prepared using a "sol-gel-dispersion-adsorption" and calcination method, uniformly coating the surface of the graphene nanosheets with tin dioxide, thereby effectively improving the hydrophilicity of the graphene support surface, facilitating the uniform loading of subsequent catalysts thereon, thereby achieving higher catalyst utilization and a greater current for ethanol oxidation. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 TEM image of the Pt-SnO2GN described in Example 1;

[0032] Figure 2 The XRD patterns of the composite catalysts prepared in Examples 1 to 6 are as follows;

[0033] Figure 3 The Raman spectra of the composite catalysts prepared in Examples 1 to 6 are shown;

[0034] Figure 4 This is a comparison chart of the activities of the composite catalysts described in Examples 3 to 5 and the catalyst (Pt-GN) described in Comparative Example 1 for the electrocatalytic oxidation of ethanol. DETAILED DESCRIPTION

[0035] The present invention provides a composite catalyst comprising a composite carrier and a noble metal supported on the surface of the composite carrier;

[0036] The composite carrier includes graphene and tin dioxide coated on the surface of the graphene;

[0037] The noble metal includes Pt and / or Pd.

[0038] In the present invention, the mass percentage of the precious metal in the composite catalyst is preferably 1-20%, more preferably 4-15%, and most preferably 9-11%; the molar ratio of the precious metal to the tin atoms in tin dioxide is preferably (0.1-2):1, more preferably (0.5-1.8):1, and most preferably (0.8-1.2):1.

[0039] The present invention also provides a method for preparing the composite catalyst described in the above technical solution, comprising the following steps:

[0040] mixing graphene with concentrated nitric acid for pretreatment to obtain pretreated graphene;

[0041] Mixing an ammonia solution and a tin tetrachloride solution, mixing the mixture with the pretreated graphene, and then performing rotary evaporation and calcination in sequence to obtain a composite carrier;

[0042] Mixing an ethylene glycol solution of sodium citrate, a noble metal precursor and the composite support, and performing a hydrothermal reaction to obtain the composite catalyst;

[0043] The noble metal precursor is a platinum precursor and / or a palladium precursor.

[0044] In the present invention, unless otherwise specified, all preparation raw materials are commercially available products well known to those skilled in the art.

[0045] The present invention mixes graphene and concentrated nitric acid for pretreatment to obtain pretreated graphene.

[0046] In the present invention, the concentration of the concentrated nitric acid is preferably 10 to 16 mol / L, more preferably 12 to 15 mol / L, and most preferably 13 to 14 mol / L.

[0047] In the present invention, the mass ratio of the graphene to concentrated nitric acid is preferably (0.001-0.2):1, more preferably (0.005-0.1):1, and most preferably (0.01-0.05):1.

[0048] In the present invention, the pretreatment process preferably comprises heating the concentrated nitric acid and mixing the resulting concentrated nitric acid vapor with the graphene for pretreatment. In the present invention, the heating temperature is preferably 100-150°C, more preferably 110-140°C, and most preferably 120-130°C; the heating time is preferably 6-12 hours, more preferably 8-10 hours. After the pretreatment is completed, the present invention also preferably includes standing for a period of preferably 20-32 hours, more preferably 23-30 hours, and most preferably 25-28 hours.

[0049] In an embodiment of the present invention, the pretreatment process is specifically as follows: placing the graphene in a glass tube equipped with a sand plate, heating concentrated nitric acid so that the obtained concentrated nitric acid vapor rises into the glass tube for pretreatment, and then standing.

[0050] After the standing is completed, the present invention further preferably includes filtering, washing, and drying the obtained graphene in sequence. The present invention does not have any particular limitations on the filtering and washing processes, and can be performed using processes well known to those skilled in the art, so long as the obtained graphene is neutral. In the present invention, the drying temperature is preferably 70 to 95°C, more preferably 75 to 90°C, and most preferably 80 to 85°C; the drying time is preferably 6 to 12 hours, more preferably 8 to 10 hours.

[0051] After obtaining the pretreated graphene, the present invention mixes an ammonia solution and a tin tetrachloride solution, mixes the solution with the pretreated graphene, and then sequentially performs rotary evaporation and calcination to obtain a composite carrier.

[0052] In the present invention, the concentration of the aqueous ammonia solution is preferably 0.3-0.6 mol / L, more preferably 0.4-0.5 mol / L; the concentration of the tin tetrachloride solution is preferably 0.05-0.2 mol / L, more preferably 0.10-0.15 mol / L.

[0053] In the present invention, the volume ratio of the ammonia solution to the tin tetrachloride solution is preferably (0.1-10):1, more preferably (0.5-5):1, and most preferably (0.8-1.5):1.

[0054] In the present invention, the mixing of the ammonia solution and the tin tetrachloride solution is preferably performed by adding the ammonia solution dropwise to the tin tetrachloride solution and stirring. The present invention does not have any particular limitation on the stirring process, and a process well known to those skilled in the art can be used.

[0055] After the stirring, the present invention further preferably includes standing, and the standing time is preferably 24 to 36 hours, more preferably 28 to 32 hours.

[0056] After the standing, the present invention further preferably includes removing the supernatant to obtain a tin hydroxide colloidal precipitate. The present invention has no particular limitation on the process of removing the supernatant, and the process can be performed using a process well known to those skilled in the art.

[0057] In the present invention, the molar ratio of the pretreated graphene to the tin hydroxide colloidal precipitate is preferably (0.001-0.1):1, more preferably (0.003-0.03):1, and most preferably (0.006-0.01):1.

[0058] In the present invention, the mixing of the pretreated graphene and the tin hydroxide colloidal precipitate is preferably carried out under stirring conditions. The present invention does not have any particular limitations on the stirring process. The stirring process can be carried out using a process well known to those skilled in the art, and the tin hydroxide colloidal precipitate and the pretreated graphene are dispersed and then uniformly mixed. In the present invention, the stirring time is preferably 5 hours.

[0059] In the present invention, the temperature of the rotary evaporation is preferably 60-90°C, more preferably 65-85°C, and most preferably 70-80°C; the rotation speed is preferably 100-180r / min, more preferably 120-160r / min, and most preferably 130-140r / min; the time is preferably 30-90min, more preferably 45-60min.

[0060] In the present invention, the calcination temperature is preferably 300-1000°C, more preferably 400-800°C, and most preferably 500-600°C; the calcination time is preferably 1-4 hours, more preferably 2-3 hours. In the present invention, the calcination is preferably carried out in a nitrogen atmosphere.

[0061] After the calcination is completed, the present invention further preferably includes cooling. The present invention has no particular limitation on the cooling process, and the cooling process may be performed using a process well known to those skilled in the art and ensuring that the cooling reaches room temperature. In an embodiment of the present invention, the cooling is preferably natural cooling.

[0062] After obtaining the composite support, the present invention mixes the ethylene glycol solution of sodium citrate, the noble metal precursor and the composite support, and performs a hydrothermal reaction to obtain the composite catalyst.

[0063] In the present invention, the concentration of sodium citrate in the ethylene glycol solution of sodium citrate is preferably 0.01 to 0.1 mol / L, more preferably 0.02 to 0.06 mol / L, and most preferably 0.03 to 0.05 mol / L.

[0064] In the present invention, the mass ratio of sodium citrate, noble metal precursor and composite support in the ethylene glycol solution of sodium citrate is preferably (0.1-2):(0.01-1):1, more preferably (0.5-1.5):(0.05-0.5):1, and most preferably (0.8-1.0):(0.2-0.3):1.

[0065] In the present invention, the noble metal precursor preferably includes chloroplatinic acid, platinum chloride, or palladium chloride, more preferably chloroplatinic acid or platinum chloride, and most preferably chloroplatinic acid.

[0066] In the present invention, the mixing is preferably performed by mixing the ethylene glycol solution of sodium citrate and the noble metal precursor, and then adding the composite support. In the present invention, the mixing of the ethylene glycol solution of sodium citrate and the noble metal precursor is preferably performed under stirring. The present invention does not have any special restrictions on the stirring process, and the process well known to those skilled in the art can be used. In the present invention, after adding the composite support, mixing is preferably performed under ultrasonic conditions. The present invention does not have any special restrictions on the ultrasonic conditions, and the process well known to those skilled in the art can be used.

[0067] After the mixing is completed, the present invention preferably further comprises adjusting the pH value of the obtained mixed solution using sodium hydroxide. The adjusted pH value is preferably 8-11, more preferably 9-11.

[0068] In the present invention, the temperature of the hydrothermal reaction is preferably 120-200° C., more preferably 130-190° C., most preferably 140-160° C.; the time is preferably 8-15 h, more preferably 10-14 h, most preferably 11-13 h.

[0069] After the hydrothermal reaction is completed, the steps of cooling, adjusting the pH, filtering, and washing are preferably performed in sequence. The cooling, filtering, and washing steps are not particularly limited in the present invention and can be performed using procedures well known to those skilled in the art. In the present invention, the pH after adjustment is preferably between 3 and 5, more preferably between 3.5 and 4.5.

[0070] After the washing is completed, the present invention also preferably includes vacuum drying, cooling and grinding carried out in sequence. In the present invention, the temperature of the vacuum drying is preferably 70 to 110°C, more preferably 80 to 100°C, and most preferably 85 to 95°C; the present invention does not have any special restrictions on the time of the vacuum drying, and a time familiar to those skilled in the art can be used to ensure sufficient drying. The present invention does not have any special restrictions on the cooling process, and a process familiar to those skilled in the art can be used for natural cooling. In the present invention, the grinding time is preferably 0.5 to 1.5 hours, more preferably 0.8 to 1.2 hours.

[0071] The present invention also provides the use of the composite catalyst described in the above technical solution or the composite catalyst prepared by the preparation method described in the above technical solution in the electrocatalytic oxidation of ethanol. The present invention does not have any particular limitations on the method of application, and the method can be performed using methods well known to those skilled in the art.

[0072] The composite catalyst provided by the present invention, its preparation method and application are described in detail below with reference to the examples, but they should not be construed as limiting the scope of protection of the present invention.

[0073] Example 1

[0074] 5 g of graphene was placed on a sand plate equipped with a glass tube, and 200 mL of 14 mol / L concentrated nitric acid (176.428 g) was heated to 130°C to allow concentrated nitric acid vapor to rise into the glass tube and maintain for 8 hours. The mixture was then allowed to stand for 26 hours, and the graphene was taken out, filtered, washed until neutral, and dried in a drying oven at 80°C for 10 hours to obtain pretreated graphene.

[0075] Under stirring conditions, 2.28 mL of 0.4 mol / L ammonia water was added dropwise to 2.28 mL of 0.1 mol / L tin tetrachloride solution, and the mixture was allowed to stand for 28 h. The supernatant was removed to obtain a stable tin hydroxide gel precipitate (2.28 × 10 -4 mol), 365.6 mg of pretreated graphene was added and stirred for 5 h, heated to 75 ° C and rotary evaporated to dryness for 50 min using a rotary evaporator (the speed of rotary evaporation was 135 r / min), calcined at 400 ° C in a nitrogen atmosphere for 2 h, and naturally cooled to room temperature to obtain SnO2GN;

[0076] 360 mg of sodium citrate and ethylene glycol were mixed and stirred until fully dissolved to obtain a sodium citrate ethylene glycol solution with a concentration of 0.04 mol / L, 2.28 mL of 0.1 mol / L chloroplatinic acid (hexachloroplatinic acid hydrate) solution was added, and after stirring evenly, 400 mg of the SnO2GN was added, and stirred evenly under ultrasonic conditions. The pH value of the solution was adjusted to 10 with sodium hydroxide, and then the obtained mixed solution was hydrothermally treated (the temperature of the hydrothermal treatment was 160 ° C, and the time was 12 h). After the hydrothermal treatment was completed and cooled, the pH was adjusted to 4, and filtered and washed until no Cl was detected. - , after vacuum drying at 90℃ for 8h, grinding for 1h, a composite catalyst (Pt-SnO2GN-400℃) with a mass fraction ratio of Pt:SnO2:GN=1:0.77:8.23 was obtained;

[0077] The Pt-SnO2GN was subjected to TEM test, and the test results were as follows: Figure 1 As shown by Figure 1 It can be seen that the surface of the composite support has a wrinkled structure, and the metal nanoparticles on the surface of the composite support are dispersed relatively evenly, indicating that the precious metal Pt nanoparticles are reduced and loaded on the support, and the particle size is relatively uniform, mainly distributed in the range of 1 to 2.5 nm.

[0078] Example 2

[0079] Refer to Example 1, except that the calcination temperature is 500°C to obtain a composite catalyst (Pt-SnO2GN-500°C).

[0080] Example 3

[0081] Refer to Example 1, except that the calcination temperature is 600°C to obtain a composite catalyst (Pt-SnO2GN-600°C).

[0082] Example 4

[0083] Refer to Example 1, except that the calcination temperature is 700°C to obtain a composite catalyst (Pt-SnO2GN-700°C).

[0084] Example 5

[0085] Refer to Example 1, except that the calcination temperature is 800°C to obtain a composite catalyst (Pt-SnO2GN-800°C).

[0086] Example 6

[0087] Refer to Example 1, except that the calcination temperature is 900°C to obtain a composite catalyst (Pt-SnO2GN-900°C).

[0088] Comparative Example 1

[0089] Preparation process of Pt-GN: The pretreatment process of GN is consistent with that in Example 1. 360 mg of sodium citrate and ethylene glycol are mixed and stirred until fully dissolved, and then 2.28 mL of 0.1 mol / L chloroplatinic acid solution is added. After stirring evenly, 400 mg of the GN is added and stirred evenly under ultrasonic conditions. The pH value of the solution is adjusted to 10 with sodium hydroxide, and the obtained mixed solution is hydrothermally treated (the temperature of the hydrothermal treatment is 160 ° C. and the time is 12 h). After cooling, the pH is adjusted to 4, and the solution is filtered and washed until no Cl is detected. - After vacuum drying at 90°C for 8 h and grinding for 1 h, a catalyst Pt-GN with a mass fraction ratio of Pt:GN = 1:9 was obtained.

[0090] Comparative Example 2

[0091] Preparation process of Pt-ZSM5-C: 1.3 mg of ZSM5 zeolite particles and 67 μL of 38 mmol / L chloroplatinic acid were added to distilled water and ultrasonically mixed, and then NaBH4 solution was added dropwise. The color of the solution changed from yellow to black, proving that the Pt-ZSM5 hybrid catalyst had been formed; then 1.3 mg of activated VulcanXC carbon was added to the above solution, ultrasonically stirred for 3 hours, and then the prepared catalyst was washed with distilled water and vacuum dried to obtain the Pt-ZSM5-C catalyst.

[0092] Comparative Example 3

[0093] Preparation of Pt-SnO2Sb: 10.517g of SnCl2·5H2O, 0.342g of SbCl3, and 4.6mL of 37% HCl were mixed in distilled water. 0.06g / mL of NaOH was added to bring the solution volume to 150mL. The solution was then transferred to a three-necked flask and refluxed at 100°C for 2 hours. The mixture was cooled naturally, washed by centrifugation, and the solids were separated. The resulting powder was dried in a drying oven. The dried powder was placed in a tube furnace and heat-treated in air at 400°C for 1 hour to complete the synthesis of SnO2Sb.

[0094] 0.8 g of chloroplatinic acid was added to 200 mL of ethanol containing 0.1 mol of NaOH and refluxed at 160°C for 30 minutes to form a platinum colloid. The platinum colloid was then added to an aqueous solution of SnO2Sb, followed by aqueous sulfuric acid. After thorough mixing, the mixture was filtered, washed, and dried. The resulting Pt-SnO2Sb was heat-treated in a tube furnace at 160°C under a nitrogen atmosphere for 2 hours to complete the synthesis of Pt-SnO2Sb nanoparticles.

[0095] Test Case

[0096] The composite catalysts prepared in Examples 1 to 6 were subjected to XRD testing. The test results are as follows: Figure 2 As shown by Figure 2 It can be seen that the composite catalysts described in Examples 1 to 6 all have characteristic peaks of a typical face-centered cubic structure of Pt (JCPDS87-0636). Due to the small amount of SnO2 added, only some weak and broad peaks can be seen in the XRD spectrum, indicating that the SnO2 in the catalyst exists in a crystalline form.

[0097] The composite catalysts prepared in Examples 1 to 6 were subjected to Raman spectroscopy testing. The test results are as follows: Figure 3 As shown in Table 1, Figure 3 Middle D peak (I D ) and G peak (I G ) of the peak intensity ratio I D / I G The degree of defects inside the catalyst crystal can be determined. D / I G The values ​​are listed in Table 1, and it can be seen that the I D / I G The ratios of the carbon lattice peaks are all greater than 1, ranging from 1.24 to 1.47, indicating that the internal defects of the carbon lattice represented by the D peak dominate. The interaction between the catalyst metal nanoparticles and the graphene support accelerates the electron transfer efficiency, indicating that the catalyst prepared by this method has good electron conductivity.

[0098] Table 1 I of the composite catalyst described in Examples 1 to 6 D / I G ratio

[0099] Example <![CDATA[I D / I G Ratio]]> Example 1 1.28 Example 2 1.24 Example 3 1.30 Example 4 1.47 Example 5 1.28 Example 6 1.29

[0100] Application Examples

[0101] The composite catalysts described in Examples 1 to 6 were used for electrochemical performance testing of ethanol electrooxidation. The electrochemical performance testing was performed on a Shanghai Chenhua electrochemical workstation CH1660E. The testing process included the following steps:

[0102] 1) Preparation of the working electrode: 2 mg of the composite catalyst described in Examples 1 to 6 was mixed with 51 μL of Nafion solution (Nafion:EG volume ratio of 2:8) and 255 μL of deionized water to prepare an electrode slurry. 15 μL of the slurry was then dropped onto a 5 mm diameter glassy carbon electrode and dried using an infrared lamp to obtain a working electrode.

[0103] 2) Cyclic voltammetry test: The test was carried out at a constant temperature of 25°C. Before each test, N2 was ventilated for 20 minutes to remove dissolved oxygen in the solution. Cyclic voltammetry (CV) was tested in an electrolyte solution of H2SO4 with a concentration of 0.5 mol / L at a scan rate of 50 mv / s, and the electrochemically active surface area (ECSA) of the catalyst was calculated based on the CV graph. Cyclic voltammetry (CV) was tested in an electrolyte solution of 0.5 MH2SO4 + 0.5 MC2H5OH to evaluate the activity of the catalyst in catalyzing the electrooxidation of ethanol and its stability over 1500 cycles. The anodic peak current density (I f ) and the anodic peak current density (I b ) ratio (I f / I b ) to evaluate the accumulation of residual intermediates during ethanol oxidation;

[0104] The ECSA, I f / I b The electrochemical performance data are shown in Table 2. The activity of electrocatalytic oxidation of ethanol is shown in Figure 4 The 1500-cycle cycle stability data is shown in Table 3:

[0105] Table 2 Ethanol electrooxidation performance of the composite catalysts described in Examples 1 to 6

[0106] Example <![CDATA[ECSA / m 2 ·g -1 Pt ]]> <![CDATA[I f / I b ]]> Example 1 15.2 1.17 Example 2 54.2 0.93 Example 3 97.2 1.77 Example 4 77.4 1.60 Example 5 62.3 1.56 Example 6 49.6 1.00

[0107] As shown in Table 2, after adding SnO2 as a composite support on the support graphene, the ECSA value of the catalyst shows a trend of first increasing and then decreasing. When the calcination temperature of SnO2GN is 600℃, the electrochemical active area per unit mass of Pt in the composite catalyst is the largest, reaching 97.2m 2 ·g -1 Pt , I of six composite catalysts in ethanol electrooxidation f / I b It shows that when the calcination temperature of SnO2GN is 600℃, I f / I b The maximum value is 1.77, indicating that this sample has the best ability to resist poisoning by intermediate toxic species during ethanol oxidation;

[0108] Figure 4 The activity comparison diagram of the electrocatalytic oxidation of ethanol by the composite catalysts described in Examples 3 to 5 and the catalyst (Pt-GN) described in Comparative Example 1 (cycle 25) is shown. Figure 4It can be seen that the current density of ethanol oxidation catalyzed by the composite catalysts described in Examples 3 to 5 is higher than that of the catalyst described in Comparative Example 1. Among them, the current density of ethanol oxidation catalyzed by the composite catalyst described in Example 5 is the highest, which is about 13.8 times the current density of ethanol oxidation catalyzed by the Pt-GN catalyst;

[0109] Table 3 Stability of the composite catalysts described in Examples 3 and 4 after 1500 cycles in sulfuric acid

[0110]

[0111] As shown in Table 3, with the increase of the number of cycles, the current density of the composite catalyst in Example 4 reaches the highest current density of 196 mA mg at the 160th cycle. -1 Pt Then it gradually decreased. The current density at the 1500th cycle was 32.7% lower than the maximum current density, showing a trend of current density attenuation. The composite catalyst described in Example 3 reached a maximum current density of 207 mA·mg at the 176th cycle. -1 Pt The current density after 1500 cycles is still 205 mA mg -1 Pt , only reduced by 2mA·mg -1 Pt , showing very stable cycle performance, which may be due to the best synergistic effect of graphene, SnO2 and Pt in the catalyst of the composite support calcined at 600℃;

[0112] Table 4 Electrochemical cycle stability of the composite catalyst described in Example 3 and the catalysts described in Comparative Examples 1 to 3

[0113]

[0114] As shown in Table 4, the composite catalyst prepared by the present invention exhibits more excellent ethanol electro-oxidation cycle stability, and both the maximum oxidation peak current density and the degree of current density reduction are greatly improved.

[0115] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a composite catalyst, characterized in that: The following steps are involved: mixing graphene with concentrated nitric acid for pretreatment to obtain pretreated graphene; Mixing an ammonia solution and a tin tetrachloride solution, then mixing with the pretreated graphene, and sequentially performing rotary evaporation and calcination to obtain a composite carrier; The ethylene glycol solution of sodium citrate, the noble metal precursor and the composite support are mixed and subjected to a hydrothermal reaction to obtain the composite catalyst; the mass percentage of the noble metal in the composite catalyst is 1 to 20%; The molar ratio of the noble metal to the tin atoms in tin dioxide is (0.1-2):1; The noble metal precursor is a platinum precursor and / or a palladium precursor; The pretreatment process comprises: heating the concentrated nitric acid and mixing the obtained concentrated nitric acid vapor with the graphene for pretreatment; The calcination temperature is 600°C and the calcination time is 1.5 to 4 hours; The composite catalyst comprises a composite support and a noble metal supported on the surface of the composite support; The composite carrier includes graphene and tin dioxide coated on the surface of the graphene; and the noble metal is loaded at a position adjacent to the tin dioxide in the composite carrier; The noble metal includes Pt and / or Pd; The temperature of the hydrothermal reaction is 120-200°C and the time is 8-15h; The pH value of the reaction solution before the hydrothermal reaction is 8-11, and the pH value of the product solution after the hydrothermal reaction is 3-5.

2. The preparation method according to claim 1, wherein The heating temperature during the pretreatment is 100-150°C and the heating time is 6-12 hours; After the pretreatment is completed, the process further includes allowing the patient to stand for 20 to 32 hours.

3. The preparation method according to claim 1, wherein The concentration of the ammonia solution is 0.3-0.6 mol / L; The concentration of the tin tetrachloride solution is 0.05-0.2 mol / L; The volume ratio of the ammonia solution to the tin tetrachloride solution is (0.1-10):

1.

4. The preparation method according to claim 1, wherein The temperature of the rotary evaporation is 60-90° C., the rotation speed is 100-180 r / min, and the time is 30-90 min.

5. The preparation method according to claim 1, wherein The mass ratio of sodium citrate, noble metal precursor and composite support in the ethylene glycol solution of sodium citrate is (0.1-2):(0.01-1):1; The concentration of the noble metal precursor in the reaction solution of the hydrothermal reaction is 0.08 to 0.18 mol / L.

6. Use of the composite catalyst prepared by the preparation method according to any one of claims 1 to 5 in the electrocatalytic oxidation of ethanol.

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