A rhodium-bismuth anode catalyst and its preparation method and application

Abstract

The present invention provides a rhodium-bismuth anode catalyst, a preparation method thereof, and an application thereof. The present invention utilizes different reduction orders to regulate the synthesis of different Bi components, and constructs a rhodium-bismuth alloy and a rhodium-bismuth hydroxide heterojunction by this method. The unique third-body effect of bismuth on the precious metal rhodium is utilized to reduce the poisoning of rhodium while greatly improving the ethanol oxidation activity of rhodium. The present invention directionally constructs the rhodium-bismuth alloy structure and the rhodium-bismuth hydroxide interface structure by regulating the order of addition of alkali and reducing agent, and improves the ethanol electro-oxidation activity of rhodium by regulating the electron cloud density of the rhodium d band by bismuth, and the bifunctional mechanism and synergistic effect generated at the rhodium-bismuth hydroxide interface. The method of the present invention is simple, easy to operate, and suitable for industrial preparation. The present invention introduces a small amount of Bi component on the surface of the Rh-based catalyst in order to effectively regulate the work of the Rh surface components and improve the problem of low activity of the Rh-based catalyst for EOR reaction.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells and energy materials, and in particular to a rhodium-bismuth anode catalyst and a preparation method and application thereof. Background Art

[0002] In recent years, the negative impact of the energy crisis on business production and residents' lives has been increasing, and people are urgently seeking clean and efficient fuels to replace non-renewable fossil energy. Fuel cells, as a new energy technology, can directly convert chemical energy into electrical energy, significantly reducing losses during the energy conversion process. Polymer electrolyte membrane fuel cells (PEMFCs) are one such technology. Compared to PEMFCs, direct liquid fuel cells (DLFCs) offer a simpler structure, easier fuel transportation and storage, and safer use, making them suitable for use as mobile portable power sources and attracting widespread attention.

[0003] Among direct liquid fuel cells (DLFCs), direct ethanol fuel cells (DEFCs) have broad application prospects due to their high specific energy (8.0 kWh / kgl) and wide range of fuel sources. Although the complete mechanism of the ethanol oxidation reaction (EOR) remains unclear, there is a general consensus that the dual-pathway mechanism is involved.

[0004] Studies have shown that the dual pathway mechanism includes C1 pathway and C2 pathway. An efficient catalyst needs to break the CC bond in ethanol and ads ) oxidizes the intermediate species to achieve complete electro-oxidation catalysis of ethanol. Studies have shown that the existing Pt or Pd, its ethanol oxidation activity and C1 pathway selectivity are difficult to meet the requirements. For now, how to develop efficient ethanol electro-oxidation catalysts remains a very challenging topic. Researchers have found that Rh has the ability to break the CC bond of organic molecules, which shows that Rh-based catalysts have the potential to completely catalyze the oxidation of ethanol. However, the activity of Rh itself for ethanol oxidation is still too low, and because the surface energy of Rh is too high, there is no better method for regulating the surface components of Rh.

[0005] Based on the defects of current Rh-based catalysts, it is necessary to improve them. Summary of the Invention

[0006] In view of this, the present invention provides a rhodium-bismuth anode catalyst and a preparation method and application thereof to solve the defects of Rh-based catalysts in the prior art.

[0007] In a first aspect, the present invention provides a method for preparing a rhodium-bismuth anode catalyst, comprising the following steps:

[0008] Adding rhodium salt and bismuth salt to water, then adding carbon source, dispersing, and then adding sodium citrate and / or sodium oxalate to obtain a mixed solution;

[0009] Dissolve NaBH4 and / or KBH4 and NaOH in water to prepare an alkaline aqueous solution;

[0010] Adding the alkaline aqueous solution dropwise to the mixed solution, reacting at 70-90° C. for 4-8 hours, filtering to obtain a solid product, and calcining the solid product to obtain a rhodium-bismuth anode catalyst;

[0011] Alternatively, Na2CO3 is added to the mixed solution, reacted at 70-90°C for 1-2 hours, then NaOH is added to adjust the pH of the solution to 11-12, and finally NaBH4 solution is added, reacted at 70-90°C for 4-8 hours, filtered to obtain a solid product, and the solid product is calcined to obtain a rhodium-bismuth anode catalyst.

[0012] Preferably, in the method for preparing the rhodium-bismuth anode catalyst, the rhodium salt includes at least one of rhodium trichloride, rhodium nitrate, rhodium sulfate, and sodium chlororhodate.

[0013] Preferably, in the method for preparing the rhodium-bismuth anode catalyst, the bismuth salt includes at least one of bismuth nitrate, bismuth chloride, and bismuth citrate.

[0014] Preferably, in the method for preparing the rhodium-bismuth anode catalyst, the carbon source includes at least one of activated carbon and carbon powder.

[0015] Preferably, the method for preparing the rhodium-bismuth anode catalyst comprises adding a rhodium salt and a bismuth salt to water, then adding a carbon source, dispersing, and then adding sodium citrate to obtain a mixed solution; and in the step of adding Na2CO3 to the mixed solution, the mass ratio of the rhodium salt, the bismuth salt, the carbon source, the sodium citrate, the Na2CO3 and the water is (5-20):(0.5-2):(10-30):(150-250):(5-20):(20-100).

[0016] Preferably, in the method for preparing the rhodium-bismuth anode catalyst, in the step of calcining the solid product, the calcination temperature is 90-110° C. and the time is 1-3 hours.

[0017] Preferably, in the preparation method of the rhodium-bismuth anode catalyst, in the step of dissolving NaBH4 and / or KBH4 and NaOH in water, the mass ratio of NaBH4 and / or KBH4, NaOH and water is (1-5):(1-3):(800-1200).

[0018] Preferably, in the method for preparing the rhodium-bismuth anode catalyst, rhodium salt and bismuth salt are added to water, then a carbon source is added, and after dispersion, sodium citrate and / or sodium oxalate are added to obtain a mixed solution. The mass ratio of rhodium salt, bismuth salt, carbon source, sodium citrate and / or sodium oxalate, and water is (5-20):(0.5-2):(10-30):(150-250):(20-100).

[0019] In the step of adding the alkaline aqueous solution dropwise to the mixed solution, the mass ratio of the alkaline aqueous solution to the mixed solution is (2-6):(3-7).

[0020] In a second aspect, the present invention further provides a rhodium-bismuth anode catalyst prepared using the above-mentioned preparation method.

[0021] In a third aspect, the present invention further provides a rhodium-bismuth anode catalyst prepared by the preparation method or the use of the rhodium-bismuth anode catalyst in catalytic oxidation of ethanol in an ethanol fuel cell.

[0022] The preparation method of the rhodium-bismuth anode catalyst of the present invention has the following beneficial effects compared with the prior art:

[0023] The preparation method of the rhodium-bismuth anode catalyst of the present invention utilizes different reduction orders to regulate the synthesis of different Bi components, and constructs a rhodium-bismuth alloy and a rhodium-bismuth hydroxide heterojunction by this method. The unique third-body effect of bismuth on the precious metal rhodium is utilized to reduce the poisoning of rhodium while significantly improving the ethanol oxidation activity of rhodium. The present invention can directionally construct a rhodium-bismuth alloy structure and a rhodium-bismuth hydroxide interface structure by regulating the order of addition of alkali and reducing agent, and improve the ethanol electrooxidation activity of rhodium through the regulation of bismuth on the rhodium d-band electron cloud density and the dual functional mechanism and synergistic effect generated at the rhodium-bismuth hydroxide interface. This method is simple and easy to operate, suitable for industrial preparation, and can also be used for research work on other systems. The present invention introduces a small amount of Bi component on the surface of the Rh-based catalyst in order to effectively regulate the work of the Rh surface components and improve the problem of low activity of Rh-based catalysts for EOR reactions. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0025] Figure 1 is the X-ray diffraction (XRD) pattern of the rhodium-bismuth anode catalyst prepared in Example 1 of the present invention;

[0026] Figure 2 This is a transmission electron micrograph of the rhodium-bismuth anode catalyst prepared in Example 1 of the present invention;

[0027] Figure 3 This is a graph showing the electrooxidation activity of the catalysts prepared in Examples 1 and 2 of the present invention and Comparative Example 1 under alkaline conditions;

[0028] Figure 4 This is a stability test chart of the catalysts prepared in Examples 1 and 2 of the present invention and Comparative Example 1 under alkaline conditions;

[0029] Figure 5 This is a graph showing the thousand-cycle durability test of the rhodium-bismuth anode catalyst prepared in Example 1 of the present invention under alkaline conditions. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] The embodiments of the present application provide a rhodium-bismuth anode catalyst, a preparation method thereof, and an application thereof. Detailed descriptions are given below. It should be noted that the order of description of the following embodiments does not limit the preferred order of the embodiments. In addition, in the description of the present application, the term "including" means "including but not limited to". Various embodiments of the present invention may be presented in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be understood as a rigid limitation on the scope of the present invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the numbered range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fraction or integer) within the indicated range.

[0032] The present invention provides a method for preparing a rhodium-bismuth anode catalyst, comprising the following steps:

[0033] S1. Add rhodium salt and bismuth salt to water, then add carbon source, disperse, and then add sodium citrate and / or sodium oxalate to obtain a mixed solution;

[0034] S2, dissolving NaBH4, KBH4 and NaOH in water to prepare an alkaline aqueous solution;

[0035] S3, adding the alkaline aqueous solution dropwise to the mixed solution, reacting at 70-90° C. for 4-8 hours, filtering to obtain a solid product, and calcining the solid product to obtain a rhodium-bismuth anode catalyst;

[0036] Alternatively, Na2CO3 is added to the mixed solution, reacted at 70-90°C for 1-2 hours, then NaOH is added to adjust the pH of the solution to 11-12, and finally NaBH4 solution is added, reacted at 70-90°C for 4-8 hours, filtered to obtain a solid product, and the solid product is calcined to obtain a rhodium-bismuth anode catalyst.

[0037] It should be noted that the preparation method of the rhodium-bismuth anode catalyst of the present application is to add an alkaline aqueous solution dropwise to the mixed solution, react at 70-90°C for 4-8 hours, filter to obtain a solid product, and calcine the solid product to obtain a rhodium-bismuth anode catalyst, which is a RhBi / C catalyst; add Na2CO3 to the mixed solution, react at 70-90°C for 1-2 hours, then add NaOH to adjust the pH of the solution to 11-12, and finally add NaBH4 solution, react at 70-90°C for 4-8 hours, filter to obtain a solid product, and calcine the solid product to obtain a rhodium-bismuth anode catalyst, which is a Rh-Bi(OH)3 / C catalyst.

[0038] The present application adopts a liquid phase synthesis method to prepare a rhodium-bismuth anode catalyst. Specifically, different reduction orders are used to regulate the synthesis of different Bi components, and rhodium-bismuth hydroxide heterojunctions are constructed by this method. The unique third body effect of bismuth on the precious metal rhodium is used to reduce the poisoning of rhodium while greatly improving the ethanol oxidation activity of rhodium. The present application can directionally construct a rhodium-bismuth alloy structure and a rhodium-bismuth hydroxide interface structure by regulating the order of addition of alkali and reducing agent, and improve the ethanol electro-oxidation activity of rhodium by regulating the electron cloud density of the rhodium d band by bismuth, and the dual functional mechanism and synergistic effect generated at the rhodium-bismuth hydroxide interface. This method is simple and easy to operate, suitable for industrial preparation, and can also be used for research work on other systems. The present application introduces a small amount of Bi component on the surface of the Rh-based catalyst in the hope of effectively regulating the work of the Rh surface components and improving the problem of low activity of Rh-based catalysts for EOR reactions.

[0039] In some embodiments, the rhodium salt includes at least one of rhodium trichloride, rhodium nitrate, rhodium sulfate, and sodium chlororhodate.

[0040] In some embodiments, the bismuth salt includes at least one of bismuth nitrate, bismuth chloride, and bismuth citrate.

[0041] In some embodiments, the carbon source includes at least one of activated carbon and carbon powder.

[0042] In some embodiments, the water used is ultrapure water.

[0043] Preferably, the rhodium salt is RhCl3·3H2O, the bismuth salt is Bi(NO3)3·5H2O, and the carbon source is XC-72 carbon powder.

[0044] In some embodiments, a small amount of HCl may be added to dissolve the bismuth salt to facilitate dissolution.

[0045] In some embodiments, rhodium salt and bismuth salt are added to water, and then a carbon source is added. After dispersion, sodium citrate and / or sodium oxalate are added to obtain a mixed solution; in the step of adding Na2CO3 to the mixed solution, the mass ratio of rhodium salt, bismuth salt, carbon source, sodium citrate and / or sodium oxalate, Na2CO3 and water is (5~20):(0.5~2):(10~30):(150~250):(5~20):(20~100).

[0046] In some embodiments, in the step of calcining the solid product, the calcination temperature is 90-110° C. and the calcination time is 1-3 hours.

[0047] In some embodiments, in the step of dissolving NaBH4 and / or KBH4 and NaOH in water, the mass ratio of NaBH4 and / or KBH4, NaOH and water is (1-5):(1-3):(800-1200).

[0048] In some embodiments, in the step of adding a rhodium salt and a bismuth salt to water, then adding a carbon source, dispersing, and then adding sodium citrate to obtain a mixed solution, the mass ratio of the rhodium salt, the bismuth salt, the carbon source, the sodium citrate and / or the sodium oxalate and the water is (5-20):(0.5-2):(10-30):(150-250):(20-100);

[0049] In the step of adding the alkaline aqueous solution of NaBH4 dropwise to the mixed solution, the mass ratio of the alkaline aqueous solution of NaBH4 to the mixed solution is (2-6):(3-7).

[0050] In some embodiments, the solid product is filtered and dried for 12 to 24 hours, and then calcined to obtain a rhodium-bismuth anode catalyst.

[0051] Based on the same inventive concept, an embodiment of the present application also provides a rhodium-bismuth anode catalyst, which is prepared using the above-mentioned preparation method.

[0052] The best rhodium-bismuth anode catalyst (Example 1) obtained by the present invention has greatly improved catalytic activity, stability and durability for ethanol electrooxidation. The best rhodium-bismuth anode catalyst has an ethanol oxidation catalytic activity of up to 850 mA / mgRh ( Figure 3 ), which is 17 times that of the carbon-supported rhodium catalyst (Example 3) at the same potential. After 1 hour of stability test (potential: 0.5V vs RHE), the catalytic activity retained 170mA / mgRh, which is 35 times that of the steady-state current of the carbon-supported rhodium catalyst under the same conditions ( Figure 4 At the same time, the catalyst still has high catalytic activity after 1000 CV cycles ( Figure 5 The catalyst has low preparation costs, simple processes, and is easy to operate, making it suitable for industrial production. The preparation and research methods for directing the construction of different structures are also applicable to the study of other systems.

[0053] Based on the same inventive concept, an embodiment of the present application further provides a rhodium-bismuth anode catalyst prepared by the above-mentioned preparation method or the use of the above-mentioned rhodium-bismuth anode catalyst in catalytic oxidation of ethanol in an ethanol fuel cell.

[0054] The following further illustrates the preparation method and application of the rhodium-bismuth anode catalyst of the present application with specific examples. This section further illustrates the content of the present invention in conjunction with specific examples, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0055] Example 1

[0056] The present invention provides a method for preparing a rhodium-bismuth anode catalyst, comprising the following steps:

[0057] S1. Add 14 mg of RhCl3·3H2O and 1 mg of Bi(NO3)3·5H2O to 50 ml of ultrapure water, then add 20 mg of XC-72 carbon powder, and ultrasonically disperse for 1 hour to form a uniform dispersion. Then, add 200 mg of sodium citrate and stir to obtain a mixed solution.

[0058] S2. Add 10 mg of Na2CO3 to the mixed solution in step S1, react at 80°C for 2 h, then add NaOH to adjust the pH of the solution to 11, and finally add 40 ml of 3 g / L NaBH4 solution (NaBH4 is added to water to obtain NaBH4 solution), react at 80°C for 6 h, filter to obtain a solid product, and dry the solid product for 20 h, then calcined at 100°C for 1 h to obtain a rhodium-bismuth anode catalyst (i.e., Rh-Bi(OH)3 / C catalyst).

[0059] Example 2

[0060] The present invention provides a method for preparing a rhodium-bismuth anode catalyst, comprising the following steps:

[0061] S1. Add 14 mg of RhCl3·3H2O and 1 mg of Bi(NO3)3·5H2O to 50 ml of ultrapure water, then add 20 mg of XC-72 carbon powder, and ultrasonically disperse for 1 hour to form a uniform dispersion. Then, add 200 mg of sodium citrate and stir to obtain a mixed solution.

[0062] S2. Dissolve 120 mg of NaBH4 and 40 mg of NaOH in 40 ml of water to prepare an alkaline aqueous solution of NaBH4;

[0063] S3. Add the alkaline aqueous solution of NaBH4 in step S2 dropwise to the mixed solution in step S1, react at 80°C for 6 hours, filter to obtain a solid product, and dry the solid product for 20 hours, then calcine at 100°C for 1 hour to obtain a rhodium-bismuth anode catalyst (i.e., RhBi / C catalyst).

[0064] Comparative Example 1

[0065] This comparative example provides a method for preparing a carbon-supported rhodium catalyst, comprising the following steps:

[0066] S1. Add 14 mg of RhCl3·3H2O to 50 ml of ultrapure water, then add 20 mg of XC-72 carbon powder, and ultrasonically disperse for 1 hour to form a uniform dispersion. Then, add 200 mg of sodium citrate and stir to obtain a mixed solution.

[0067] S2. Dissolve 120 mg of NaBH4 and 40 mg of NaOH in 40 ml of water to prepare an alkaline aqueous solution of NaBH4;

[0068] S3. Add the alkaline aqueous solution of NaBH4 in step S2 dropwise to the mixed solution in step S1, react at 80°C for 6 hours, filter to obtain a solid product, and dry the solid product for 20 hours, then calcine at 100°C for 1 hour to obtain a carbon-supported rhodium catalyst (i.e., Rh / C catalyst).

[0069] Performance Characterization

[0070] Figure 1 This is the X-ray diffraction (XRD) pattern of the rhodium-bismuth anode catalyst (ie, Rh-Bi(OH)3 / C catalyst) prepared in Example 1.

[0071] from Figure 1It can be seen that the rhodium-bismuth anode catalyst prepared in Example 1 is mainly composed of rhodium, and no peak of bismuth hydroxide is observed. This may be because the amount of bismuth hydroxide is small, and it is amorphous bismuth hydroxide.

[0072] Figure 2 This is a transmission electron microscope image of the rhodium-bismuth anode catalyst prepared in Example 1. Figure 2 The average particle size of the catalyst was found to be 2.05 nm.

[0073] Figure 3 The electrochemical activity test diagram of ethanol electrooxidation under alkaline conditions for the Rh-Bi(OH)3 / C catalyst prepared in Example 1, the RhBi / C catalyst prepared in Example 2, and the Rh / C catalyst prepared in Comparative Example 1 (all the following electrochemical tests were performed using a three-electrode system and covered with catalyst materials (catalyst loading of 0.285 mg*cm -2 ) was used as the working electrode, a carbon rod and a mercury / mercuric oxide electrode were used as the counter electrode and the reference electrode, respectively. 1 mol / L NaOH + 1 mol / L C2H5OH solution was selected as the electrolyte. The electrodes were subjected to cyclic voltammetry at room temperature with a scan rate of 50 mv / s and a scan potential of 0 to 1.2 V relative to the reversible hydrogen electrode).

[0074] from Figure 3 It can be seen that the mass activity of the Rh-Bi(OH)3 / C catalyst prepared in Example 1 is 850 mA / mg Rh , which is 17 times that of the Rh / C catalyst in Comparative Example 1. At the same time, its onset potential is about 80 mV lower than that of the Rh / C catalyst. The RhBi / C catalyst prepared in Example 2 is a carbon-supported rhodium-bismuth alloy catalyst. Although its activity is only 75% of that of the Rh-Bi(OH)3 / C catalyst, its activity is still 12 times higher than that of the Rh / C catalyst prepared in Comparative Example 1.

[0075] Figure 4 This is a stability test chart of the Rh-Bi(OH)3 / C catalyst prepared in Example 1, the RhBi / C catalyst prepared in Example 2, and the Rh / C catalyst prepared in Comparative Example 1 under alkaline conditions (scanning potential is 0.5 V relative to the reversible hydrogen electrode).

[0076] The stability of the RhBi / C catalyst prepared in Example 2 was poor, and its activity decreased significantly after a 1-hour cycle. However, it was significantly improved compared to the Rh / C catalyst prepared in Comparative Example 1.

[0077] Figure 5This is a thousand-cycle durability test chart of the Rh-Bi(OH)3 / C catalyst prepared in Example 1 under alkaline conditions (1000 cycles of cyclic voltammetry test, scan rate 100 mv / s, scan potential 0.3V~0.7V relative to the reversible hydrogen electrode).

[0078] from Figure 5 It can be seen that the Rh-Bi(OH)3 / C catalyst still retains strong ethanol oxidation activity after a thousand cycles, showing good durability.

[0079] It can be seen from the above Examples 1 to 2 and Comparative Example 1 that, compared with the ordinary carbon-supported rhodium Rh / C catalyst in Comparative Example 1, the addition of only a small amount of Bi component can greatly improve the activity and stability of rhodium for ethanol electrooxidation, proving the feasibility of the method of the present application for regulating the morphology of Rh surface components.

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a rhodium-bismuth anode catalyst, characterized in that: The following steps are involved: Adding rhodium salt and bismuth salt to water, then adding carbon source, dispersing, and then adding sodium citrate to obtain a mixed solution; Adding Na2CO3 to the mixed solution, reacting at 70-90°C for 1-2 hours, then adding NaOH to adjust the pH of the solution to 11-12, and finally adding NaBH4 solution, reacting at 70-90°C for 4-8 hours, filtering to obtain a solid product, and calcining the solid product to obtain a rhodium-bismuth anode catalyst; The rhodium salt is rhodium trichloride; The bismuth salt is bismuth nitrate; The carbon source is carbon powder; adding a rhodium salt and a bismuth salt to water, then adding a carbon source, dispersing the mixture, and then adding sodium citrate to obtain a mixed solution; in the step of adding Na2CO3 to the mixed solution, the mass ratio of the rhodium salt, the bismuth salt, the carbon source, the sodium citrate, the Na2CO3, and the water is 14:1:20:200:10:50; In the step of calcining the solid product, the calcination temperature is 100° C. and the calcination time is 1 hour.

2. A rhodium-bismuth anode catalyst, characterized in that The preparation method according to claim 1 is used for preparation.

3. Use of the rhodium-bismuth anode catalyst prepared by the preparation method according to claim 1 or the rhodium-bismuth anode catalyst according to claim 2 in catalytic oxidation of ethanol in an ethanol fuel cell.

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