Carbon supported rhodium-based ordered intermetallic compounds, preparation and use as catalysts

Abstract

The present application relates to carbon supported rhodium-based ordered intermetallic compound and preparation and application as catalyst, and belongs to the technical field of liquid fuel cell. The preparation method is that carbon carrier is dispersed in a solution of rhodium salt and non-noble metal salt, or the carbon carrier is dispersed in a solution of rhodium salt, other platinum group metal salt and non-noble metal salt, and the metal salt is loaded on the carbon carrier; the dried sample is ground and subjected to two-step heat treatment at low temperature and high temperature under a reducing atmosphere to obtain carbon supported rhodium intermetallic compound. The rhodium intermetallic compound electrocatalyst reduces the overpotential of formic acid oxidation reaction, and improves the catalytic activity, which is significantly superior to the catalytic performance of single metal rhodium, and the catalyst synthesis method is simple and feasible, and is suitable for mass production.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of liquid fuel cell, more particularly, it relates to carbon supported rhodium-based ordered intermetallic compound and preparation and application as catalyst, especially to a preparation method of carbon supported rhodium-based ordered intermetallic compound and application thereof as an electrocatalyst for formic acid electro-oxidation reaction. BACKGROUND

[0002] Fuel cell has the advantages of high energy conversion efficiency and environmental friendliness. When using liquid as fuel, the energy density is further improved, and the liquid transportation is more portable. When formic acid is used as fuel, it is difficult for formic acid to diffuse to the cathode through the polymer membrane. The reaction of anodic formic acid electro-oxidation is that formic acid molecules release two electrons to generate carbon dioxide, which mainly includes direct route and indirect route through carbon monoxide intermediate. Since the further oxidation of adsorbed carbon monoxide intermediate to carbon dioxide requires a very high overpotential, the carbon monoxide intermediate is considered to be a toxic intermediate, and avoiding its formation is beneficial to improving the energy conversion efficiency. However, platinum group metals with catalytic activity usually catalyze formic acid oxidation reaction through indirect route. In order to promote platinum group metals to catalyze formic acid oxidation through direct route, the binding strength of carbon monoxide intermediate can be reduced by inhibiting continuous metal sites, and the selectivity of catalyzing formic acid oxidation reaction can be improved. The current research on rhodium catalyzing formic acid oxidation is limited, and the overpotential of single-metal rhodium catalyzing formic acid oxidation is large, so how to simultaneously improve the selectivity and activity of rhodium catalyzing formic acid oxidation needs to further optimize the coordination environment of rhodium-based catalyst. SUMMARY

[0003] The purpose of the present application is to provide a carbon supported rhodium-based ordered intermetallic compound and a preparation method thereof. In the carbon supported rhodium-based ordered intermetallic compound, rhodium atoms are isolated by other metal atoms. The selectivity and activity of the catalyst catalyzing formic acid electro-oxidation reaction are obviously improved, and the catalyst can be applied to an anode catalyst of direct formic acid fuel cell.

[0004] According to the first aspect of the present application, a preparation method of carbon supported rhodium-based ordered intermetallic compound is provided, which comprises the following steps:

[0005] (1) dispersing a carbon support in a metal salt solution containing rhodium salt and non-noble metal salt, fully mixing, and then evaporating the solvent to make the metal salt be adsorbed on the carbon support;

[0006] (2) grinding the intermediate product obtained in step (1) and placing it in a reducing atmosphere, first heating at a low temperature of 150-300℃ to reduce the metal salt to disordered nanoparticles, and then heating at a high temperature of 500-700℃ to obtain carbon supported rhodium-based ordered intermetallic compound.

[0007] Preferably, the metal salt solution further contains a salt of another platinum group metal other than rhodium.

[0008] Preferably, the rhodium salt is at least one of rhodium chloride, rhodium nitrate, rhodium acetate and rhodium acetylacetonate.

[0009] Preferably, in step (2), the heating time under low temperature condition is 1-3h, and the heating time under high temperature condition is 2-10h; the heating rate under low temperature condition and the heating rate under high temperature condition are both 5-10℃ / min.

[0010] Preferably, the salt of another platinum group metal other than rhodium is a platinum salt, an iridium salt or a ruthenium salt.

[0011] Preferably, the platinum salt is at least one of chloroplatinic acid, sodium chloroplatinate, potassium chloroplatinate, potassium chloroplatous acid, platinum acetylacetonate, dichloroplatinum and tetrachloroplatinum; the iridium salt is at least one of iridium acetate, iridium chloride, sodium chloroiridate, iridium tetrachloride hydrate, iridium acetylacetonate and potassium hexachloroiridate; the ruthenium salt is at least one of ruthenium chloride, ruthenium acetylacetonate, ruthenium acetate, ruthenocene, potassium ruthenate, ammonium chlororuthenate, sodium chlororuthenate and potassium chlororuthenate.

[0012] Preferably, the non-noble metal salt is an iron salt, a zinc salt or a bismuth salt.

[0013] Preferably, the iron salt is at least one of iron chloride, ferrous chloride, iron acetylacetonate, iron acetate, iron sulfate and iron nitrate; the zinc salt is at least one of zinc chloride, zinc acetate, zinc acetylacetonate hydrate, zinc sulfate and zinc nitrate hydrate; the bismuth salt is at least one of bismuth chloride, bismuth acetate, bismuth sulfate and bismuth nitrate pentahydrate.

[0014] Preferably, the carbon carrier is at least one of carbon nanotube, carbon nanofiber, carbon black, graphene oxide and reduced graphene oxide.

[0015] According to another aspect of the present application, there is provided a carbon-supported rhodium-based ordered intermetallic compound prepared by any of the above-mentioned methods.

[0016] Preferably, the mass fraction of rhodium in the carbon-supported rhodium-based ordered intermetallic compound is 20%-50%.

[0017] According to another aspect of the present application, there is provided the use of the carbon-supported rhodium-based ordered intermetallic compound in an anode catalyst for formic acid fuel cells.

[0018] In general, the above technical solutions conceived by the present application have the following technical advantages compared with the prior art:

[0019] (1) The preparation method of carbon supported rhodium-based ordered intermetallic compounds, the carbon carrier is dispersed in a solution containing rhodium and non-noble metal (iron, zinc or bismuth), the carbon carrier is dispersed in a solution containing rhodium, other platinum group metal (platinum, iridium or ruthenium) and non-noble metal (iron, zinc or bismuth), the solvent is evaporated and ground, and then placed in a reducing atmosphere, and then subjected to two-step heat treatment steps of low temperature and high temperature to obtain carbon supported binary or ternary rhodium intermetallic compound nanoparticles. In the present application, the rhodium atoms in the carbon supported rhodium-based ordered intermetallic compounds are isolated by other metal atoms, and the combination of carbon monoxide intermediates and hydrogen atoms is weakened, and the single metal rhodium with continuous rhodium sites has stronger combination of carbon monoxide intermediates, so that the preparation of rhodium-based ordered intermetallic compounds makes the formic acid molecules be directly oxidized to carbon dioxide, and the overpotential is reduced.

[0020] (2) The binary intermetallic compound isolates the rhodium active site by the group effect, reduces the overpotential of the formic acid oxidation reaction, and further prepares ternary rhodium-based ordered intermetallic compounds, which have two active sites and optimize the electronic structure between each other, so that the activity and stability are improved.

[0021] (3) The carbon supported rhodium-based ordered intermetallic compound nanoparticles prepared by the present application reduce the overpotential of the formic acid oxidation reaction and improve the catalytic activity, so that the rhodium-based catalyst becomes a potential new type of anode fuel cell catalyst. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 X-ray diffraction patterns of carbon supported binary rhodium-iron intermetallic compounds, rhodium-zinc intermetallic compounds, rhodium-bismuth intermetallic compounds, ternary rhodium-platinum-iron intermetallic compounds, rhodium-iridium-iron intermetallic compounds, and rhodium-ruthenium-iron intermetallic compounds.

[0023] Figure 2 X-ray diffraction patterns of carbon supported rhodium-iron after different temperature treatment.

[0024] Figure 3 Linear sweep voltammetry curves of carbon supported binary and ternary rhodium-based intermetallic compounds for electrocatalytic formic acid oxidation.

[0025] Figure 4 Linear sweep voltammetry curves of carbon supported rhodium, binary rhodium-iron, and ternary rhodium-platinum-iron intermetallic compounds for electrocatalytic formic acid oxidation. DETAILED DESCRIPTION

[0026] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0027] The present application is a preparation method of carbon-supported rhodium-based intermetallic compounds for formic acid electro-oxidation reaction, comprising the following steps:

[0028] (1) dispersing the carbon carrier in a solution of rhodium salt and non-noble metal (iron, zinc or bismuth) salt, or dispersing the carbon carrier in a solution of rhodium salt, other platinum group metal (platinum, iridium or ruthenium) salt and non-noble metal (iron, zinc or bismuth) salt, stirring, ultrasonicating, heating to solvent evaporation to dryness to obtain a solid;

[0029] (2) grinding the solid powder obtained in step (1) and then performing low-temperature pre-reduction in a reducing atmosphere, followed by high-temperature heat treatment to obtain carbon-supported rhodium-based intermetallic compound nanoparticles.

[0030] In some embodiments, in step (1), the heating temperature is 50-70°C; the solvent for dissolving the metal salt is at least one of water, ethanol and methanol.

[0031] In some embodiments, the reducing atmosphere mainly includes H2 / Ar with a volume fraction of 2-10%.

[0032] In some embodiments, the rhodium salt is at least one of rhodium chloride, rhodium nitrate, rhodium acetate and rhodium acetylacetonate.

[0033] In some embodiments, the platinum salt in the other platinum group metal (platinum, iridium, ruthenium) salt is at least one of chloroplatinic acid, sodium chloroplatinate, potassium chloroplatinate, potassium chloroplatous acid, platinum acetylacetonate, dichloroplatinum, tetrachloroplatinum, the iridium salt is at least one of iridium acetate, iridium chloride, sodium chloroate, iridium tetrachloride hydrate, iridium acetylacetonate, potassium hexachloroiridate, and the ruthenium salt is at least one of ruthenium chloride, ruthenium acetylacetonate, ruthenium acetate, ruthenium dicyclopentadiene, potassium ruthenate, ammonium chlororuthenate, sodium chlororuthenate and potassium chlororuthenate.

[0034] In some embodiments, the iron salt in the non-noble metal (iron, zinc, bismuth) salt is at least one of iron chloride, ferrous chloride, iron acetylacetonate, iron acetate, iron sulfate and iron nitrate, the zinc salt is at least one of zinc chloride, zinc acetate, zinc acetylacetonate hydrate, zinc sulfate and zinc nitrate hydrate, and the bismuth salt is at least one of bismuth chloride, bismuth acetate, bismuth sulfate and bismuth nitrate pentahydrate.

[0035] In some embodiments, the carbon support is at least one of carbon nanotubes, carbon nanofibers, carbon black, graphene oxide, and reduced graphene oxide.

[0036] In some embodiments, the low-temperature temperature during the heating process in step (2) is 150-300 DEG C, and the high-temperature heat treatment process temperature is 500-700 DEG C.

[0037] In some embodiments, the atomic ratio of rhodium-other platinum group metal-non-noble metal is (0.9-1):(0-0.1):1.

[0038] In some embodiments, the low-temperature reduction time is 1-3 h, the high-temperature heat treatment heating time is 2-10 h, and the heating rate is 5-10 DEG C / min.

[0039] The carbon-supported rhodium-based intermetallic compound prepared by the method has a rhodium element mass fraction of 20-50% in the catalyst.

[0040] The carbon-supported rhodium-based intermetallic compound prepared by the method is used for an anode catalyst for a direct formic acid fuel cell.

[0041] Example 1

[0042] First step: rhodium chloride, chloroplatinic acid, and iron chloride are dissolved in water, and then Vulcan carbon is dispersed in the solution, the atomic ratio of rhodium, platinum, and iron is controlled to be 0.9:0.1:1, and the solvent is evaporated by alternately performing ultrasonic and stirring heat treatment;

[0043] Second step: the sample of the first step is further dried and ground, is reduced in a hydrogen volume fraction of 10% argon-hydrogen mixed gas at 200 DEG C for 2 h to room temperature, is heated to 700 DEG C at a heating rate of 10 DEG C / min from room temperature for heat treatment for 4 h, and is naturally cooled to room temperature to obtain carbon-supported ternary rhodium-platinum-iron intermetallic compound nanoparticles.

[0044] Example 2

[0045] First step: rhodium chloride and iron chloride are dissolved in water, and then Vulcan carbon is dispersed in the solution, the atomic ratio of rhodium and iron is controlled to be 1:1, and the solvent is evaporated by alternately performing ultrasonic and stirring heat treatment;

[0046] Second step: the sample of the first step is further dried and ground, is reduced in a hydrogen volume fraction of 10% argon-hydrogen mixed gas at 200 DEG C for 2 h to room temperature, is heated to 700 DEG C at a heating rate of 10 DEG C / min from room temperature for heat treatment for 4 h, and is naturally cooled to room temperature to obtain carbon-supported ternary rhodium-platinum-iron intermetallic compound nanoparticles.

[0047] Example 3

[0048] First step: Dissolve rhodium chloride, iridium chloride and iron chloride in water, then disperse Vulcan carbon in the solution, control the atomic ratio of rhodium, iridium and iron to be 0.9:0.1:1, and evaporate the solvent by heating treatment with alternately ultrasonic and stirring;

[0049] Second step: After further drying and grinding the sample of the first step, reduce it in 10% argon-hydrogen mixed gas at 200℃ for 2h, then heat it to 700℃ at a rate of 10℃ / min for 4h, and obtain carbon-supported ternary rhodium-iridium-iron intermetallic compound nanoparticles after natural cooling to room temperature.

[0050] Example 4

[0051] First step: Dissolve rhodium chloride and zinc chloride in water, then disperse Vulcan carbon in the solution, control the atomic ratio of rhodium and zinc to be 1:1, and evaporate the solvent by heating treatment with alternately ultrasonic and stirring;

[0052] Second step: After further drying and grinding the sample of the first step, reduce it in 10% argon-hydrogen mixed gas at 200℃ for 2h, then heat it to 700℃ at a rate of 10℃ / min for 4h, and obtain carbon-supported binary rhodium-zinc intermetallic compound nanoparticles after natural cooling to room temperature.

[0053] Example 5

[0054] First step: Dissolve rhodium chloride and bismuth chloride in water, then disperse Vulcan carbon in the solution, control the atomic ratio of rhodium and bismuth to be 1:1, and evaporate the solvent by heating treatment with alternately ultrasonic and stirring;

[0055] Second step: After further drying and grinding the sample of the first step, reduce it in 10% argon-hydrogen mixed gas at 200℃ for 2h, then heat it to 700℃ at a rate of 10℃ / min for 4h, and obtain carbon-supported binary rhodium-bismuth intermetallic compound nanoparticles after natural cooling to room temperature.

[0056] Example 6

[0057] First step: Dissolve rhodium chloride, ruthenium chloride and iron chloride in water, then disperse Vulcan carbon in the solution, control the atomic ratio of rhodium, ruthenium and iron to be 0.9:0.1:1, and evaporate the solvent by heating treatment with alternately ultrasonic and stirring;

[0058] Second step: after further drying the sample of the first step, grinding, reducing in 10% argon-hydrogen mixed gas at 200℃ for 2h, cooling to room temperature, then heating to 700℃ at a rate of 10℃ / min, and keeping for 4h, cooling to room temperature naturally, carbon supported ternary Rh-Ru-Fe intermetallic compound nanoparticles are obtained.

[0059] Example 7

[0060] 5mg of catalyst powder is dispersed in 1mL of Nafion / isopropanol mixed solution with 0.1% of Nafion, ultrasonic treatment for 5-10min to make catalyst dispersed uniformly, then 10μL of the dispersion is taken and dropped on glassy carbon electrode, dried naturally to form a uniform and dense thin layer. The glassy carbon electrode coated with catalyst layer is used as working electrode, reversible hydrogen electrode as reference electrode, carbon rod as counter electrode, polarization curve of catalytic formic acid oxidation reaction is measured in nitrogen-saturated solution containing 0.5mol / L of sulfuric acid and 0.5mol / L of formic acid at a scanning speed of 5mV / s.

[0061] Figure 1 X-ray diffraction (XRD) patterns of carbon supported (a) Rh-Bi, (b) Rh-Zn, (c) Rh-Fe, (d) of examples 1-6, by comparison with the corresponding standard cards, the formation of binary and ternary Rh-based ordered intermetallic compound structure is consistent.

[0062] Figure 2 X-ray diffraction (XRD) patterns of carbon supported Rh-Fe of example 2 in the initial heating reduction treatment (200℃) and subsequent heat treatment (700℃ or 400℃), by comparing the samples treated at 400℃ and 200℃, the shift of the strongest diffraction peak and the change of the number of diffraction peaks indicate that the crystal phase transition occurs, from face-centered cubic to body-centered cubic. By comparing the samples treated at 400℃ and 700℃, the increase of diffraction peaks indicates that the atomic arrangement is converted to a higher degree of order.

[0063] Figure 3 Linear sweep voltammetry curves of carbon supported (a) binary Rh-based intermetallic compound and (b) ternary Rh-based intermetallic compound and Rh of examples 1-7 catalyzing formic acid oxidation, the results show that the onset potential of Rh-based intermetallic compound prepared catalyzing formic acid oxidation reaction decreases, indicating that the overpotential decreases, which is beneficial to improve the output voltage of direct acid fuel cell. The current density of ternary Rh-based intermetallic compound catalyzing formic acid oxidation is larger than that of binary Rh-based intermetallic compound, indicating that the catalytic performance is further improved by introducing the second active noble metal.

[0064] Figure 4Linear sweep voltammetry curves of carbon supported binary Rh-Fe intermetallic compounds, ternary Rh-Pt-Fe intermetallic compounds and Rh for formic acid oxidation in Example 1, 2 and 7 show that the overpotential of formic acid oxidation reaction can be reduced by forming binary Rh-Fe intermetallic compounds which isolate Rh active sites. The same crystal type of ternary Rh-Pt-Fe intermetallic compounds is prepared by replacing part of Rh with Pt, which keeps the advantage of reducing overpotential and further improves catalytic activity.

[0065] Those skilled in the art will readily understand that the above described are only the preferred embodiments of the present application, and are not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A process for the preparation of carbon supported rhodium based ordered intermetallic compounds, characterized in that, The method comprises the following steps: (1) dispersing a carbon carrier in a metal salt solution, wherein the metal salt solution contains a rhodium salt, a platinum group metal salt and a non-noble metal salt, the non-noble metal salt is an iron salt, and the platinum group metal salt is a platinum salt, an iridium salt or a ruthenium salt; after being mixed well, the solvent is evaporated to make the metal salt be adsorbed on the carbon carrier; the ratio of the amount of substance of rhodium atoms in the rhodium salt, the amount of substance of platinum atoms in the platinum salt and the amount of substance of iron atoms in the iron salt is 0.9:0.1:1, or the ratio of the amount of substance of rhodium atoms in the rhodium salt, the amount of substance of iridium atoms in the iridium salt and the amount of substance of iron atoms in the iron salt is 0.9:0.1:1, or the ratio of the amount of substance of rhodium atoms in the rhodium salt, the amount of substance of ruthenium atoms in the ruthenium salt and the amount of substance of iron atoms in the iron salt is 0.9:0.1:1; (2) The intermediate product obtained in step (1) is ground and placed in a reducing atmosphere, heated at 150 o C~300 o C under low temperature conditions to reduce the metal salt into disordered nanoparticles; then heated at 500 o C~700 o C under high temperature conditions to obtain carbon-supported rhodium-based ordered intermetallic compounds.

2. The method of claim 1, wherein the carbon-supported rhodium-based intermetallic compound is prepared by the steps of: The rhodium salt is at least one of rhodium chloride, rhodium nitrate, rhodium acetate and rhodium acetylacetonate.

3. The method for preparing the carbon-supported rhodium-based ordered intermetallic compound as described in claim 1, characterized in that, In step (2), the heating time under low temperature condition is 1-3 h, and the heating time under high temperature condition is 2-10 h; the heating rate of the heating under low temperature condition and the heating under high temperature condition is 5-10 o C / min.

4. The method for preparing the carbon-supported rhodium-based ordered intermetallic compound as described in claim 1, characterized in that, The platinum salt is at least one of chloroplatinic acid, sodium chloroplatinate, potassium chloroplatinate, potassium chloroplatous acid, platinum acetylacetonate, dichloroplatinum and tetrachloroplatinum; the iridium salt is at least one of iridium acetate, iridium chloride, sodium chloroiridate, iridium tetrachloride hydrate, iridium acetylacetonate and potassium hexachloroiridate; and the ruthenium salt is at least one of ruthenium chloride, ruthenium acetylacetonate, ruthenium acetate, ruthenium dicyclopentadiene, potassium ruthenate, ammonium chlororuthenate, sodium chlororuthenate and potassium chlororuthenate.

5. The method for preparing the carbon-supported rhodium-based ordered intermetallic compound as described in claim 1, characterized in that, The iron salt is at least one of ferric chloride, ferrous chloride, iron acetylacetonate, iron acetate, iron sulfate and iron nitrate.

6. The method for preparing the carbon-supported rhodium-based ordered intermetallic compound as described in claim 1, characterized in that, The carbon carrier is at least one of carbon nanotubes, carbon nanofibers, carbon black, graphene oxide and reduced graphene oxide.

7. A carbon-supported rhodium-based ordered intermetallic compound prepared by the method according to any one of claims 1-6.

8. The carbon supported rhodium-based ordered intermetallic compound of claim 7, wherein, The mass fraction of rhodium in the carbon-supported rhodium-based ordered intermetallic compound is 20%-50%.

9. Use of a carbon-supported rhodium-based ordered intermetallic compound according to claim 7 or 8, characterized in that, An anode catalyst for a formic acid fuel cell.

Images