CN101332425A - Nanoporous gold-supported ultra-thin platinum-group metal film catalyst and preparation method thereof - Google Patents

Abstract

The invention discloses a nanoporous gold-supported ultra-thin platinum-group metal film catalyst. The catalyst has a thickness of 0.1-100 micrometers, a width of 0.1-10 centimeters, a length of 0.1-20 centimeters, and a surface uniformly covered with platinum-group metals. Atomic layer alloy flakes; the thin film catalyst of the present invention deposits copper, silver or lead on the nanoporous gold under potential, and then replaces it with platinum metal cations to deposit a platinum metal thin film on the surface of the porous gold to obtain a nanometer Porous gold-supported ultrathin platinum-group metal thin-film catalysts. The catalyst material prepared by the method of the invention is easy to control the pore size, the thickness of the pore wall and the thickness of the platinum group metal film, and has the characteristics of high specific surface area, high utilization rate of the platinum group metal, good catalytic activity and high anti-poisoning performance.

Description

Nanoporous gold-supported ultra-thin platinum-group metal film catalyst and preparation method thereof

technical field

The invention relates to a nanoporous composite metal catalyst with low noble metal loading which can be used for electrocatalytic oxidation of small organic molecules (methanol, formic acid, ethanol, etc.), electrocatalytic reduction of oxygen, oxidation of hydrogen, catalytic hydrogenation and the like. The preparation method particularly relates to a nanoporous gold-supported ultra-thin platinum group metal (alloy) film catalyst and a preparation method thereof.

Background technique

Fuel cell is a new type of clean energy, which can directly and efficiently convert the chemical energy of hydrogen, methanol, formic acid, ethanol and other fuels into electrical energy, and has the advantages of high fuel utilization rate, high energy density, clean and pollution-free. However, there are two bottlenecks in its widespread use, one is that the activity of the electrode catalyst is not high, and the other is that the cost of the catalyst is too high. It is well known that platinum group metals (platinum, palladium, ruthenium, iridium, rhodium, etc.) and their alloys (platinum-ruthenium alloy, platinum-iridium alloy, etc.) have good catalytic activity for fuel cell electrode reactions. Although the commercial catalyst carbon-supported platinum nanoparticles has greatly improved the dispersion and catalyst utilization than the platinum black used in the past, it is prone to carbon monoxide poisoning, and the easy aggregation of platinum nanoparticles will also cause a decline in catalyst activity. Therefore, many researchers have been devoting themselves to exploring new catalyst types and preparation and treatment methods to improve the activity of fuel cell catalysts and reduce the loading of noble metals to reduce the cost of catalysts. The selection of supported catalyst supports mainly focuses on various forms of carbon materials. However, amorphous carbon is easy to lose in corrosive acidic medium and electrochemical oxidation environment, resulting in the loss and agglomeration of catalyst; carbon black can achieve a higher specific surface area, but generally the surface has more micropores, and the catalyst inside Particles are difficult to contact the solution, which further reduces the utilization rate of precious metals. Therefore, finding suitable catalyst supports and preparation methods to improve the utilization rate and catalytic activity of platinum group metals has become a focus of attention. In the late 1980s, Japanese scientists Haruta and others discovered that nanoscale gold particles, especially gold particles smaller than 5 nanometers, carried on iron oxide carriers have good catalytic activity for low-temperature catalytic oxidation of carbon monoxide. Recently, the applicant discovered that nanometer Porous gold also has good catalytic activity for carbon monoxide, so it is considered that the catalytic oxidation activity of nanoporous gold for carbon monoxide can be used to improve the anti-poisoning performance of platinum-based catalysts.

The applicant once reported in 2004 the achievement of obtaining a high specific surface area porous gold film by corroding commercial gold-silver alloy foil (Jonah Erlebacher, Yi Ding "Method of forming nanoporous membranes" US Patent, 6,805,972, Oct.19, 2004; Worldwide Patent, WO 2004/020064, March 11, 2004), and deposited platinum metal on porous gold by electroless plating (Jonah Erlebacher, Yi Ding "Method of Plating Metals Leafs and Metal Membranes" WORLDWIDE PATENT, WO2004/021481, November 3, 2004). However, the electroless plating method is difficult to accurately control the thickness of the deposited layer, the plating layer is not uniform, and the repeatability is poor.

As we all know, the phenomenon of underpotential deposition (upd) is the occurrence of a single atomic layer or submonoatomic layer at a potential that is more correct than the thermodynamic potential before the electrochemical bulk deposition (bulk deposition) of a metal on another metal. layer deposition phenomenon. Generally speaking, more active metals such as copper, silver, lead, etc. can be deposited under potential on relatively inert metals, such as gold, platinum, ruthenium, etc. In addition, due to the difference in electrode potential, active metals can undergo redox displacement reactions with cations of more inert metals. In the reaction, active metals are oxidized to metal cations, while inert metals are reduced to simple substances. Combining underpotential deposition and redox replacement can deposit inert metals on the substrate in a precise and controllable manner in monoatomic or sub-monatomic layers. . Using the underpotential deposited metal as a sacrificial template to make it react with noble metal ions on the surface of the substrate material, a noble metal deposition layer with a single atomic layer or even a sub-monatomic thickness can be obtained. Taking copper as an example, its principle can be expressed by the following formula:

nCu _upd +2M ⁿ⁺ = nCu ²⁺ +2M (M=Pt, Pd, Ru, etc.)

This is the ideal catalyst dispersion situation, where all catalyst atoms are on the surface and can participate in the catalytic reaction. Therefore, the design and application of the underpotential deposition-replacement method can precisely control the thickness of the coating at the atomic level and realize the efficient utilization of platinum-group metal catalysts.

After searching, there is no report on the preparation of ultra-thin platinum-group metal (alloy) films on porous gold using underpotential deposited metals as sacrificial templates.

Contents of the invention

Aiming at the deficiencies in the catalytic performance and preparation technology of existing catalysts, the purpose of the present invention is to provide a catalyst with high catalytic activity, good anti-poisoning performance, supported nanoporous gold-supported ultra-thin platinum group metal (alloy) film catalyst and its preparation method.

The basic technical concept of the present invention is to firstly deposit a single atomic layer of metals (copper, silver, lead) on the surface of nanoporous gold under potential, and then replace it with platinum-group metal cations to obtain ultra-thin platinum-group metals (alloys) loaded on nanoporous gold. Thin film catalyst.

The present invention adopts the method of underpotential deposition-replacement on the surface of nanoporous gold to prepare supported ultra-thin platinum group metal (alloy) thin film, and its scientific basis is: metals deposited under potential are generally monoatomic or submonoatomic layer The form exists on the surface of the substrate. When it is replaced by platinum-group metal cations, the platinum-group metal atoms replace the original underpotential deposited metal atoms, thereby forming an atomic-level or even sub-monatomic layer-thick platinum-group metal (alloy) film. Taking copper as an example, the reaction formula is as follows:

2Cu _upd +PtCl ₆ ^2- ＝2Cu ²⁺ +Pt+6Cl ^-

Cu _upd +PtCl ₄ ^2- ＝Cu ²⁺ +Pt+ ^4Cl-

Cu _upd +Pd ²⁺ ＝Cu ²⁺ +Pd

3Cu _upd +2Ru ³⁺ ＝3Cu ²⁺ +2Ru

Since the underpotential deposition can continue on the surface of the platinum group metal (alloy), another substitution will add another atomic layer of the platinum group metal (alloy), and so on, the thickness of the platinum group metal catalyst film can be precisely adjusted. Get the ideal catalyst.

The nanoporous gold-supported ultra-thin platinum-group metal thin film catalyst of the present invention is characterized in that the catalyst is 0.1-100 microns in thickness, 0.1-10 cm in width, and 0.1-20 cm in length, and the surface is uniformly covered with platinum An alloy flake of a metal atomic layer; wherein the surface morphology of the alloy flake is a bicontinuous nanoporous structure, the pore size or pore wall thickness is 2-100 nm, and the composition of the alloy flake is 80-99.8 at.% elemental gold , 0.1-10 at.% elemental silver, 0.1-10 at.% platinum group metal, the platinum group metal refers to platinum, palladium, ruthenium, rhodium or iridium or their alloys.

The above-mentioned nanoporous gold-supported ultra-thin platinum-series metal thin-film catalyst preferably has a thickness of 0.1-25 microns, a width of 0.5-2 cm, a length of 2-5 cm, and a surface evenly covered with platinum-series metals. An alloy sheet of a metal atomic layer; wherein the surface morphology of the alloy sheet is a bicontinuous nanoporous structure, and the pore size or pore wall thickness is 2 to 40 nm, and the platinum group metal refers to platinum, palladium, ruthenium or a platinum-ruthenium alloy, The atomic layer thickness of the platinum group metal is 1 to 20 atomic diameters of the platinum group metal.

The preparation method of the nanoporous gold-supported ultra-thin platinum metal thin film catalyst of the present invention consists of the following steps:

(1) Put an alloy with a thickness of 0.1 to 100 microns, a width of 0.1 to 10 centimeters, and a length of 0.1 to 20 centimeters, whose composition is 10 to 50 at.% of gold and 50 to 90 at.% of silver in a concentration of In 0.1-70wt.% nitric acid, at a temperature of -20-60°C, corrode for 1-1000 minutes, and then wash the surface of the alloy and the nitric acid in the pores with deionized water to obtain nanoporous gold;

(2) At 20-35°C, use the above-mentioned porous gold as the working electrode, platinum, gold or graphite sheet as the counter electrode, and a saturated calomel electrode or a mercury-mercurous sulfate electrode as a reference electrode to form a three-electrode system. In the acidic solution (pH 0.1-5) containing 0.01-100mM copper, silver or lead ions deoxygenated by nitrogen gas, under-potential deposition at -0.5-0.0V relative to the reference electrode for 1-60 minutes, then immerse the working electrode in The acidic solution (pH value 0.1-5) containing 0.01-100mM platinum-series metal cations is replaced for 1-60 minutes to obtain a nanoporous gold-supported platinum-series metal thin film catalyst whose surface is uniformly covered with a monoatomic layer thickness.

In the preparation method of the above-mentioned nanoporous gold-supported ultra-thin platinum-group metal film catalyst,

The alloy described in step (1) is preferably an alloy with a thickness of 0.1 to 25 microns, a width of 0.5 to 2 centimeters, a length of 2 to 5 centimeters, and a composition of 26 at.% gold atomic percent; the concentration of the nitric acid is preferably 65- 68wt.%; the corrosion temperature is preferably 20-35°C.

The preferred platinum or gold of described counter electrode of step (2); The preferred mercury-mercurous sulfate electrode of described reference electrode; The potential of described underpotential deposited metal is preferably-0.5～-0.3V; The potential of described underpotential deposited metal The time is preferably 1-10 minutes; the replacement time of the underpotential deposition metal and the platinum group metal cation is preferably 5-30 minutes.

It is further preferred that the counter electrode of step (2) is platinum; the reference electrode is a mercury-mercurous sulfate electrode; the underpotential deposition metal is copper, and the potential of the underpotential deposition copper is -0.45 V; the time for the underpotential deposition of copper is 2 minutes; the replacement time for the underpotential deposition of copper and platinum group metal cations is 10 minutes.

In the preparation method of the above-mentioned nanoporous gold-supported ultra-thin platinum-group metal thin film catalyst, if the operation described in step (2) is repeated once for the prepared electrode deposited with platinum-group metal, the platinum-group metal layer will be increased by one monoatomic layer thickness.

In the preparation method of the nanoporous gold-supported ultrathin platinum-group metal film catalyst, the platinum-group metal refers to platinum, palladium, ruthenium, rhodium or iridium or their alloys.

Compared with the existing catalyst preparation technology, the method of the present invention has the following advantages:

(1) The platinum group metal loading is greatly reduced, and the thickness of the platinum group metal (alloy) film can be precisely controlled (as shown in the aforementioned substitution reaction formula, when the underpotential Ag monoatomic layer reacts with PtCl ₆ ^2- ions, the resulting The thickness of the platinum group metal film can be precisely controlled to a quarter of the monoatomic layer coverage);

(2) When the thickness of monoatomic and subatomic layers (that is, the coverage of a single atomic layer is less than one layer), the use efficiency of catalysts in platinum-group metal thin films is the highest, and it has better anti-poisoning ability and carbon-supported platinum nanoparticles than commercial catalysts. catalytic activity;

(3) The method is simple in technology, easy to operate, good in repeatability, low in platinum group metal loading in the product, and high in catalyst use efficiency, while traditional supported metal nanoparticle catalysts based on carbon materials are complicated in preparation process and poor in repeatability. It is not efficient to use.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings.

Figure 1 is an alloy with a gold atomic percentage of 26at.%, a thickness of 0.1mm, free corrosion at 30°C for 60 minutes, and then deposited at a potential of -0.45V relative to the mercurous sulfate electrode for 2 minutes, and immersed in PtCl ₄ ² containing platinum group metal cations ⁺ in the acidic solution of + for 10 minutes, and then repeat the underpotential deposition-the transmission electron microscope (TEM) photo of the porous gold-supported platinum thin film catalyst obtained by the replacement, the film thickness is 2 platinum atomic layers, about 0.5nm, and the porous structure size is about 30nm.

Fig. 2 is the high-resolution transmission electron microscope (HRTEM) picture of catalyst described in Fig. 1, and film thickness is 2 platinum atomic layers, about 0.5nm, can find out by the streak in the image, platinum forms single crystal on the surface of porous gold form and evenly cover the porous gold surface.

Fig. 3 is a cyclic voltammogram of the catalyst described in Fig. 1 and nanoporous gold in 0.5M dilute sulfuric acid solution. The solid line is the nanoporous gold, and the dashed line is the platinum thin film catalyst. It can be seen that the catalyst has only the reduction peak of platinum, but no reduction peak of gold oxide, indicating that the nanoporous gold is completely covered by platinum. Combined with the TEM photos in Figure 1, it can be concluded that the platinum thin film evenly covers the surface of nanoporous gold.

Fig. 4 is the electrochemical cyclic voltammetry curve of methanol oxidation by the catalyst described in Fig. 1, wherein the dotted line is the cyclic voltammetry curve of the commercial catalyst under the same conditions. It can be seen that the catalyst of the present invention has better catalytic activity for methanol oxidation than the commercial catalyst, and the anti-poisoning effect obtained from the ratio of the forward sweep and reverse sweep peak currents also suggests that the catalyst of the present invention is better than the commercial catalyst.

Detailed ways

Example 1:

(1) A gold-silver alloy foil with a thickness of 25 microns, a width of 1 cm, a length of 2 cm, and a gold atomic percentage of 26 at.% is placed in nitric acid with a concentration of 65-68 wt.%, and the corrosion time is 60 minutes. Then use deionized water to clean the nitric acid remaining in the pores to obtain nanoporous gold;

(2) At 25°C, using a three-electrode electrochemical system, using the nanoporous gold prepared above as the working electrode, platinum as the counter electrode, mercury-mercurous sulfate electrode as the reference electrode, 0.5M H ₂ SO ₄ + In 0.5mM CuSO ₄ , deposit at -0.45V potential for 2 minutes, and then transfer to 1mM PdCl ₂ for replacement for 10 minutes to obtain a composite metal catalyst with a monoatomic layer of palladium film covering the porous gold surface.

Example 2:

(1) A gold-silver alloy foil with a thickness of 0.1 micron, a width of 2 cm, a length of 2 cm, and a gold atomic percentage of 26 at.% is placed in nitric acid with a concentration of 65-68 wt.%, and the corrosion time is 90 minutes. Then use deionized water to clean the nitric acid remaining in the pores to obtain nanoporous gold;

(2) At 25°C, a three-electrode electrochemical system was adopted, with the nanoporous gold prepared above as the working electrode, the platinum sheet as the counter electrode, and the mercurous sulfate electrode as the reference electrode, 0.5M H ₂ SO ₄ +0.5mM CuSO ₄ was deposited at -0.45V for 5 minutes, and then transferred to 1 mM K ₂ PtCl ₆ for 10 minutes. Afterwards, it was washed with deionized water to obtain a composite metal catalyst in which half of the atomic layer of platinum covered the surface of the porous gold.

Example 3:

(1) A gold-silver alloy foil with a thickness of 0.1 micron, a width of 1 cm, a length of 1 cm, and a composition of 26 at.% gold atomic percentage is placed in nitric acid with a concentration of 65-68 wt.%, and the corrosion time is 60 minutes. Then use deionized water to clean the nitric acid remaining in the pores to obtain nanoporous gold;

(2) At 25°C, using a three-electrode electrochemical system, with the nanoporous gold prepared above as the working electrode, the platinum sheet as the counter electrode, and the mercurous sulfate electrode as the reference electrode, in 0.5M H ₂ In SO ₄ +0.5mM CuSO ₄ solution, deposit at -0.45V potential for 2 minutes, then transfer to 1mM K ₂ PtCl ₄ for replacement for 10 minutes; then in the above dilute sulfuric acid solution containing CuSO ₄ , -0.4V potential Copper was deposited for 2 minutes and replaced in 1 mM K ₂ PtCl ₄ for 10 minutes to obtain a composite nanoporous metal catalyst loaded with two atomic layers of platinum.

The TEM and HRTEM photos of this catalyst are shown in Figure 1 and Figure 2, respectively. The cyclic voltammetry curves of the catalyst in dilute sulfuric acid and dilute sulfuric acid plus methanol are shown in Figure 3 and Figure 4, respectively.

Example 4:

(1) A gold-silver alloy foil with a thickness of 0.1 micron, a width of 1 cm, a length of 1 cm, and a composition of 26 at.% gold atomic percentage is placed in nitric acid with a concentration of 65-68 wt.%, and the corrosion time is 60 minutes. Then use deionized water to clean the nitric acid remaining in the pores to obtain nanoporous gold;

(2) At 25°C, a three-electrode electrochemical system was adopted, with the nanoporous gold prepared above as the working electrode, the platinum sheet as the counter electrode, and the mercurous sulfate electrode as the reference electrode, 0.5M H ₂ SO ₄ +0.5mM In Ag ₂ SO ₄ , deposit at -0.45V potential for 2 minutes, and then transfer to 1mM PdCl ₂ solution for replacement for 10 minutes, that is, the porous gold-supported palladium thin film catalyst.

Example 5:

(1) A gold-silver alloy foil with a thickness of 0.1 micron, a width of 0.5 cm, a length of 0.5 cm, and a composition of 26 at.% gold atomic percentage is placed in nitric acid with a concentration of 65-68 wt.%, and the corrosion time is 60 minutes. Then use deionized water to clean the nitric acid remaining in the pores to obtain nanoporous gold;

(2) At 25°C, use nanoporous gold in a three-electrode electrochemical system, use the porous gold prepared above as the working electrode, use the platinum sheet as the counter electrode, and the mercurous sulfate electrode as the reference electrode, 0.5M H ₂ SO ₄ + In 0.5mM CuSO ₄ , deposit at -0.45V potential for 2 minutes, and then transfer to 1mM RuCl ₃ +1mM K ₂ PtCl ₄ solution for replacement for 10 minutes, and the porous gold-supported platinum-ruthenium alloy thin film catalyst is obtained.

Claims (9)

1. a nano porous gold-loaded ultrathin platinum metallic film catalyst is characterized in that, described catalyst is that thickness is that 0.1～100 micron, width are that 0.1～10 centimetre, length are the alloy sheet that 0.1～20 centimetre, surface evenly cover the platinum metal atomic layer; The surface topography of wherein said alloy sheet is the co-continuous nano-porous structure, aperture size or pore wall thickness are 2～100nm, the composition of described alloy sheet is 80～99.8at.% simple substance gold, 0.1～10at.% simple substance silver, 0.1～10at.% platinum metal, described platinum metal refer to platinum, palladium, ruthenium, rhodium or iridium or their alloy.

2. nano porous gold-loaded ultrathin platinum metallic film catalyst as claimed in claim 1, it is characterized in that described catalyst is that thickness is that 0.1～25 micron, width are that 0.5～2 centimetre, length are the alloy sheet that 2～5 centimetres, surface evenly cover the platinum metal atomic layer; The surface topography of wherein said alloy sheet is the co-continuous nano-porous structure, aperture size or pore wall thickness are 2～40nm, described platinum metal refers to platinum, palladium, ruthenium or platinum-ruthenium alloys, and described platinum metal atomic layer level thickness is the thickness of 1～20 platinum metal atomic diameter.

3. the preparation method of claim 1 or 2 described nano porous gold-loaded ultrathin platinum metallic film catalysts, be made up of following step:

(1) be that 0.1～100 micron, width are that 0.1～10 centimetre, length are 0.1～20 centimetre with thickness, composition is that to place concentration be the nitric acid of 0.1～70wt.% to the alloy of gold atom percentage 10～50at.%, silver atoms percentage 50～90at.%, under-20～60 ℃ of temperature, corroded 1～1000 minute, with the nitric acid in clean alloy surface of deionized water and the hole, get nano-porous gold then;

(2) under 20～35 ℃, with above-mentioned porous gold is working electrode, platinum, gold or graphite flake are to electrode, saturated calomel electrode or mercury-mercurous sulfate electrode are that reference electrode is formed three-electrode system, earlier containing 0.01～100mM copper through the nitrogen deoxygenation, in the acid solution of silver or lead ion, still owed the electromotive force deposition 1～60 minute with respect to reference electrode-0.5～0.0V, then working electrode is immersed to contain in the cationic acid solution of 0.01～100mM platinum metal and replaced 1～60 minute, get the nano porous gold-loaded platinum metallic film catalyst of surperficial even covering monoatomic layer thickness.

4. as the preparation method of nano porous gold-loaded ultrathin platinum metallic film catalyst as described in the claim 3, it is characterized in that, the described alloy of step (1) is that thickness is that 0.1～25 micron, width are that 0.5～2 centimetre, length are 2～5 centimetres, and composition is the alloy of gold atom percentage 26at.%; The concentration of described nitric acid is 65-68wt.%; Described corrosion temperature is 20～35 ℃.

5. as the preparation method of nano porous gold-loaded ultrathin platinum metallic film catalyst as described in the claim 3, it is characterized in that step (2) is described to be platinum or gold to electrode; Described reference electrode is a mercury-mercurous sulfate electrode; The described current potential of owing the electromotive force plated metal is-0.5～-0.3V; The described time of owing the electromotive force plated metal is 1～10 minute; Describedly owe the electromotive force plated metal and the cationic time swap of platinum metal is 5～30 minutes.

6. as the preparation method of nano porous gold-loaded ultrathin platinum metallic film catalyst as described in the claim 3, it is characterized in that step (2) is described to be platinum to electrode; Described reference electrode is a mercury-mercurous sulfate electrode; The described electromotive force plated metal of owing is a copper, and the described current potential of owing the electromotive force deposited copper is-0.45V; The described time of owing the electromotive force deposited copper is 2 minutes; Describedly owe the electromotive force deposited copper and the cationic time swap of platinum metal is 10 minutes.

7. as the preparation method of nano porous gold-loaded ultrathin platinum metallic film catalyst as described in the claim 3, it is characterized in that the described acid solution pH of step (2) value is 0.1～5.

8. as the preparation method of nano porous gold-loaded ultrathin platinum metallic film catalyst as described in the claim 3, it is characterized in that, to the deposition that makes the electrode of platinum metal, if the described operation of its step (2) is repeated once, the platinum metal layer promptly increases a monoatomic layer thickness.

9. as the preparation method of nano porous gold-loaded ultrathin platinum metallic film catalyst as described in the claim 3, it is characterized in that described platinum metal refers to platinum, palladium, ruthenium, rhodium or iridium or their alloy.

Images