CN107623131B - Preparation and application of membrane electrode based on platinum or platinum alloy nanotube - Google Patents

Abstract

The invention describes the preparation and application of a membrane electrode based on platinum or platinum alloy nanotubes, including the formation of an ordered electrode microstructure, the preparation of platinum or platinum alloy nanotubes and the assembly of the membrane electrode. Firstly, regular orientation Co‑OH‑CO3 nanorod arrays are grown on the substrate, then catalysts are supported on the arrays, and the catalyst-loaded Co‑OH‑CO3 nanorod arrays are annealed. Finally, the arrays are heated The membrane electrode is obtained by pressing on the ion exchange membrane, and the membrane electrode is purified, and the constructed membrane electrode can be applied to a fuel cell. The membrane electrode constructed by the present invention has the advantages of low catalyst loading, high catalyst utilization rate, easy amplification and the like.

Description

Preparation of Membrane Electrodes Based on Platinum or Platinum Alloy Nanotubes and Their Applications

technical field

The invention relates to a preparation method of a membrane electrode, belonging to the field of fuel cells.

Background technique

A fuel cell is an efficient energy conversion device that efficiently converts chemical energy stored in chemicals into electrical energy. At present, fuel cells have been applied in many fields such as electric vehicles, distributed power stations, and aviation. Proton exchange membrane fuel cells have attracted extensive attention due to their high power density, fast startup speed, high conversion efficiency, and environmental friendliness.

The membrane electrode assembly (MEA) is the core component of the electrochemical reaction of the fuel cell. It consists of a catalytic layer and a gas diffusion layer located on both sides of the proton exchange membrane. Membrane electrodes are mainly divided into gas diffusion electrodes (Gas Diffusion Electrode, GDE), thin-layer coated membrane electrodes (catalyst coated membrane, CCM) and ordered nano-thin layer electrodes (nanostructured thin film, NSTF) represented by 3M Company in the United States. ordered MEAs. GDE is prepared by screen printing, electrostatic spraying and other processes. The catalyst slurry composed of catalyst, hydrophobic agent and organic solvent is brushed onto the gas diffusion layer. After high temperature treatment, Naifon solution is sprayed on the surface of the catalytic layer to realize the electrode three-dimensionalization; CCM currently Generally, spraying, transfer printing and other preparation processes are used to spray the slurry composed of catalyst, ion conductor resin and organic solvent onto the membrane, or the slurry is first sprayed onto other carriers and then transferred to the membrane to form a membrane catalytic layer. Integrated electrode. The traditional CCM electrodes and GDE electrodes have mature preparation processes, but the thickness of the catalytic layer of the electrodes is large and the catalysts are stacked in disorder, which makes the amount of catalysts high and the utilization rate of catalysts low. In order to solve the problems of high consumption of precious metals and low catalyst utilization in fuel cells, 3M Company has developed an ordered thin film electrode (NSTF electrode, Nanostructured Thin Film electrode), which has the characteristics of microscopic order and low catalyst loading. , which can effectively reduce the mass transfer resistance and improve the utilization rate of the catalyst.

Patent US5039561 introduces a method for preparing an ordered nanowhisker array, specifically depositing an organic thin film on a substrate, and then annealing the organic thin film under high temperature and high vacuum conditions to obtain a highly ordered nanowhisker array . The nanowhisker array prepared by the invention has excellent chemical stability and mechanical strength.

Patent US20110151353A1 introduces a preparation method of NSTF electrodes, which is to deposit Pt, Mn, Co, Ir and other metals on the ordered nanowhisker array by magnetron sputtering technology, and then deposit the nanorod arrays loaded with catalysts Transferred to one or both sides of the ion exchange membrane, the prepared electrode is suitable for fuel cells and water electrolysis cells. The electrode prepared by the invention has the advantages of low noble metal dosage, high electrochemical activity, good stability, low mass transfer resistance and the like.

Patent CN201310690828.X introduces a method for preparing a self-supporting catalytic layer, specifically preparing an ordered nanorod array by hydrothermal method, then using magnetron sputtering technology to support catalyst on the array, and finally transferring the catalyst onto the ion exchange membrane. The electrode prepared in this patent has the characteristics of low load and thin thickness, but the catalytic layer prepared in this patent is composed of a mechanical mixture of platinum and other metals, which is a disordered macroporous thin film electrode.

The invention prepares membrane electrodes based on platinum and its alloy nanotubes on the basis of patent CN201310690828.X. The prepared electrodes consist of platinum or platinum alloy nanotubes. The morphology and composition of the prepared electrodes are different from those of the patent CN201310690828.X. The method adopted in the present invention has mild conditions and simple operation, and can effectively reduce the amount of precious metal in the electrode.

SUMMARY OF THE INVENTION

A method for preparing a membrane electrode based on platinum or platinum alloy nanotubes, comprising the following steps:

1) Prepare a reaction solution; the reaction solution is an aqueous solution of 1-30 mM ammonium fluoride, 1-30 mM urea, and 1-50 mM cobalt nitrate;

2) Immerse the substrate into the reaction solution, react in an autoclave at 90-150°C for 30min-24h, and prepare a Co-OH- _CO3 array on the substrate; the substrate used can be glass, nickel sheet, nickel Mesh, stainless steel or titanium sheet;

3) The catalyst is supported on the Co-OH-CO ₃ array. The methods of supporting the catalyst include physical vapor deposition and chemical vapor deposition. The supported catalysts are Pt, Pd, Ru, Co, Ni, Fe, Cu, Au , a metal or an alloy of several metals among Ag, Mn, Ir, Cr, and the atomic ratio of Pt to other metals is 1:5 to 9:1;

4) Perform annealing treatment on the Co-OH-CO ₃ array loaded with catalyst, the annealing temperature is 200℃～1000℃, and the annealing atmosphere is H ₂ , N ₂ , Ar, He, or H ₂ -Ar, H ₂ - The mixed gas of N ₂ and H ₂ -He, the content of H ₂ in the mixed gas is 1vol.%～99vol.%, and the annealing time is 10min-7days;

5) Transfer the annealed array to one or both sides of the ion exchange membrane by the transfer method, and remove the substrate; the pressure applied during transfer is 0.1-50MPa, the time is 1s-30min, and the temperature is 20- 200℃, the ion exchange membrane used is a cation exchange membrane or an anion exchange membrane;

6) Pickling the ion-exchange membrane transferred with the catalytic layer, the pickling can be HCl, H ₂ SO ₄ , HNO ₃ or HF solution, the acid concentration is 1mM-10M, and the pickling temperature is 20℃～100℃ , the pickling time is 1min-24h;

7) Wash the acid-washed membrane electrode with water to remove the acid remaining in the membrane electrode. The washing temperature is 25℃～100℃, and the washing time is 1min-24h;

8) Immerse the electrode in an aqueous solution of hydrogen peroxide to remove organics introduced during the preparation of the electrode. The mass concentration of hydrogen peroxide is 1% to 10%, the immersion temperature is 25°C to 100°C, and the immersion time is 1min- 24h;

9) Put the electrode in the sulfuric acid solution of 20℃～100℃ and boil for 30min～1h, the mass concentration of sulfuric acid is 1wt.%～30wt.%;

10) Washing the electrode after the above steps, the washing temperature is 20°C to 100°C, and the washing time is 20s-24h.

The present invention has the following characteristics:

1. The catalytic layer of the membrane electrode prepared by the present invention is composed of platinum or platinum alloy nanotubes;

2. The electrode preparation method described in the present invention has the characteristics of mild preparation conditions and simple operation;

3. The membrane electrode prepared by the present invention has the characteristics of low consumption of precious metals, adjustable catalyst components, and thin catalyst layer thickness;

4. Full-cell tests show that the membrane electrodes based on platinum or platinum alloy nanotubes have high mass specific power and catalyst utilization

Description of drawings

FIG. 1 is a flow chart of the preparation of membrane electrodes in Example 1. FIG.

2 is a scanning electron microscope image of the Co-OH-CO ₃ nanorod array prepared in Example 1.

FIG. 3 is a scanning electron microscope image of the platinum nanorod array prepared in Example 1. FIG.

FIG. 4 is a scanning electron microscope image of the membrane electrode prepared in Example 1. FIG.

FIG. 5 is an XRD pattern of the membrane electrode prepared in Example 1. FIG.

FIG. 6 is the I-V performance curve of the membrane electrode prepared in Example 1 in the fuel cell.

FIG. 7 is a scanning electron microscope image of the platinum-cobalt nanorod array prepared in Example 2. FIG.

FIG. 8 is a scanning electron microscope image of the membrane electrode prepared in Example 2. FIG.

FIG. 9 is an XRD pattern of the membrane electrode prepared in Example 2. FIG.

FIG. 10 is the I-V performance curve of the membrane electrode prepared in Example 2 in the fuel cell.

FIG. 11 is a scanning electron microscope image of the platinum-iron nanorod array prepared in Example 3. FIG.

FIG. 12 is a scanning electron microscope image of the membrane electrode prepared in Example 3. FIG.

FIG. 13 is the XRD pattern of the membrane electrode prepared in Example 3. FIG.

FIG. 14 is the I-V performance curve of the membrane electrode prepared in Example 3 in the fuel cell.

Detailed ways

The following examples are further illustrations of the invention, which protects both obvious modifications and equivalent alternatives.

Example 1

Co-OH- _CO3 arrays were prepared by a hydrothermal method using stainless steel as a substrate. The reaction solution was 10 mM ammonium fluoride, 25 mM urea, 5 mM cobalt nitrate. In an autoclave at 120 °C for 5 h, a Co-OH-CO ₃ array was prepared on the substrate. Figure 2 shows the SEM images of the as-prepared Co-OH _- CO nanorod arrays. It can be seen from the figure that the Co-OH- _CO3 nanorod arrays are uniformly grown on the substrate, and the growth direction is substantially perpendicular to the substrate. The length of the Co-OH-CO ₃ nanorods is about 3 μm, the diameter is about 100 nm, and the areal density of the Co-OH-CO ₃ nanorods is 3-4e ⁹ /cm ² .

Pt was supported on the Co-OH- _CO3 array by magnetron sputtering method. The magnetron sputtering power was 150W, the sputtering time was 10min, and the operating pressure was 1.0Pa. The Pt-loaded Co-OH-CO ₃ arrays were annealed at 300 °C in a H ₂ -Ar (H ₂ volume fraction of 5%) atmosphere for 60 min. Figure 3 shows the scanning electron microscope images of the fabricated nanorod arrays. It can be seen from the figure that the magnetron sputtering supports a uniform Pt layer on the Co-OH- _CO3 array, and the thickness of the Pt layer is about 20 nm. The annealing treatment did not destroy the order of the array, and the Pt-loaded Co-OH- _CO3 nanorods were about 2 μm in length and 140 nm in diameter.

212膜。转印压力为4MPa，转印温度为140℃，转印时间为1min。ICP测试表明所制备的膜电极的铂担量为68.1μg cm^-2。The annealed platinum nanorod array was transferred to one side of the ion-exchange membrane, and the ion-exchange membrane used was

212 film. The transfer pressure was 4MPa, the transfer temperature was 140°C, and the transfer time was 1min. The ICP test showed that the platinum loading of the prepared membrane electrode was 68.1 μg cm ^-2 .

The stainless steel substrate was removed, and the membrane electrode was purified. The treatment process was as follows: placing the ion exchange membrane carrying the catalytic layer in a 0.5M sulfuric acid solution, removing the Co-OH-CO ₃ array as a template, and placing the membrane electrode in a 0.5M sulfuric acid solution. Rinse in deionized water to remove residual acid. The membrane electrode was boiled in a 0.5M sulfuric acid solution at 80°C for 30min, the residual acid was washed away in deionized water, and then boiled in a 5% aqueous hydrogen peroxide solution at 80°C for 30min, and finally the electrode was deionized at 80°C. Boil in water for 30 min, dry the membrane electrode and encapsulate it into a membrane electrode assembly. Figure 4 is a scanning electron microscope image of the prepared membrane electrode. It can be seen from the figure that the prepared catalytic layer is composed of nanotubes. The diameter of the nanotubes is 140 nm, the length is about 2 μm, and the thickness of the tube wall is about 20 nm. FIG. 5 is the XRD pattern of the prepared electrode, from which it can be seen that the catalytic layer prepared by magnetron sputtering is composed of a single element platinum.

212膜。The prepared membrane electrode was packaged into a membrane electrode assembly, the packaging pressure was 0.5 MPa, and the temperature was 140 °C. The anode of the membrane electrode assembly adopts a gas diffusion electrode, the anode Pt/C (70wt.%, Johnson Matthey) load is 0.2mg cm ^-2 , and the electrolyte separator is

212 film.

Battery test conditions: H ₂ /O ₂ flow rate: 50/100sccm; battery temperature 75°C, saturated humidification, battery back pressure 0.2MPa. Figure 6 shows the IV performance curves in a platinum nanotube-based membrane electrode fuel cell with a maximum output of 736 mW cm ^-2 . It can be seen from the figure that the mass specific power of the single cell is as high as 2.745kW g ^-1 Pt.

Example 2

Co-OH- _CO3 arrays were prepared by a hydrothermal method using stainless steel as a substrate. The reaction solution was 10 mM ammonium fluoride, 25 mM urea, 5 mM cobalt nitrate. After reacting at 120 °C for 4 h in an autoclave, a Co-OH- _CO3 array was prepared on the substrate.

PtCo ( ₃ :1 atomic ratio) was supported on Co-OH-CO arrays by magnetron sputtering. The magnetron sputtering power was 100W, the sputtering time was 20min, and the operating pressure was 1.0Pa. The PtCo-loaded Co-OH- _CO3 arrays were annealed at 400 °C in an _H2 -Ar (5% _H2 volume fraction) atmosphere for 1 h. Figure 7 shows the scanning electron microscope image of the prepared platinum cobalt nanotube array. It can be seen from the figure that the uniform PtCo catalyst is supported on the surface of the Co-OH-CO ₃ nanorod array by magnetron sputtering. The thickness of the PtCo coating is about 18 nm, and the annealing treatment does not destroy the order of the array. The Co-OH-CO nanorods loaded with PtCo coating are about ₃ μm in length and 136 nm in diameter.

212膜。转印压力为0.5MPa，转印温度为150℃，转印时间为2min。ICP测试表明所制备的膜电极的Pt担量为40.15μg cm^-2，Co担量为3.825μg cm^-2。The annealed platinum nanorod array was transferred to one side of the ion-exchange membrane, and the ion-exchange membrane used was

212 film. The transfer pressure was 0.5MPa, the transfer temperature was 150°C, and the transfer time was 2min. The ICP test showed that the Pt loading of the prepared membrane electrode was 40.15 μg cm ^-2 and the Co loading was 3.825 μg cm ^-2 .

The stainless steel substrate was removed, and the membrane electrode was subjected to purification treatment. See Example 1 for the treatment flow. 8 is a scanning electron microscope image of the prepared membrane electrode. It can be seen from the figure that the diameter of the PtCo nanotube is about 136 nm, the thickness of the tube wall is about 18 nm, and the length of the PtCo nanotube is about 2-3 μm. FIG. 9 is an XRD pattern of the prepared electrode. XRD test shows that the prepared nanotubes are PtCo alloy nanotubes, and some Pt atoms form alloys with Co.

212膜。电池测试条件：H₂/O₂流量：50/100sccm；电池温度75℃，饱和增湿，电池背压为0.2MPa。图10所示为基于铂钴纳米管阵列的膜电极燃料电池中的I-V性能曲线，电池的最大输出功率为685mWcm^-2，由图可以看出单电池的质量比功率高达2.85kWg^-1Pt。The prepared membrane electrode was packaged into a membrane electrode assembly, the packaging pressure was 0.5 MPa, and the temperature was 140 °C. The anode of the membrane electrode assembly adopts a gas diffusion electrode, the anode Pt/C (70wt.%, Johnson Matthey) load is 0.2mg cm ^-2 , and the electrolyte separator is

212 film. Battery test conditions: H ₂ /O ₂ flow rate: 50/100sccm; battery temperature 75°C, saturated humidification, battery back pressure 0.2MPa. Figure 10 shows the IV performance curve of the membrane electrode fuel cell based on platinum cobalt nanotube arrays. The maximum output power of the cell is 685mWcm ^-2 . It can be seen from the figure that the mass specific power of the single cell is as high as 2.85kWg ^-1 Pt.

Example 3

See Example 2 for the preparation method of Co-OH-CO ₃ arrays.

PtFe (atomic ratio 1:1) was supported on Co-OH _- CO arrays by magnetron sputtering. The magnetron sputtering power was 100W, the sputtering time was 20min, and the operating pressure was 1.0Pa. The PtFe-loaded Co-OH- _CO3 arrays were annealed at 600 °C in a _H2 -Ar (5% _H2 volume fraction) atmosphere for 1 h. Figure 11 shows the scanning electron microscope image of the prepared nanorod array. It can be seen from the figure that the prepared PtFe nanorods grow vertically on the substrate with a certain orientation, and the length of the Co-OH _- CO nanorods carrying the PtFe coating is About 2.5μm, about 130nm in diameter.

Refer to Example 2 for the preparation process of the membrane electrode. 12 is a scanning electron microscope image of the prepared membrane electrode. It can be seen from the figure that the prepared catalytic layer is composed of PtFe nanotubes. The diameter of the nanotubes is about 130 nm, the thickness of the tube wall is about 15 nm, and the length is about 1-2.5 μm. The ICP test showed that the Pt loading of the prepared membrane electrode was 49.735 μg cm ^-2 and the Fe loading was 1.875 μg cm ^-2 . 13 is the XRD pattern of the prepared electrode, wherein the diffraction peak position of PtFe is located between the peak positions of PtCo alloy and PtFe alloy, indicating that the prepared electrode is a PtFe alloy.

212膜。电池测试条件：H₂/O₂流量：50/100sccm；电池温度75℃，饱和增湿，电池背压为0.2MP_a。图14所示为基于PtF_e纳米管的膜电极燃料电池中的I-V性能曲线，电池的最大输出功率为830mW cm^-2，电池的质量比功率为3.32kW g^-1Pt。The prepared membrane electrode was packaged into a membrane electrode assembly, the packaging pressure was 0.5 MPa, and the temperature was 140 °C. The anode of the membrane electrode assembly adopts a gas diffusion electrode, the anode Pt/C (70wt.%, Johnson Matthey) load is 0.2mg cm ^-2 , and the electrolyte separator is

212 film. Battery test conditions: H ₂ /O ₂ flow rate: 50/100sccm; battery temperature 75°C, saturated humidification, battery back pressure _0.2MPa . Figure 14 shows the IV performance curve in the _PtFe nanotube-based membrane electrode fuel cell, the maximum output power of the cell is 830mW cm ^-2 , and the mass specific power of the cell is 3.32kW g ^-1 Pt.

Claims (7)

1. A membrane electrode based on platinum alloy nanotubes is characterized in that: the catalyst layer of the membrane electrode is composed of platinum alloy nanotubes which are annealed, and the prepared catalyst layer is positioned on one side or two sides of the ion exchange membrane; the tube wall of the nanotube is of an open structure;

the catalyst layer is composed of platinum alloy nanotubes with the diameter of 10 nm-200 nm and the length of 50 nm-5 mu m, the thickness of the catalyst layer is 50 nm-10 mu m, and the adopted ion exchange membrane is a cation exchange membrane or an anion exchange membrane;

the transition metal other than platinum, which constitutes the platinum alloy, is one or more of Fe, Co, Ni, Cu, Au, Ru, Pd, Ir, Mn, Cr and Ag, and the atomic ratio of platinum to transition metal is 1:5 to 9: 1.

2. A method for producing the membrane electrode of claim 1, characterized in that:

(1) growing Co-OH-CO vertical to substrate on substrate by hydrothermal method₃A nanorod array;

(2) in the presence of Co-OH-CO₃The nano-rods uniformly support a metal catalyst;

(3) Co-OH-CO loaded with catalyst₃Carrying out annealing treatment on the array;

(4) transferring the nanorod array loaded with the catalyst to one side or two sides of the ion exchange membrane;

(5) and (5) purifying the membrane electrode.

3. The method for producing a membrane electrode according to claim 2, wherein: the substrate in the step (1) is glass, a nickel sheet, a nickel net, a stainless steel sheet or a titanium sheet;

Co-OH-CO in step (1)₃The growth of the array is prepared by a high pressure hydrothermal method, comprising the following steps:

A. preparing a reaction solution, wherein the reaction solution is an aqueous solution containing 1-30mM of ammonium fluoride, 1-30mM of urea and 1-50mM of cobalt nitrate;

B. soaking the substrate in the reaction solution in a high-pressure reaction kettle for 90-150 times^oReacting for 30min-24h under C to prepare Co-OH-CO on the substrate₃And (4) array.

4. The method for producing a membrane electrode according to claim 2, wherein: the method for supporting the catalyst in the step (2) comprises physical vapor deposition or chemical vapor deposition;

the catalyst carried in the step (2) is a platinum alloy, the catalyst is composed of Pt or platinum and one or more than two elements of Fe, Co, Ni, Cu, Au, Pd, Ru, Ir, Mn, Cr and Ag, the atomic ratio of platinum to other metals is 1: 5-9: 1, and the catalyst loading is 1 mu g cm^-2~5 mg cm^-2。

5. The method for producing a membrane electrode according to claim 2, wherein: the annealing temperature in the step (3) is 200-1000 ℃, and the annealing atmosphere is H₂、N₂Ar, He, or H₂-Ar、 H₂-N₂、H₂Mixed gas of-He and H in the mixed gas₂The content of (1) vol% to 99 vol%, and the annealing time is 10min to 7 days;

in the step (4), the pressure applied during transfer printing is 0.1-50 MPa, the time is 1 s-30 min, and the temperature is 20-200 ℃.

6. The method for producing a membrane electrode according to claim 2, wherein: the membrane electrode purification step in the step (5) is as follows:

(1) pickling the washed membrane electrode; the adopted acid is nitric acid, sulfuric acid or hydrochloric acid, the concentration is 5 mM-10M, the acid treatment temperature is 20-100 ℃, and the acid treatment time is 1min-24 h;

(2) washing the membrane electrode after acid washing with water at the temperature of 20-100 ℃;

(3) cleaning the membrane electrode in a hydrogen peroxide aqueous solution; the mass concentration of the hydrogen peroxide is 1-10%, and the cleaning temperature is 20-100 ℃;

(4) placing the membrane electrode in sulfuric acid solution for cleaning; the mass concentration of the sulfuric acid is 1-30 wt%, and the cleaning temperature is 20-100 ℃;

(5) and (3) cleaning the membrane electrode in deionized water at the temperature of 20-100 ℃.

7. Use of a membrane electrode according to claim 1, characterized in that: the prepared electrode is used for a fuel cell.

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