CN1713425A - Proton exchange membrane fuel cell electrode and preparation method thereof - Google Patents

Abstract

The invention relates to a solid polymer proton exchange membrane fuel cell electrode and a preparation method thereof, and is a fuel cell electrode catalyst layer and a preparation method thereof. In this method, the electrode precursor with the catalytic layer is roasted at 250-450°C, preferably at 280-380°C under the protection of an inert gas, so that the solid polymer electrolyte in the catalytic layer is partially decomposed and loses sulfonate groups, and the remaining organic groups Hydrophobic, undecomposed solid polymer electrolyte is hydrophilic, forming a three-dimensional proton exchange membrane fuel cell electrode catalyst layer with uniform distribution of hydrophilic structure and hydrophobic structure, and then making membrane fuel cell electrodes by conventional methods . The electrode catalytic layer expands the three-dimensional reaction area of the fuel cell, which not only ensures sufficient contact between the catalytic active components and the proton conductor and electron conductor, but also provides sufficient gas channels and water channels, thereby improving battery performance.

Description

Proton exchange membrane fuel cell electrode and preparation method thereof

technical field

The invention relates to a solid polymer proton exchange membrane fuel cell electrode and a manufacturing method thereof, in particular to a catalytic layer between a gas diffusion layer and a proton exchange membrane in a solid polymer proton exchange membrane fuel cell and a preparation method thereof.

Background technique

A proton exchange membrane fuel cell (PEMFC) is a power generation device that directly converts the chemical energy in fuel and oxidant into electrical energy through an electrochemical reaction. It uses a solid polymer membrane with good proton conductivity as the electrolyte. One side of the membrane is an anode composed of a catalytic layer and a gas diffusion layer, and the other side is a cathode composed of a catalytic layer and a gas diffusion layer. The layer is between the gas diffusion layer and the proton exchange membrane, and the electrode catalyst layer provides the electrochemical reaction. The anode, solid polymer electrolytic membrane and cathode are pressed together to form the core component of the proton exchange membrane fuel cell (PEMFC) - the membrane electrode three-in-one (MEA), and the two sides of the membrane electrode three-in-one are equipped with gas flow channels Graphite plates or surface-modified metal plates (bipolar plates) form single cells of proton exchange membrane fuel cells, and several to hundreds of single cells are stacked in a filter press to form a stack. A fuel such as hydrogen or reformed gas is supplied to the anode. When an oxidant such as oxygen or air is supplied to the cathode, an electrochemical reaction occurs on the membrane electrode three-in-one (MEA), and the chemical energy in the fuel and oxidant is directly converted into electrical energy.

When the anode uses hydrogen (H ₂ ) as the fuel and the cathode uses oxygen or air as the oxidant, the following electrode reactions occur respectively under the action of the electrode catalyst.

anode:

cathode:

It can be seen from the above formula that in the proton exchange membrane fuel cell (PEMFC), the necessary condition for the electrochemical reaction is not only the reaction substance, but also the supply, conduction and acceptance of protons and electrons. That is, the electrochemical reaction is carried out simultaneously on the three-phase interface of the reactant gas, proton conductor, and electron conductor. The electrode catalyst particles not only play a catalytic role, but also play the role of conducting electrons (electronic channels), and the polymer electrolyte plays the role of conducting protons ( proton channels). The fine pores in the electrode function as passageways for reactants (hydrogen (H ₂ ), oxygen (O ₂ )) and products (water (H ₂ O)). In order to obtain a three-phase interface in the anode and cathode, the electrode usually adopts a gas diffusion electrode composed of a gas diffusion layer and a catalytic layer.

Generally speaking, there are three methods for preparing the catalytic layer of the fuel cell electrode. One is to uniformly mix the carbon-supported metal active component (catalyst) with a certain amount of PTFE emulsion and solution and coat it on the gas diffusion layer, after roasting at a certain temperature, spray or immerse the Nafion solution on the surface of the catalytic layer, and then The anode and cathode electrodes with gas diffusion layer and catalytic layer and proton exchange membrane are hot-pressed under certain conditions to form a membrane electrode three-in-one (MEA).

The electrode prepared by this method is both hydrophilic and hydrophobic, with sufficient gas and water channels. However, the Nafion solution sprayed or immersed is usually difficult to be uniformly distributed inside the catalytic layer and fully contacted with the catalyst. In the catalytic layer, the solid polymer electrolyte is unevenly distributed. Therefore, the utilization rate of the catalyst is low.

The second is to uniformly mix the carbon-supported metal active component (catalyst) with a certain amount of solid polymer electrolyte solution and coat it on the gas diffusion layer, dry it at a certain temperature, and then put the anode with the gas diffusion layer and the catalytic layer And the cathode and the proton exchange membrane are hot-pressed under certain conditions to form a membrane electrode three-in-one (MEA). The electrode prepared by this method has hydrophilicity and is more suitable for proton exchange membrane fuel cells operating under normal pressure. For pressurized operation (>0.1MPa), the electrochemical reaction of the electrode catalytic layer produces mostly liquid water. If a hydrophilic electrode catalytic layer is used, the catalytic layer is easily "flooded" and the performance of the fuel cell, especially When the current density is high, the performance of the fuel cell drops significantly.

The third is to make the catalytic layer directly on the solid polymer proton exchange membrane. This kind of catalytic layer is usually a hydrophilic catalytic layer, and there is a phenomenon of "water flooding".

Wilson et al. [M.S.Wilson, S.Gottesfeld, J.Electro.Chem.Soc., 139(1992), L28] used Nafion as a binder without PTFE to prepare a hydrophilic electrode. Shin et al. [J.Power Sources 106 (2002), 146-152] mixed Pt/C with Nafion solution equivalent to 8wt.% of the catalyst to make a colloidal slurry and coated it on the diffusion layer, and sprayed it on the surface of the electrode catalyst layer. Electrodes were prepared in 25wt.% Nafion solution of Pt/C catalyst. Patent CN1349267A provides an electrode catalyst layer using Nafion as proton conductor and binder. The above-mentioned electrodes are all sintered at a low temperature of 80-150°C. The carbon-supported catalytic active component (catalyst) of this type of hydrophilic electrode is in good contact with Nafion, but there is no hydrophobe or hydrophobic group. Therefore, this type of electrode It is easy to "flood", thereby affecting the transfer or diffusion of reactants, and greatly reducing the performance of the fuel cell.

Contents of the invention

In order to overcome the "water flooding" problem existing in the above-mentioned fuel cell hydrophilic electrode catalytic layer, the object of the present invention is to provide a fuel cell electrode catalytic layer with both a hydrophilic structure and a hydrophobic structure, and to make the carbon-supported metal active A high-performance proton exchange membrane fuel cell electrode catalyst layer with components (catalysts) uniformly mixed and fully contacted, and a preparation method thereof. Improved transfer and diffusion of reactant gases and produced water enhances fuel cell performance, especially at high current densities.

In order to achieve the above object, the technical solution of the present invention provides a kind of preparation method of proton exchange membrane fuel cell electrode, and it comprises the following steps:

a) uniformly mixing the carbon-supported catalytically active component with a perfluorinated or partially fluorinated solid polymer electrolyte containing sulfonic acid groups to form a slurry;

b) making the slurry evenly on the surface of the gas diffusion layer to form an electrode precursor with a catalytic layer;

c) The electrode precursor with the catalytic layer is baked under the protection of an inert gas, so that the perfluorinated or partially fluorinated solid polymer electrolyte in the catalytic layer is partially decomposed and loses the sulfonate group to become a hydrophobic group, undecomposed Solid polymer electrolytes are hydrophilic;

d) making the electrode precursor obtained in step c) into an anode and a cathode as required;

e) Place the anode and cathode sheets obtained in step d) on both sides of the proton exchange membrane, and hot press to obtain a proton exchange membrane fuel cell electrode with uniform distribution of hydrophilic structure and hydrophobic structure, and fully having a three-phase reaction interface. .

In the preparation method, in the slurry in step a), the carbon-supported catalytic active component is one or one of Pt, Au, Ru, Rh, Ag, Ir, Pd, Co, Fe, Ti, Mn More than one mixed catalyst component; the loading amount of the catalytically active component is 20-80wt.%; the perfluorinated or partially fluorinated solid polymer electrolyte accounts for 5-50wt.% of the catalyst, preferably 10-35wt.%. .

In the preparation method, the step b) uniformly prepares the slurry on the surface of the gas diffusion layer, and the method includes spray coating, doctor blade coating or screen printing.

In the preparation method, the step c) is to bake the electrode precursor with the catalytic layer at 250-450°C, preferably 280-360°C, for 0.5-15 hours under nitrogen protection, preferably It is roasting for 1 to 10 hours.

In the preparation method, the gas diffusion layer is carbon paper or carbon cloth, and the carbon paper or carbon cloth is a proton exchange membrane fuel cell electrode support that has undergone hydrophobic treatment.

In the preparation method, one or both sides of the gas diffusion layer are leveled with carbon powder or carbon powder and a hydrophobic organic compound.

The preparation method further includes, after step c), naturally cooling the baked electrode precursor to room temperature, and then spraying a solid electrolyte with a Nafion content of 0.1-0.2 mg/cm ² on the surface of the catalytic layer.

For the proton exchange membrane fuel cell electrode produced by the preparation method, the thickness of the catalytic layer is 3-30 μm, preferably 5-25 μm.

In the proton exchange membrane fuel cell electrode, the catalytic layer is composed of a carbon-supported catalytic active component and a perfluorinated or partially fluorinated solid polymer electrolyte, wherein the perfluorinated or partially fluorinated solid polymer electrolyte accounts for 5-50 wt.%, preferably 10-35 wt.%, of the carbon-supported catalytically active component.

In the proton exchange membrane fuel cell electrode, the carbon-supported catalytic active component is one or more of Pt, Au, Ru, Rh, Ag, Ir, Pd, Co, Fe, Ti, Mn Mixed catalyst components; the loading amount of the catalytic active component is 20-80wt.%.

In the proton exchange membrane fuel cell electrode, the amount of platinum used in the cathode catalyst layer is 0.2-0.6 mg/cm ² , and the amount of platinum used in the anode catalyst layer is 0.1-0.3 mg/cm ² .

Effect of the present invention:

1. Roasting at high temperature decomposes the sulfonic acid group, so that the solid polymer electrolyte loses the sulfonate group, and the remaining organic groups are hydrophobic, so that the hydrophilic and hydrophobic pores are evenly distributed, providing a good gas transmission channel for the electrode and drainage channels.

2. Combining the advantages of the hydrophobic electrode and the thin-layer hydrophilic electrode, it makes up for the shortcomings of the two, expands the three-dimensional reaction area, increases the three-phase interface, and improves the electrode performance.

Below through embodiment and comparative example, in conjunction with accompanying drawing, technology of the present invention is given further description. However, the technology of the present invention is not limited to the examples.

Description of drawings

Fig. 1 is a graph showing H ₂ /Air VI curves of a single cell composed of a fuel cell electrode of the present invention and a three-in-one membrane electrode prepared by Nafion 1135 membrane and a single cell composed of a three-in-one membrane electrode prepared in a comparative example.

Fig. 2 is a graph showing the H ₂ /Air VI curves of a single cell composed of fuel cell electrodes baked at different temperatures and membrane electrodes made of Nafion 1135 membranes.

Fig. 3 is a single cell H ₂ /Air VI curve diagram of electrodes with different Nafion contents in the catalytic layer prepared by the fuel cell electrode preparation method of the present invention.

Detailed ways

The present invention will be further described below by way of embodiments and in conjunction with the accompanying drawings.

The electrode catalyst layer of the proton exchange membrane fuel cell provided by the invention adopts perfluorinated or partially fluorinated solid polymer electrolyte as proton conductor and binder. For example (but not limited to): perfluorosulfonic acid solid polymer electrolyte resin or partially fluorinated sulfonic acid solid polymer resin.

Proton exchange membrane fuel cell electrode catalytic layer provided by the present invention adopts the carbon powder that specific surface area is greater than 100m ² /g, such as (but not limited to) Vulcan XC-72, acetylene black, carbon powder such as black pearl as electron conductor (catalyst carrier) ), using one or more metal components in Pt, Au, Ru, Rh, Ag, Ir, Pd, Co, Fe, Ti, Mn as the catalytic active component, that is, using carbon-supported metal active components as a catalyst.

The proton exchange membrane fuel cell electrode catalytic layer provided by the invention and its preparation method are characterized in that solid polymer electrolyte and catalyst are uniformly mixed with well-known methods, such as (but not limited to) spraying, scraping or screen printing, etc. In the method, the fuel cell electrode catalyst layer is fabricated on the gas diffusion layer. After drying, it is roasted at a higher temperature for a certain period of time to decompose part of the sulfonate groups in the solid polymer electrolyte and lose the sulfonate groups to become hydrophobic organic groups. Thus, the hydrophilic phase with sulfonic acid groups and the hydrophobic phase without sulfonic acid groups are evenly distributed in the catalytic layer. It not only provides the transmission and diffusion channel of reaction gas, but also provides the transmission and diffusion channel of water (H ₂ O), reduces the ohmic resistance of the catalytic layer, and improves the utilization rate of the catalyst.

The perfluorinated or partially fluorinated solid polymer electrolyte in the catalyst layer slurry accounts for 5-50wt.% of the catalyst, preferably 10-35wt.%.

The electrode with the catalytic layer is baked at 250-450° C., preferably 280-360° C., for 0.5-15 hours, preferably 1-10 hours, under the protection of an inert gas.

The gas diffusion layer is made of carbon paper or carbon cloth, such as (but not limited to): carbon paper produced by TORAY or SGL. One or both sides of the carbon paper or carbon cloth used as the gas diffusion layer are leveled with carbon powder or a mixture of carbon powder and a hydrophobic organic compound.

Example 1:

After weighing an appropriate amount of catalyst, Nafion and solvent in a certain proportion, they are mixed by ball milling to form a uniformly mixed slurry, wherein the amount of Nafion resin is 7wt.%. Then, make this slurry on the surface of the gas diffusion layer through the leveling process by scraping to obtain the fuel cell electrode precursor containing the catalyst layer, and the usage amount of platinum (Pt) in the cathode catalyst layer is controlled at 0.2-0.6mg /cm ² , the amount of platinum (Pt) used in the anode catalytic layer is controlled at 0.1-0.3 mg/cm ² . After drying, bake at 330°C for 80 minutes under the protection of nitrogen (N ₂ ), then cool naturally to room temperature, and then spray a solid electrolyte with a Nafion content of 0.1-0.2 mg/cm ² on the surface of the electrode catalyst layer. Using Nafion 1135 membrane, the anode and cathode are placed on both sides of the Nafion 1135 membrane, and hot-pressed at 180°C to obtain a three-in-one membrane electrode. Add the anode and cathode flow field plates on both sides of the three-in-one membrane electrode, the current collector plate and the end plate to form a single cell. The above embodiment is just an example, and the present invention is not limited to this example.

Comparative example:

Weigh a certain amount of Pt/C catalyst, add an appropriate amount of PTFE emulsion and ethanol in proportion, mix evenly and apply it on the surface of the gas diffusion layer side that has been pre-hydrophobized and leveled. The amount of Pt used in the catalytic layer is 0.5mg/cm ² , after roasting at 390°C under the protection of nitrogen, spray Nafion solution on the surface of the electrode catalyst layer with a loading of 0.5mg/cm ² . The anode and cathode with the catalytic layer were placed on both sides of the Nafion 1135 membrane, and hot-pressed at 180°C to obtain a three-in-one membrane electrode.

Example 2:

According to the method of Example 1, after preparing the precursor containing the catalytic layer, the calcination temperatures were 280°C, 320°C, and 340°C respectively, and the membrane-electrode three-in-one and the single cell were prepared according to the method of Example 1.

Example 3:

According to the method of embodiment 1, the amount of Nafion resin in the catalytic layer is adjusted to 15wt.% and 30wt.% by the 7wt.% of embodiment 1 to prepare electrodes, and the method of embodiment 1 is used to prepare membrane-electrode three-in-one and single cell . Add the anode and cathode flow field plates on both sides of the three-in-one membrane electrode, the current collector plate and the end plate to form a single cell.

Claims (11)

1. A preparation method of a proton exchange membrane fuel cell electrode is characterized by comprising the following steps:

a) uniformly mixing a carbon-supported catalytic active component and a perfluorinated or partially fluorinated solid polymer electrolyte containing sulfonic groups to form slurry;

b) uniformly preparing the slurry on the surface of one side of a gas diffusion layer to form an electrode precursor with a catalyst layer;

c) roasting the electrode precursor with the catalytic layer under the protection of inert gas to enable the perfluoro or partially fluorinated solid polyelectrolyte in the catalytic layer to be partially decomposed and lose the sulfonate groups and become a solid polyelectrolyte with hydrophobic groups and undecomposed solid polyelectrolyte with hydrophilicity;

d) preparing the electrode precursor obtained in the step c) into an anode and a cathode according to requirements;

e) and d), placing the anode and cathode sheets obtained in the step d) on two sides of a proton exchange membrane, and carrying out hot pressing to obtain the proton exchange membrane fuel cell electrode which is uniform in distribution of a hydrophilic structure and a hydrophobic structure and fully has the characteristics of a three-phase reaction interface.

2. The method of claim 1, wherein: a) in the slurry, the carbon-supported catalytic active component is one or more mixed catalyst components of Pt, Au, Ru, Rh, Ag, Ir, Pd, Co, Fe, Ti and Mn; the loading amount of the catalytic active component is 20-80wt.%; the perfluoro or partially fluorinated solid polyelectrolyte accounts for 5-50 wt% of the catalyst, preferably 10-35 wt%.

3. The method of claim 1, wherein: and b) uniformly preparing the slurry on the surface of one side of the gas diffusion layer by spraying, blade coating or screen printing.

4. The method of claim 1, wherein: and c), roasting the electrode precursor with the catalytic layer for 0.5-15 hours, preferably for 1-10 hours at 250-450 ℃, preferably 280-360 ℃ under the protection of nitrogen.

5. The method of claim 1, wherein: the gas diffusion layer is carbon paper or carbon cloth which is an electrode support body of the proton exchange membrane fuel cell subjected to hydrophobization treatment.

6. The production method according to claim 1 or 5, characterized in that: one side or two side surfaces of the gas diffusion layer are leveled by carbon powder or carbon powder and hydrophobic organic compound.

7. The method of claim 1, wherein: after the step c), naturally cooling the roasted electrode precursor to normal temperature, and then spraying Nafion with the content of 0.1-0.2 mg/cm on the surface of the catalyst layer²The solid electrolyte of (1).

8. The proton exchange membrane fuel cell electrode manufactured by the manufacturing method according to claim 1, characterized in that: the thickness of the catalytic layer is 3-30 μm, preferably 5-25 μm.

9. The pem fuel cell electrode ofclaim 8 wherein: the catalyst layer is composed of a carbon-supported catalytic active component and a perfluorinated or partially-fluorinated solid polyelectrolyte, wherein the perfluorinated or partially-fluorinated solid polyelectrolyte accounts for 5-50 wt%, preferably 10-35 wt% of the carbon-supported catalytic active component.

10. The pem fuel cell electrode of claim 9 wherein: the carbon-supported catalytic active component is one or more mixed catalyst components of Pt, Au, Ru, Rh, Ag, Ir, Pd, Co, Fe, Ti and Mn; the loading amount of the catalytic active component is 20-80 wt.%.

11. The pem fuel cell electrode of claim 8 wherein: the usage amount of platinum in the cathode catalyst layer is 0.2-0.6 mg/cm²The usage amount of platinum in the anode catalyst layer is 0.1-0.3 mg/cm²。

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