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 catalyst 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
A Proton Exchange Membrane Fuel Cell (PEMFC) is a power generation device that directly converts chemical energy in a fuel and an oxidant into electrical energy through an electrochemical reaction. The membrane uses a solid polymer membrane with good proton conductivity as an electrolyte, one side of the membrane is an anode consisting of a catalytic layer and a gas diffusion layer, the other side of the membrane is a cathode consisting of the catalytic layer and the gas diffusion layer, namely, the catalytic layer is arranged between the gas diffusion layer and the proton exchange membrane, and the electrode catalytic layer provides electrochemical reaction. The anode, the solid polymer electrolyte membrane and the cathode are pressed together to form a core component of a Proton Exchange Membrane Fuel Cell (PEMFC) -membrane electrode triad (MEA), graphite plates or surface modified metal plates (bipolar plates) with gas flow channels are arranged on two sides of the membrane electrode triad to form single cells of the PEMFC, and a plurality of to hundreds of single cells are overlapped in a filter press mode to form a stack. Fuel such as hydrogen gas or reformed gas is supplied to the anode. When oxygen or air and other oxidants are supplied to the cathode,electrochemical reaction is generated on the membrane electrode three-in-one (MEA), and chemical energy in the fuel and the oxidants is directly converted into electric energy.
When the anode is filled with hydrogen (H)2) When oxygen or air is used as an oxidant for the cathode, the following electrode reactions occur in the cathode under the action of an electrode catalyst.
as can be seen from the above formula, in a Proton Exchange Membrane Fuel Cell (PEMFC), the electrochemical reaction is required to have supply, conduction, and transfer of protons and electrons, in addition to the reaction substance. That is, the electrochemical reaction is carried out simultaneously at three-phase interfaces of reactant gas, proton conductor and electron conductorThe electrode catalyst particles function both as a catalyst and as a conduction electron (electron channel), and the polymer electrolyte functions as a conductionProton (proton channel) function. Pores in the electrode act as a reactant (hydrogen (H)2) Oxygen (O)2) Water (H)), product (water (H)2O)) of a transfer channel. In order to obtain a three-phase interface in the anode and the cathode, a gas diffusion electrode composed of a gas diffusion layer and a catalytic layer is generally used as the electrode.
There are three general methods for preparing the electrode catalyst layer of the fuel cell. One is that the carbon-carried metal active component (catalyst) is mixed with a certain amount of PTFE emulsion and solution uniformly and then coated on a gas diffusion layer, after being roasted at a certain temperature, Nafion solution is sprayed or immersed on the surface of a catalyst layer, and then an anode electrode and a cathode electrode with the gas diffusion layer and the catalyst layer and a proton exchange membrane are hot-pressed under a certain condition to form membrane electrode three-in-one (MEA).
The electrode prepared by the method has both hydrophilicity and hydrophobicity, and has sufficient gas channels and water channels. But it is generally difficult to uniformly distribute the injected or immersed Nafion solution into the catalytic layer and to sufficiently contact the catalyst. In the catalyst layer, the solid polymer electrolyte is not uniformly distributed. Therefore, the catalyst utilization is low.
The other is that the carbon-carried metal active component (catalyst) is mixed with a certain amount of solid polymer electrolyte solution uniformly and then coated on the gas diffusion layer, dried at a certain temperature, and then the anode, the cathode and the proton exchange membrane with the gas diffusion layer and the catalyst layer are hot-pressed under a certain condition to form membrane electrode three-in-one (MEA). The electrode prepared by the method has hydrophilicity and is more suitable for a proton exchange membrane fuel cell running at normal pressure. In the case of pressurized operation (greater than 0.1MPa), most of the water generated by electrochemical reaction of the electrode catalyst layer is liquid water, and if the hydrophilic electrode catalyst layer is used, the catalyst layer is easily flooded by water, so that the performance of the fuel cell, especially the performance of the fuel cell at high current density, is greatly reduced.
And thirdly, the catalyst layer is directly manufactured on the solid polymer proton exchange membrane. Such catalytic layers are typically hydrophilic catalytic layers and suffer from a "flooding" phenomenon.
Wilson et al [ M.S. Wilson, S.Gottesfeld, J.electro.chem.Soc., 139(1992), L28]prepared a hydrophilic electrode using Nafion as a binder without the addition of PTFE. Shin et al (J.Power Sources 106(2002), 146-&152) mix Pt/C with Nafion solution corresponding to 8 wt.% of catalyst to make colloidal slurry, coat the colloidal slurry on the diffusion layer, and spray Nafion solution corresponding to 25 wt.% of Pt/C catalyst on the surface of electrode catalyst layer to make electrode. Patent CN1349267A provides an electrode catalyst layer using Nafion as proton conductor and binder. The electrodes are sintered at the low temperature of 80-150 ℃, and the carbon-supported catalytic active component (catalyst) of the hydrophilic electrode is better contacted with Nafion but has no hydrophobe or hydrophobic group, so the electrodes are easy to be flooded by water, thereby influencing the transfer or diffusion of reactants and greatly reducing the performance of the fuel cell.
Disclosure of Invention
In order to overcome the problem of 'flooding' of the hydrophilic electrode catalyst layer of the fuel cell, the invention aims to provide the high-performance proton exchange membrane fuel cell electrode catalyst layer and the preparation method thereof, wherein the electrode catalyst layer of the fuel cell has both a hydrophilic structure and a hydrophobic structure, and carbon-supported metal active components (catalysts) are uniformly mixed and fully contacted. Improves the transmission and diffusion of the reaction gas and the generated water, and improves the performance of the fuel cell, particularly the performance at high current density.
In order to achieve the above object, the technical solution of the present invention is to provide a method for preparing an electrode of a proton exchange membrane fuel cell, which comprises 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.
In the slurry in the step a), 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.%; the perfluoro or partially fluorinated solid polyelectrolyte accounts for 5-50 wt% of the catalyst, preferably 10-35 wt%.
The preparation method, wherein the slurry is uniformly prepared on the surface of one side of the gas diffusion layer in the step b), and the preparation method comprises spraying, blade coating or screen printing.
In the preparation method, in the step c), the electrode precursor with the catalyst layer is roasted for 0.5 to 15 hours, preferably for 1 to 10 hours, at the temperature of 250 to 450 ℃, preferably 280 to 360 ℃ under the protection of nitrogen.
In the preparation method, the gas diffusion layer is carbon paper or carbon cloth, and the carbon paper or the carbon cloth is a proton exchange membrane fuel cell electrode support body subjected to hydrophobization treatment.
According to the preparation method, one side or two sides of the surface of the gas diffusion layer are leveled by carbon powder or carbon powder and a hydrophobic organic compound.
The preparation method also comprises the step c), 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).
The thickness of the catalytic layer of the proton exchange membrane fuel cell electrode manufactured by the preparation method is 3-30 μm, and preferably 5-25 μm.
The catalyst layer of the proton exchange membrane fuel cell electrode 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% of the carbon-supported catalytic active component, and preferably 10-35 wt%.
The carbon-supported catalytic active component of the proton exchange membrane fuel cell electrode 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.%.
The usage amount of platinum in the cathode catalyst layer of the proton exchange membrane fuel cell electrode is0.2-0.6 mg/cm2The usage amount of platinum in the anode catalyst layer is 0.1-0.3 mg/cm2。
The invention has the following effects:
1. roasting at high temperature to decompose the sulfonic group to make the solid polymer electrolyte lose the sulfonic group, and the residual organic group has hydrophobicity, so that hydrophilic pore channels and hydrophobic pore channels are uniformly distributed, and good gas transfer channels and water drainage channels are provided for the electrodes.
2. The advantages of the hydrophobic electrode and the thin-layer hydrophilic electrode are integrated, the defects of the hydrophobic electrode and the thin-layer hydrophilic electrode are overcome, the three-dimensional reaction area is expanded, the three-phase interface is increased, and the electrode performance is improved.
The technique of the present invention will be further described below by way of examples and comparative examples, with reference to the accompanying drawings. The techniques of this disclosure are not limited to the embodiments.
Drawings
FIG. 1 shows a unit cell consisting of a fuel cell electrode and a membrane electrode made of Nafion1135 membrane and a unit cell H consisting of a membrane electrode made of a comparative example2V-I plot of Air.
FIG. 2 shows a single cell H consisting of a fuel cell electrode calcined at different temperatures and a membrane electrode prepared from a Nafion1135 membrane2V-I plot of Air.
FIG. 3 is a single cell H of an electrode with different Nafion contents in the catalytic layer prepared by the fuel cell electrode preparation method of thepresent invention2V-I plot of Air.
Detailed Description
The invention is further illustrated by the following examples 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 a proton conductor and a binder. For example (but not limited to): perfluorosulfonic acid solid polymer electrolyte resin or partially fluorinated sulfonic acid solid polymer resin.
The electrode catalyst layer of the proton exchange membrane fuel cell provided by the invention adopts a specific surface area of more than 100m2The carbon powder/g, such as (but not limited to) Vulcan XC-72, acetylene black, black pearl, etc. carbon powder is used as an electronic conductor (catalyst carrier), and one or more metal components selected from Pt, Au, Ru, Rh, Ag, Ir, Pd, Co, Fe, Ti, Mn is used as a catalytic active component, i.e. a carbon-supported metal active component is used as a catalyst.
The electrode catalyst layer of proton exchange membrane fuel cell and the preparation method thereof provided by the invention are characterized in that the electrode catalyst layer of the fuel cell is manufactured on the gas diffusion layer by a known method, such as (but not limited to) spraying, blade coating or screen printing and the like after the solid polymer electrolyte and the catalyst are uniformly mixed. Drying and roasting at a higher temperature for a certain time to decompose part of sulfonic acid groups in the solid polyelectrolyte so that the sulfonic acid groups are lost and become hydrophobic organic groups. Therefore, the hydrophilic phase with sulfonic acid group and the hydrophobic phase without sulfonic acid group in the catalyst layer are distributed uniformly. Providing both a reaction gas transfer and diffusion path and water (H)2O), and reduces the ohmic resistance of the catalyst layer, and improves the utilization rate of the catalyst.
The perfluoro or partially fluorinated solid polyelectrolyte in the catalyst layer slurry accounts for 5-50 wt%, preferably 10-35 wt% of the catalyst.
The electrode with the catalytic layer is roasted for 0.5 to 15 hours, preferably for 1 to 10 hours at the temperature of 250-450 ℃ and preferably at the temperature of 280-360 ℃ under the protection of inert gas.
The gas diffusion layer is made of carbon paper or carbon cloth, for example (but not limited to): carbon paper manufactured by TORAY corporation or SGL corporation, and the like. One or both side surfaces of carbon paper or carbon cloth used as a gas diffusion layer are leveled with carbon powder or a mixture of carbon powder and a hydrophobic organic compound.
Example 1:
weighing a proper amount of catalyst, Nafion and a solvent according to a certain proportion, and then carrying out ball milling and mixing to prepare uniformly mixed slurry, wherein the amount of Nafion resin is 7 wt.%. Then, the slurry is prepared on the surface of the gas diffusion layer after leveling treatment by a blade coating method to obtain a fuel cell electrode precursor containing a catalytic layer, wherein the usage amount of platinum (Pt) in the cathode catalytic layer is controlled to be 0.2-0.6 mg/cm2The amount of platinum (Pt) used in the anode catalyst layer is controlled to be 0.1-0.3 mg/cm2. After drying, nitrogen (N) at 330 ℃2) Roasting for 80 minutes under protection, naturally cooling to normal temperature, and then spraying Nafion on the surface of the electrode catalyst layer withthe content of 0.1-0.2 mg/cm2The solid electrolyte of (1). And (3) adopting a Nafion1135 membrane, placing the anode and the cathode on two sides of the Nafion1135 membrane, and carrying out hot pressing at 180 ℃ to obtain the membrane electrode three-in-one. The anode and cathode flow field plates, collector plate and end plate are added to the three sides of membrane electrode to form single cell. The above embodiments are merely examples, and the present invention is not limited thereto.
Comparative example:
weighing a certain amount of Pt/C catalyst, adding a proper amount of PTFE emulsion and ethanol according to a proportion, uniformly mixing, coating on the surface of one side of a gas diffusion layer subjected to pre-hydrophobization treatment and leveling treatment, wherein the use amount of Pt in a catalyst layer is 0.5mg/cm2Baking at 390 ℃ under the protection of nitrogen, and spraying Nafion solution on the surface of the electrode catalyst layer, wherein the supported amount is 0.5mg/cm2. And placing the anode with the catalytic layer and the cathode on two sides of a Nafion1135 membrane, and carrying out hot pressing at 180 ℃ to obtain the membrane electrode assembly.
Example 2:
after the precursor containing the catalyst layer was prepared according to the method of example 1, the calcination temperatures were 280 ℃, 320 ℃, 340 ℃, and the three-in-one and single-cell membrane electrodes were prepared according to the method of example 1.
Example 3:
electrodes were prepared by the method of example 1 by adjusting the amount of Nafion resin in the catalytic layer from 7 wt.% of example 1 to 15 wt.% and 30 wt.% and a membrane electrode triad and single cell were prepared by the method of example 1. The anode and cathode flow field plates, collector plate and end plate are added to the three sides of membrane electrode to form single cell.