CN114566653B - Non-uniform catalyst layer, membrane electrode and preparation method thereof - Google Patents

Abstract

The invention relates to the technical field of membrane electrodes, in particular to a non-uniform electrode catalyst layer for a fuel cell or an electrolytic cell, a membrane electrode and a preparation method thereof. The heterogeneous catalyst layer comprises at least two first catalyst layer films and second catalyst layer films which are sequentially spliced in the advancing direction of reaction gas flow; the first catalyst layer film comprises a first electrolyte layer and a first catalyst uniformly distributed in the first electrolyte layer; the second catalyst layer film comprises a second electrolyte layer and a second catalyst which is uniformly distributed in the second electrolyte layer; the catalytic activity site of the second catalyst layer membrane is greater than the catalytic activity site of the first catalyst layer membrane.

Description

Heterogeneous catalyst layer, membrane electrode and preparation method thereof

Technical Field

The invention relates to the technical field of membrane electrodes, in particular to a non-uniform electrode catalyst layer for a fuel cell or an electrolytic cell, a membrane electrode and a preparation method thereof.

Background

The adoption of sustainable clean energy technology is one of the necessary measures for improving the environment and realizing sustainable benign development of the human society; the storage, conversion and utilization of clean energy can help to reduce the influence of the traditional energy technology, solve various severe problems of the current energy, environment and the like, realize curve overtaking in the technical field of energy, and improve the serious dependence degree of China on external energy. The hydrogen energy and fuel cell technology is a solution with wide application prospect in the field of renewable energy, is an important component for constructing a clean energy society, and is an important ring of a clean energy system; the research, development and utilization of the method are more and more widely concerned and highly valued, the industrialization is initially started and gradually goes on the right track, and the method is a new strength and a new growth point in the national energy and economic development layout.

The fuel cell is a device for directly converting chemical energy into electric energy, has the characteristics and advantages of abundant and various fuel sources, high energy conversion efficiency, small environmental influence, zero emission or low emission, simple structure, strong operability, wide application range, quick response and the like, and is known as a novel efficient energy technology capable of replacing the traditional internal combustion engine and generator. The ion (including cation, anion or both) exchange membrane fuel cell adopting the solid electrolyte membrane has the advantages of low working temperature, high specific energy, compact structure, convenient maintenance, quick start, wide application range and the like, and has wide application prospect in the scenes of power supplies, mobile power supplies, standby power supplies and the like.

After the scientific workers have been making more than half century continuous efforts, the key technology of the ion exchange membrane fuel cell, especially the proton exchange membrane fuel cell (including various direct alcohol fuel cells), has been developed sufficiently, and the industrialization is gradually formed, but the large-scale commercial application still faces two main obstacles: i.e., the overall cost is too high, the system life needs to be further enhanced. The two problems are related to each other, and the main reason of high comprehensive cost is that the price of the core material required by the fuel cell is high, for example, noble metal platinum with high activity, high price and scarce resources is adopted as an electrode catalyst, and various ion conduction membranes with high price, especially proton exchange membranes and the like are adopted; the life limit of the fuel cell mainly comes from two aspects of catalyst and membrane electrode: the supported platinum catalyst has good activity, but poor electrochemical stability, and has the problems of metal particle aggregation, enlargement, loss, corrosion of a catalyst carrier and the like in long-term actual operation; the problems of drying, flooding, reduction of ionic conductivity, peeling of catalyst layers and the like caused by uneven distribution and uneven stress of products such as water, heat, electrons and the like in the working process of the membrane electrode can even have disastrous consequences such as perforation, tearing and the like of the membrane electrode.

A membrane electrode or a Membrane Electrode Assembly (MEA) of a fuel cell is mainly composed of an ion exchange membrane (also called a solid electrolyte membrane) and anode and cathode electrodes, wherein the anode and cathode electrodes are porous electrodes disposed on two sides of the solid electrolyte membrane, and the porous electrodes are composed of catalyst layers (an anode catalyst layer and a cathode catalyst layer) and respective gas diffusion layers. The electrode catalyst layer is the site of the electrochemical reaction, and its performance, especially long-term stability, is at the heart of controlling the performance and lifetime of the overall fuel cell system. The membrane electrode is the heart of the proton exchange membrane fuel cell, which not only determines the comprehensive performance of the fuel cell, but also determines the cost of the fuel cell due to the use of expensive platinum-based catalyst and ion exchange membrane, and plays a decisive role in the power density, the service life and the cost of the whole fuel cell system and the product application end.

There are various ways to realize the preparation or production of the membrane electrode, such as the traditional hot pressing method and the current CCM (catalyst-coated membrane) three-in-one method. The former method mainly comprises the steps of loading a cathode catalyst layer or an anode catalyst layer (cathode) on a gas diffusion layer (gas-diffusion layer) of the cathode or the anode respectively to form a complete electrode, clamping a solid electrolyte membrane by using a cathode and an anode, and combining the cathode catalyst layer and the anode catalyst layer together through hot pressing to form a sandwich structure similar to a sandwich, wherein patents US2010/0279196A1 and US5316871 and the like disclose preparation methods of membrane electrode assemblies of the type. The current mainstream CCM three-in-one membrane electrode is prepared by coating electrode catalyst layers on two side surfaces of a solid electrolyte membrane, respectively forming a cathode and anode catalyst layer (CCM, i.e., an electrolyte membrane with a catalyst coating or a catalyst layer loaded on the solid electrolyte membrane) on the surface of the solid electrolyte membrane, and combining the cathode and anode catalyst layers with gas diffusion layers on two sides of the cathode and anode in a manner of seal measurement and the like to form a five-layer structure of a Membrane Electrode Assembly (MEA), i.e., a middle proton exchange membrane, an anode catalyst layer and a cathode catalyst layer on two sides of the middle proton exchange membrane, and an anode gas diffusion layer and a cathode gas diffusion layer on the outer sides of the catalyst layers; in more complex structures, the catalyst layer or gas diffusion layer may further be composed of more layers, such as the membrane electrode assembly structure disclosed in U.S. Pat. No. 8,148,026.

The electrode catalyst layer of the membrane electrode mainly comprises an electrode catalyst, ion exchange resin (used as a solid electrolyte) and other additives, the adopted electrode catalyst comprises a platinum-based catalyst, a transition metal, a nitrogen-doped carbon-based non-noble metal catalyst and the like, the adopted solid electrolyte generally has the capability of conducting ions of the same kind with the adopted solid electrolyte membrane, and is generally consistent with the basic composition raw material of the solid membrane, and is made of the same material in most cases, but different substances are adopted and have the capability of transferring ions of the same kind. In addition, the electrode catalyst layer may further contain various additives such as pore-forming agents, oxides or composite materials, etc. to promote gas transmission, ionic or electronic conduction, and achieve drainage or moisture retention.

Currently, most widely used membrane electrodes with a high degree of commercialization are manufactured by CCM, i.e., a catalyst is directly or indirectly supported on a solid electrolyte membrane to form a three-in-one structure of a supported catalyst layer, as shown in fig. 1, a cathode catalyst layer 102 and an anode catalyst layer 103 are respectively disposed on both sides of a solid electrolyte membrane 101 in a fuel cell unit.

As is apparent from the published patents and documents, the CCM is mainly produced by a direct method in which a catalyst slurry is directly applied to the surface of a solid electrolyte membrane by a single or combined method such as printing, spraying, or coating, and an indirect method, and the methods are widely used, and there are known: US2010/0216052A1, JP2002280003, US5234777, US5316871 and the like. In the direct coating method, a catalyst slurry or a catalyst ink (ink) is often used, but patent publication, for example, CN1269428A discloses that a catalyst, an electrolyte resin, various binders and other additives are prepared in advance as a solid mixture, and then the solid mixture is directly sprayed on the surface of a solid electrolyte membrane to form a catalyst layer. The indirect CCM method is a method of applying a prepared catalyst slurry to a transfer medium film in advance by screen printing, doctor blading, spraying, printing, or the like to form a catalyst layer, and then transferring (printing) the catalyst layer to the surface of a solid electrolyte film by hot pressing or the like, and is an indirect method as disclosed in patents CN1560949, US5211984, US4272383, CN1263189C, CN269429A, US5415888, and the like. The indirect voltage conversion CCM method can avoid the direct contact between the solid electrolyte membrane and the solvent, avoid the problems of membrane swelling deformation and the like in the membrane electrode preparation process, ensure that the binding force between the catalyst layer and the solid electrolyte membrane is stronger, the catalyst layer is not easy to peel off, and is beneficial to prolonging the service life of the membrane electrode to a certain extent; however, the catalyst layer becomes dense due to the hot pressing process, and the like, and has a certain influence on gas transmission.

At present, catalyst layers of a cathode and an anode in a mainstream membrane electrode or a membrane electrode assembly are uniformly distributed, and the uniform distribution has two meanings:

one means that the distribution of the components constituting the catalyst layer and their mutual ratios are uniform and fixed everywhere in the catalyst layer facing or cross section, or should be uniform and fixed in theory according to the preparation target of the electrode catalyst layer. By each component constituting the catalyst layer is meant the electrode catalyst employed, the ion-conducting medium (i.e., the solid electrolyte), and any other component added when preparing the electrode catalyst slurry. When the catalyst layers of such membrane electrodes are composed of a plurality of catalyst layers, the contents of the respective species and the ratios thereof to each other in the three-dimensional directions of the catalyst layers of each layer are uniform.

By uniformly distributed second layer is meant that the various properties of each point within the layer due to the uniform distribution of the components within the catalyst layer described above are also uniformly distributed. Various properties of the so-called electrode catalyst layer include, but are not limited to, electron conducting property, ion conducting property, gas transporting property, liquid transporting property and affinity property, pore size and distribution in the catalyst layer, and the like. The term liquid includes, but is not limited to, liquid fuels or solutions thereof, liquid oxidants or solutions thereof, liquid electrode reaction products such as water and the like, and water added to humidify gaseous reactants, and the like.

The electrode catalyst layer with uniform distribution has the advantages of relatively simple preparation process, single material type and the like. The prepared electrode catalyst layer, the membrane electrode or the components thereof have no so-called 'head-tail' sequence limitation on the same side, namely, the electrode reactant feed end and the electrode reaction product discharge end in the same catalyst layer can be mutually exchanged for use, and the membrane electrode performance is basically not influenced. The electrode reactants of a so-called fuel cell include fuel and other reactants or additives entering the anode side, and oxidant and other reactants or additives entering the cathode side; the so-called electrode products include electrons (current distribution), ions, gases such as carbon dioxide, liquids such as water, heat, and the like; the electrode discharge end often also contains a portion of the reactants and additives that are not completely consumed, and so on.

However, in actual practice, the distribution of substances involved in the electrode reaction of the fuel cell, particularly electrode reaction products, is not uniform throughout the face and depth of the electrode catalyst layer on the same side, and such so-called non-uniformity includes the following meanings: on the one hand, the so-called uneven distribution of the electrode reaction products; on the other hand, the method means that the properties, stress and the like of each part in the electrode catalyst layer become non-uniform due to non-uniform distribution of products, and the wetting degree and ion conduction performance of each part in the membrane are different; in addition, due to the consumption of reactants, the dilution effect caused by reaction products such as water and carbon dioxide, etc., and the design and distribution of flow field channels are not ideal enough, and the distribution of reactants along the surface and the cross section of the electrode catalyst layer is also uneven caused by various factors such as the difference of the reactant transmission performance at each position in the electrode diffusion layer and the catalyst layer. This non-uniformity inside the membrane electrode, particularly inside the catalyst layer, is further exacerbated by the continued long-term operation of the fuel cell application, i.e., the continued progress of the electrode reaction. Meanwhile, as the accumulated water and the like on the local part of the flow field increase, the electrode catalyst layer can be locally over-wetted and even flooded in long-term operation; the other part may be partially dried, which may cause various problems such as peeling of the catalyst layer and the solid electrolyte membrane, loss of the catalyst, reduction of ion conductivity in the electrolyte membrane and the electrode catalyst layer, and reduction of electron conductivity of the electrode catalyst layer, and even may cause problems such as hole breaking and tearing of the solid electrolyte membrane, resulting in serious damage to complete failure of the fuel cell stack. The above problem is one of the direct reasons that the performance of the fuel cell power generation system is reduced and the stability and the life cannot reach the standard, and the root cause is that the electrode reaction distribution on the catalyst layer and in the interior is not uniform.

The uniform distribution of the products of the electrode reaction, particularly hydrothermal reaction and the like, is the key to greatly improve the service life and long-term stability of the fuel cell, but the uniform distribution of the reaction and the products is not enough only by the uniform distribution of reactants, and necessary modification needs to be made on the electrode structure, particularly a catalyst layer.

Disclosure of Invention

The invention aims to: aiming at the problem that substances related to the electrode reaction of the existing fuel cell, particularly electrode reaction products, are distributed unevenly on the surface and in the depth of the electrode catalyst layer on the same side, an uneven catalyst layer is provided. That is, in the membrane electrode assembly, the catalyst layers of the electrodes are non-uniformly distributed, and the use of the non-uniform catalyst layers takes advantage of the physical properties and properties of the catalyst layers to cope with non-uniform distribution of reactants and reaction environments, so that the chemical reactions of the electrodes in the fuel cell and the products thereof are uniformly distributed in the catalyst layers.

In order to achieve the purpose, the invention adopts the technical scheme that:

the heterogeneous catalyst layer comprises at least two first catalyst layer membranes and second catalyst layer membranes which are sequentially spliced in the advancing direction of reaction gas flow;

the first catalyst layer membrane comprises a first electrolyte layer and a first catalyst which is uniformly distributed in the first electrolyte layer; the second catalyst layer film comprises a second electrolyte layer and a second catalyst which is uniformly distributed in the second electrolyte layer;

the second catalyst layer membrane has more catalytically active sites than the first catalyst layer membrane in the same volume.

The heterogeneous catalyst layer comprises at least two catalyst layer films along the advancing direction of the reaction gas flow. The catalyst layers are arranged in sequence, so that the catalyst layers can be in an uneven state with gradually increased catalytic activity sites. The catalyst in each catalyst layer membrane is uniformly distributed.

The catalytically active sites in the catalyst layer membrane are usually expressed in terms of the amount of platinum or other major active component used per unit area (loading), usually in grams per square meter or milligrams per square centimeter.

The catalytic active site range of the catalyst layer, i.e., the amount of platinum used, is in the range of 0.01 to 1.0 mg per square centimeter. In the catalyst layer structure, the amount of platinum used per unit area or the catalytically active sites increases gradually along the direction of the gas flow, in particular the oxygen or air on the cathode side.

Dividing the whole catalyst layer area on each side of the membrane electrode into a plurality of different cells, wherein the catalyst layers in the cells are uniformly distributed, but the catalyst layers among the cells are not completely the same; when the area of each cell is as small as possible, the overall state is close to the ideal uneven state of gradual change.

Further, the hydrophobicity of the second catalyst layer membrane is greater than the hydrophobicity of the first catalyst layer membrane.

The hydrophobicity refers to the water repellency and the water flooding prevention of the catalyst layer membrane, and generally, in the single proton exchange membrane cell, the mass ratio of the catalyst to the proton exchange membrane resin in the catalyst layer, the chemical Equivalent Weight (EW) value of the proton exchange membrane resin used, and the type and amount of the hydrophilic compound or the hydrophobic compound added to the catalyst layer slurry determine the hydrophobic and hydrophilic characteristics of the catalyst layer. The hydrophobicity in the present invention is characterized by the contact angle of the water bead catalyst layer surface on the catalyst layer surface. In general, the greater the contact angle of the bead with the catalyst layer, the more hydrophobic the surface and the less hydrophilic.

The contact angle (hydrophobicity) of the catalyst layer ranges from 120 to 160 degrees, and the hydrophobicity, particularly the hydrophobicity of the catalyst layer on the cathode side, gradually increases in the gas flow advancing direction. In the present invention, the contact angle is measured on the surface of the catalyst layer film of the pressure transfer medium.

Further, the first catalyst and the second catalyst are both platinum-containing catalysts, and the platinum content of the second catalyst is greater than or equal to that of the first catalyst.

Further, the first catalyst is a platinum catalyst supported on a first carrier; the second catalyst is a platinum catalyst loaded on a second carrier;

the second carrier has a hydrophobicity greater than the hydrophobicity of the first carrier; the second carrier has an air permeability greater than or equal to the air permeability of the first carrier.

The porosity of the second support is greater than or equal to the porosity of the first support.

The porosity is the ratio of the total volume of micro-voids in the porous medium to the total volume of the porous medium, and generally, the higher the porosity of the material is, the better the air permeability of the material is. The porosity of the material can be determined by mercury porosimetry, densitometry, or isothermal desorption and desorption. In the invention, the porosity of the catalyst layers in different areas is obtained by measuring the catalyst layer membrane loaded on the pressure transfer medium by a mercury intrusion method. The porosity of the catalyst layer ranges from 30 to 60%, and the gas permeability thereof gradually increases in the direction of the gas flow.

The electrode catalyst used in the current proton exchange membrane fuel cell mainly comprises a carbon carrier and various metal materials including platinum, wherein the carrier materials have different properties such as pore structure and hydrophobicity due to different types of carbon carriers or different processing conditions. The carrier of the platinum-based electrode catalyst is subjected to acid washing and oxidation treatment in advance, and the hydrophilicity of the catalyst can be improved by performing sulfonation treatment on a catalyst product; on the contrary, if the carrier is subjected to high-temperature gas phase treatment, reduction treatment, graphitization, or the like in advance, or the catalyst is subjected to high-temperature treatment or the like, the hydrophobicity of the catalyst can be improved. In the catalyst layer, the hydrophobic catalyst is selected step by step in different catalyst layer regions along the gas advancing direction, particularly along the oxygen or air advancing direction on the cathode side.

Further, the first carrier is a first carbon carrier, and the second carrier is a second carbon carrier.

Further, the first electrolyte layer comprises a first type of proton exchange resin, and the second electrolyte layer comprises a second type of proton exchange resin;

the second type of proton exchange resin has a resin equivalent weight greater than or equal to the first type of proton exchange resin.

The chemical equivalent of a proton exchange resin monomer refers to the weight of polymer required to provide 1 mole of exchangeable protons, which is the reciprocal of the Ion Exchange Capacity (IEC). The chemical equivalent of the perfluorosulfonic acid resin used in the proton exchange membrane fuel cell at present is from 700 to 1200, and generally speaking, the lower the EW is, the more hydrophilic the resin is, and conversely, the more hydrophobic the resin is. When a high EW proton exchange resin is used in the catalyst layer, the catalyst layer will be more hydrophobic.

Furthermore, in each catalytic membrane layer, the mass ratio of the catalyst to the proton exchange resin is 1. The stoichiometric amount of the selected proton exchange resin is gradually increased along the advancing direction of the gas flow. The mass ratio of the first catalyst to the first type of proton exchange resin is 1. The mass ratio of the second catalyst to the second type of proton exchange resin is 1.

Further, when the same or similar EW proton exchange resin is used, the mass ratio of the second catalyst to the second type of proton exchange resin is larger than the mass ratio of the first catalyst to the first type of proton exchange resin; the general trend of this ratio in the area of successive splices along the direction of airflow progression is gradually increasing.

When using proton exchange resins having a large difference in EW, the mass ratio of the second catalyst to the second type of proton exchange resin should be greater than or equal to the mass ratio of the first catalyst to the first type of proton exchange resin. The general trend of this ratio in the area of successive splices along the direction of airflow progression is gradually increasing.

A heterogeneous membrane electrode comprising a proton conducting solid electrolyte membrane having a heterogeneous catalyst layer as described above disposed on at least one side of said solid electrolyte membrane, said heterogeneous catalyst layer being in close proximity to said solid electrolyte membrane.

A preparation method of the non-uniform membrane electrode comprises the following steps,

s1, preparing each catalyst layer membrane,

preparing slurry of each catalyst layer membrane according to a preset proportion;

coating the catalyst layer film slurry on the surface of a polytetrafluoroethylene film to form catalyst layer films;

s2, preparing a membrane electrode,

dividing a region in a predetermined shape on one side of the solid electrolyte membrane;

cutting each catalyst layer film into a shape corresponding to each region, and applying the cut catalyst layer film to the corresponding region;

hot pressing, bonding each catalyst layer membrane with the solid electrolyte membrane;

and removing each polytetrafluoroethylene membrane to obtain the membrane electrode.

Further, more specific steps are as follows,

firstly, according to the quantity and the requirement of the catalyst layer area division, respectively preparing different catalyst slurry, wherein each slurry respectively contains and adopts different types and quantities of electrocatalysts and types and quantities of proton exchange membrane resins, so that each slurry is different. If non-uniform catalyst layers are required on both sides of the membrane electrode, catalyst pastes are prepared in the corresponding regions, respectively.

And secondly, adopting the polytetrafluoroethylene membrane as a supporting surface and a pressure transfer medium, and respectively spraying different sizing agents on the surface of the polytetrafluoroethylene membrane to respectively form different catalyst layer membranes.

And thirdly, cutting the required catalyst layer films into corresponding shapes according to the divided areas, and pasting the catalyst layer films on the surfaces facing the proton exchange membrane. And respectively applying corresponding catalyst layer membranes to each area.

And fourthly, combining the catalyst layer membrane with the proton exchange membrane through hot pressing, and removing the polytetrafluoroethylene membrane on the back of each area catalyst layer to prepare the required heterogeneous membrane electrode.

Fifthly, one side of the non-uniform membrane electrode is a uniform catalyst layer, and the other side of the non-uniform membrane electrode is a non-uniform catalyst layer; the uniform catalyst layer and the non-uniform catalyst layer on the other side are prepared together by hot pressing; or the non-uniform catalyst layer and the uniform catalyst layer are sequentially and respectively loaded on two side surfaces of the proton exchange membrane.

In summary, due to the adoption of the technical scheme, the invention has the beneficial effects that:

the non-uniform catalyst layer of the invention adapts to the non-uniform reaction environment by forming the non-uniform membrane electrode, so that the electrode chemical reaction and the product thereof in the fuel cell are uniformly distributed in the catalyst layer, thereby achieving the purpose of prolonging the service life of the membrane electrode and realizing the high-efficiency utilization of the noble metal material.

Drawings

FIG. 1 is a structural schematic diagram of a membrane electrode structure, wherein a is a top view and b is a side view;

in FIG. 1, 101-electrolyte membrane; 102-a cathode catalyst layer; 103-anode catalyst layer; 201-battery test fixture; 202-middle membrane electrode assembly.

FIG. 2 is a schematic view of a proton exchange membrane fuel cell single cell testing fixture.

Fig. 2A is a schematic diagram of a pem fuel cell testing fixture 201 and a middle mea 202 (sealing frame not shown). Fig. 2B is a view of the side of the cell test fixture 201 facing the membrane electrode assembly 202.

In FIG. 2, 211-the fixture flow field; 212-clamp feed inlet; 214-clamp product discharge port; 213-Clamp fixation Port.

Fig. 3 is a schematic view of the structure of a non-uniform membrane electrode (cathode side) used in examples 2 and 3 of the present invention.

In FIG. 3, 21-proton exchange membrane; 22-cathode side catalyst layer; 221-intake corresponding point; 222-exhaust emission corresponding points; 223-cathode side first catalyst layer membrane; 224 — cathode side second catalyst layer membrane; 225-cathode side third catalyst layer membrane; 226 — cathode side fourth catalyst layer membrane.

Fig. 4 is a schematic view of a one-sided structure of the uniform membrane electrode in comparative example 4.

Fig. 5 is a polarization experiment result (current-voltage curve) of a pem fuel cell unit testing different membrane electrode assemblies.

FIG. 6 shows the life test results of the PEM fuel cell unit using a fuel cell without a MEA in example 3 and comparative example 4.

FIG. 7 is a schematic view showing the distribution of (a) different catalyst layer membranes on the anode side and (b) different catalyst layer membranes on the cathode side of the heterogeneous membrane electrode shown in example 6.

In FIG. 7, 310-proton exchange membrane;

anode side, 320 — catalyst layer on anode side; 321-the hydrogen inlet end corresponds to the position; 322-hydrogen tail gas output end corresponding position; 323 — anode side first catalyst layer membrane; 324-an anode side second catalyst layer membrane; 325-anode side third catalyst layer membrane; 326 — anode side fourth catalyst layer membrane;

cathode side, 420 — catalyst layer on cathode side; 421 oxygen (or air) enters the corresponding position of the end; 422-oxygen (or air) tail gas output end corresponding position; 423-cathode side first catalyst layer membrane; 424 — cathode side second catalyst layer membrane; 425-cathode side third catalyst layer membrane; 426-cathode side fourth catalyst layer membrane; 427-cathode side fifth catalyst layer membrane; 428-cathode side sixth catalyst layer membrane.

Detailed Description

The present invention will be described in detail below with reference to the accompanying drawings.

In order to more fully and clearly illustrate the properties, characteristics and effects of the non-uniform membrane electrode according to the present invention, the following detailed description will be given with reference to the accompanying drawings and examples to explain the specific design, implementation, structure, characteristics and effects of the non-uniform membrane electrode according to the present invention. In the description that follows, particular features, structures, or characteristics of one or more embodiments may be combined in any suitable manner. However, the following embodiments do not represent the whole content of the present invention and do not limit the whole content of the present invention, and particularly, the listed region division and the shape of each region are only examples for clearly expressing the core content of the present invention, and do not limit the application scope of the present invention. The non-uniform catalyst layers disclosed in the practice of the present invention may have smaller and more irregular zone shapes to accommodate more practical operating requirements of fuel cells or electrolyzers, achieving higher efficiency and better durability, based on certain catalyst layer preparation techniques and having more advanced equipment.

Example 1 proton exchange membrane fuel cell test fixture and test conditions

As shown in fig. 2, fig. 2A is a schematic diagram of a pem fuel cell testing fixture 201 and a middle mea 202 (sealing frame not shown). Fig. 2B is a view of the side of the cell test fixture 201 facing the mea 202, where the flow field 211 is used to transport a dispersed reactant gas (hydrogen, oxygen, or air) that enters the feed port 212 and exits the product discharge port 214; the fixture attachment port 213 is used to attach the battery test fixture 201. During testing, the membrane electrode assembly is sandwiched and fixed by the cell test jig 201.

Example 2

The heterogeneous membrane electrode comprises a proton exchange membrane 21, a cathode side catalyst layer 22 and an anode side catalyst layer. The catalyst layer on the anode side adopts a conventional uniform catalyst layer, and the catalyst layer on the cathode side is a non-uniform catalyst layer. The proton exchange resin selected was a Gore (Gore) reinforced membrane with a thickness of 15 microns.

The design and preparation of the cathode side heterogeneous catalyst layer 22 is as follows:

as shown in fig. 3, on one side of the proton exchange membrane 21, four regions are respectively divided along the direction from the air inlet end to the air outlet end of the air or oxygen: the entire cathode-side catalyst layer is rectangular, and four regions are formed by connecting the midpoint of the short side and the midpoint of the long side, and the diagonal lines. Preparing four different catalyst slurries respectively, spraying the catalyst slurries onto the surface of the PTFE membrane to form four catalyst layer membranes, and cutting out corresponding areas according to the designed shape, namely a cathode side first catalyst layer membrane 223, a cathode side second catalyst layer membrane 224, a cathode side third catalyst layer membrane 225 and a cathode side fourth catalyst layer membrane 226; the cathode side first catalyst layer film 223, the cathode side second catalyst layer film 224, the cathode side third catalyst layer film 225, and the cathode side fourth catalyst layer film 226 are applied to the proton exchange membrane 21 at an area ratio of 1:3:3:1. wherein the intake corresponding point 221 is located in the first catalyst layer film 223 area and the exhaust emission corresponding point 222 is located in the fourth catalyst layer film 226 area. The gas enters from the intake corresponding point 221, sequentially passes through the four cathode side catalyst layer membranes, and is discharged from the exhaust emission corresponding point 222.

The electrode catalyst used to prepare the cathode catalyst layer 22 was carbon-supported platinum nanoparticles (product of Johnson Matthey corporation), in which the platinum mass content was 40%; the proton-conducting resin used was a perfluorosulfonic acid resin (Kemu product)

EW 1100). In the present embodiment, the four regions of the cathode-side catalyst layer are mainly different in that: (1) The ratio of the electrode catalyst to the proton-conducting resin in the catalyst slurry used in the different regions is different; (2) The platinum usage (or loading) varies from zone to zone. The total solid mass ratio of the electrode catalyst to the Nafion resin in the entire cathode side catalyst layer was 2.1.

The preparation method is as follows,

s1, preparing slurry of each catalyst layer membrane according to a preset proportion;

coating the catalyst layer film slurry on the surface of a polytetrafluoroethylene film to form each catalyst layer film;

s2, preparing a membrane electrode,

dividing a region in a predetermined shape on one side of the solid electrolyte membrane;

cutting each catalyst layer film into a shape corresponding to each region, and applying the catalyst layer film to the corresponding region;

hot pressing, bonding each catalyst layer membrane with the solid electrolyte membrane;

and removing each polytetrafluoroethylene membrane to obtain the membrane electrode.

In the specific manufacturing method of this example, four different electrocatalyst slurries were prepared in advance using a mixed solvent of isopropanol and water (the volume ratio of isopropanol to water is 4. And dispersing all the catalyst slurry uniformly, and then respectively spraying the catalyst slurry on the surface of polytetrafluoroethylene to respectively form a cathode side first catalyst layer film, a cathode side second catalyst layer film, a cathode side third catalyst layer film and a cathode side fourth catalyst layer film for later use. And cutting the membrane according to the shapes of the four areas, tightly adhering the membrane to the surface of a Gore (Gore) reinforced membrane (15 microns), carrying out hot pressing at 140 ℃ for 2 minutes, and removing the polytetrafluoroethylene membrane to obtain the membrane loaded with the non-uniform cathode side catalyst layer.

Specific contents of electrocatalysts and resin ratios in different regions of the cathode side catalyst layer are shown in table 1, for example:

TABLE 1 information on the cathode side catalyst layer of the membrane electrode of example 2

A catalyst layer on the anode side is formed,

the catalyst used on the anode side of the membrane electrode is carbon-supported platinum nano particles (Johnson Matthey), wherein the mass content of platinum is 40%; the proton-conducting resin used is a perfluorosulfonic acid resin (C: (A)

EW 1100) wherein platinum was used in an amount of 0.1 mg/cm and the mass ratio of electrocatalyst to Nafion resin was 2. In this example, all the catalyst slurry was uniformly dispersed with a mixed solvent of isopropyl alcohol and water (the volume ratio of isopropyl alcohol to water was 4. Obtaining the heterogeneous membrane electrode.

Example 3

This example used the same proton exchange membrane and anode side catalyst layer as example 2. And the electrode catalyst layer was prepared in the same manner as in example 2. Except that the cathode side electrode catalyst layer information is as shown in table 2, in which the main change is that two platinum carbon catalysts were used, the mass contents of platinum of which were different; the total solid mass ratio of the total electrode catalyst to the total Nafion resin on the entire cathode side was about 2.0; the catalyst layer film thickness in the third and fourth region of the cathode side catalyst layer is reduced due to the use of a high platinum loading catalyst.

TABLE 2 information on cathode side catalyst layer of membrane electrode in example 3

Comparative example 4

A platinum-carbon catalyst (Johnson Matthey, platinum mass content 40%) was dispersed in a mixed solvent of isopropyl alcohol and deionized water (isopropyl alcohol to water volume ratio 4: 1), and a perfluorosulfonic acid resin solution (40% by mass of platinum) was added (b)

The mass content of the resin is 5%), the resin is uniformly dispersed by ultrasonic, uniform and single catalyst slurry is prepared, and then the catalyst slurry is loaded on a Gore membrane by a spraying technology to prepare a uniform membrane electrode; wherein the dosage of platinum in the anode catalyst layer (hydrogen side) is 0.1 mg/square centimeter, and the mass ratio of the electrocatalyst to the Nafion resin is 2; the cathode side cathode catalyst layer was 0.4 mg/cm, and the mass ratio of electrocatalyst to Nafion resin was 2.1.

Test example 5

The membrane electrode assemblies of example 2, example 3 and comparative example 4 were hot-pressed with carbon paper and a sealing frame to prepare a membrane electrode assembly, wherein the carbon paper used was SGL 38BC. The membrane electrode assembly was fixed in the single cell test fixture shown in example 1, wherein for the membrane electrode assemblies of examples 2 and 3, the cathode side first catalyst layer membrane 223 or point I of the gas inlet zone had to correspond to the oxygen inlet, and the cathode side fourth catalyst layer membrane 226 of the gas outlet zone had to correspond to the cathode off-gas outlet. Then hydrogen and oxygen are respectively introduced into the anode and the cathode, the back pressure is 0.2 atmosphere, wherein the hydrogen is humidified by 100 percent, the oxygen is not humidified, and the temperature of the battery and the humidification temperature are both 60 ℃. Each membrane electrode sample was previously activated at 0.8V, 0.7V, and 0.65V for 2 hours, and 4 hours, respectively, and then data was collected. And (3) data acquisition conditions: the cell test temperature is 60 ℃, the gas back pressure is 1 atmosphere, the flow rates of hydrogen and oxygen are 150 ml/min and 200 ml/min respectively, 100% of hydrogen is humidified, and oxygen is not humidified. In a voltage scanning polarization experiment, the voltage of a single cell is scanned to 0.25 volt from open circuit voltage, and the current is recorded; in the constant voltage polarization experiment, the output voltage of the single cell was fixed at 0.65 volts. The results of the experiment are shown in FIG. 5.

It can be seen from the experimental results of fig. 5 that the polarization performance of the single cell using the non-uniform membrane electrode is significantly better than that of the single cell using the uniform membrane electrode. The current density difference is about 20% under the potential of 0.7V; the highest output power density of single cells adopting two membrane electrodes can be different by about 37 percent, and the difference is obvious.

From the comparative test results of fig. 6, the difference in stability between the two membrane electrodes was not very significant in the short run, but the single cell current density of the non-uniform membrane electrode was still substantially stable at 0.7 a/cm after 75 hours; the output current density of the single cell adopting the uniform membrane electrode is slightly reduced to about 0.696 ampere/square centimeter from 0.7 ampere/square centimeter after continuous discharge for 60 hours. However, the latter has a large fluctuation in output current, which is manifested by a particularly large number of burrs on the curve, and this is caused by various factors in which water generated by reaction blocks the electrode gas transmission passage. The non-uniform membrane electrode is slightly better than the uniform membrane electrode in terms of operation stability.

Example 6

In this embodiment, the cathode catalyst layer and the anode catalyst layer on both sides of the proton exchange membrane are non-uniform catalyst layers. The multi-zone division is suitable for membrane electrodes with larger areas. The area division of the catalyst layers on both sides of the proton exchange membrane is shown in fig. 7, and the preparation process of the catalyst layer membrane is the same as that of example 2, except that a plurality of catalyst slurries need to be prepared.

As shown in fig. 7a, the hydrogen (anode) side electrode catalyst layer is divided into regions, and an anode side catalyst layer 320 is provided on a proton exchange membrane 310. The gas enters from the position 321 corresponding to the hydrogen inlet end, passes through the anode side first catalyst layer membrane 323, the anode side second catalyst layer membrane 324, the anode side third catalyst layer membrane 325 and the anode side fourth catalyst layer membrane 326 in sequence, and is discharged from the position 322 corresponding to the hydrogen off-gas outlet end. Wherein the anode side first catalyst layer film 323 and the anode side fourth catalyst layer film 326 are semicircular, and the radius thereof is half of the width of the catalyst layer; the anode side third catalyst layer film 325 and the anode side fourth catalyst layer film 326 have the same area. The information of the catalyst layer in each region of the anode is shown in table 3a, and the difference between the regions is mainly that two platinum-carbon catalysts are used, and the mass ratio of the electrocatalyst to the Nafion resin in each region is slightly different.

TABLE 3a information on the anode-side catalyst layer of the membrane electrode of example 6

Region marking	323	324	325	326
					Platinum content in platinum-carbon catalyst	40％	40％	60％	60％
Platinum dosage (mg/cm)	0.05	0.1	0.125	0.15
					Mass ratio of electrocatalyst to Nafion resin	1.5	2.0	2.0	3.0

As shown in fig. 7b, the cathode-side electrode catalyst layer area is divided, and a cathode-side catalyst layer 420 is provided on the back surface of the proton exchange membrane 310. Air or oxygen enters from the position 421 corresponding to the oxygen (or air) entering end, and passes through the cathode side first catalyst layer film 423, the cathode side second catalyst layer film 424, the cathode side third catalyst layer film 425, the cathode side fourth catalyst layer film 426, the cathode side fifth catalyst layer film 427, and the cathode side sixth catalyst layer film 428 in this order; and is discharged from the oxygen (or air) tail gas output end corresponding to the position 422.

Wherein the cathode side first catalyst layer film 423 and the cathode side sixth catalyst layer film 428 are semicircular in shape, and the radius thereof is one quarter of the width of the catalyst layer; the three double-dashed lines are at one-quarter, one-half, and three-quarters of the length of the catalyst layer region for dividing the other catalyst layer regions. The information of the catalyst layer of each region on the cathode side is shown in table 3b, and two kinds of platinum carbon catalysts are respectively used in each region, and the mass ratio of the electrocatalyst to the Nafion resin and the use amount of platinum in each region are gradually increased along the flow direction of oxygen (or air). Because different platinum-carbon catalysts are used and the ratio of the catalyst to the proton exchange resin is different in each region, the hydrophobicity (contact angle) and porosity of the catalyst layer film are different in each region.

TABLE 3b information on the cathode side catalyst layer of the membrane electrode of example 6

The above description is only exemplary of the present invention and should not be taken as limiting, and any modifications, equivalents, improvements, etc. made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (7)

1. The heterogeneous catalyst layer is characterized by comprising at least two first catalyst layer films and second catalyst layer films which are sequentially spliced in the advancing direction of reaction gas flow;

the first catalyst layer membrane comprises a first electrolyte layer and a first catalyst which is uniformly distributed in the first electrolyte layer; the second catalyst layer membrane comprises a second electrolyte layer and a second catalyst which is uniformly distributed in the second electrolyte layer;

the catalytic activity sites of the second catalyst layer membrane are more than the catalytic activity sites of the first catalyst layer membrane in the same volume;

the second catalyst layer membrane has a hydrophobicity that is greater than the hydrophobicity of the first catalyst layer membrane;

the first catalyst is a platinum catalyst supported by a first carrier; the second catalyst is a platinum catalyst loaded on a second carrier; the second carrier has a hydrophobicity greater than the hydrophobicity of the first carrier; the second carrier has a gas permeability greater than the gas permeability of the first carrier;

the first electrolyte layer comprises a first type of proton exchange resin and the second electrolyte layer comprises a second type of proton exchange resin; the second type of proton exchange resin has a resin equivalent weight greater than or equal to the first type of proton exchange resin.

2. The non-uniform catalyst layer according to claim 1, wherein the first catalyst and the second catalyst are both platinum-containing catalysts; the platinum content of the second catalyst is greater than or equal to the platinum content of the first catalyst.

3. The non-uniform catalyst layer as recited in claim 1, wherein the first support is a first carbon support and the second support is a second carbon support.

4. The non-uniform catalyst layer according to claim 1, wherein in each catalytic membrane layer, the mass ratio of the catalyst to the proton exchange resin is 1.

5. The non-uniform catalyst layer according to claim 4, wherein a mass ratio of the second catalyst to the second type of proton exchange resin is greater than a mass ratio of the first catalyst to the first type of proton exchange resin.

6. A heterogeneous membrane electrode comprising a proton conducting solid electrolyte membrane having at least one side provided with a heterogeneous catalyst layer according to any one of claims 1 to 5 in close proximity to said solid electrolyte membrane.

7. The method for preparing a non-uniform membrane electrode according to claim 6, comprising the steps of,

s1, preparing each catalyst layer membrane,

preparing slurry of each catalyst layer membrane according to a preset proportion;

coating the catalyst layer film slurry on the surface of a polytetrafluoroethylene film to form each catalyst layer film;

s2, preparing a membrane electrode,

dividing a region in a predetermined shape on one side of the solid electrolyte membrane;

cutting each catalyst layer film into a shape corresponding to each region, and applying the cut catalyst layer film to the corresponding region;

hot pressing, bonding each catalyst layer membrane with the solid electrolyte membrane;

and removing each polytetrafluoroethylene membrane to obtain the membrane electrode.

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