Patent Application
20240327583
The present disclosure relates to a method for manufacturing a gas diffusion layer for a fuel cell and to a gas diffusion layer for a fuel cell.
A polymer electrolyte fuel cell includes a fuel cell stack formed by stacking multiple single cells. Each single cell includes a membrane electrode assembly that includes a solid polymer electrolyte membrane (hereinafter, referred to as “electrolyte membrane”) and two catalyst layers sandwiching the electrolyte membrane, two gas diffusion layers sandwiching the membrane electrode assembly, an anode-side separator, and a cathode-side separator. The anode-side separator and the cathode-side separator sandwich the two gas diffusion layers.
As such a gas diffusion layer, Japanese Laid-Open Patent Publication No. 2022-42074 discloses a gas diffusion electrode. The gas diffusion electrode disclosed in this publication includes a sheet-shaped porous base and a microporous layer disposed in contact with one surface of the porous base. Examples of the porous base include carbon paper, carbon cloth, and carbon nonwoven fabric. The microporous layer is formed by coating one surface of the porous base with a paste-like coating liquid in which conductive fine particles, a binder, a solvent, a thickener, and the like are mixed and dispersed. The conductive particles are carbon black such as acetylene black having an average particle size in a range of 20 nm to 150 nm. The binder is, for example, polytetrafluoroethylene (PTFE).
There is a demand for such gas diffusion layers for fuel cells to be manufacturable by a simple method. In addition, there is a demand for further improvement of gas diffusion layers for fuel cells in regard to conductivity, gas diffusibility, and adjustment of water retention amount.
This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
In one general aspect, a method for manufacturing a gas diffusion layer for a fuel cell is provided. The method includes agitating a solution containing copper methylacetylide as a precursor to form wire-shaped structures of the precursor and entangle the wire-shaped structures in the solution, adding the precursor to a surface layer portion of a porous base sheet or a base sheet precursor so as to fill pores in the surface layer portion, and calcining the base sheet or the base sheet precursor and the precursor in a range of 1000° C. to 1200° C. to grow multilayer cavity walls of graphene and thermally remove copper, thereby forming a porous carbon that is composed of multilayer cavity walls of graphene and has mesoporosity and a hollow wire-shaped crystal structure.
In another general aspect, a method for manufacturing a gas diffusion layer for a fuel cell is provided. The method includes agitating a solution containing copper methylacetylide as a precursor to form wire-shaped structures of the precursor and entangle the wire-shaped structures in the solution, calcining the precursor in a range of 1000° C. to 1200° C. to grow multilayer cavity walls of graphene and thermally remove copper, thereby forming a porous carbon that is composed of multilayer cavity walls of graphene and has mesoporosity and a hollow wire-shaped crystal structure, pulverizing the porous carbon while maintaining the crystal structure, adding the porous carbon to a surface layer portion of a porous base sheet by applying or spraying a solution containing the pulverized porous carbon to the surface layer portion, thereby filling pores in the surface layer portion, and calcining the base sheet and the porous carbon to integrate the porous carbon with the base sheet.
In a further general aspect, a gas diffusion layer for a fuel cell includes a porous base sheet and a porous carbon that is integrally formed with the base sheet so as to fill pores in a surface layer portion of the base sheet. The porous carbon is composed of multilayer cavity walls of graphene and includes a structure in which hollow wire-shaped crystals having mesoporosity are entangled. Wire diameters of the crystals are in a range of 100 nm to 500 nm. Diameters of pores formed by the entangled crystals are in a range of 10 nm to 200 nm.
Other features and aspects will be apparent from the following detailed description, the drawings, and the claims.
Throughout the drawings and the detailed description, the same reference numerals refer to the same elements. The drawings may not be to scale, and the relative size, proportions, and depiction of elements in the drawings may be exaggerated for clarity, illustration, and convenience.
This description provides a comprehensive understanding of the methods, apparatuses, and/or systems described. Modifications and equivalents of the methods, apparatuses, and/or systems described are apparent to one of ordinary skill in the art. Sequences of operations are exemplary, and may be changed as apparent to one of ordinary skill in the art, except for operations necessarily occurring in a certain order. Descriptions of functions and constructions that are well known to one of ordinary skill in the art may be omitted.
Exemplary embodiments may have different forms, and are not limited to the examples described. However, the examples described are thorough and complete, and convey the full scope of the disclosure to one of ordinary skill in the art.
In this specification, “at least one of A and B” should be understood to mean “only A, only B, or both A and B.”
A gas diffusion layer for a fuel cell and a method for manufacturing a gas diffusion layer for a fuel cell according to a first embodiment will now be described with reference to
A polymer electrolyte fuel cell includes a fuel cell stack formed by stacking multiple single cells 10.
As shown in
As shown in
The base sheet 21 of the present embodiment is a carbon cloth having a fiber diameter of about 7 μm and pores of about 1 to 2 μm.
As shown in
As shown in
As shown in
The wire diameters of the crystals are in a range of 100 nm to 500 nm. The diameters of pores formed by the entangled crystals are in a range of 10 nm to 200 nm.
Next, a manufacturing procedure of the gas diffusion layer 20 of the present embodiment will be described with reference to
As shown in
The precursor synthesizing step is a step for synthesizing copper methylacetylide as a precursor by a known method.
The agitating step is a step for agitating a solution containing copper methylacetylide as a precursor to form wire-shaped structures, and to entangle the wire-shaped structures in the solution. Water is used as solvent. Adding a small amount of ethanol to the solvent facilitate stretching of the precursor.
In the agitating step, the wire-shaped structures of the precursor are formed by agitating the solution containing copper methylacetylide. At this time, in the subsequent heating step, the copper becomes spherical or elliptical due to the difference in specific gravity between copper and carbon, and the carbon becomes wires covering the copper. In addition, the wire-shaped structures of the precursor are entangled in the solution.
As shown in
In the adding step, the precursor 22A is added to the surface layer portion 21a by applying or spraying a solution containing the precursor 22A to the surface layer portion 21a. In the present embodiment, the phenol resin solution containing the precursor 22A is applied to the surface layer portion 21a of the base sheet 21, so that the solution penetrates into the pores in the surface layer portion 21a of the base sheet 21.
The drying step is a step for heating the precursor 22A added to the surface layer portion 21a of the base sheet 21 to a temperature in a range of 170° C. to 300° C. under vacuum to dry the precursor 22A. Accordingly, although phase separation of copper and carbon occurs, the shape of the precursor 22A is readily maintained.
The calcining step is a step for calcining the base sheet 21 and the precursor 22A in a range of 1000° C. to 1200° C. to grow multilayer cavity walls of graphene and thermally remove copper so as to form a porous carbon 22.
The calcining step is preferably performed under a pressure lower than normal pressure.
In the calcining step, the precursor 22A is calcined in a range of 1000° C. to 1200° C. together with the base sheet 21 so as to sublimate and remove copper. The copper in contact with a portion of the carbon of the precursor 22A melts at a temperature higher than or equal to 1000° C. At this time, an ideal two-dimensional surface of carbon is generated due to surface tension generated in the carbon, so that the carbon grows into multilayer cavity walls of graphene. This forms the porous carbon 22 that is composed of multilayer cavity walls of graphene and includes a structure in which hollow wire-shaped crystals having mesoporosity are entangled.
The melting point of copper is 1085° C. However, in a case of particles of sizes less than or equal to 50 nm, liquefaction of copper proceeds at 1000° C. or less due to the depression of melting point.
The present embodiment has the following advantages.
(1-1) The method for manufacturing the gas diffusion layer 20 includes the agitating step, the adding step, and the calcining step.
With this method, since the calcining temperature is in a range of 1000° C. to 1200° C., the calcining temperature is lowered as compared with, for example, a conventional manufacturing method in which silver methylacetylide is calcined at 2000° C. This allows the size of the calcining furnace and the energy required for calcination to be reduced.
In addition, copper is preferable to silver in order to grow thick multilayer cavity walls of graphene so as to increase conductivity.
Accordingly, the above-described method enables the acquisition of the gas diffusion layer 20, in which the pores of the surface layer portion 21a of the base sheet 21 are filled with the porous carbon 22, through simple steps. The porous carbon 22 functions as a microporous layer 23. Therefore, the gas diffusion layer 20 having the microporous layer 23 can be manufactured by a simple method.
(1-2) In the adding step, the precursor 22A is added to the surface layer portion 21a by applying or spraying a solution containing the precursor 22A to the surface layer portion 21a.
With this method, the precursor 22A is added to the surface layer portion 21a by applying or spraying a solution containing the precursor 22A to the surface layer portion 21a in the adding step. Accordingly, the precursor 22A is readily added to the surface layer portion 21a of the porous base sheet 21 so as to fill the pores in the surface layer portion 21a.
(1-3) The gas diffusion layer 20 includes the porous base sheet 21 and the porous carbon 22, which is formed integrally with the base sheet 21 so as to fill the pores in the surface layer portion 21a of the base sheet 21. The porous carbon 22 is composed of multilayer cavity walls of graphene and includes a structure in which hollow wire-shaped crystals having mesoporosity are entangled. The wire diameters of the crystals are in a range of 100 nm to 500 nm, and the diameters of the pores formed by the entangled crystals are in a range of 10 nm to 200 nm.
Since the porous carbon 22 is formed integrally with the base sheet 21, this configuration increases the rigidity of the porous carbon 22, although the porous carbon 22 itself is brittle. Also, since the porous carbon 22 is composed of multilayer cavity walls of graphene, the porous carbon 22 has a high conductivity. In addition, the wire diameters of the crystals are in a range of 100 nm to 500 nm, and the diameters of pores formed by the entangled crystals are in a range of 10 nm to 200 nm. The porous carbon 22 thus has a high gas diffusibility. Since water can be stored in and discharged from a great number of mesopores in the crystals, the porous carbon 22 is excellent in adjusting the water retention amount. The porous carbon 22 thus functions as the microporous layer 23. In a fuel cell, when protons move from the anode to the cathode, water functions as a carrier for transporting the protons. As described above, since the porous carbon 22 of the gas diffusion layer 20 is adjacent to the catalyst layer 12, the humidity of the catalyst layer 12 is regulated by the porous carbon 22. As a result, the amount of water in the catalyst layer 12 can be increased, which contributes to an improvement in the output of the fuel cell.
A second embodiment will now be described with reference to
As shown in
The sheet forming step is a step for forming the precursor 22A into a sheet-shaped precursor.
In the sheet forming step, the wire-shaped structures of the precursor 22A, which are entangled, are formed into a sheet-shaped precursor. Examples of the method for forming the wire-shaped structures of the precursor 22A into a sheet-shaped precursor include a method of filtering a solution containing the precursor 22A with filter paper to form a sheet on the filter paper, a method of applying the solution to a planar jig, and a method of spraying the solution onto a planar jig.
The drying step is a step for heating the sheet-shaped precursor to a temperature in a range of 170° C. to 300° C. under vacuum to dry the precursor. Accordingly, although phase separation of copper and carbon occurs, the shape of the precursor is readily maintained.
As shown in
After the adding step is performed, the calcining step is performed in the same manner as in the first embodiment.
The present embodiment has the following advantages.
(2-1) The method for manufacturing the gas diffusion layer 20 includes the sheet forming step for forming the precursor 22A into a sheet-shaped precursor. In the adding step, the sheet-shaped precursor 22A is pressed against the surface layer portion 21a in a state in which the sheet-shaped precursor 22A is overlaid on the surface layer portion 21a.
With this method, the precursor 22A having a uniform thickness is readily added to the surface layer portion 21a of the porous base sheet 21 so as to fill the pores in the surface layer portion 21a.
(2-2) Since the porous carbon 22 has a structure in which hollow wire-shaped crystals are entangled, the microporous layer 23 can be readily formed into a thin film. Forming the microporous layer 23 into a thin film reduces the resistance overvoltage of the microporous layer 23.
A third embodiment will now be described with reference to
As shown in
The precursor synthesizing step and the agitating step are the same as those in the first and second embodiments.
The first calcining step is a step for calcining a precursor in a range of 1000° C. to 1200° C. to grow multilayer cavity walls of graphene and thermally remove copper so as to form a porous carbon 22.
The first calcining step is preferably performed under a pressure lower than normal pressure.
The first calcining step is same as the calcining step according to the first embodiment in that copper is sublimated and removed by calcining the precursor 22A in a range of 1000° C. to 1200° C.
The pulverizing step is a step for pulverizing the porous carbon 22 while maintaining the crystal structure.
As shown in
The second calcining step is a step for calcining the base sheet 21 and the porous carbon 22 to integrate the porous carbon 22 with the base sheet 21.
The present embodiment has the following advantages.
(3-1) The method for manufacturing the gas diffusion layer 20 includes the agitating step, the first calcining step, the pulverizing step, the adding step, and the second calcining step.
With the above-described method, since the calcining temperature of the first calcining step is a range of 1000° C. to 1200° C., the calcining temperature is lowered as compared with, for example, a conventional manufacturing method in which silver methylacetylide is calcined at 2000° C. This allows the size of the calcining furnace and the energy required for calcination to be reduced.
In addition, copper is preferable to silver in order to grow thick multilayer cavity walls of graphene so as to increase conductivity.
Accordingly, the above-described method enables the acquisition of the gas diffusion layer 20, in which the pores of the surface layer portion 21a of the base sheet 21 are filled with the porous carbon 22, through simple steps. The porous carbon 22 functions as a microporous layer 23. Therefore, the gas diffusion layer 20 having the microporous layer 23 can be manufactured by a simple method.
The above-described embodiments may be modified as follows. The above-described embodiments and the following modifications can be combined if the combined modifications remain technically consistent with each other.
The fiber diameters of the carbon fibers forming the base sheet 21 and the sizes of the pores in the base sheet 21 can be changed.
The base sheet 21 is not limited to carbon cloth, and may be carbon paper or carbon nonwoven fabric.
In the first and second embodiments, copper methylacetylide as a precursor is added to the surface layer portion 21a of the base sheet 21 in the adding step. Thereafter, in the calcining step, the base sheet 21 and the precursor are calcined in a range of 1000° C. to 1200° C. Alternatively, copper methylacetylide as a precursor may be added to the surface layer portion of a base sheet precursor in the adding step. Thereafter, the base sheet precursor and the precursor may be calcined in a range of 1000° C. to 1200° C. in the calcining step. The base sheet precursor may be any type as long as it becomes a base sheet by being calcined, and is preferably, for example, a nonwoven fabric or paper made of polyacrylonitrile. Further, nonwoven fabric or paper made of cellulose may be used. In this case, the base sheet precursor is calcined to form a base sheet. Therefore, when the precursor is calcined, the base sheet precursor is calcined at the same time to form carbon paper or carbon nonwoven fabric as the base sheet.
Various changes in form and details may be made to the examples above without departing from the spirit and scope of the claims and their equivalents. The examples are for the sake of description only, and not for purposes of limitation. Descriptions of features in each example are to be considered as being applicable to similar features or aspects in other examples. Suitable results may be achieved if sequences are performed in a different order, and/or if components in a described system, architecture, device, or circuit are combined differently, and/or replaced or supplemented by other components or their equivalents. The scope of the disclosure is not defined by the detailed description, but by the claims and their equivalents. All variations within the scope of the claims and their equivalents are included in the disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-052312 | Mar 2023 | JP | national |
