CA1075308A - Electrolyte reservoir for a fuel cell - Google Patents
Electrolyte reservoir for a fuel cellInfo
- Publication number
- CA1075308A CA1075308A CA283,132A CA283132A CA1075308A CA 1075308 A CA1075308 A CA 1075308A CA 283132 A CA283132 A CA 283132A CA 1075308 A CA1075308 A CA 1075308A
- Authority
- CA
- Canada
- Prior art keywords
- facing surface
- catalyst
- impregnations
- reservoir layer
- layer
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/02—Details
- H01M8/0289—Means for holding the electrolyte
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
Abstract
ELECTROLYTE RESERVOIR FOR A FUEL CELL
ABSTRACT OF THE DISCLOSURE
An electrolyte reservoir layer disposed behind and adjacent one of the catalyst layers of a fuel cell is porous and hydrophilic to the electrolyte. In one embodiment the reservoir layer includes impregnations of hydrophobic material to provide reactant gas passages through the reser-voir layer to the catalyst layer, Additionally the reservoir layer includes impregnations of a material similar to the fuel cell electrolyte retaining matrix material to improve electrolyte transfer from the matrix into the reservoir.
The impregnations of hydrophobic material are designed to provide good distribution of the reactant gas into the catalyst layer without consuming a large volume of the reservoir. In a preferred embodiment the reservoir is also the electrode substrate whereby the catalyst layer is bonded to the surface thereof.
ABSTRACT OF THE DISCLOSURE
An electrolyte reservoir layer disposed behind and adjacent one of the catalyst layers of a fuel cell is porous and hydrophilic to the electrolyte. In one embodiment the reservoir layer includes impregnations of hydrophobic material to provide reactant gas passages through the reser-voir layer to the catalyst layer, Additionally the reservoir layer includes impregnations of a material similar to the fuel cell electrolyte retaining matrix material to improve electrolyte transfer from the matrix into the reservoir.
The impregnations of hydrophobic material are designed to provide good distribution of the reactant gas into the catalyst layer without consuming a large volume of the reservoir. In a preferred embodiment the reservoir is also the electrode substrate whereby the catalyst layer is bonded to the surface thereof.
Description
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BACKGROUND OF THE INVENTION
Field of the Invention - This invention relates to fuel cells, and more particularly to electrolyte volume control within a fuel cell.
Description of the Prior Art - In a fuel cell, electro-lyte is disposed between a pair of spaced apart electrodes.
The electrodes often comprise a substrate and a catalyst;
the substrate is provided simply to carry the catalyst and must be designed such that during operation the catalyst is in continuous contact with the electrolyte. The electrode must also be constructed to permit the reactant, such as gaseous hydrogen, to enter the substrate and also contact the catalyst. In the prior art it is generally ~onsidered that a three phase intPrface is formed between the reactant gas, the catalyst, and the electrolyte, at which Flace the electrochemical reaction occurs. Many early electrodes, such as those used in the cells described in U.S. Patents 2,969,315 and 2,928,783 used porous nickel e]lectrodes wherein the catalyst was distributed uniformly throughout the thickness of the entire electrode. These early cells incorporated a circulating electrolyte so that the water could be either added or removed external of the cell, thereby maintaining a relatively constant volume of electrolyte within the cell.
In any event, small changes in electrolyte volume simply changed the location o the three-phase interface within the electrode swbstrate.
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BACKGROUND OF THE INVENTION
Field of the Invention - This invention relates to fuel cells, and more particularly to electrolyte volume control within a fuel cell.
Description of the Prior Art - In a fuel cell, electro-lyte is disposed between a pair of spaced apart electrodes.
The electrodes often comprise a substrate and a catalyst;
the substrate is provided simply to carry the catalyst and must be designed such that during operation the catalyst is in continuous contact with the electrolyte. The electrode must also be constructed to permit the reactant, such as gaseous hydrogen, to enter the substrate and also contact the catalyst. In the prior art it is generally ~onsidered that a three phase intPrface is formed between the reactant gas, the catalyst, and the electrolyte, at which Flace the electrochemical reaction occurs. Many early electrodes, such as those used in the cells described in U.S. Patents 2,969,315 and 2,928,783 used porous nickel e]lectrodes wherein the catalyst was distributed uniformly throughout the thickness of the entire electrode. These early cells incorporated a circulating electrolyte so that the water could be either added or removed external of the cell, thereby maintaining a relatively constant volume of electrolyte within the cell.
In any event, small changes in electrolyte volume simply changed the location o the three-phase interface within the electrode swbstrate.
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, ' 7S3~8 Later cells went to a noncirculating or trapped electrolyte disposed in a matrix sandwiched between the electrodes, In these cells water produced during operation is removed by evaporating it into one of the reactant gas streams. In order to reach ~he reactant gas stream water vapor must be able to pass through the electrode, yet one could not permit the electrode to completely fill with liquid since this might prevent the reactant gas from entering the electrode to react with the electrolyte at the catalyst sites. Efforts to avoid this type of problem resulted in the development o biporous electrodes. One such biporous electrode is described in U.S. Patent
, ' 7S3~8 Later cells went to a noncirculating or trapped electrolyte disposed in a matrix sandwiched between the electrodes, In these cells water produced during operation is removed by evaporating it into one of the reactant gas streams. In order to reach ~he reactant gas stream water vapor must be able to pass through the electrode, yet one could not permit the electrode to completely fill with liquid since this might prevent the reactant gas from entering the electrode to react with the electrolyte at the catalyst sites. Efforts to avoid this type of problem resulted in the development o biporous electrodes. One such biporous electrode is described in U.S. Patent
3,077,508 beginning at line 2 of co~umn 4. As described therein, the biporous structure generally includes a large pore layer on the gas contacting side and a small or fine pore layer on the electrolyte contacting side. The fine pore layer would necessarily be activated with a catalyst.
This might also be true of the large pore layer, although it is not a requirement. The high capillary action in the fine pore layer strongly held the electrolyte, while the large pore layer would remain relatively free from electrolyte and would therefore always permit the reactant gas to enter the electrode substrate~ The electrochemical reaction took place at approximately the boundary between ; the large and small pore layers wherein a three-phase interface exists. However, the small pore layers of these early cells were generally very thin such that other provisions were required for electrolyte volume changes~
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In an electrode having a catalyst uniformly distributed throughout the substrate it does not matter if, for example, the electrolyte fills half or three-quarters of the elec-trode thickness since there is always catalyst a~ the boundary between the electroly~e and reac~nt gas. Thus, it is only necessary that the reactant gas be able to penetrate through the portion of the electrode not illed with electrolyteO However, electrochemical activity only occurs at the three-phase interface, and catalyst not disposed at that interface does not react and is virtually being wasted. Further development led to electrodes wherein the catalyst was not dispersed througout the entire substrate, but was rather applied as a very thin layer to the surface of the substrate adjacent the elec~
trolyte. In that type of electrode it is required that there always be gas passageways extending all the way through the substrate to the catalyst layer. In order to ensure that the reactant gas reaches ~he catalys~ layer, it has always been considered necessary to use a hydrophobic substra~e which cannot hold significant electrolyte and therefore cannot block the passage of reactant gas through the substrate to the catalyst layer. This is the most common - type of electrode in use today. However, in noncirculating . ., electrolyte type cells, it is still necessary to remove excess water by evaporating it into one of the reactant gas streams and/or to be able to store exces6 electrolyte ,
This might also be true of the large pore layer, although it is not a requirement. The high capillary action in the fine pore layer strongly held the electrolyte, while the large pore layer would remain relatively free from electrolyte and would therefore always permit the reactant gas to enter the electrode substrate~ The electrochemical reaction took place at approximately the boundary between ; the large and small pore layers wherein a three-phase interface exists. However, the small pore layers of these early cells were generally very thin such that other provisions were required for electrolyte volume changes~
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In an electrode having a catalyst uniformly distributed throughout the substrate it does not matter if, for example, the electrolyte fills half or three-quarters of the elec-trode thickness since there is always catalyst a~ the boundary between the electroly~e and reac~nt gas. Thus, it is only necessary that the reactant gas be able to penetrate through the portion of the electrode not illed with electrolyteO However, electrochemical activity only occurs at the three-phase interface, and catalyst not disposed at that interface does not react and is virtually being wasted. Further development led to electrodes wherein the catalyst was not dispersed througout the entire substrate, but was rather applied as a very thin layer to the surface of the substrate adjacent the elec~
trolyte. In that type of electrode it is required that there always be gas passageways extending all the way through the substrate to the catalyst layer. In order to ensure that the reactant gas reaches ~he catalys~ layer, it has always been considered necessary to use a hydrophobic substra~e which cannot hold significant electrolyte and therefore cannot block the passage of reactant gas through the substrate to the catalyst layer. This is the most common - type of electrode in use today. However, in noncirculating . ., electrolyte type cells, it is still necessary to remove excess water by evaporating it into one of the reactant gas streams and/or to be able to store exces6 electrolyte ,
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volume some place within the cell, particularly at shutdown when ~he water vapor within the gas streams condenses to a liquid. With hydrophilic substrates the condensed water vapor would increase the volume of the electrolyte and may form a film of liquid on ~he backside or inside the sub-strate which acts as a barrier to gas flow through the sub-strate when the cell is put back into operation.
Solutions to the above disrussed problems are shown and described in commonly owned U.S. Patents 39779,811 and 3,905,832. In the former patent a porous electrolyte reservoir plate (ERP) is disposed in the reactant gas passage and is spaced from the electrode. Porous pins provide electrolyte communication between the porous plate and the electrode. The electrolyte volume of the cell is controlled by electrolyte movement through the pins of the porous plate, thereby stabilizing the electrochemical performance of the cell and preventing flooding of the electrodeO Note that in the embodiment described therei~
the electrode comprises"a conductive nickel s~reen embedded in a uniform admixture of platinum plus polytetrafluoro-ethylene particles thereby making the electrode basically hydrophobic. In the '832 patent hydrophilic material is , .
disposed behind and in contact with a hydrophobic elec-trode substrate to act as an electrolyte reservoir.
- Communication between the reservoir material and the elec-trolyte matrix is provided by, for example, holes through the electrode filled with a hydrophilic material or by . .
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leaving discrete portions of the electrode substrate hydro-philic ~o provide wicking paths between the electrolyte matrix and the reservoir material. In this manner excess electrolyte has a place to go without significantly affecting the flow of gas through the hydrophobic areas of the sub-strate.
While the inventions described in the foregoing two patents work well, they have certain drawbacks. One draw-back is increased cell thickness. Another is the increase in IR losses due to either reduced contact between the elec-trode and separator plate or by ~he addition of additional material through which the electric current must pass.
Increased cost is another problem; this i5 not only due to the cost of the reservoir layer or material itself, but may also include increased electrode fabrication costs, such as would be required with the invention described in the '832 patent.
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SUMMARY OF THE INVENTION
An object of the present invention is a fuel cell which can accommodate changes in electrolyte volume without flooding or drying out.
According to the present invention, an electrolyte .,.' reservoir layer for use adjacent the catalyst layer of a fuelcel?lis hydrophilic; a large portion but not all of the :~
catalyst facing surface of the reservoir layer is impregnated with hydrophobic material to a shallow depth. The reservoir ~7~i3~3 layer also includes additional nonelectrolyte retaining portions distributed substantially uniformly throughout the reservoir layer leading from the noncatalyst facing surface to ~he hydrophobic material a~ the other surface. Nonhydro-phobic areas of the catalyst facing surface are impregnated with electrolyte matrix material to a substantial depth but in an amount only sufficient to fill a minor portion of the remaining hydrophilic volume of the reservoir layer.
Unlike electrochemical cells of the prior art, there is no need for separate hydrophobic and hydrophilic layers behind the catalyst. In this invention a large portion of the reservoir layer remains hydrophilic and can retain excess electrolyte. The nonelectrolyte retaining portions permit reactant flow to the catalyst layer adjacent the reservoir layer. The hydrophobic rnaterial which impregnates the catalyst facing surface permits diffusion of the reactant gas over a large area of the catalyst layer. The volume of the reservo~r layer impregnated with matrix ma~erial will have a pore size similar to that of the electrolyte matrix and somewhat smaller than the pore size of the surrounding nonimpregnated hydrophilic areas; this aids wleking of the electrolyte from the matrix into the reservoir and better ;~ distributes the excess electrolyte throughout the reservoir.
Preferably the matrix material extends from the matrix through the reservoir layer such that it is exposed to the reactant gas behind the reservoir layer; under certain , ' ' . ' .
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conditions this construction helps wick excess liquid in the gas path back into the electrolyte matrix.
Some electrode substrate materials, such as carbon paper, which are highly desirable for use as phosphoric acid electrolyte reservoirs for phosphoric acid cells due to their inertness in the acid and good electrical properties, lose their hydrophilic characteristics with time~ Thus, if the reservoir layer were carbon paper, the hydrophilic portions might become hydrophobic with time and the reservoir would 0 lose its capability to store electrolyte. In the present invention part of the hydrophilic portions of the reservoir layer are impregnated with matrix material. Good matrix materials, such as silicon carbide, do not become hydrophobic with time. Thus, another advantage of the present invention is that at least the areas of the reservoir layer impregnated with the matrix material will always remain hydrophilic~
It is also contemplated that the reservoir layer also functions as an e]ec~rode substrate, wherein the catalyst layer is disposed on the surface thereof and is bonded thereto.
~0 In accordance with an embodiment of the invention there is provided an electrolytic reserve reservoir layer for use adjacent the catalyst layer of a fuel cell, said reservoir layer being porous and including a catalyst facing surface - and a non~catalyst facing surface, said ca~alyst facing sur-face including first impregnations of hydrophobic material to a shallow depth over a major portion of its area, said catalyst facing surface also including uniformly distributed areas not - impregnatëd with hydrophobic material, said reservoir layer also including uni~ormly distributed nonelectrolyte retaining ;O portions leading from said noncatalyst facing surface to said impregnations of hydrophobic material at said other surface, said nonelectrolyte retaininy portions comprising only a . ~ .
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small portion of the volume of said reservoir layer9 said reservoir layer being hydrophilic in all portions other than said nonelectrolyte retaining portlons and said first lmpreg-nations, said reservoir layer also including impregnations of an electrolyte retaining matrix material extending from said areas of said catalyst facing surface not impregnated with hydrophobic material into said hydrophilic portions, said matrix material impregnating less than half of said hydro-philic port.ionsO
From a different aspect, and in accordance with an embodiment of the invention, there is provided, a fuel cell electrode comprising an electrolyte reservoir layer and a catalyst layer, said reservoir layer being porous and including a catalyst facing surface and a noncatalyst facing surface, said catalyst facing surface including first impregnations of hydrophobic material to a shallow depth over a major portion of its area, said catalyst facing surface also including uniform-ly distributed areas not impregnated with hydrophobic material, said reservoir layer further including uniformly distributed nonelectrolyte retaining portions leading from said noncat-alyst facing surface to said impregnations of hydrophobic material at said other surtace, said nonelectrolyte retaining portions comprising only a small portion of the volume of said ¦
reservoir layer, said reservoir layer being hydrophilic in all portions other than said nonelectrolyte retaining portions and said first impregnations, said reservoir layer including impregnations of an electrolyte retaining matrix material ex-tending from said areas of said catalyst facing surface not impregnated with hydrophobic material into said hydrophilic portions, said matrix material impregnating less than half `
of said hydrophilic portions, said catalyst layer being bonded to said catalyst facing surface and including holes there-a -n : ,.. .. ...... .
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through in communication with said impregnations of electro-lyte retaining matrix materialO
In a more specific embodiment there is provided, in a fuel cell comprising an electrolyte retaining matrix9 an anode catalyst layer disposed on one side of and in contact with said matrix and a cathode catalyst layer disposed on the other side of and in contact with said matrix, the improvement comprising: an electrolyte reservoir layer in contact with the nonmatrix facing side of at least one of said catalyst layers, said reservoir layer being porous and including a catalyst facing surface and a noncatalyst facing surface, said catalyst facing surface including first impregnations of hydrophobic material to a shallow depth over a major portion .- of its area, said catalyst facing surface also including uniformly distributed areas not impregnated with hydrophobic material9 said reservoir layer also including second impreg-nations of hydrophobic material leading from said noncatalyst ; facing surface to said first impregnations of hydrophobic : material 9 said second impregnations comprising only a small portion of the volume of said reservoir. layer, said reservoir layer being hydrophilic in all portions okher than said first and second impregnations9 said reservoir layer including third impregnations of a material essentially the same as the material of said matrix9 said third impregnations extending from said areas of said catalyst facing surface not impregnated with hydrophobic material into said hydrophilic portions, said third impregnations impregnating less than half of said hydrophilic portions, said hydrophilic portions having substantially no : pores smaller than the largest pores of said matrix.
- 30 Ihe foregoing and other objects, features9 and advan-tayes of the present invention will become more apparent in the :
light of the following detailed description of preferred embodi~
: ~ ments thereof as illustrated in the accompanying drawing.
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BRIEF DESCRIPTION OF THE DRAWING
Fig. 1 is a transverse sectional view of an electro-chemical cell incorporating the present invention, Fig. 2 is a sectional view taken along the line 2-2 of Fig. 1.
Fig. 3 is a sectional view taken along the line 3-3 of Fig. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As an exemplary embodiment of the present invention ; 10 consider the eLectrochemical cell 10 as shown in Figs. 1-3. ~;
` The cell includes a fuel or anode electrode 12, a cathode electrode 14, an electrolyte retaining matrix 16 sandwiched between the electrodes, and walls 18, 20 spaced from the electrodes 12, 14 and defining a fuel space 22 behind the anode electrode 12 and an oxidant space 24 behind the cathode 14. In a typical stack of fuel cells, wherein the individual cells are connected electrically in series, the . . . .
walls 18, 20 may be elect~ically conductive separa~or plates having fuel flowing on one side thereof feeding the anode electrode of one cell and having oxida~t flowing on the other side thereof feeding the cathode electrode of the adjacent cell, Such constructions are well ~nown to those skilled in the art.
The cathode electrode 14 comprises a substrate 26 and ~` a catalyst layer 28 bonded to the surface thereof. In this j .:
particular embodiment the cathode electrode 14 is simply a . . .:
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gas diffusion electrode of well known design. For example, assuming that the electrolyte in this embodiment is phosphoric acid, the catalyst layer may comprise an admix-: ture of carbon supported platinum particles and polytetra-fluoroethylene (PTFE). The PTFE binds the catalyst particles :; together and also prevents the catalyst layer from becoming ~ flooded with electrolyte to the exclusion of the reactant gas necessary for the electrochemical reaction. The sub-strate 26 may be porous carbon paper impregnated with PTFE
to make it basically hydrophobic so that it cannot completely fill wikh electrolyte and prevent reactant gas from reaching the catalyst layer 28.
. The anode electrode 12 comprises a catalyst layer 30 and an electrolyte reservoir layer 32. The catalyst layer 30 .~ is bonded to the reservoir layer 32 at the surface 34. The ; reservoir layer 32 is made from porous material which is ` hydrophilic to the electrolyte or which has been treated so that it is hydrophilic to the electrolyte. For ex~ample, it may be made from carbon paper if the electrolyte is phosphoric acid; or it may be a porous plaque made of silver felt metal, sintered powered silver, gold or other metal if the electrolyte is a base such as potassium hydroxide. The pores of the reservoir layer ma~erial should be no smaller than and preferably somewhat larger than the largest pores of the matrix 16 so that only excess electrolyte wicks into and is stored in the reservoir layer 32.
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The surface 34, adjacent the catalyst layer 30, is impregnated to a depth A over a major portion of its area with a hydrophobic matèrial or wetproofing agent such as PTFE. This hydrophobic portion is designated by the numeral 36 (Figs. 1 and 2) and in this embodiment is only interrup~ed by small circular nonwetproofed areas 37.
The reservoir layer 32 also includes a plurality of columns 38 of hydrophobic material leading from the non-.
; catalyst facing surface 40 of the reservoir layer 32 to the hydrophobic portion 36. Since the reservoir layer 32 will always be at least partially filled with electrolyte, the columns 38 and portion 36 guarantee a clear path for the reactant gas or fuel to reach the catalyst layer 30.
Also, the gas will diffuseradially outwardly from the columns 38 into the hydrophobic portion 36 thereby being distributed over a large area of catalyst. The hydrophobic area of the surface 34 should be as large as possible so as to maximize utilization of the catalyst in the layer 30.
Probably at least 50 percent of the surface will have to be wetproofed in order to obtain satisfactory catalyst ;
utilization and cell performance, although greater than 90% is preferred With regard to the maximum amount of area which may be wetproofed, the limiting factor is that the nonwetprooed areas 37 (Fig. 2) must have enough surface area to permit ready transfer of the electrolyte between the matrix 16 and the hydrophilic portions 41 of '''" ~
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the r~servoir layer 32. It is estimated that at least about 2 percent of the surface area of the surface 3~ will have to remain nonwetproofed. Also, the nonwetproofed - areas 37 should be uniformly distributed over the surface 34;
however, the shape of the nonwetproofed areas 37 is not critical. For example, the hydrophobic portion 36 may instead be a plurality of separate rectangular areas with the nonwetproofed areas being the spaces between the rectangles and forming an interconnecting grid.
From the point of view of weight, siæe~ and perhaps cost, it is desirable to make the reservoir layer 32 as thin as possible, yet thick enough to absorb and hold the maximum amount of excess liquid which the cell may be ` expected to produce. With this in mind, it is apparent that the volume of the nonelectrolyte retaining portions (i.e., columns 38 and hydrophobic portion 36) should be as small as possible. Thus, the depth A of the portion 36 should be no greater than is necessary to permit rea~y radial diffusion of the reactant gas from the columns 38 into the portion 36. A minimum of about 3 mils in depth will probably be required; however, depths of up to 50 percent of the reservoir layer thickness may be acceptable in some instances. In order that sufficient reactant gas reaches the catalyst layer 30, it is estimated that the sum of the minimum cross-sectional areas of the columns 38 .
should be at least about 2%:of the total area-~of the surface 40.
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/.i 53~t8 As a further aspect of the present invention the reservoir layer includes an impregnation of matrix material 42 extending from the nonwetproofed areas 37 at th~ surface 34 into the hydrophilic portion 41. The catalyst lay~er 30 includes holes 44 corresponding to the areas 37; these holes are filled with matrix material such ~hat there is a continuous path of matrix material from the surface 46 of the matrix 16 to the surface 40 of the reservoir layer 32.
The holes 44 may remain empty, but this is not preferred.
The portion of the reservoir layer impregnated with matrix material will have a somewhat reduced pore size which will be similar to that of the electrolyte matrix 16. It will be the first portion of the reservoir layer ~o fill with excess electrolyte and aids in the distribution of excess electrolyte throughout the surrounding hydrophilic regions of the reservoir layer.
Since impregnation of the reservoir layer with matrix material somewhat reduces the pore size and thus the volume of electrolyte which can be stored, it is preferred that less than half of the hydrophilic portion 41 be impregnated.
Furthermore~ in this embodiment the impregnation of matrix material extends to the surface 40 to aid wicking of liquid from the fuel space to the matrix 16. This is preferred but not required~ and the invention is not to ke construed ; as limited thereto.
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It should also be understood that the matrix 16 may include a binder as well as the basic matrix material. For example, a typical silicon carbide matrix composition may be 96% silicon carbide powder plus 4% PTFE binder, such as des-cribed in Canadian patent application Serial No. 256,211 filed on July 2, 1976. Impregnation of the reservoir layer with the matrix material preferably includes only enough binder to keep the material in the reservoir layer during operation. This may be less binder than used in the matrix itself, One way of making the reservoir layer 32 is to mask the areas 37 of the surface 34 and apply an aqueous solution of the hydrophobic material to the nonmasked areas, such as by screen printing. For example, if the reservoir layer is carbon paper having a thickness of 13 mils, a mean pore size of 41 microns, and 75% of its pores have`a size of from 19-85 microns, the printing ink may have a composition consisting of 225 grams TFE-30, 265 grams of a 2% aqueous solution of Carbopo ~ 934~
500 grams H20 and 8 ml NH40H 28% solution. TFE-30 is made by Dupont and comprise~ about 60% polytetrafl~oroethylene, 34%
; 20 H20 and 6% surfactant, by weight. Carbopol 934 is a powder ~ade by B. F. Goodrich, when mixed with NH40H, a neutrali~ing agent, a neutral salt is formed which is the thickening agent~ The - ~H40M iq added after the other ingredients have been combined and stirred so that air bubbles are not present.
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The columns 38 could be simllariy printed using a less vi~cous ink by masking the appropri~te areas o~ the surface 40. Fcr example, assumlng the same carbon paper substrate a~ mentioned above, the ~nk may have a compo~ition consi~ting o 625 gram~ TFE-30, 660 grams o~ a 2~/o aqueous solution of Carbopol 934, 1190 grams H20 and 20 ml N~140H 28% solution, Impregnating the reservoir layer with matrix material 4~ ~ay also be done by screen prlnting, but may require printlng from the gas facing surface 40 as well a from the catalyst facing sur.~ace 34. An ink composition which may be used for this purpose to impregnate the carbon paper mentioned above consists of 1800 grams of a 1% aqueous solu-tion of polyethylene oxide such as Polyo~ made by Union Carbide Corporation, 2940 grams S~k~ I 1000 grit green ~ silicon carbide powder from Carbo:rundum Co., 700 grams `` Teflon 3170 which ~ s an aqueous suspension of polyt~tra- -fluoroethylene plus suxactant made by Dupont,and 3S5 ml H20. Tke holes 44 can be f~llad by the screen printing proces~ after ~he cataly~t layer has been applied to the surface 34.
When screen printing is used, the depth to which the ink solutlon impregnates the reservoir layer is controlled :- by th~ viscosit~ of the ink and the ~umber o~ passes made ~urlng the screen printing proces.q. Inklng vehicles and other unde~irable volatile ingred~ents such as surfactants are ~ubsequently volatil~zed during sintering of the catalyst layer.
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' ~7536:~8 AlthDugh in the embodiment of Fig. 1 the reservoir layer 32 acts as a sl-bstrate for the catalyst layer 30 which may be applied thereto such as by spraying, filtering, printing or other suitable means, it should be apparent ~o those having ordinary skill in the art that the matrix 16 may be used as the catalyst layer substrate rather than the reser-voir layer 32. Thus, the catalyst layer 30 may be applied and bonded to the matrix 16 and simply be in intimate con-tact with but not bonded to the surface 34 of the reservoir layer.
As will also be obvi~us to those having ~rdinary skill in the art 3 the substrate 26 of the cathode electrode 14 may be replaced by a reservoir layer similar to or identical to the reservoir layer 32. However, this additional reservoir volume is usually not requiredO If only:a single reservoir layer is to be used, it is preferred that it be on the anode side of the cell since the anode is more tolerant to reduced availability of hydrogen than the cathode is ~o reduced availability of oxygen.
Although the invention has been shown and described with respect to a preferred embodiment thereof, it should be understood by those skilled in the art that other various :
changes and omissions in the orm and detail thereof may be made therein without departing from the spirit and the scope of the invention.
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volume some place within the cell, particularly at shutdown when ~he water vapor within the gas streams condenses to a liquid. With hydrophilic substrates the condensed water vapor would increase the volume of the electrolyte and may form a film of liquid on ~he backside or inside the sub-strate which acts as a barrier to gas flow through the sub-strate when the cell is put back into operation.
Solutions to the above disrussed problems are shown and described in commonly owned U.S. Patents 39779,811 and 3,905,832. In the former patent a porous electrolyte reservoir plate (ERP) is disposed in the reactant gas passage and is spaced from the electrode. Porous pins provide electrolyte communication between the porous plate and the electrode. The electrolyte volume of the cell is controlled by electrolyte movement through the pins of the porous plate, thereby stabilizing the electrochemical performance of the cell and preventing flooding of the electrodeO Note that in the embodiment described therei~
the electrode comprises"a conductive nickel s~reen embedded in a uniform admixture of platinum plus polytetrafluoro-ethylene particles thereby making the electrode basically hydrophobic. In the '832 patent hydrophilic material is , .
disposed behind and in contact with a hydrophobic elec-trode substrate to act as an electrolyte reservoir.
- Communication between the reservoir material and the elec-trolyte matrix is provided by, for example, holes through the electrode filled with a hydrophilic material or by . .
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leaving discrete portions of the electrode substrate hydro-philic ~o provide wicking paths between the electrolyte matrix and the reservoir material. In this manner excess electrolyte has a place to go without significantly affecting the flow of gas through the hydrophobic areas of the sub-strate.
While the inventions described in the foregoing two patents work well, they have certain drawbacks. One draw-back is increased cell thickness. Another is the increase in IR losses due to either reduced contact between the elec-trode and separator plate or by ~he addition of additional material through which the electric current must pass.
Increased cost is another problem; this i5 not only due to the cost of the reservoir layer or material itself, but may also include increased electrode fabrication costs, such as would be required with the invention described in the '832 patent.
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SUMMARY OF THE INVENTION
An object of the present invention is a fuel cell which can accommodate changes in electrolyte volume without flooding or drying out.
According to the present invention, an electrolyte .,.' reservoir layer for use adjacent the catalyst layer of a fuelcel?lis hydrophilic; a large portion but not all of the :~
catalyst facing surface of the reservoir layer is impregnated with hydrophobic material to a shallow depth. The reservoir ~7~i3~3 layer also includes additional nonelectrolyte retaining portions distributed substantially uniformly throughout the reservoir layer leading from the noncatalyst facing surface to ~he hydrophobic material a~ the other surface. Nonhydro-phobic areas of the catalyst facing surface are impregnated with electrolyte matrix material to a substantial depth but in an amount only sufficient to fill a minor portion of the remaining hydrophilic volume of the reservoir layer.
Unlike electrochemical cells of the prior art, there is no need for separate hydrophobic and hydrophilic layers behind the catalyst. In this invention a large portion of the reservoir layer remains hydrophilic and can retain excess electrolyte. The nonelectrolyte retaining portions permit reactant flow to the catalyst layer adjacent the reservoir layer. The hydrophobic rnaterial which impregnates the catalyst facing surface permits diffusion of the reactant gas over a large area of the catalyst layer. The volume of the reservo~r layer impregnated with matrix ma~erial will have a pore size similar to that of the electrolyte matrix and somewhat smaller than the pore size of the surrounding nonimpregnated hydrophilic areas; this aids wleking of the electrolyte from the matrix into the reservoir and better ;~ distributes the excess electrolyte throughout the reservoir.
Preferably the matrix material extends from the matrix through the reservoir layer such that it is exposed to the reactant gas behind the reservoir layer; under certain , ' ' . ' .
i3~D~
conditions this construction helps wick excess liquid in the gas path back into the electrolyte matrix.
Some electrode substrate materials, such as carbon paper, which are highly desirable for use as phosphoric acid electrolyte reservoirs for phosphoric acid cells due to their inertness in the acid and good electrical properties, lose their hydrophilic characteristics with time~ Thus, if the reservoir layer were carbon paper, the hydrophilic portions might become hydrophobic with time and the reservoir would 0 lose its capability to store electrolyte. In the present invention part of the hydrophilic portions of the reservoir layer are impregnated with matrix material. Good matrix materials, such as silicon carbide, do not become hydrophobic with time. Thus, another advantage of the present invention is that at least the areas of the reservoir layer impregnated with the matrix material will always remain hydrophilic~
It is also contemplated that the reservoir layer also functions as an e]ec~rode substrate, wherein the catalyst layer is disposed on the surface thereof and is bonded thereto.
~0 In accordance with an embodiment of the invention there is provided an electrolytic reserve reservoir layer for use adjacent the catalyst layer of a fuel cell, said reservoir layer being porous and including a catalyst facing surface - and a non~catalyst facing surface, said ca~alyst facing sur-face including first impregnations of hydrophobic material to a shallow depth over a major portion of its area, said catalyst facing surface also including uniformly distributed areas not - impregnatëd with hydrophobic material, said reservoir layer also including uni~ormly distributed nonelectrolyte retaining ;O portions leading from said noncatalyst facing surface to said impregnations of hydrophobic material at said other surface, said nonelectrolyte retaininy portions comprising only a . ~ .
~53~
small portion of the volume of said reservoir layer9 said reservoir layer being hydrophilic in all portions other than said nonelectrolyte retaining portlons and said first lmpreg-nations, said reservoir layer also including impregnations of an electrolyte retaining matrix material extending from said areas of said catalyst facing surface not impregnated with hydrophobic material into said hydrophilic portions, said matrix material impregnating less than half of said hydro-philic port.ionsO
From a different aspect, and in accordance with an embodiment of the invention, there is provided, a fuel cell electrode comprising an electrolyte reservoir layer and a catalyst layer, said reservoir layer being porous and including a catalyst facing surface and a noncatalyst facing surface, said catalyst facing surface including first impregnations of hydrophobic material to a shallow depth over a major portion of its area, said catalyst facing surface also including uniform-ly distributed areas not impregnated with hydrophobic material, said reservoir layer further including uniformly distributed nonelectrolyte retaining portions leading from said noncat-alyst facing surface to said impregnations of hydrophobic material at said other surtace, said nonelectrolyte retaining portions comprising only a small portion of the volume of said ¦
reservoir layer, said reservoir layer being hydrophilic in all portions other than said nonelectrolyte retaining portions and said first impregnations, said reservoir layer including impregnations of an electrolyte retaining matrix material ex-tending from said areas of said catalyst facing surface not impregnated with hydrophobic material into said hydrophilic portions, said matrix material impregnating less than half `
of said hydrophilic portions, said catalyst layer being bonded to said catalyst facing surface and including holes there-a -n : ,.. .. ...... .
~7~;3~
through in communication with said impregnations of electro-lyte retaining matrix materialO
In a more specific embodiment there is provided, in a fuel cell comprising an electrolyte retaining matrix9 an anode catalyst layer disposed on one side of and in contact with said matrix and a cathode catalyst layer disposed on the other side of and in contact with said matrix, the improvement comprising: an electrolyte reservoir layer in contact with the nonmatrix facing side of at least one of said catalyst layers, said reservoir layer being porous and including a catalyst facing surface and a noncatalyst facing surface, said catalyst facing surface including first impregnations of hydrophobic material to a shallow depth over a major portion .- of its area, said catalyst facing surface also including uniformly distributed areas not impregnated with hydrophobic material9 said reservoir layer also including second impreg-nations of hydrophobic material leading from said noncatalyst ; facing surface to said first impregnations of hydrophobic : material 9 said second impregnations comprising only a small portion of the volume of said reservoir. layer, said reservoir layer being hydrophilic in all portions okher than said first and second impregnations9 said reservoir layer including third impregnations of a material essentially the same as the material of said matrix9 said third impregnations extending from said areas of said catalyst facing surface not impregnated with hydrophobic material into said hydrophilic portions, said third impregnations impregnating less than half of said hydrophilic portions, said hydrophilic portions having substantially no : pores smaller than the largest pores of said matrix.
- 30 Ihe foregoing and other objects, features9 and advan-tayes of the present invention will become more apparent in the :
light of the following detailed description of preferred embodi~
: ~ ments thereof as illustrated in the accompanying drawing.
,."' *~
~ - 8b -.:
~753~
BRIEF DESCRIPTION OF THE DRAWING
Fig. 1 is a transverse sectional view of an electro-chemical cell incorporating the present invention, Fig. 2 is a sectional view taken along the line 2-2 of Fig. 1.
Fig. 3 is a sectional view taken along the line 3-3 of Fig. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As an exemplary embodiment of the present invention ; 10 consider the eLectrochemical cell 10 as shown in Figs. 1-3. ~;
` The cell includes a fuel or anode electrode 12, a cathode electrode 14, an electrolyte retaining matrix 16 sandwiched between the electrodes, and walls 18, 20 spaced from the electrodes 12, 14 and defining a fuel space 22 behind the anode electrode 12 and an oxidant space 24 behind the cathode 14. In a typical stack of fuel cells, wherein the individual cells are connected electrically in series, the . . . .
walls 18, 20 may be elect~ically conductive separa~or plates having fuel flowing on one side thereof feeding the anode electrode of one cell and having oxida~t flowing on the other side thereof feeding the cathode electrode of the adjacent cell, Such constructions are well ~nown to those skilled in the art.
The cathode electrode 14 comprises a substrate 26 and ~` a catalyst layer 28 bonded to the surface thereof. In this j .:
particular embodiment the cathode electrode 14 is simply a . . .:
. .
.. ~ .
. .: .
~7~3~1~
gas diffusion electrode of well known design. For example, assuming that the electrolyte in this embodiment is phosphoric acid, the catalyst layer may comprise an admix-: ture of carbon supported platinum particles and polytetra-fluoroethylene (PTFE). The PTFE binds the catalyst particles :; together and also prevents the catalyst layer from becoming ~ flooded with electrolyte to the exclusion of the reactant gas necessary for the electrochemical reaction. The sub-strate 26 may be porous carbon paper impregnated with PTFE
to make it basically hydrophobic so that it cannot completely fill wikh electrolyte and prevent reactant gas from reaching the catalyst layer 28.
. The anode electrode 12 comprises a catalyst layer 30 and an electrolyte reservoir layer 32. The catalyst layer 30 .~ is bonded to the reservoir layer 32 at the surface 34. The ; reservoir layer 32 is made from porous material which is ` hydrophilic to the electrolyte or which has been treated so that it is hydrophilic to the electrolyte. For ex~ample, it may be made from carbon paper if the electrolyte is phosphoric acid; or it may be a porous plaque made of silver felt metal, sintered powered silver, gold or other metal if the electrolyte is a base such as potassium hydroxide. The pores of the reservoir layer ma~erial should be no smaller than and preferably somewhat larger than the largest pores of the matrix 16 so that only excess electrolyte wicks into and is stored in the reservoir layer 32.
10~
1~753C3B
The surface 34, adjacent the catalyst layer 30, is impregnated to a depth A over a major portion of its area with a hydrophobic matèrial or wetproofing agent such as PTFE. This hydrophobic portion is designated by the numeral 36 (Figs. 1 and 2) and in this embodiment is only interrup~ed by small circular nonwetproofed areas 37.
The reservoir layer 32 also includes a plurality of columns 38 of hydrophobic material leading from the non-.
; catalyst facing surface 40 of the reservoir layer 32 to the hydrophobic portion 36. Since the reservoir layer 32 will always be at least partially filled with electrolyte, the columns 38 and portion 36 guarantee a clear path for the reactant gas or fuel to reach the catalyst layer 30.
Also, the gas will diffuseradially outwardly from the columns 38 into the hydrophobic portion 36 thereby being distributed over a large area of catalyst. The hydrophobic area of the surface 34 should be as large as possible so as to maximize utilization of the catalyst in the layer 30.
Probably at least 50 percent of the surface will have to be wetproofed in order to obtain satisfactory catalyst ;
utilization and cell performance, although greater than 90% is preferred With regard to the maximum amount of area which may be wetproofed, the limiting factor is that the nonwetprooed areas 37 (Fig. 2) must have enough surface area to permit ready transfer of the electrolyte between the matrix 16 and the hydrophilic portions 41 of '''" ~
~ . . .
'. :
. .
, ~ 7 53~ ~
the r~servoir layer 32. It is estimated that at least about 2 percent of the surface area of the surface 3~ will have to remain nonwetproofed. Also, the nonwetproofed - areas 37 should be uniformly distributed over the surface 34;
however, the shape of the nonwetproofed areas 37 is not critical. For example, the hydrophobic portion 36 may instead be a plurality of separate rectangular areas with the nonwetproofed areas being the spaces between the rectangles and forming an interconnecting grid.
From the point of view of weight, siæe~ and perhaps cost, it is desirable to make the reservoir layer 32 as thin as possible, yet thick enough to absorb and hold the maximum amount of excess liquid which the cell may be ` expected to produce. With this in mind, it is apparent that the volume of the nonelectrolyte retaining portions (i.e., columns 38 and hydrophobic portion 36) should be as small as possible. Thus, the depth A of the portion 36 should be no greater than is necessary to permit rea~y radial diffusion of the reactant gas from the columns 38 into the portion 36. A minimum of about 3 mils in depth will probably be required; however, depths of up to 50 percent of the reservoir layer thickness may be acceptable in some instances. In order that sufficient reactant gas reaches the catalyst layer 30, it is estimated that the sum of the minimum cross-sectional areas of the columns 38 .
should be at least about 2%:of the total area-~of the surface 40.
`:
'':
. .
/.i 53~t8 As a further aspect of the present invention the reservoir layer includes an impregnation of matrix material 42 extending from the nonwetproofed areas 37 at th~ surface 34 into the hydrophilic portion 41. The catalyst lay~er 30 includes holes 44 corresponding to the areas 37; these holes are filled with matrix material such ~hat there is a continuous path of matrix material from the surface 46 of the matrix 16 to the surface 40 of the reservoir layer 32.
The holes 44 may remain empty, but this is not preferred.
The portion of the reservoir layer impregnated with matrix material will have a somewhat reduced pore size which will be similar to that of the electrolyte matrix 16. It will be the first portion of the reservoir layer ~o fill with excess electrolyte and aids in the distribution of excess electrolyte throughout the surrounding hydrophilic regions of the reservoir layer.
Since impregnation of the reservoir layer with matrix material somewhat reduces the pore size and thus the volume of electrolyte which can be stored, it is preferred that less than half of the hydrophilic portion 41 be impregnated.
Furthermore~ in this embodiment the impregnation of matrix material extends to the surface 40 to aid wicking of liquid from the fuel space to the matrix 16. This is preferred but not required~ and the invention is not to ke construed ; as limited thereto.
~.
. . -3~1~
It should also be understood that the matrix 16 may include a binder as well as the basic matrix material. For example, a typical silicon carbide matrix composition may be 96% silicon carbide powder plus 4% PTFE binder, such as des-cribed in Canadian patent application Serial No. 256,211 filed on July 2, 1976. Impregnation of the reservoir layer with the matrix material preferably includes only enough binder to keep the material in the reservoir layer during operation. This may be less binder than used in the matrix itself, One way of making the reservoir layer 32 is to mask the areas 37 of the surface 34 and apply an aqueous solution of the hydrophobic material to the nonmasked areas, such as by screen printing. For example, if the reservoir layer is carbon paper having a thickness of 13 mils, a mean pore size of 41 microns, and 75% of its pores have`a size of from 19-85 microns, the printing ink may have a composition consisting of 225 grams TFE-30, 265 grams of a 2% aqueous solution of Carbopo ~ 934~
500 grams H20 and 8 ml NH40H 28% solution. TFE-30 is made by Dupont and comprise~ about 60% polytetrafl~oroethylene, 34%
; 20 H20 and 6% surfactant, by weight. Carbopol 934 is a powder ~ade by B. F. Goodrich, when mixed with NH40H, a neutrali~ing agent, a neutral salt is formed which is the thickening agent~ The - ~H40M iq added after the other ingredients have been combined and stirred so that air bubbles are not present.
' ' , i3~
The columns 38 could be simllariy printed using a less vi~cous ink by masking the appropri~te areas o~ the surface 40. Fcr example, assumlng the same carbon paper substrate a~ mentioned above, the ~nk may have a compo~ition consi~ting o 625 gram~ TFE-30, 660 grams o~ a 2~/o aqueous solution of Carbopol 934, 1190 grams H20 and 20 ml N~140H 28% solution, Impregnating the reservoir layer with matrix material 4~ ~ay also be done by screen prlnting, but may require printlng from the gas facing surface 40 as well a from the catalyst facing sur.~ace 34. An ink composition which may be used for this purpose to impregnate the carbon paper mentioned above consists of 1800 grams of a 1% aqueous solu-tion of polyethylene oxide such as Polyo~ made by Union Carbide Corporation, 2940 grams S~k~ I 1000 grit green ~ silicon carbide powder from Carbo:rundum Co., 700 grams `` Teflon 3170 which ~ s an aqueous suspension of polyt~tra- -fluoroethylene plus suxactant made by Dupont,and 3S5 ml H20. Tke holes 44 can be f~llad by the screen printing proces~ after ~he cataly~t layer has been applied to the surface 34.
When screen printing is used, the depth to which the ink solutlon impregnates the reservoir layer is controlled :- by th~ viscosit~ of the ink and the ~umber o~ passes made ~urlng the screen printing proces.q. Inklng vehicles and other unde~irable volatile ingred~ents such as surfactants are ~ubsequently volatil~zed during sintering of the catalyst layer.
.~
-15- .
' ~7536:~8 AlthDugh in the embodiment of Fig. 1 the reservoir layer 32 acts as a sl-bstrate for the catalyst layer 30 which may be applied thereto such as by spraying, filtering, printing or other suitable means, it should be apparent ~o those having ordinary skill in the art that the matrix 16 may be used as the catalyst layer substrate rather than the reser-voir layer 32. Thus, the catalyst layer 30 may be applied and bonded to the matrix 16 and simply be in intimate con-tact with but not bonded to the surface 34 of the reservoir layer.
As will also be obvi~us to those having ~rdinary skill in the art 3 the substrate 26 of the cathode electrode 14 may be replaced by a reservoir layer similar to or identical to the reservoir layer 32. However, this additional reservoir volume is usually not requiredO If only:a single reservoir layer is to be used, it is preferred that it be on the anode side of the cell since the anode is more tolerant to reduced availability of hydrogen than the cathode is ~o reduced availability of oxygen.
Although the invention has been shown and described with respect to a preferred embodiment thereof, it should be understood by those skilled in the art that other various :
changes and omissions in the orm and detail thereof may be made therein without departing from the spirit and the scope of the invention.
, ~'
Claims (17)
1. An electrolyte reservoir layer for use adjacent the catalyst layer of a fuel cell, said reservoir layer being porous and including a catalyst facing surface and a non-catalyst facing surface, said catalyst facing surface including first impregnations of hydrophobic material to a shallow depth over a major portion of its area, said catalyst facing surface also including uniformly distributed areas not impregnated with hydrophobic material, said reservoir layer also including uniformly distributed nonelectrolyte retaining portions leading from said noncatalyst facing surface to said impregnations of hydrophobic material at said other surface, said nonelectrolyte retaining portions comprising only a small portion of the volume of said reser-voir layer, said reservoir layer being hydrophilic in all portions other than said nonelectrolyte retaining portions and said first impregnations, said reservoir layer also including impregnations of an electrolyte retaining matrix material extending from said areas of said catalyst facing surface not impregnated with hydrophobic material into said hydrophilic portions, said matrix material impregnating less than half of said hydrophilic portions.
2. The reservoir layer according to claim 1 wherein said nonelectrolyte retaining portions are second impregna-tions of hydrophobic material extending from said noncatalyst facing surface to said first impregnations of hydrophobic material.
3. The reservoir layer according to claim 2 wherein said impregnation of matrix material extends from said catalyst facing surface to said noncatalyst facing surface.
4. The reservoir layer according to claim 1 wherein the area of said catalyst facing surface not impregnated with hydrophobic material is at least 2% of the total area of said catalyst facing surface, said depth of said first impregnations is no more than 50% of the thickness of said reservoir layer and no less than 3 mils, and the minimum total cross sectional area of said nonelectrolyte retaining portions is 2% of the total cross-sectional area of said noncatalyst facing surface.
5. The electrolyte reservoir layer according to claim 4 wherein said reservoir layer comprises carbon paper.
6. The electrolyte reservoir layer according to claim 4 wherein said matrix material comprises silicon carbide.
7. A fuel cell electrode comprising an electrolyte reservoir layer and a catalyst layer, said reservoir layer being porous and including a catalyst facing surface and a noncatalyst facing surface 7 said catalyst facing surface including first impregnations of hydrophobic material to a shallow depth over a major portion of its area, said catalyst facing surface also including uniformly distributed areas not impregnated with hydrophobic material, said reservoir layer further including uniformly distributed nonelectrolyte retaining portions leading from said noncatalyst facing sur-face to said impregnations of hydrophobic material at said other surface, said nonelectrolyte retaining portions comprising only a small portion of the volume of said reservoir layer, said reservoir layer being hydrophilic in all portions other than said nonelectrolyte retaining portions and said first impregnations, said reservoir layer including impregnations of an electrolyte retaining matrix material extending from said areas of said catalyst facing surface not impregnated with hydrophobic material into said hydrophilic portions, said matrix material impregnating less than half of said hydrophilic portions, said catalyst layer being bonded to said catalyst facing surface and including holes therethrough in communication with said impregnations of electrolyte retaining matrix material.
8. The fuel cell electrode according to claim 7 wherein said impregnations of matrix material extend from said catalyst facing surface to said noncatalyst facing surface.
9. The fuel cell electrode according to claim 7 wherein said area of said catalyst facing surface not impregnated with hydrophobic material is at least 2% of the total area of said catalyst facing surface, said depth of said first impregnations is no more than 50% of the thickness of said reservoir layer and no less than 3 mils, and the minimum total cross-sectional area of said nonelectrolyte retaining portions is 2% of the total cross-sectional area of said noncatalyst facing surface.
10. In a fuel cell comprising an electrolyte retaining matrix, an anode catalyst layer disposed on one side of and in contact with said matrix and a cathode catalyst layer disposed on the other side of and in contact with said matrix, the improvement comprising:
an electrolyte reservoir layer in contact with the nonmatrix facing side of at least one of said catalyst layers, said reservoir layer being porous and including a catalyst facing surface and a noncatalyst facing surface, said catalyst facing surface including first impregnations of hydrophobic material to a shallow depth over a major portion of its area, said catalyst facing surface also including uniformly distributed areas not impregnated with hydrophobic material, said reservoir layer also including second impregnations of hydrophobic material leading from said noncatalyst facing surface to said first impregnations of hydrophobic material, said second impregnations comprising only a small portion of the volume of said reservoir layer, said reservoir layer being hydrophilic in all portions other than said first and second impregnations, said reservoir layer including third impregnations of a material essentially the same as the material of said matrix, said third impregnations extending from said areas of said catalyst facing surface not impregnated with hydrophobic material into said hydrophilic portions, said third impregnations impregnating less than half of said hydrophilic portions, said hydrophilic portions having substantially no pores smaller than the largest pores of said matrix.
an electrolyte reservoir layer in contact with the nonmatrix facing side of at least one of said catalyst layers, said reservoir layer being porous and including a catalyst facing surface and a noncatalyst facing surface, said catalyst facing surface including first impregnations of hydrophobic material to a shallow depth over a major portion of its area, said catalyst facing surface also including uniformly distributed areas not impregnated with hydrophobic material, said reservoir layer also including second impregnations of hydrophobic material leading from said noncatalyst facing surface to said first impregnations of hydrophobic material, said second impregnations comprising only a small portion of the volume of said reservoir layer, said reservoir layer being hydrophilic in all portions other than said first and second impregnations, said reservoir layer including third impregnations of a material essentially the same as the material of said matrix, said third impregnations extending from said areas of said catalyst facing surface not impregnated with hydrophobic material into said hydrophilic portions, said third impregnations impregnating less than half of said hydrophilic portions, said hydrophilic portions having substantially no pores smaller than the largest pores of said matrix.
11. The improvement according to claim 10 wherein said one catalyst layer is said anode catalyst layer.
12. The improvement according to claim 11 wherein said anode catalyst layer is bonded to said reservoir layer.
13. The improvement according to claim 11 wherein said catalyst layer includes a plurality of uniformly distributed holes therethrough aligned with said third impregnations, said holes being filled with essentially the same material of which said matrix is made.
14. The improvement according to claim 13 wherein said reservoir layer comprises carbon paper.
15. The improvement according to claim 14 wherein said matrix comprises silicon carbide with a hydrophobic polymer binder.
16. The improvement according to claim 12 wherein said areas of said catalyst facing surface not impregnated with hydrophobic material are at least 2% of the total area of said catalyst facing surface, said depth of said first impregnations are no more than 50% of the thickness of said reservoir layer and no less than 3 mils, and the minimum total cross-sectional area of said second impregnations is 2% of the total cross-sectional area of said noncatalyst facing surface.
17. The improvement according to claim 16 wherein said third impregnations extend from said catalyst facing surface to said noncatalyst facing surface.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/719,875 US4038463A (en) | 1976-09-01 | 1976-09-01 | Electrode reservoir for a fuel cell |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1075308A true CA1075308A (en) | 1980-04-08 |
Family
ID=24891726
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA283,132A Expired CA1075308A (en) | 1976-09-01 | 1977-07-20 | Electrolyte reservoir for a fuel cell |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4038463A (en) |
| JP (1) | JPS5332353A (en) |
| CA (1) | CA1075308A (en) |
| DE (1) | DE2736883A1 (en) |
| FR (1) | FR2363907A1 (en) |
| GB (1) | GB1541541A (en) |
| IL (1) | IL52727A0 (en) |
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| US4125676A (en) * | 1977-08-15 | 1978-11-14 | United Technologies Corp. | Carbon foam fuel cell components |
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| US4185145A (en) * | 1978-09-11 | 1980-01-22 | United Technologies Corporation | Fuel cell electrolyte reservoir layer and method for making |
| US4276356A (en) | 1979-03-27 | 1981-06-30 | Energy Research Corporation | Matrix member for containing fuel cell acid electrolyte |
| US4219611A (en) * | 1979-07-30 | 1980-08-26 | United Technologies Corporation | Fuel cell electrolyte reservoir layer and method for making |
| US4374906A (en) * | 1981-09-29 | 1983-02-22 | United Technologies Corporation | Ribbed electrode substrates |
| US4463068A (en) * | 1982-09-30 | 1984-07-31 | Engelhard Corporation | Fuel cell and system for supplying electrolyte thereto with wick feed |
| US4467019A (en) * | 1982-09-30 | 1984-08-21 | Engelhard Corporation | Fuel cell with electrolyte feed system |
| US4505992A (en) | 1983-04-11 | 1985-03-19 | Engelhard Corporation | Integral gas seal for fuel cell gas distribution assemblies and method of fabrication |
| US4596751A (en) * | 1984-12-10 | 1986-06-24 | United Technologies Corporation | Molten carbonate fuel cell with improved electrolyte storage |
| US4738872A (en) * | 1985-07-02 | 1988-04-19 | International Fuel Cells | Carbon-graphite component for an electrochemical cell and method for making the component |
| US4670300A (en) * | 1985-07-03 | 1987-06-02 | International Fuel Cells Corporation | Carbon-graphite component for an electrochemical cell and method for making the component |
| US4652502A (en) * | 1985-12-30 | 1987-03-24 | International Fuel Cells, Inc. | Porous plate for an electrochemical cell and method for making the porous plate |
| US4756981A (en) * | 1986-12-29 | 1988-07-12 | International Fuel Cells | Seal structure for an electrochemical cell |
| JPS63187574A (en) * | 1987-01-29 | 1988-08-03 | Japan Gore Tex Inc | Fuel cell electrode-matrix monobloc forming and its manufacture |
| US4855194A (en) * | 1988-02-05 | 1989-08-08 | The United States Of America As Represented By The United States Department Of Energy | Fuel cell having electrolyte inventory control volume |
| US4913706A (en) * | 1988-09-19 | 1990-04-03 | International Fuel Cells Corporation | Method for making a seal structure for an electrochemical cell assembly |
| JP3583897B2 (en) * | 1997-04-11 | 2004-11-04 | 三洋電機株式会社 | Fuel cell |
| US6024848A (en) * | 1998-04-15 | 2000-02-15 | International Fuel Cells, Corporation | Electrochemical cell with a porous support plate |
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| US20070141464A1 (en) * | 2005-12-21 | 2007-06-21 | Qunjian Huang | Porous metal hydride electrode |
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| US8945790B2 (en) * | 2013-03-15 | 2015-02-03 | Ford Global Technologies, Llc | Microporous layer structures and gas diffusion layer assemblies in proton exchange membrane fuel cells |
| KR20150004680A (en) * | 2013-07-03 | 2015-01-13 | 삼성에스디아이 주식회사 | Membrane-electrode assembly for fuel cell and fuel cell stack including same |
| US10707494B2 (en) * | 2015-11-19 | 2020-07-07 | Panasonic Intellectual Property Management Co., Ltd. | Gas diffusion layer for fuel cell, method for manufacturing said layer, membrane-electrode assembly, and fuel cell |
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| US3905832A (en) * | 1974-01-15 | 1975-09-16 | United Aircraft Corp | Novel fuel cell structure |
-
1976
- 1976-09-01 US US05/719,875 patent/US4038463A/en not_active Expired - Lifetime
-
1977
- 1977-07-20 CA CA283,132A patent/CA1075308A/en not_active Expired
- 1977-08-12 IL IL52727A patent/IL52727A0/en unknown
- 1977-08-16 DE DE19772736883 patent/DE2736883A1/en not_active Withdrawn
- 1977-08-24 FR FR7725782A patent/FR2363907A1/en not_active Withdrawn
- 1977-08-25 GB GB35668/77A patent/GB1541541A/en not_active Expired
- 1977-08-31 JP JP10471177A patent/JPS5332353A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| US4038463A (en) | 1977-07-26 |
| IL52727A0 (en) | 1977-10-31 |
| GB1541541A (en) | 1979-03-07 |
| JPS5332353A (en) | 1978-03-27 |
| FR2363907A1 (en) | 1978-03-31 |
| DE2736883A1 (en) | 1978-03-02 |
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