EP0546116A1 - Procede et appareil pour introduire un fluide d'impregnation dans une region d'un substrat poreux - Google Patents

Procede et appareil pour introduire un fluide d'impregnation dans une region d'un substrat poreux

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Publication number
EP0546116A1
EP0546116A1 EP91918427A EP91918427A EP0546116A1 EP 0546116 A1 EP0546116 A1 EP 0546116A1 EP 91918427 A EP91918427 A EP 91918427A EP 91918427 A EP91918427 A EP 91918427A EP 0546116 A1 EP0546116 A1 EP 0546116A1
Authority
EP
European Patent Office
Prior art keywords
die
impregnant
substrate
plunger
seal
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.)
Withdrawn
Application number
EP91918427A
Other languages
German (de)
English (en)
Inventor
James L. Mcguire
James E. Dayton
Robert C. Stewart
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
UTC Power Corp
Original Assignee
International Fuel Cells Corp
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by International Fuel Cells Corp filed Critical International Fuel Cells Corp
Publication of EP0546116A1 publication Critical patent/EP0546116A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C70/00—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts
    • B29C70/68—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts by incorporating or moulding on preformed parts, e.g. inserts or layers, e.g. foam blocks
    • B29C70/74—Moulding material on a relatively small portion of the preformed part, e.g. outsert moulding
    • B29C70/76—Moulding on edges or extremities of the preformed part
    • B29C70/763—Moulding on edges or extremities of the preformed part the edges being disposed in a substantial flat plane
    • 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
    • H01M8/0271—Sealing or supporting means around electrodes, matrices or membranes
    • 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to the introduction of impregnating substances into porous substrate regions in general, and more particularly to a method of forming an improved impregnated seal, especially an edge seal or a corrosion resistant coating or seal, in a porous electrode substrate of a fuel cell, using dispersions, for example, aqueous, highly thixotropic, non-Newtonian dispersions of graphite and carbon for the edge seals, or, for further example, aqueous dispersions of wetproofing materials such as, for example, fluorocarbons, for the corrosion resistant seal, using specialized tooling.
  • dispersions for example, aqueous, highly thixotropic, non-Newtonian dispersions of graphite and carbon for the edge seals, or, for further example, aqueous dispersions of wetproofing materials such as, for example, fluorocarbons, for the corrosion resistant seal, using specialized tooling.
  • the invention also relates to specialized tooling used to form, for example, such impregnated edge seals and corrosion resistant coatings or seals in porous electrode substrates to uniformly force the impregnant into the substrate with, for example, consistent shear forces in the impregnant throughout the seal area, overcoming the effects of thixotropy. Additionally, the present invention relates to the modification of the dispersions of graphite and carbon for the edge seals to maintain such disper ⁇ sions in an enhanced.liquid state.
  • Fuel cell powerplants produce electric power by electrochemically combining a fuel and an oxidant in one or more electrochemical cells.
  • the oxidant may be pure oxygen or a mixture of gases containing oxygen, such as air.
  • the fuel may be hydrogen.
  • Each fuel cell generally has electrodes to which the respective gases are supplied, including an anode electrode for the gaseous fuel and a cathode electrode for the gaseous oxidant, with the electrodes being provided in the form of porous substrates to be permeable to such gases.
  • the cathode electrode is spaced from the anode electrode, and a matrix saturated with electrolyte (acid or alkaline) typically is disposed between the electrodes.
  • a fuel cell electrolyte retention section is included to retain the electrolyte within the cell.
  • a matrix layer filled with electrolyte typically is sandwiched between a pair of electrodes, a cathode and an anode making up each pair.
  • Each electrode comprises a substrate with a thin layer of catalyst disposed on the surface thereof facing the electrolyte.
  • Each electrode substrate is constructed to permit a reactant gas (generally either air or hydrogen) to pass therethrough and contact the catalyst. This is the gas diffusion type of electrode.
  • a common characteristic of all fuel cells is the necessity for preventing leakage and inadvertent mixing of the reactant gases both within and externally of the cell. Since the electrode substrates (and certain other components of the fuel cell stack) are gas permeable or porous, means must be provided for preventing "in-plane” gas leakage through the edge regions of these substrates.
  • edge seals in the electrode substrates, either by densification or impregnation.
  • edge sealing by densification or impregnation of fuel cell components
  • exemplary impregnants to form edge seals include impregnant dispersions made up of, for example, aqueous, highly thixotropic, non-Newtonian dispersions of graphite and carbon.
  • impregnant dispersions made up of, for example, aqueous, highly thixotropic, non-Newtonian dispersions of graphite and carbon.
  • Such edge seal areas when properly impregnated and heat treated or otherwise dried, effectively contain the acid electrolyte of the fuel cell(s) within the confines of the fuel cell electrolyte retention section.
  • the dispersions of graphite and carbon which can contain up to, for example, sixty-six percent (66%) of carbon or graphite by weight, were forced into the edge regions of the porous electrode substrates using hydraulic pressure existing in the dispersion as was is being supplied to such regions.
  • 66% sixty-six percent
  • the prior art method included the method disclosed in a commonly assigned U.S. patent No. 4,855,840 to Messrs.
  • the present invention in general is thus par ⁇ ticularly applicable to properly impregnating selected areas or regions of porous substrates or articles, especially of components of fuel cells, particularly electrode substrates, to either form edge seals using impregnant dispersions made up of, for example, aqueous or non-aqueous, highly thixotropic, non-Newtonian dispersions of graphite and carbon, or to form corrosion resistant seals using impregnant dispersions made up of aqueous or non-aqueous dispersions of wetproofing materials, particularly fluorocarbons.
  • the method of the present invention using specialized tooling and related methodology, as explained more fully below, results in a more uniform seal, whether for an edge seal or for a corrosion resistant seal, with improved dimensional control. It also is more amenable to continuous production techniques, takes less time and using relatively simple tooling.
  • edge sealing it has been found that, although the particle size of the dispersion was supposed to be below, for example, one micron, in fact due to agglomerations of the particles being formed, the effective "particle" size became much greater, increasing the tendency of the impregnant to solidify, diminishing the sealing effectiveness of the impregnating process.
  • Another methodological aspect of the present invention which uses a chemical additive for the impregnant, solves this prior art problem.
  • a further object of the present invention is to enhance the flow characteristics and reduce the solidification tendencies of the impregnant to be used to form the edge seals.
  • a concomitant object of the present invention is to develop both mechanical and chemical means capable of to accomplish the overall desired results contemplated by the invention, insofar as the invention relates to edge seals, including maintaining the aqueous dispersion in a liquid state using a pH increasing chemical additive, as well as to overcoming the effects of thixotropy using specialized but simple tooling.
  • one feature of the present invention resides in a method of impregnating a selected region of a porous substrate, this method comprising the steps of:
  • a system for making an area seal in a porous substrate using an impregnant which is to be forced into the porous substrate in the region to be sealed to seal such region area comprising: a platen; a die associated with said platen, said die having an opening in it and a movable surface contained within said opening, said opening and said movable surface defining an impregnant cavity into which the impregnant is placed prior to its being forced into the porous substrate; a work area located between said platen and said die of a size in which the substrate to have the region on it sealed can be positioned, said opening in said die extending out to the exterior surface of said die facing said work area forming an open top in the die; sealing means associated with said die extending at least around said open top for sealing the portion of said die about said open top to the substrate in the substrate area to be impregnated; and pressure means associated with said movable surface for applying pressure in the direction of said platen to said movable surface
  • the properties of the impregnant are improved by adding thereto a minor percentage of a concentrated solution of an alkaline or caustic substance, such as, for example, ammonium hydroxide.
  • an alkaline or caustic substance such as, for example, ammonium hydroxide.
  • Experimental observations conducted as part of the inventior indicate that the tendency of, for example, aqueous carbon/graphite dispersions to solidify as the solids content exceeds, for example, sixty-six (66%) percent can be mitigated by adding a minor amount of a concentrated solution of an alkaline or caustic material, such as preferably ammonium hydroxide, to the dispersion to increase its pH level.
  • Sufficient ammonium hydroxide should be added to increase the pH level, preferably up to about a range of 10.5 to 11.5.
  • An optimized solution has been found to be up to about fifty-eight percent of ammonium hydroxide (e.g., about 58% by weight of the NH.OH in water, which is equivalent to about 28-30% by weight of the NH- gas added to water to make the aqueous solution) , with the concentrated solution being added being up to about seven percent (7%) by weight of the total mixed impregnant.
  • ammonium hydroxide e.g., about 58% by weight of the NH.OH in water, which is equivalent to about 28-30% by weight of the NH- gas added to water to make the aqueous solution
  • the maintenance of the dispersion in a liquid state is very important if satisfactory substrate penetration and sealing impregnation is to occur, and the present invention with its modified impregnant maintains the dispersion in such an enhanced liquid state.
  • the special tooling used in this invention to overcome the effect of thixotropy comprises, as an example, an extended, rigid die chamber or channel having a movable, rigid, internal surface, such as, for example, a bottom surface or plunger.
  • a movable, rigid, internal surface such as, for example, a bottom surface or plunger.
  • the volume of the impregnant is constrained by the volume of the chamber, and consequently a seal is produced which is uniform in density and dimensionally controlled by the shape of the channel, rather than being distorted by varying shear forces, as occurred in the hydraulic pumping system of the prior art.
  • a rigid die channel with a rigid, internal moving surface, such as a plunger similar to that used to make edge seals, to impregnate the desired corrosion resistant sealing areas of the cathode substrate also produces a superior corrosion resistant seal, with the corrosion resistant seal being made in less time and with greater simplicity than the coatings of the prior art.
  • Figure 1 is a simplified, partial, close-up, side, cross-sectional view of an exemplary embodiment of the specialized tooling used in the preferred embodiment of the present invention
  • Figure 2 is a similar side view of the specialized tooling of Figure 1, but in a subsequent stage of impregnation, with the plunger of the tooling having been pushed in against compression springs to begin the initial step of impregnation;
  • Figure 3 is a similar side view of the specialized tooling of Figures 1 and 2, but in the final stage of impregnation, with the plunger of the tooling having been pushed completely up against the compression springs to perform the final step of impregnation;
  • Figure 4 is a simplified, plan view of an exemplary cathode substrate with the areas of the edge seals and the corrosion resistant seals produced using the preferred methodology and specialized tooling of the present invention indicated in phantom line;
  • Figure 5 is a view similar to that of Figure 1 but showing a modified construction of the specialized tooling.
  • one exemplary embodiment of a specialized tooling constructed in accordance with the present invention includes a lower tooling assembly 10 underlying a stationary, combined vacuum chuck and platen 20, which carries on its underside the electrode substrate "E.S.”
  • the electrode substrate E.S. is maintained in place on the vacuum chuck 20 by means of vacuum pressure.
  • the vacuum chuck aspect of the stationary platen 20 could be eliminated, in which case the electrode substrate E.S. could be placed and carried on the upper side of the lower tooling 10.
  • the lower, impregnating tooling 10 includes a movable plunger 11 riding in an opening in a rigid die structure 12 with a set of compression springs 14 between them, holding or biasing them apart, but allowing for reciprocal, "up” and “down” movement of the plunger stem 11A within the die 12.
  • the plunger 11 is rigid, with its stem 11A made of, for example, "Teflon", and its head 11B made of a suitable metal, such as, for example, aluminum.
  • an elongated cavity or channel trough 13 of a certain volume is formed above the stem 11A of the plunger 11 within the opening in the die 12 into which the plunger stem 11A moves and into which channel 13 an impregnant 30 is eventually placed (see Fig. 2) .
  • the channel 13 has an elongated, rectangularly configured top opening through which the impregnant 30 will ultimately be forced into the substrate region to be impregnated, and it in essence forms a moat across the upper side of the die 12.
  • the elongated channel 13 has four, fixed sides and a movable bottom surface formed by the stem ending of the plunger 11.
  • the compression springs 14 can be regular springs as illustrated or be in other forms, such as, for example, elastomeric springs, or a combination of the two. Additionally, by including threaded bolts extending through the body of the die 12 and threaded into the head 11A of the plunger 11, the plunger 11 can be preloaded to a desired initial pressure by screwing down the bolts, thereby lessening the volume of the impregnant chamber 13 and increasing the preloaded pressure on the plunger 11 tending to overcome some of the biasing pressure of the spring members 14.
  • the spring members 14 and the threaded, preloading bolts are provided between the die 12 and the plunger 11 in a spaced series positioned along the length of the elongated plunger 11.
  • a series of "O" type, surrounding rings 15 is included around the stem 11A of the plunger 11 interfacing with the sides 12A of the die opening to provide a seal, preventing loss of the impregnant down about the plunger stem 11A.
  • An additional series of “O” type rings 16 is provided on the upper side of the die 12 extending peripherally about the die opening for sealing the interface with the underside of the substrate E.S. when the die 12 is pressed up against the substrate E.S. , working against the fixed platen 20. This second set of sealing rings 16 prevents the sideward escape of the impregnant 30 when the die 12 is pushed up against the underside of the substrate E.S. and the plunger 11 is forced upward, i.e. when the plunger 11 and the die 12 are in the dispositions of Figures 2 and 3.
  • the electrode substrate E. . is typically rectangular in plan view (note Fig. 4) and the plunger 11 and die 12 are longitudinally extended along and parallel to the side edges of the substrate E.S. to be sealed, defining the extended channel or trough 13 for the impregnant 30.
  • the plunger 11 and die 12 are longitudinally extended along and parallel to the side edges of the substrate E.S. to be sealed, defining the extended channel or trough 13 for the impregnant 30.
  • the plunger 11 and die 12 are longitudinally extended along and parallel to the side edges of the substrate E.S. to be sealed, defining the extended channel or trough 13 for the impregnant 30.
  • the plunger 11 and die 12 are longitudinally extended along and parallel to the side edges of the substrate E.S. to be sealed, defining the extended channel or trough 13 for the impregnant 30.
  • the plunger 11 and die 12 are longitudinally extended along and parallel to the side edges of the substrate E.S. to be sealed, defining the extended
  • the upper, open parts of the cL .inels 13 are positioned sufficiently close together in the abutted plunger/die sections 11/12 that the edge seals formed are continuous, being interconnected about all four sides of the substrate C.S. in the regions 1 to 4.
  • the dimensions of the open top of the channel 13 are comparable to the region(s) 1 to 4 to be sealed but typically a little less than them, because some side flow of the impregnant will occur during the forced impregnation steps.
  • edge seal regions 1 and 2 that are parallel to ribs 5 of the cathode substrate C.S. are wider than the two edge seal regions 3 and 4 that are perpendicular to the ribs 5.
  • two corrosion resistant seal regions 6 and 7 are included.
  • Exemplary dimensions for the width of the impregnant channel or trough 13 to produce edge seals in a cathode substrate C.S. for the wider regions 1 and 2 and for the narrower regions 3 and 4 are about one and three-tenths inches to about one and eighth-tenths inches (1.3" - 1.8"), and about a half inch to about seven-tenths of an inch (0.5" - 0.7"), respectively.
  • Exemplary dimensions for the width of the impregnant channel or trough 13 to produce edge seals in an anode substrate for the regions comparable to the cathode regions l and 2 is about one and one-tenths inches minimum to about one and seven-tenths inches maximum (1.1" min. to 1.7" max.) .
  • a typical width of the impregnant channel 13 would be about one and a quarter inches (1.25") .
  • these width dimensions are merely exemplary and, of course, are subject to much variation.
  • an exemplary size of a cathode die, made up of four, orthogonal die sections 12, is approximately forty-five inches by approximately forty-five inches (45"x45”) in plan view.
  • the impregnant chamber 13 may be many times longer in its height or depth (viewed in the perspective of Figs. 1-3) than it is wide.
  • an operator initially fills up the impregnant channels 13 defined by the various plunger/die sections 11/12 by pouring in the desired impregnant, preferably using a metered container.
  • a metered container preferably a metered container.
  • mechanized, traveling flow lines with metered or timed pumps could be used.
  • the lower assembly tool 10 and/or the platen 20 are moved relative to one another until the impregnating tool 10 is appropriately positioned under the substrate E.S. If the vacuum chuck aspect is not being used, the substrate E.S. is appropriately positioned on top of the die 12.
  • a work area between the die 12 the platen 20 exists having a size to accommodate the fuel cell component, typically an electrode substrate E.S. , having one or more regions to be sealed.
  • the fuel cell component typically an electrode substrate E.S.
  • regions to be sealed, it should be understood that a three dimensional volume is actually being considered, namely the volume underlying the surface areas of the substrate E.S. through which the impregnant is to be forced, and the seal will typically extend from the surface area on the side directly exposed to the open top of the die 12 all the way through to the opposite side.
  • pressure is applied to the head 11B of the plunger 11, driving it upwards and forcing the impregnant 30 out of the channel 13 and into the porous substrate E.S, with the quantity of the impregnant thusly introduced into the substrate E.S. being indicated at 31.
  • the driving pressure can be applied to the head 11B of the plunger 11 by suitable mechanical, hydraulic and/or pneumatic means (note lower directional arrows in Figure 2 representing the upwardly directed, initial forces on the head 11B of the plunger 11) .
  • the substrate E.S. is dried, preferably with heating, to remove the liquid components of the impregnant quantity 31 from the substrate E.S., leaving behind a dry edge seal forming an effective edge seal in the substrate E.S.
  • FIG. 5 of the drawing depicts an alternative construction of the tooling of the present invention that is similar to that discussed above in conjunction with Figures 1 to 3 of the drawing that the same reference numerals, merely supplemented with primes where needed, have been used to identify corresponding parts therein.
  • the assembly 10' consisting of the die 12' and the plunger 11', is shown therein in a situation occurring basically between those depicted in Figures 1 and 2, that is, after the channel 13' has been filled to the desired extent with the metered amount of the impregnant 30 but before the assembly 10* has been brought toward and into contact with the electrode substrate E.S.
  • the material of the die 12' is elastically yieldable or elastomeric so that it can be compressed to occupy only a fraction of its original volume that is illustrated in Figure 5.
  • this die material is of the foamed type, be it foamed rubber, foamed latex, or a similar foamed elastomeric material.
  • this material is of the so-called closed-cell variety, i.e. it includes a great number of relatively minuscule "air bubbles" or voids which do not communicate with one another. In this case, at least some of the externally or internally exposed zones of the die 12' (i.e.
  • the plunger head 11*B in this instance is constructed as a rigid, preferably metallic (aluminum, for example) plate that constitutes a rigid support and force transmission and distribution medium for the elastically yieldable or compressible die 12* .
  • the previously mentioned springs 14 are omitted in the construction of Figure 4.
  • the die material is elastomeric, it will seal the respective interfaces on its own, so that the O-ring seals 15 and 16 are not needed in, and thus are absent from, the construction of Figure 5.
  • the plunger head or plate 11'B is shown to be provided with a recess that partially accommodates the die 12' (or separate portions thereof).
  • the die 12' (or its portions) can be held in such a recess by friction and/or gravity alone, but if a greater degree of retention security is needed, it or they could be additionally held in the recess or in the respective associated recesses by an adhesive or the like.
  • the recess or recesses could be omitted from the plunger plate 11'B and the die 12' (or its portions) could be held on the plate 11'B by adhesion alone.
  • the plunger stem 11'A includes, in addition to a metal portion thereof that is constituted by a projection of the plunger head or plate 11*B, a contact portion 11'C which covers the metal portion in its entirety and thus separates the latter from the channel 13 ' , thus presenting a bottom surface bounding the channel 13• .
  • the contact portion 11•C is preferably of a material exhibiting at least a small degree of elasticity, such as of hard rubber. Because of its compliancy, this material will not damage or exert undue pressure on the electrode substrate should it come into contact therewith.
  • the contact portion 11'C is connected, for instance adhesively, to the metallic portion of the plunger stem 11'A so as to share in its movement.
  • this expedient can also be used in the construction depicted in Figures 1 to 3 of the drawing, if so desired.
  • the assembly 10* is to be used in a manner similar to that of the assembly or tooling 10, namely, the channel 13' is to be filled with a metered amount of the impregnant 30 first, resulting in the situation illustrated in Figure 5. Thereafter, the assembly 10' is brought into contact with the electrode substrate E.S. in the same manner as discussed above in conjunction with Figures 1 and 2 of the drawing, and pressure is exerted against the plunger head or plate 11*B, like it is in Figures 2 and 3. However, this time it is the die 12' (rather than any now absent springs) that resiliently yields or is compressed to enable the plunger stem 11*A to move toward the electrode substrate E.S.
  • a particular advantage of this latter approach is that of an improved sealing effect at the various interfaces. This is especially true with respect to the interface between the die 12* and the electrode substrate E.S. where, because of its resiliency, the material of the die 12' will "go around the corner" at the outer edge of the substrate E.S., thus increasing the sealing effect at this area.
  • Figure 5 also shows, in broken lines, a modified approach that is particularly useful when the electrode substrate E.S. is relatively thick.
  • a strip or component 17' of, for instance, hard rubber is connected, preferably adhesively, to the top surface of the die 12' in such a manner that its inward lateral surface, that that which is closer to the channel 13' , is in substantial registry with the outwardly facing lateral surface of the electrode substrate E.S. in the position illustrated in Figure 5.
  • This registry is useful not only because it facilitates proper positioning of the electrode substrate E.S.
  • the electrode substrate E.S. typically is made of a porous carbon material and is to be edge sealed using for the impregnant an aqueous, highly thixotropic, non-Newtonian di version of graphite and carbon.
  • dispersions of this kind can contain up to sixty-six percent (66%) of carbon or graphite by weight. However, in such high concentrations, such a dispersion has a tendency toward solidification.
  • An exemplary impregnant 30, prior to modification by the addition of an alkaline or caustic solution to increase its pH in accordance with an aspect of the invention, would be an aqueous dispersion of less than one micron size particles of carbon black, graphite, silicon carbide, or other inorganic solids compatible with phosphoric acid at, for example, temperatures of 400 F, or mixtures of such solids.
  • the final solids content of the impregnant generally can be in the range of, for example, about fifty percent (50%) to about seventy-four percent (74%) by weight, although about a sixty-six percent (66%) by weight is considered the most practical from a manufacturing standpoint. Additionally, solids content below about fifty-seven percent (57%) is considered outside the preferred range.
  • a suitable binder for example, a fluorocarbon
  • a stearic type of thickener may be added to optimize the impregnant rheology, in particular raising its viscosity, shear sensitivity and its pseudo-plasticity.
  • a dispersant of a suitable concentration may be necessary to minimize particle settling over long storage periods.
  • the dispersion is modified by adding a minor amount of a concentrated solution of an alkaline or caustic material, such as, for example, ammonium hydroxide or sodium hydroxide, to the dispersion before it is impregnated into the electrode substrate E.S. , thereby enhancing the flow characteristics of the modified dispersion and reducing the solidification tendencies of the dispersion.
  • an ammonium hydroxide or sodium hydroxide solution as an alkaline or caustic material increases the pH of the mixed dispersion, and, it is believed, causes the particles to become charged, repelling one another and thereby chemically breaking up any agglomerations of particles.
  • Sufficient alkaline or caustic material preferably ammonium hydroxide, should be added to increase the pH level up to about a range of 10.5 to 11.5.
  • alkaline or caustic material whichever alkaline or caustic material is used, it should not leave any fuel cell "poisonous" residue after the impregnated substrate is dried.
  • Ammonium hydroxide decomposes and is driven off in the drying stage, leaving no fuel cell “poisonous” residue, and is preferred. Testing has shown that up to about a seven percent (7%) by weight of about a fifty-eight percent (58%) by weight concentrated aqueous solution of ammonium hydroxide can be used and is preferred.
  • the maximum amount of ammonium hydroxide available is desired as needed to increase the pH level to about a range of 10.5 to 11.5.
  • an ammonium hydroxide solution is substantially greater than "58%", it can be difficult to handle and use.
  • adding substantially more than a "7%” solution to the impregnant can decrease the solids contents of the modified impregnant to too great an extent, decreasing its effectiveness in the sealing process.
  • the methodology of the invention insofar as it applies to making edge seals preferably includes the preliminary step of adding the aforementioned minor amount of such a concentrated solution to the aqueous dispersion, thereby modifying it to have an increased pH level up to about a range of 10.5 to 11.5.
  • the then so modified dispersion 30 is poured or pumped in metered fashion into each of the rigid channels 13 above the plunger stem 11A of each of the plunger/die sections 11/12 in the construction of Figure 1, or into the channel 13• of the construction of Figure 5.
  • the rigid die 12, or the elastomeric die 12 ' after the channel 13 or 13 • has been filled with the impregnant 30 and with its plunger 11 preferably unpressurized, is placed or driven up against the underside of the edge area of the substrate E.S. for the rigid die 12 to be sealed by the ring seals 16 to the substrate E.S. and for the elastomeric die 12 ' to seal the affected interface by itself due to its compliancy, or, as the case may be, the substrate E.S. itself is placed on top of the die 12 or 12' in sealed engagement therewith.
  • the head 11B of the plunger 11 of each section is pressurized or otherwise driven upward, causing the preferably modified impregnant 30 to be forced into the porous substrate E.S. , as shown in Figure 2. Because of the shape of the channel 13 and the use of an integral moving wall portion, namely the plunger head 11A, the lower tool assembly 10 uniformly forces the impregnant 30 into the substrate E.S.
  • each section is further pressurized, or driven up until the desired amount of impregnation is reached, which typically is designed to occur when the plungers 11 have fully forced all of the impregnant 30, which previously had occupied the channels 13, into the porous substrate E.S. (note Fig. 3) .
  • This causes the edge areas of the electrode substrate E.S. to become sealed all of the way through the depth of the substrate E.S.
  • the die 12 and its plunger 11 are then drawn back down to the disposition of Figure 1 for recharging of each of the channels 13 with impregnant (after the impregnated substrate E.S. has been removed from the die 12 if it had been carried up on the die 12) and subsequent re-positioning of the die and plunger 12 and 11 for use in edge sealing another electrode substrate E.S.
  • the edge impregnated substrate E.S. is then removed from the work station for drying out the impregnated areas (e.g., areas 1-4), typically by heating it, removing the liquid carrier materials and leaving the solids in the interstices of the impregnated areas of the substrate E.S.
  • the corrosion seals preferably will extend all of the way through the substrate body E.S.
  • Suitable fluorocarbon materials in aqueous dis ⁇ persions are Dupont's "Teflon 30" and "FEP 120".
  • a thickening agent for example, B.F. Goodrich's "Carbopol” (grade 941) , which is an acrylic acid polymer having the following chemical structure:
  • fluorocarbon dispersions used to make corrosion resistant coatings using the methodology of the prior art were diluted down, rather than thickened, to create a dispersion having a concentration compatible with the amount of "Teflon" desired for the final product.
  • a suitable exemplary impregnant 30 for making a corrosion resistant seal using the specialized tooling of Figure 1 has been found to be:

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Abstract

Le procédé décrit, qui sert à produire une jointure d'étanchéité imprégnée sur le bord d'une pile à combustible, consiste à modifier au moyen d'un outillage spécialisé la dispersion type de l'imprégnant au carbone/graphite, qui peut contenir par exemple 66 % en poids de carbone ou de graphite, en ajoutant à cette dispersion une petite quantité (par exemple 7 %) d'une solution concentrée d'hydroxyde d'ammonium (ayant par exemple une proportion d'environ 58 % en poids de NH4OH dans l'eau, équivalente à environ 28 à 30 % en poids de NH3 gazeux ajouté à l'eau pour obtenir la solution), en augmentant le pH de l'imprégnant jusqu'à un niveau d'environ 10,5 à 11,5, en améliorant les caractéristiques d'écoulement de la dispersion et en réduisant la tendance de la dispersion à se solidifier pendant le processus d'imprégnation. L'imprégnant ainsi modifier est injecté de force dans la zone de bord du substrat d'électrode (E.S.) de la pile à combustible, en vue de produire un joint d'étanchéité de bord en une seule pièce, grâce à l'utilisation d'un outil spécialisé (10 ou 10') comportant une matrice rigide (12) ou une matirce élastiquement flexible (12') pourvue d'un plongeur associé sensiblement rigide (11 ou 11'), lesquels définissent entre eux une chambre ou un canal allongé (13 ou 13') pour le passage de l'imprégnant (30; voir figures 1-3 ou 5). Un tel outil (10 ou 10') permet d'éliminer les effets de la thixotropie, dès lors que le volume de l'imprégnant (30) est limité par le volume de la chambre (13 ou 13'), ce qui permet de produire une jointure d'étanchéité de densité uniforme et dont les dimensions sont régulées par la forme du canal (13), éliminant ainsi les variations des forces de cisaillement observées dans la technique actuelle. L'outillage spécialisé (10 ou 10') peut également être utilisé pour imprégner un substrat d'électrode en y injectant un matériau étanche à l'eau, tel que notamment un fluorocarbone afin de former ainsi des jointures d'étanchéité résistant à la corrosion.
EP91918427A 1990-08-28 1991-08-28 Procede et appareil pour introduire un fluide d'impregnation dans une region d'un substrat poreux Withdrawn EP0546116A1 (fr)

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US57394590A 1990-08-28 1990-08-28
US573945 1995-12-18

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WO (1) WO1992003854A2 (fr)

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EP1156546B1 (fr) * 1997-07-16 2003-10-08 Ballard Power Systems Inc. Procede de fabrication d'une etancheite resiliente destinee a un ensemble electrodes a membrane (mea) dans une cellule a carburant electrochimique
US6423439B1 (en) 1997-07-16 2002-07-23 Ballard Power Systems Inc. Membrane electrode assembly for an electrochemical fuel cell
ATE216138T1 (de) * 1997-07-16 2002-04-15 Ballard Power Systems Elastische dichtung für eine membranelektrodenanordnung in einer elektrochemischen brennstoffzelle und herstellungsverfahren dafür
JP4008819B2 (ja) * 2001-02-07 2007-11-14 シーメンス アクチエンゲゼルシヤフト 燃料電池

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CH505687A (de) * 1967-03-11 1971-04-15 Harder Paul Verfahren und Vorrichtung zur Behandlung von Spanholzplatten und nach dem Verfahren behandelte Spanholzplatte
GB2121350A (en) * 1982-06-01 1983-12-21 John Albert Avery Bradbury Composite foamed articles and process for their production
US4555324A (en) * 1983-05-09 1985-11-26 Kabushiki Kaisha Toshiba Porous gas diffusion electrode and method of producing the same
US4756981A (en) * 1986-12-29 1988-07-12 International Fuel Cells Seal structure for an electrochemical cell
US4786568A (en) * 1988-03-01 1988-11-22 International Fuel Cells Corporation Electrode substrate with integral edge seal and method of forming the same

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See references of WO9203854A2 *

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CA2090477A1 (fr) 1992-03-01
WO1992003854A2 (fr) 1992-03-05

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