Fuel cell anode and fuel cell

Abstract: A nickel anode electrode component comprised of a support member and a porous coherent member formed from a non-sintered nickel alloy constituent. The support member and porous coherent member are laminated together and the nickel anode electrode component is assembled within a fuel cell and formed into an anode electrode in situ within the cell.

Description: Background of the Invention This invention relates to an anode for a fuel cell and, in particular, to an anode for a fuel cell comprised of a nickel alloy material. Anode electrodes comprised of nickel alloy material are used in molten carbonate fuel cells. These so-called "nickel anodes" when suitably fabricated provide increased resistance to creepage, thereby helping to preserve fuel cell performance and life. Fabrication procedures for nickel anodes are disclosed in US-A-5,041,159. US-A-5,229,221 discloses a standard process for fabricating nickel anodes, wherein a porous cohesive member comprised of a nickel alloy constituent is first formed. This is preferably accomplished by tape casting the member using a slurry containing the nickel alloy constituent. Typical alloy materials for the nickel alloy constituent might be aluminum, yttrium, magnesium, titanium, tantalum, molybdenum, chromium and cerium. After tape casting, the porous cohesive member is subjected to a sintering procedure in which the nickel alloy constituent is sintered and selectively oxidized. Sintering is accomplished by subjecting the member to elevated temperatures in a preselected atmosphere. A typical temperature range for the elevated temperature might be 800°C to 1100°C and a typical atmosphere might be an atmosphere comprised of water and hydrogen in amounts providing partial pressures of the gases in a range of 25:1 to 110:1. Following the sintering process, the sintered member is then subjected to a filling process in which the pores of the member are partially filled with a preselected amount of electrolyte material. This completes the anode electrode fabrication and the completed electrode is then assembled with other elements, including a cathode electrode element and an electrolyte tile, to form a complete fuel cell. In the aforesaid anode electrode fabrication, the process of forming the metal alloy slurry and the processes of sintering the cohesive porous member and filling the sintered member with electrolyte are batch processes. Accordingly, the processes are costly to carry out, since each process has yield associated losses. Additionally, the sintering process results in a fragile sintered member whose thickness must be kept at or above a minimum value, typically 18 mils, to realize acceptable yields. This increases the anode material required, which adds to the overall cost of the anode. In order to eliminate certain of these batch processes, it has been proposed to carry out the sintering and filling processes, in situ, i.e., within the fuel cell. With this method, the tape cast cohesive member is appropriately assembled in the fuel call in the anode electrode location and the fuel cell operated. This causes the cohesive member to be subjected to an elevated temperature and to a water and hydrogen atmosphere sufficient to sinter and oxidize its nickel alloy constituent and to partially fill the pores of the sintered structure with electrolyte. While this provides the desired nickel anode electrode structure, certain undesirable effects such as, for example, unwanted sagging of the cohesive member, have been found to occur. These effects result in loss of contact and increased resistance for the anode electrode which over time, can seriously degrade fuel cell performance. JP-A-60154467 discloses a process for the manufacture of a fuel cell electrode wherein a paste obtained from a mixed powder of nickel and another metal is spread in a porous body such as a screen or expanded metal. The anode is then assembled in a molten carbonate fuel cell without sintering. Sintering is not performed before assembling the fuel cell and it occurs during increasing the temperature for operation or at operating temperature. It is mentioned that a binder solution can be mixed to the material to prepare the paste. A thermoplastic resin can be used as binder in addition to the binder solution and, after smoothing the coated surface or pressing, the coated porous body can be heated at a temperature at which the resin powder is melted. Summary of the Invention The invention as claimed in claims 1, 14 and 21 solves the problem of how to reduce degradation of fuel cell performance over time. The nickel anode electrode component comprises a porous cohesive member and a support plate to which the cohesive member is laminated. The porous cohesive member is formed from a nickel alloy constituent which is non-sintered. The laminating procedure is carried out with an applied pressure in the range of 6.9 to 20.7 MPa (1000 to 3000 psi) and results in the support member being embedded in the cohesive member by an amount which is in the range of 0.0127 to 0.127 mm (0.0005 to 0.005 of an inch). The nickel anode electrode component so fabricated is assembled with other elements into a fuel cell. Operation of the fuel cell sinters and oxidizes the nickel alloy constituent of the porous cohesive member and also results in electrolyte partially filling the pores of the sintered member. This provides in situ completion of the anode electrode. Preferably, the support member of the nickel anode electrode component is a metallic member having a plurality of through openings each having a size which is within the range of 0.0127 to 0.762 (0.005 to 0.030 of an inch). Also, preferably, the thickness of the nickel anode electrode component is within a range of 0.127 to 0.635 mm (0.005 to 0.025 of an inch). Brief Description of the Drawings The above and other features and aspects of the present invention will become more apparent upon reading the following detailed description in conjunction with the accompanying drawings in which: FIG. 1 shows a nickel anode electrode component in accordance with the principles of the present invention; FIG. 1A shows a further type of support member usable with the nickel anode electrode component of FIG. 1; FIG. 2 shows the nickel anode electrode component of FIG. 1 assembled into a fuel cell; FIG. 3 shows the processing steps for making the nickel anode electrode component of FIG. 1 and for transforming the component into an anode electrode; FIG. 4 shows schematically equipment for carrying out the laminating process of FIG. 1; FIGS. 5 and 6 show the operating characteristics of single cell fuel cells constructed with the nickel anode electrode component of FIG. 1; and FIG. 7 shows the operating characteristics of a large area (5500 cm 2 ) fuel cell stack utilizing fuel cells constructed as shown in FIG. 2. Detailed Description FIG. 1 shows a fuel cell anode electrode component 1 in accordance with the principles of the present invention. As shown, the component 1 includes a porous cohesive member 2 which is laminated to a support member 3. The porous cohesive member 2 comprises a non-sintered nickel alloy constituent. Typical alloys for the non-sintered nickel alloy constituent might be aluminum, yttrium, magnesium, titanium, tantalum, molybdenum, chromium and cerium. The support member 3 comprises a metallic material. Typical metallic materials might be nickel, copper or other similar corrosion resistant materials. The support member 3 also includes through openings 4 each of which preferably has a size in the range of 0.127 to 0.762 mm (0.005 to 0.030 of an inch). In the case of FIG. 1, the support member 3 is in the form of a plate with the openings 4 formed by perforations in the plate. Alternately, the member 3 can be formed as an expanded member having interruptions to form the through openings. Such a member is illustrated in FIG. 1A. The overall thickness of the component 1 formed by the lamination of the porous cohesive member 2 and support member 3 is, preferably, in the range of 0.127 to 0.635 mm (0.005 to 0.025 of an inch). Of this thickness, the thickness of the member 2 is in a range of 0.0762 to 0.381 mm (0.003 to 0.015 of an inch). The member 2 and overall anode electrode component 1 are thus of relatively thin configuration. The ability to utilize a thin member 2 decreases the amount of nickel alloy constituent required to form the anode component 1, thereby reducing its overall cost. As a result of the pressure applied during the lamination process, the support member 3 extends into the porous cohesive member 2 by an amount which is in the range of 0.0127 to 0.127 mm (0.0005 to 0.005 of an inch). This results in an effective adherence or securement of the members together during the in situ formation of the component 1 into an anode electrode of a fuel cell. FIG. 2 shows the nickel anode electrode component 1 assembled with other elements to form a fuel cell 11, shown as a high temperature carbonate type fuel cell. The cell 11 includes an electrolyte tile 12 whose one face abuts the porous cohesive member 2 of the anode electrode component 1 and whose other face abuts a cathode electrode 13. A separator plate 15 abuts the peak regions of a corrugated current collector plate 14 whose valley regions abut the support member 3 of the anode component 1. A similar cathode current collector plate 15 with transverse corrugations abuts the cathode electrode component 13. The passages 14A and 15A defined by the plates 14 and 15 carry fuel and oxidant gas to the cell 11. As above-indicated, the nickel anode electrode component 1 is formed into a completed nickel anode electrode in the cell 11, i.e., in situ, by initial operation of the cell. During such operation, the temperature of the cell becomes elevated, i.e., rises to above 600°C, and a mixture of gases (hydrogen, carbon dioxide and water) is produced adjacent the anode electrode component. These conditions of the cell, when maintained over a period of time, are sufficient to result in sintering and oxidizing of the nickel alloy constituent of the porous coherent member 2 of the anode component 1. They also result in the sintered component having its pores partially filled with electrolyte from the tile 12 which becomes molten at the operating temperature of the cell. This transforms the anode component 1 into a completed anode electrode. More particularly, the elevated temperature of the fuel cell 11 is above the Tamman temperature for nickel, i.e., above about 586°C, which is the approximate temperature at which particulate nickel begins to sinter. Also, at this temperature, as above-indicated, the electrolyte tile is molten so that liquid phase sintering takes place which enhances the nickel sintering significantly. Additionally, the oxygen partial pressure in the fuel cell gas composition as determined by the water to hydrogen ratio is sufficient to internally oxidize the dispersed alloy in the nickel alloy constituent of the porous coherent member 2. Once this occurs, the continued heating sinters the nickel alloy constituent and an anode electrode in the form of a porous plaque partially filled with electrolyte results. The anode electrode so formed is found to exhibit creep stabilization and resistance to deformation. The latter characteristic is, in part, attributable to the support member 3 which prevents particle flow of the alloy constituent of the coherent member 2 during the oxidation and sintering. More particularly, it is believed that the porous coherent member 2 during in situ formation, has the tendency to undergo particle flow and rearrangement after burnout of the organic binders in the member. This occurs during the temperature rise of the fuel cell and prior to sintering. These effects, as opposed to creep, are believed to cause the resultant anode electrode to deform during use of the fuel cell. With the present anode electrode component 1, this flow and rearrangement of the nickel alloy constituent of the member 2 is significantly reduced owing to lamination of the member 2 to the support member 3. Moreover, the relatively small through openings 4 of the member 3 are further believed to enhance adherence and embedment of the member 3 into the member 2. This promotes less thickness change in the resultant in situ formed anode electrode. FIG. 3 shows the above-described process steps for the anode electrode formation. First, in step 41 a slurry of the nickel alloy constituent is formed. In step 42, the slurry is tape cast to produce the porous coherent member 2. The member 2 and support member 3 are then subjected to a lamination step 43 which results in the nickel anode electrode component 1. The component 1 is then assembled into the fuel cell 1 at step 44. The fuel cell 11 is then operated at step 45 to transform the component 1 into the anode electrode of the cell. The lamination step 43 in the process of FIG. 3 can be carried out in a number of ways. As shown in FIG. 4, the porous coherent member 2 and support member 3 are laminated using two facing rollers 51 and 52. The members 2 and 3 are passed into the nip of these rollers so that the members are pressed together under high pressure. This pressure is in the range of 6.9 to 20.7 MPa (1000 to 3000 psi). The use of the rollers 51 and 52 provides greater embedment of the support member 3 into the coherent member 2. Other laminating techniques might include using a press to press the members 2 and 3 together under high pressure. FIGS. 5 and 6 show the operating characteristics of two single cell fuel cells assembled with a nickel anode electrode component in accordance with the invention. As can be seen, the cell of FIG. 5 operated continuously for almost 6000 hours with very stable performance over the first 4000 hours. The cell of FIG. 6 also showed very little performance decay (less than 10 mV) for 800 hours of continuous operation. Upon disassembly of these cells, both were found to exhibit little anode deformation of the anode plaque into the support member beyond the 0.0254 mm (0.001 of an inch) due to the laminated construction. A large area (5500 cm 2 ) stack of six fuel cells with anode electrodes formed in accordance with the invention were assembled and the performance characteristic of this cell is shown in FIG. 7. As can be seen, stable operation for the fuel cell stack was realized for approximately 1700 hours of continuous operation.

Claims: A method to form a nickel anode electrode component (1) comprising the steps of: applying a nickel alloy constituent to a support member (3); characterized by: first forming said nickel alloy constituent into a non-sintered porous cohesive member (2) and then applying said non-sintered porous cohesive member (2) to said support member (3) by laminating said non-sintered porous cohesive member (2) to said support member (3) under a pressure in the range of 6.9 to 20.7 MPa (1000 to 3000 psi), the support member (3) being embedded in the cohesive member (2) by an amount which is in the range of 0.0127 to 0.127 mm (0.0005 to 0.005 of an inch). A method in accordance with claim 1 further comprising: assembling said nickel anode electrode component (1) with other elements to form a fuel cell (11); and operating said fuel cell (11) to sinter said nickel alloy constituent of said porous cohesive member (2) of said nickel anode electrode component (1). A method in accordance with claim 2 wherein: said operating of said fuel cell (11) selectively oxidizes said nickel alloy constituent of said porous cohesive member (2) of said nickel anode electrode component (1). A method in accordance with claim 3 wherein: said operating of said fuel cell is such as to expose said nickel alloy constituent of said porous cohesive member (2) of said nickel anode electrode component (1) to an elevated temperature and to a gaseous atmosphere. A method in accordance with claim 4 wherein: said gaseous atmosphere includes a mixture of water and hydrogen at preselected partial pressures. A method in accordance with any one of claims 1 to 5 wherein: said support member (3) includes a plurality of through openings (4). A method in accordance with claim 6 wherein: each of said through openings (4) is of a size within a range of 0.127 to 0.762 mm (0.005 to 0.030 of an inch). A method in accordance with claim 7 wherein: said support member (3) comprises a metallic plate having perforations forming said through openings (4) or an expanded metallic plate (Fig. 1A) having interruptions forming said through openings. A method in accordance with claim 7 wherein: said nickel anode electrode component (1) has a thickness within a range of 0.127 to 0.635 mm (0.005 to 0.025 of an inch). A method in accordance with any one of claims 1 to 11 wherein: said bringing of said porous cohesive member (2) and said support member (3) into contact under pressure is carried out by passing said porous cohesive member (2) and said support member (3) between two spaced rollers (51, 52). A method in accordance with any one of claims 1 to 10 wherein: said forming step comprises tape casting said nickel alloy constituent to form said porous cohesive member (2). A method in accordance with any one of claims 1 to 11 wherein: an element of said nickel alloy constituent is aluminum, yttrium, magnesium, titanium, tantalum, molybdenum, chromium or cerium. A method in accordance with claim 12 wherein: said support material comprises a metallic material. Apparatus for use with a fuel cell comprising: a nickel anode electrode component (1) including: a support member (3); and a nickel alloy constituent affixed to said support member, characterized by said nickel alloy constituent having been formed when separate from the support member (3) as a non-sintered porous cohesive member (2), and then having been laminated to said support member (3) by bringing said non-sintered porous cohesive member (2) and said support member (3) into contact under a pressure in the range of 6.9 to 20.7 MPa (1000 to 3000 psi), the support member (3) having been embedded in the cohesive member (2) by an amount which is in the range of 0.0127 to 0.127 mm (0.0005 to 0.005 of an inch). Apparatus in accordance with claim 14 wherein: said nickel anode electrode component has a thickness within a range of 0.127 to 0.635 mm (0.005 to 0.025 of an inch). Apparatus in accordance with any one of claims 14 and 15 wherein: said nickel anode electrode component (1) has a thickness within a range of 0.127 to 0.635 mm (0.005 to 0.025 of an inch) ; and said support member has through openings (4) each of which is of a size within a range of 0.127 to 0.762 mm (0.005 to 0.030 of an inch). Apparatus in accordance with claim 14 wherein: said support member (3) has a plurality of through openings (4). Apparatus in accordance with claim 17 wherein: each of said through openings (4) is of a size within a range of 0.127 to 0.762 mm (0.005 to 0.030 of an inch). Apparatus in accordance with any one of claims 14 to 18 wherein: said support member (3) comprises a metallic plate having perforations forming said through openings (4) or an expands metallic plate having interruptions forming said through openings. Apparatus in accordance with any one of claims 14 to 19 wherein: an element of said nickel alloy constituent is aluminum, yttrium, magnesium, titanium, tantalum, molybdenum, chromium or cerium. A fuel cell comprising: an apparatus in accordance with any one of claims 14 to 20. A fuel cell in accordance with claim 21 wherein: said nickel alloy constituent of said non-sintered porous cohesive member (2) is sintered by operation of said fuel cell (11). A fuel cell in accordance with claim 21 or 22 further comprising: a cathode element; and an electrolyte tile. A fuel cell in accordance with claim 23 wherein: said electrolyte is a carbonate electrolyte.

Inventors: DOYON JOEL D, DOYON, JOEL D.
Applicants: ENERGY RES CORP, ENERGY RESEARCH CORPORATION (A CORPORATION OF THE STATE OF NEW YORK)
Application year: 1995
Main classification: H01M4
IPC codes: H01M4, H01M8