Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2000-11-09
2004-01-06
Ruthkosky, Mark (Department: 1745)
Metal working
Method of mechanical manufacture
Electrical device making
C029S623500, C429S047000
Reexamination Certificate
active
06673127
ABSTRACT:
BACKGROUND
This invention relates to a new method to coat metals, metal oxides, or metal alloys onto solid polymer electrolytes or other ion-conducting polymer surfaces. Materials prepared using this method would gain advantage in electrochemical and membrane-based applications. By employing dual ion-beam assisted deposition (IBAD), one can systematically prepare consistent thin films of these metals on solid polymer electrolyte membranes such as Nafions (DuPont, Wilmington, Del.), a copolymer of tetrafluoroethylene and sulfonyl fluoride vinyl ether and the membranes coated thereby and electrolytic cells containing the same.
STATE OF THE ART
The use of solid polymer electrolytes has greatly expanded the field of electrochemistry. Electrochemical processes depend on the transfer of ionic and electronic charge through the use of an anode, cathode, and an ionic liquid electrolyte. However, with the advent of the solid polymer electrolyte fuel cell, the traditional liquid phase has been replaced with a membrane composed of a polymer electrolyte that transfers ionic charge under typical electrolytic conditions. These solid polymer electrolytes are often ion-conducting membranes that are commercially available. For example, in addition to the previously mentioned Nafion (a cation exchange membrane), Asahi Chemical and Asahi Glass make perfluorinated cation exchange membranes whereby the ion exchange groups(s) are carboxylic acid/sulfonic acid or carboxylic acid. These companies produce cation exchange membranes with only the immobilized sulfonic acid group as well. Non perfluorinated ion exchange membranes are available through Raipore (Hauppauge, N.Y.) and other distributors such as The Electrosynthesis Co., Inc. (Lancaster, N.Y.). Anion exchange membranes typically employ a quaternary amine on a polymeric support and are commercially available as well. Other manufacturers and researchers fill the pores of an inert matrix with immobilized ionomer, creating an effective ion conducting membrane. (For example, see Fedkiw, P. S. and Nouel, K. M. in
Electrochemica Acta
, 1977).
Nafion is typically employed in some fuel cells. For the hydrogen/air (O
2
) fuel cell, hydrogen and oxygen are fed directly to the anode and cathode. respectively, and electricity is generated. In order for these “gas breathing” electrodes to perform, the electrode structure must be highly porous to allow three phase contact between the solid electrode, the gaseous reactant, and the electrode which can be in the form of a membrane or polymer electrolyte. This class of electrode is called a gas diffusion electrode. In addition to a gaseous hydrogen fuel and gaseous air (O
2
) oxidant, others employ a mixed phase system such as the methanol/air (O
2
) fuel cell. Here, liquid methanol is oxidized at the anode while oxygen is reduced at the cathode. Another utilization for ion-conducting membranes and gas diffusion electrodes includes the electrochemical generation of pure gases (for example see Fujita et al in
Journal of Applied Electrochemistry
, vol. 16, page 935, (1986)), electro-organic synthesis (for example see Fedkiw et al in
Journal of the Electrochemical Society
, vol. 137, no. 5, page 1451 (1990)), or as transducers in gas sensors (for example See Mayo et al in
Analytical Chimica Acta
, vol. 310, page 139, (1995)).
Typically, these electrode/ion-conducting membrane systems are constructed by forcing the electrode against the ion conducting membrane. U.S. Pat. Nos. 4,272,353; 3,134,697; and 4,364,813 all disclose mechanical methods of holding electrodes against the conducting membrane. However, the effectiveness of a mechanical method for intimately contacting the electrode to the polymer membrane electrolyte may be limited since the conducting membrane can frequently change dimensions due to alterations in hydration and temperature. Swelling or shrinking can alter the degree of mechanical contact.
Thus, a preferred method of contacting the electrodes with the polymer membrane electrolyte involves direct deposition of a thin electrode onto one or both sides of the polymer substrate. Nagel and Stucki in U.S. Pat. No. 4,326,930 disclose a method for electrochemically depositing platinum onto Nafion. Others have employed chemical methods whereby the metal salt is reduced within the polymer membrane (for example see Fedkiw et al in
Journal of the Electrochemical Society
, vol. 139, no. 1, page 15 (1992)). In both the chemical and electrochemical methods, one essentially precipitates the metal onto the ion conducting membrane. This precipitation can be difficult to control due to the nature of the ion-conducting polymer membrane, the form of the metal salt, and the specific method employed to precipitate the metal. As the goal of a thin, porous, and uniform metal layer is often not met via precipitation, practitioners have turned to other deposition methods.
Scientists and engineers have long realized that the specialized coating methods of ultra-high vacuum (UHV) evaporation, chemical vapor deposition (CVD), and sputter deposition (also called sputtering), may offer a better method to create thin metal electrode surfaces. A successful surface treatment via UHV starts with creating a clean substrate. Insuring the substrate surface is atomically clean before deposition can be of vital importance for adhesion. A source metal is contained in a water cooled copper hearth. This metal is vaporized through resistive, eddy-current, electron bombardment, or laser heating. The resulting vaporized metal diffuses to the substrate and condenses to form a film. Evaporation rates depend exponentially on temperature and thus means for precise temperature control is needed.
One method for minimizing these control problems is to heat the substrate to a temperature that still allows for condensation of the vapor. UHV is often used when freedom from contamination in both the film and the interface between the film is of the utmost importance—for example in the electronics industry. While UHV is appropriate for modifying electrode surfaces, using this technique for the direct deposit of a thin electrode layer onto an ion-conducting polymer substrate may be limited due to the temperature of deposition and constraints of an atomically clean substrate.
The chemical vapor deposition process occurs at atmospheric pressure and typically employs temperatures lower than UHV or sputtering. In CVD, the constituents of a vapor phase are often diluted with an inert carrier gas. The carrier and vapor phase are reacted at a hot surface and subjected to ions created by circular magnetrons. The substrate target is not part of the ion-creating circuit so only neutral vapors are deposited onto the target. However, unlike the condensation of UHV and sputtering, the surface reaction for CVD is considered a chemical reaction. For example, to deposit tungsten, one would mix hydrogen with tungsten hexafluoride at 800° C. Tungsten metal then deposits on the substrate via diffusion. While CVD may offer a potential method to coat an ion-conductive polymer membrane, once again the temperature restraints may allow this technique only limited application.
The most common metal deposition method is sputtering. The process begins by mounting a sample to a water-cooled support. The sample is next subjected to a vacuum, although not as high as in the UHV technique. Once vacuum is achieved, a source of metal is heated until the metal vaporizes. These metal atoms are further bombarded by positive ions of a carrier gas. The now ionized metal atoms diffuse to the substrate. Since the sample is cooled, the resulting metal vapor condenses on the sample. However, continuous ion bombardment imparts enough energy to re-evaporate the deposited metal on the substrate.
This annealing process of bombardment, condensation, and additional evaporation from the substrate eventually forms a thin metallic film. The pressure and substrate temperature employed controls the morphology of film formation. Often, substantial heating of the substrate occurs as the sputtered ions cool
Allen Robert J.
DeCastro Emory S.
Giallombardo James R.
DeNora S.p.A.
Muserlian Lucas and Mercanti
Ruthkosky Mark
LandOfFree
Method of forming robust metal, metal oxide, and metal alloy... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of forming robust metal, metal oxide, and metal alloy..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of forming robust metal, metal oxide, and metal alloy... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3188440