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  Bipolar plateUSPTO Application #: 20060088755Title: Bipolar plate Abstract: A bipolar plate has a multi-layered structure including an inner metallic layer and at least one outer metallic, corrosion-resistant layer splatted, embedded, diffused and interlocked into the inner metallic layer. (end of abstract)
Agent: Dilworth & Barrese, LLP - Uniondale, NY, US Inventors: Hazem Tawfik, Yue Hung USPTO Applicaton #: 20060088755 - Class: 429038000 (USPTO) Related Patent Categories: Chemistry: Electrical Current Producing Apparatus, Product, And Process, Fuel Cell, Subcombination Thereof Or Methods Of Operating, Housing Member, Seal, Spacer Or Fluid Distributing Or Directing Means, Having Sealing Feature, Having Support Or Spacers With Fluid Distribution Means The Patent Description & Claims data below is from USPTO Patent Application 20060088755. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATION [0001] This application is a continuation of U.S. application Ser. No. 10/302,559 filed on Nov. 22, 2002, the contents of which is incorporated herein by reference in its entirety. BACKGROUND [0002] 1. Technical Field [0003] The invention relates to the art of electrochemical cells and more particularly, to a corrosion-resistant and durable metal bipolar plate capable of functioning in the highly corrosive fuel cell environment and a method of manufacturing the same. [0004] 2. Background of Related Art [0005] Due to increasing demand in the earth's limited energy resources and low conversion efficiencies of conventional power generation systems as well as environmental concerns, the need for a clean, reliable, and renewable source of energy has greatly escalated. Fuel cells are one of the most promising techniques to meet this need. [0006] In a fuel cell, the chemical energy is provided by a fuel, such as hydrogen, and an oxidant, such as oxygen, stored outside the fuel cell. Functionally, a fuel cell has two electrodes flanking an electrolyte. Oxygen passes over one electrode and hydrogen over the other, generating electricity, water and heat. [0007] Among numerous types of fuel cells, a proton exchange membrane cell (PEM) type is known for operating at relatively low temperatures (about 200.degree. F.), as well as for having high power density and varying their output quickly to meet shifts in power demands. All of the above-mentioned characteristics are found particularly attractive to automobile industry, where PEMs have been declared "the primary candidate for high-duty vehicles." [0008] The heart of the fuel cell, including the PEM fuel cell, is a thin, solid polymer membrane-electrolyte having an anode on one face of the membrane-electrolyte, whereas the other face thereof is provided with the cathode. The membrane is sandwiched between a pair of electrically conductive contact elements which serve as a current collectors configured to deliver and distribute the fuel cell's gaseous reactants (H.sub.2 and O.sub.2/air) over the surfaces of the respective anode and cathode. [0009] A bipolar PEM fuel cell comprises a plurality of the membrane-electrode-assemblies stacked together in the electrical series while being separated one from one another by an impermeable, electrically conductive contact element known as a bipolar plate. The opposite faces of the bipolar plate are juxtaposed with the anode of one cell and the cathode of the other cell, respectively. Accordingly, the bipolar plate separates adjacent cells and electrically conducts current therebetween. Furthermore, the bipolar plates give rigidity to the PEM fuel cell stack and support the membranes. In addition, the various flow channels for air, fuel and coolant are typically incorporated into the bipolar plates. [0010] In a working PEM environment, the bipolar plates are in constant contact with highly acidic solutions. Moreover, the cathode operates in a highly oxidizing environment while being exposed to pressurized air. Also, the anode is constantly exposed to super atmospheric hydrogen and an acidic environment as well. Hence, bipolar plates must be resistant to acids, oxidation, hydrogen and brittleness. Otherwise, the bipolar plates are affected by corrosion, which is detrimental to the performance of fuel cell as it fouls the catalyst of the electrode in the membrane electrode assembly and steadily degrades the cell's power output. [0011] Graphite is currently the most popular bipolar material for fuel cell applications because of its non-corrosive property. However, graphite is brittle and porous making it extremely difficult to machine and assemble bipolar plates during the production process. Still another consequence stemming from the inherent characteristics of graphite is that it is a poor load-support structure. Note that for the operation of the fuel cell, it is necessary to generate two perfectly sealed chambers, one for oxygen and the other for hydrogen. Since high loads are detrimental to structural integrity of graphite, a fuel cell stack often leaks externally because of the lack of sufficient forces capable of reliably sealing adjacent bipolar graphite plates. In addition, the fuel cell stack leaks internally as a result of the porosity of graphite. To combat this problem, the surfaces of the graphite bipolar plates are covered by a sealant, which, unfortunately, decreases the electrical conductivity of the graphite surfaces and, thus, increases the heat loss. Both types of leakage represent a safety hazard (hydrogen is extremely explosive) and may jeopardize the operation of the fuel cell. Finally, graphite is relatively expensive. [0012] As an obvious alternative to graphite, lightweight metals such as aluminum and titanium and their alloys have been proposed. While metals are non-porous, highly electro-conductive, inexpensive, durable and have low density, their use in the PEM environment is limited because of their low resistance to corrosion. [0013] Covering metal substrates with polymeric material increases electrical resistance of the bipolar plates. Hence, electrical conductivity of the bipolar plate at the very least decreases and, in some cases, may be dramatically reduced. [0014] It is, therefore, desirable to produce reliable and efficient metal-based bipolar plates capable of exhibiting high resistance to corrosion in an acidic environment. SUMMARY OF THE INVENTION [0015] A bipolar plate made from a metal substrate and having at least one corrosion-resistant metallic layer attains this objective. In accordance with one aspect of the invention, a metallic powder directed towards the substrate at high velocities forms the corrosion-resistant layer. In practice, the powdered metallic particles possessing great kinetic energy splat across and embed into the metal substrate at a depth. As a result, the metal substrate and powdered particles interlock and form the corrosion-resistant layer. [0016] In accordance with another aspect of the invention, the above-disclosed inventive concept has been implemented by the use of a thermal spray technique allowing the metallic particles to possess the necessary kinetic energy for the particles to impregnate and interlock with the metal substrate within the boundary region. Accordingly, the thermal spray technique provides base metal forming the substrate comprising an anti-corrosion layer. In other words, the thermal spray technique improves the anti-corrosion properties of a base metal. [0017] In accordance with one sub-aspect of the invention, the thermal-spray technique utilized for providing a corrosion-resistant metallic layer includes any method providing a particle stream with high velocities. These methods include plasma coating, detonation, diamond jet and high velocity oxygen fuel (HVOF) technologies, which are all associated with elevated temperatures and high velocities. Note, that the thermal spray techniques differ from one another by respective temperatures and velocities. For example, the plasma technology utilizes highly elevated temperatures, whereas, the HVOF is known for relatively low temperatures slightly exceeding the melting temperatures of the metallic particles and very high velocities. Still another promising technique associated with extremely high velocities and low temperatures is a cold gas dynamic technology characterized by high velocities and low temperatures. [0018] The high-velocity oxygen fuel (HVOF) technology has been found highly efficient within the context of this invention and, as known, uses oxygen and a fuel (liquid or gaseous) to produce a high velocity gas stream. Entrained in the gas stream is a line of nitrogen carrying metallic powder that impacts upon the metal substrate. As a result of the impingement of the particles against the metal substrate at high velocities, the metallic powder splats, embeds and impregnates a boundary region of the metal substrate. Hence, a multi-layered all metallic structure of the bipolar plate has a highly dense corrosion-resistant metallic layer. In addition to the thermal spray technology, a vapor-deposition technology can be utilized as well. The disadvantage of the latter is its relatively slow-rate of deposition. [0019] According to a further aspect of the invention, the metallic powder impacted into the metallic substrate preferably includes nickel-based, chrome-based and/or carbide-based alloys. In a preferred embodiment, these alloys are mixed. [0020] In a further aspect of the invention, because the thermal spray technique is associated with a significant temperature gradient across the bipolar plate to be treated, the latter tends to deform. Even assuming that the opposite faces of the bipolar plate have the same thermal expansion coefficient, the sprayed-upon face still would expand more than the opposing face. Since the principle of operation of the thermal spray technology is a combination of diffusion, interlocking and embedment resulting from of the high impinging forces of the heated particles, the plates tend to deform as a result of a temperature differential between the treated side and the opposing non-treated side of the bipolar plate. Accordingly, repeated deformation of the bipolar plate leads to eventual cracking of the corrosion-resistant layer and other physical consequences detrimentally affecting the bipolar plate. [0021] To minimize a temperature gradient, the invention provides for a few alternatives. One alternative is to increase the thickness of the bipolar plate. The downside of this seemingly easy solution is an increased volume, cost and weight of fuel a cell typically comprised of many bipolar plates. Continue reading... Full patent description for Bipolar plate Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Bipolar plate patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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