Patent Application
20060088760
The present invention relates to fuel cells, and more particularly to separator plates of fuel cell stacks.
Fuel cells produce electricity through electrochemical reaction and have been used as power sources in many applications. Fuel cells can offer significant benefits over other sources of electrical energy, such as improved efficiency, reliability, durability, cost and environmental benefits. Fuel cells may eventually be used in automobiles and trucks. Fuel cells may also power homes and businesses.
There are several different types of fuel cells, each having advantages that may make them particularly suited to given applications. One type is a proton exchange membrane (PEM) fuel cell, which has a membrane sandwiched between an anode and a cathode. To produce electricity through an electrochemical reaction, hydrogen (H2) is supplied to the anode and air or oxygen (O2) is supplied to the cathode.
In a first half-cell reaction, dissociation of the hydrogen (H2) at the anode generates hydrogen protons (H+) and electrons (e−). Because the membrane is proton conductive, the protons are transported through the membrane. The electrons flow through an electrical load that is connected across the electrodes. In a second half-cell reaction, oxygen (O2) at the cathode reacts with protons (H+) and electrons (e−) are taken up to form water (H2O). Parasitic heat is generated by the reactions and must be regulated to provide efficient operation of the fuel cell stack.
Separator plates distribute anode and cathode reactants and coolant across the fuel cell stack. Adjacently stacked separator plates define a bipolar plate that forms a portion of and separates adjacent fuel cells. The bipolar plate serves several functions for fuel cell stack operation. More specifically, a surface of the bipolar plate distributes the anode reactant for a fuel cell and another surface of the bipolar plate distributes the cathode reactant for an adjacent fuel cell. Further functions of the bipolar plate include separating individual cells in the fuel cell stack, carrying current and water from the individual fuel cells, humidifying the reactants and regulating fuel cell temperature. In order to perform each of these functions, traditional bipolar plates are somewhat complex in design. More specifically, bipolar plates include straight or serpentine flow channels, internal manifolds, internal humidification and internal cooling.
Bipolar plates, however, include other design constraints. For example, the bipolar plates must be low cost, easy to manufacture, chemically compatible to the reactants and reactant products flowing therethrough, corrosion resistant, have high electrical and thermal conductivity, be gas impermeable and have sufficient mechanical strength.
Accordingly, the present invention provides a separator plate for a fuel cell stack. The separator plate includes an electrically non-conductive base plate having a reactant flow field formed in a reactant surface thereof. An electrically conductive layer is bonded to the reactant surface of the base plate.
In one feature, the electrically conductive layer is a metal layer. The metal layer comprises at least one of a metal from a group consisting of Cu, Zn, Co and Ni.
In another feature, the electrically conductive layer comprises a base layer and a covering layer. The base layer comprises at least one of a metal from a group consisting of Cu, Zn, Co and Ni. The covering layer comprises at least one of a metal from a group consisting of Au, Pt, Pd, Ag and Ir.
In still another feature, the base plate is comprised of a material from a group consisting of a thermoplastic and a thermoset.
In yet another feature, a coolant flow field formed in the base plate.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
Referring now to
The separator plates 16 of the bipolar plate 20 include an anode plate 16a and a cathode plate 16c. The anode plate 16a has an anode surface 24 and a coolant surface 26. Anode channels 30 are formed in the anode surface 24 and coolant channels 32 formed in the coolant surface 26. The cathode plate 16c includes a cathode surface 34 and a coolant surface 36. Cathode channels 38 are formed in the cathode surface 34 and coolant channels 40 are formed in the coolant surface 36. The anode plate 16a and cathode plate 16c are stacked together so the coolant surfaces 26,36 lie adjacent to one another. The coolant channels 32,40 of the coolant surfaces 26,36 align to form coolant flow paths 42.
Referring now to
In the case of the base plate 48 being a thermoplastic, a high temperature polymer blend is preferred. One such polymer blend includes NORYL GTX917™, manufactured by GE Plastics. NORYL GTX917™ is a heterogeneous polymer blend that includes nylon 66, polyphenyl oxide (PPO) and a small amount of plastic filler. The thermoplastic is molded into the based plate 48. In this manner, the reactant and coolant channels and other features of the base plate 48 are directly formed by the molding process. After molding, the base plate 48 is degreased and etched to modify the surface in preparation for deposition of the conductive layer 50. Besides etching, other surface modification processes are anticipated, including, but not limited to, sand blasting and UV or laser irradiation. After surface modification, the base plate 48 is neutralized and activated. Activation can be achieved by immersing the base plate 48 in stannous chloride and palladium chloride solutions. The electrically conductive layer 50 is then applied using the plating or metallizing process.
In the case of the base plate 48 being a thermoset, a high temperature, fiber reinforced compression molded sheet molding compound (SMC) is preferred. The thermoset preferably includes in-mold coating (IMC) on the surface with an appropriate amount of finely dispersed calcium carbonate to facilitate the plating or metallizing processes. The thermoset along with the IMC are molded into the based plate 48. As similarly described above for a thermoplastic, the reactant and coolant channels and other features of the base plate 48 are directly formed by the molding process. After molding, the base plate 48 is degreased and etched to modify the surface in preparation for deposition of the conductive layer 50. Besides etching, other surface modification processes are anticipated, including, but not limited to, sand blasting and UV or laser irradiation. After surface modification, the base plate 48 is neutralized and activated. Activation can be achieved by immersing the base plate 48 in stannous chloride and palladium chloride solutions. The electrically conductive layer 50 is then applied using the plating or metallizing process.
The electrically conductive layer 50 is deposited onto the surface of the base plate 48 by a metallizing or electroless plating process. Using electroless plating, metal can be deposited onto non-conductive materials such as composites or plastics. In terms of cost, time and complication, electroless plating is a more efficient process for depositing metal onto non-conductive materials than other processes such as chemical and physical vapor deposition processes. The electroless plating process is independent of any laws of electrical current distribution. As a result, a uniformly thick conductive layer can be deposited onto the entire reactant surface 24,34. Further, the electrically conductive layer 50 can be applied to only a portion of the reactant surface 24,34 if desired. This is achieved by masking the portions of the reactant surface 24,34 and plating the electrically conductive layer 50 on the unmasked portions. Although electroless plating is the preferred deposition process, other processes such as the chemical and vapor deposition processes can be used to deposit the electrically conductive layer 50 onto the base plate 48.
Referring now to
The composite separator plate 16 of the the present invention provides significant advantages over traditional separator plates. The separator 16 is thinner, lighter, cheaper and easier to manufacture than traditional separator plates, including traditional electrically conductive composite separator plates. The electrically conductive layer 50 is highly corrosion resistant and has both high electrical and thermal conductivity, each of which improves the durability of the fuel cell stack 10. Also, because the base plate 48 is electically non-conductive, a less expensive non-dielectric coolant can be implemented to cool the fuel cell stack 12.
The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.
