A typical fuel cell involves a redox process wherein reduction and oxidation processes are spatially separated and electrons given off in the reduction process can be passed as a current through a load, for example an electric motor of a motor vehicle. A well known example of a fuel cell entails use of hydrogen as a fuel for the reduction process and oxygen as the oxidizer for the oxidation process. For such fuel cells, a fuel that is readily available and can easily be stored, for example, a hydrocarbon such as natural gas or methanol, is reformed to provide a hydrogen-rich gas, and oxygen may be obtained by use of air.
A typical such fuel cell uses a proton exchange membrane (“PEM”) as its electrolyte. Such a membrane is an electronic insulator, but is an excellent conductor of hydrogen ions. An example of one such membrane is a copolymeric perfluorocarbon material containing a basic unit of fluorinated carbon chain and a sulphonic acid group (there may be variations in the molecular configurations of this membrane). PEMs are commercially available from a number of sources, for example, E. I. DuPont de Nemours Company offers a PEM manufactured from a perfluorcarbon material under the trademark Nafion. To fabricate a fuel cell, a PEM may be coated on both sides with active catalysts (as is also well known, catalysts may also be applied as coatings to electrodes), for example in the form of highly dispersed metal alloy particles (for example, mostly platinum). Typically, the catalyst is rough and porous so that a maximum surface area of the catalyst can be exposed to the fuel, for example, hydrogen or the oxidizer, for example, oxygen.
In practice, in one example of such a fuel cell, pressurized hydrogen gas (H2) enters the fuel cell on an anode side, and is forced through the catalyst by the pressure. Hydrogen molecules react electrochemically in the presence of the catalyst by dissociating into hydrogen atoms. The hydrogen atoms release electrons and become hydrogen ions, i.e., protons (the anode side reaction is: 2H2=>4H++4e−). The released electrons are conducted through the anode, and travel in the form of an electric current that can be utilized in an external circuit before arriving at a cathode side of the fuel cell. The hydrogen ions diffuse through the PEM to a cathode side of the fuel. At the same time, pressurized oxygen gas (O2) enters the fuel cell on the cathode side, and is forced through the catalyst by the pressure. Oxygen molecules react electrochemically in the presence of the catalyst by dissociating into oxygen atoms. The oxygen atoms accept electrons from the external circuit. Each negatively charged oxygen ion attracts two H+ ions through the PEM where they combine to form a water molecule (H2O), thus completing the overall process (the cathode side reaction is: O2+4H++4e−=>2H2O). A typical such PEM fuel cell: (a) operates at relatively low temperatures, from about 70° C. to about 85° C. (the low temperature of operation also reduces or eliminates the need for thermal insulation to protect personnel or other equipment); (b) produces water that is carried from the back of the cathode side of the fuel cell by the oxidizer gas stream; and (c) produces electrical energy which is the sum of the separate half cell reactions occurring in the fuel cell less its internal losses (typically about 0.45 to about 0.7 volts D.C. under a load). To get this voltage up to a practical level, many separate fuel cells are combined to form a fuel cell stack where multiple cells are electrically connected in series. The fuel cell stack: (a) is typically enclosed in a housing; (b) includes manifolds to direct fuel and oxidizer to the electrodes; and (c) is configured to provide cooling either by the reactants or by a cooling medium. Also included within a typical such fuel cell stack are current collectors, cell-to-cell seals, insulation, piping, and instrumentation. The stack, housing, and associated hardware make up a fuel cell module.
Some recognized advantages of fuel cells are: (a) they can power cars without polluting the environment; (b) they could enable regions with poorly developed infrastructures to generate electricity locally; (c) they exhibit high efficiency when compared to that of conventional combustion engines; and (d) their use might mean breaking dependence on crude oil and other fossil fuels.
Although there appear to be economic advantages of designs based on fuel cell stacks which utilize bipolar plates, this design has various disadvantages which have detracted from its usefulness. For example, if the voltage of a single cell in a fuel cell stack declines significantly or fails, the entire fuel cell stack (typically held together with tie bolts) must be taken out of service, disassembled, and repaired. In addition, in such fuel cell stack designs, fuel and oxidizer are directed to the electrodes by means of internal manifolds. Cooling for the fuel cell stack is provided either by the reactants, natural convection, radiation, and possibly by supplemental cooling channels and/or cooling plates. Also included in such fuel cell stack designs are current collectors, cell-to-cell seals, insulation, piping, and various instrumentation for use in monitoring cell performance. Such traditional designs are unduly large, cumbersome, and quite heavy.
In addition, further problems with fuel cells as they are produced today are: (a) such fuel cells are expensive; (b) they are fabricated utilizing parts that are difficult to machine and fabricate; (c) they are difficult to assemble (their design does not lend itself to automated assembly) and repair; (d) their shape or form is limited; (e) they are bulky and heavy; and (f) so forth.
In light of the above, there is a need in the art for a fuel cell and of fabricating a fuel cell that solves one or more of the above-identified problems.
USPTO Backgrounds
USPTO Backgrounds