Patent Application
20100000434
This invention relates to the field of fuel cells, and more particularly to the field of embedded electronics for systems that are subject to a period of “standby” prior to powering up.
In a fuel cell the chemical energy present in hydrogen and the oxidant (oxygen) is cleanly, quietly and efficiently converted electrochemically into electrical energy. The hydrogen is oxidized at the anode (negative pole) and the oxygen (or air) is reduced at the cathode (positive pole) of a single cell. The catalyst on the anode promotes the oxidation of hydrogen molecules into hydrogen ions (H+) and electrons: the hydrogen ions migrate through the membrane to the cathode, where the cathode catalyst causes the combination of the hydrogen ions, electrons and oxygen to produce water. The polymer membrane in the so-called “Proton Exchange Membrane Fuel Cell” (or PEMFC) conducts the hydrogen ions best when fully hydrated.
The flow of electrons through an external circuit produces electric current, which can be used, for example, by a direct current (DC) electric motor. An inverter provides alternating current (AC) for modem days applications.
The electrodes may be formed by a thin layer of catalyst applied to an appropriate backing placed on the opposite surface of the thin polymer membrane. Two bipolar plates are positioned against this backing, one on each side of the membrane. The bipolar plates have two functions: the transmission of electrons through the elementary cells and the release of heat to the external environment.
The side of bipolar plates facing the membrane electrode assembly (MEA) may be provided with ribs, which allow for the distribution of the gases (hydrogen and air) and the discharge of the resultant product water.
The power requirement in fuel cell technology is achieved by enlarging the cell area (to increase the ampere requirements) and by combining a number of single cells in series to produce a fuel cell stack by means of the bipolar plates (to increase voltage requirements). A number of stacks are then combined to produce a power plant as shown in
In the conventional art shown in
Next to anode end plate 2 is a membrane electric assembly 4, and bipolar plate 6. Bipolar plate 6 is followed by membrane electrode assembly 8, and then by bipolar plate 10. Finally, there is another membrane electrode assembly 12 before cathode end plate 14. As shown in the figure, the bipolar plates 6 and 10 act as an anode for one cell and a cathode for the adjacent cell. The plate may be made of metal or a conductive polymer (which may be a carbon-filled composite). The plate can incorporate flow channels for the fluid feeds and may also contain conduits for heat transfer. The membrane electrode assemblies are the structure comprising of an electrolyte (proton-exchange membrane) with surfaces coated with catalyst/carbon/binder layers and sandwiched by two microporous conductive layers (which function as the gas diffusion layers and current collectors).
The several types of fuel cells include the electrolyte type. The electrolyte in between the electrodes defines the operating temperature and, at that temperature, a suitable catalyst may be selected.
A major standby power requirement exists with respect to munitions production suitable for military application. Munitions today are “smart” which may mean they have electronics embedded in them to aid in achieving hits on the desired targets.
Currently, batteries, and in particular lithium batteries, are employed in many “smart” munitions. However, since munitions are produced during periods of non-use and subsequently stockpiled for use during period of conflict, storage or “shelf life” becomes an issue. Batteries embedded in such devices should be capable of long term survival, requiring continued reliably for perhaps decades in storage. Additionally, the embedded batteries should retain their capabilities under the most demanding environmental conditions. The alternative of enabling munitions with a battery immediately prior to its use is extremely undesirable for combat situations.
Published Patent Application No. 2003 0152815 relates generally to electrical power sources and more particularly to microscopic batteries some forms of which are integrated or integratable with and providing internal power to MEMS and integrated microcircuits, either on a retrofit or original manufacture basis. MEMS (microelectromechanical systems) involve the fabrication and use of miniature devices which comprise microscopic moving parts (such as motors, relays, pumps, sensors, accelerometers, etc.). MEMS devices can be combined with integrated circuits, and can perform numerous functions. For example, military applications for remote sensors and accelerometers include: safing and arming of fuses; friend or foe identification; embedded sensors for system integrity monitoring; communications systems monitoring, such as with satellites; low power mobile displays; flexible sensing surfaces; and numerous others. For example, the microscopic batteries of Patent Application No. 2003 0152815 do not employ fuel cell technology due to the perceived limitation of providing sufficient power to drive the microdevices.
U.S. Pat. No. 6,506,513 and U.S. Published Patent Application No. 20030082421 each disclose a fuel cell assembly in which the fuel tank is located separate from the fuel cell and feeds the fuel to the cell via capillary action using a fuel permeating material; while U.S. Published Patent Application No. 2003 0129464 discloses a fuel cell assembly employing a separate fuel source which is rupturable by a needle for drawing out the fuel which is supplied to the fuel cell.
One embodiment of this invention is to generate electricity after having a device in “standby” mode for long periods of time, i.e. many years. In another embodiment of this invention, a method of construction of a device that is able to generate electricity after being in “standby” mode for long periods of time is discussed. In general, usage in this “standby” mode is called “shelf life” and batteries have been a primary way to achieve this goal.
Although generators could be considered to fit this definition, their relative size precludes them from all but the most energy intensive applications, so they are not normally considered part of this invention, but may be utilized when size is not a concern. A variety of batteries may fill most short and medium shelf life niches with little problems. However, it is where the shelf life requirements go into the decades that batteries start to have failure issues because of their inherent chemical nature.
Thus, in another embodiment of the invention, a fuel cell may include at least one of the following features or components: a membrane, and/or storage tanks or cells for hydrogen and oxygen, and/or an “inertial” switch, which may optionally be assembled in close proximity to a membrane. The inertial switch, when activated, may rupture the membrane and allow the hydrogen and oxygen to mix in a fuel cell.
The Figures illustrates the component Fuel Cell Stack, an Inertial Switch, and the Polymer Electrolyte Membrane Battery (PEMERY) of the invention and a conventional fuel cell.
A more complete appreciation of the present invention, and one or more of the attendant advantages thereof, will be readily ascertained and/or obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
The micro fuel cell according to one exemplary embodiment is a new product configured uniquely from several emerging technologies. One exemplary embodiment also involves the process of making the new product. The micro fuel cell can include three major features or components: a polymer electrolyte membrane, or PEM, and/or a miniature nanotechnology storage tanks or cells for hydrogen and oxygen to be relied upon by the fuel cell in generating electricity which may be fracturable, frangible, rupturable, or puncturable in order to be activated to release the hydrogen and oxygen, and a miniature or nanotechnology “inertial” switch, such as a G-force switch or centrifugal-force switch. When assembled, these three features or components together may present a very small package uniquely suitable for this application.
The present invention, in one exemplary embodiment, may include a fuel cell. Current polymer electrolyte membrane (PEM) fuel cells have produced cells of 0.2 millimeters in thickness that can produce better than 0.5 ampere of current per square centimeter at 0.7 volts. Supporting structures will increase that size, and the stacking of the cells could be utilized to deliver higher voltages. Through recent advancements in design, a remarkably small cell will generate voltages and currents as good as any existing or proposed battery.
The elements of this PEM technology have developed to the point that appropriate and inventive packaging or assembling can be utilized. One embodiment of this invention depicts the utilization of such a unique assembly and the method of making such an assembly. As promising as PEM fuel cell technology is in size reduction, it is the size that's important, so any future method developed that also could be miniaturized would also work in this application.
In another exemplary embodiment of the present invention, a method and apparatus for storage of the fuel and oxidant for the fuel cell is addressed. Fuel cells may use of hydrogen and oxygen in order to operate. Typically, this supply should be proximate to the cell structure but, remote storage may work better in some applications.
To accomplish this in a miniaturized environment can require, in one embodiment of the invention, a corresponding miniaturization of conventional storage “tanks” is preferable. Alternatively, in another embodiment, these “tanks” may be constructed from very small blocks of material which are honeycombed, or otherwise “tunneled.”
In this embodiment, such small blocks of material are infiltrated with micro channels, cavities, passages, sinuses or nano-tunnels functioning as one or more storage media. In a munitions application where a very short active life is required, material constructed or otherwise provided with micro-cavities or nano-tunnels affording adequate storage capacity for the hydrogen and oxygen used to run the fuel cell for a period of time sufficient to carry out its objectives. Alternatively, in another exemplary embodiment this device may also be used for standby power, remote location and for emergency radio beacons as used in downed aircraft as a few non-limiting examples.
In another exemplary embodiment of the unique fuel cell structure and method, a connecting device placed between the PEM cell assembly and the two gas storage tanks. The purpose of this connecting device is to serve as a way to deliver the stored hydrogen and oxygen to the proximity of the power generation portion of the cells, such that the voltage generation can take place.
Many equivalent variations of this connecting device are possible, such as, for example, chemical, electrical, or mechanical switches, but a preferred embodiment for the munitions application involves a mechanical inertial switch.
An inertial switch is shown in
When sufficient G forces, for example, or any other force sufficient to activate the switch, are generated, the weight 34 forces probes 24 and 26 through membrane 28. Hydrogen is then able to flow through hollow probe 24 and oxygen is able to flow through hollow probe 26 into receivers 30 and 32, respectively, allowing for the generation of power in a fuel cell stack below the inertial switch. This is further described in
Each of these probes (24 and 26) is counterbalanced against movement. For example, a biasing force may be afforded by a spring or spring-like element, or a resilient memory material, pneumatic pressure, or other similar and equivalent means to generally and continuously (for long periods of time) maintain a first position adjacent, yet apart, from a respective membrane.
More recently, delicate, micro-inertia switches have been developed that may be employed in this structural context. Upon the imposition of dynamic forces of movement, usually expressed in terms of G forces, overcoming the biasing force, the probes move against their respective membranes, thereby rupturing or penetrating the membranes. In this way, hydrogen and oxygen are released to flow to the fuel cell region.
Since many applications of this micro fuel cell technology involve one-time use, no reset action may be necessary. However, a reset mechanism and system is an alternative embodiment for either military or commercial applications. Reset mechanisms can be valves which may optionally be mechanically or electrically operated by an operator or by an automated system.
In another embodiment of the present invention, the fuel cell and method, prior to activation (either purposeful or in response to inertial forces), has no active ongoing processes, as opposed to those that exist with respect to common batteries. Where batteries are involved, such ongoing processes typically act to deplete a battery's capacity to perform when ultimately needed. The sealed hydrogen and oxygen storage tanks of at least one embodiment of the present invention inhibit active processes from happening and reduce the problems associated with ongoing processes.
In the inventive assembly described and illustrated in
Because the barriers discussed with respect to
The novel fuel cell and the method for its fabrication may have applications across a wide range of fields, ranging from military ordnance systems to commercial signaling devices or detectors, and to space exploration where a power-up cycle may be called upon a year or even many years following a launch. Its miniature size makes the novel fuel cell particularly suitable anytime and anywhere that space is limited, weight is critical and time to power-up may be considerably long.
In some applications, an inertial switch may optionally be unnecessary. In these applications the inertial switch could be replaced by another device offering different functionality than that of the inertial switch. In one exemplary embodiment, the inertial switch could be replaced with any other on/off device giving the unit the ability to turn on run for some period and then turn off again. This would give extended life to a variety of uses, whether they are military applications or commercial in nature.
While PEM fuel cell technology is referenced many times throughout this disclosure, the concept described herein is not intended to be limited to that technology only. Indeed, as appropriate to the specific application, any fuel cell technology would work in this configuration. PEM technology, however, is presently best adaptable to miniaturization and lower cost.
Alternatives exist for the gas storage means, as well. The object is to supply the necessary hydrogen and oxygen to meet the power design parameters of the product being designed. Just as power classifications exist among AAA, AA, C and D batteries, this also is true of the micro fuel cell unit which may be designed specifically to meet a variety of power demand levels.
Additionally, the high-G inertial switch designed for military application could optionally be replaced by a low-G switch that would allow turning on a battery with a shake of the hand prior to use. Thus, it is possible, for example, to have a D battery with no shelf life. However, switching on and off may be desired, thus necessitating a reset switch incorporated into the present fuel cell design.
In another embodiment of the invention, the fuel cell and inertial switch could be used for driving micropumps for delivering medicine to remotely located patient, or for activating RB or radio signal location devices upon sudden impact such as crashes.
In another exemplary embodiment of the present invention, the fuel cell and inertial switch can be used for quiescent tracking or lighting devices that are activated when needed such as for lost individuals or persons needing emergency medical attention.
In yet another exemplary embodiment of the present invention, the fuel cell and inertial switch can be used in remote robot devices, even micro-robots, such as on remote missions, i.e., arctic exploration or space travel in which devices activated upon landing.
While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the present invention as set forth in the following claims. Furthermore, although elements of the invention may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated.
This application claims priority under 35 U.S.C. 120 to Provisional U.S. Patent Application 60/538,211, filed Jan. 23, 2004, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60538211 | Jan 2004 | US |
