EP1726055A2

EP1726055A2 - Micro fuel cell with membrane storage

Info

Publication number: EP1726055A2
Application number: EP05726569A
Authority: EP
Inventors: David J. Pristash
Original assignee: Pemery Corp
Current assignee: Pemery Corp
Priority date: 2004-01-23
Filing date: 2005-01-21
Publication date: 2006-11-29
Also published as: EP1726055A4; CA2554028A1; US20100000434A1; IL177009A0; WO2005089099A2; WO2005089099A3

Abstract

An apparatus for the generation of electricity that may be in a 'standby' mode for long periods of time, i.e. many years. Thus, in one embodiment of the invention, a fuel cell (48) may include at least one of the following features or components: a membrane and /or storage tanks or cells for hydrogen (42) and oxygen (44), and/or an 'inertial' switch (46), which may optionally be assembled in close proximity to a membrane. The inertial switch (46), when activated, may rupture the membrane and allow the hydrogen and oxygen to mix in a fuel cell.

Description

MICRO FUEL CELL WITH MEMBRANE STORAGE

CLAIM TO PRIORITY [0001] This application claims priority under 35 U.S.C. 119 to Provisional U.S.

Patent Application 60/538,211, filed January 23, 2004, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION [0002] 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.

BACKGROUND OF THE INVENTION [0003] 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. [0004] 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. [0005] 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. [0006] 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. [0007] 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 FIG. 1. [0008] In the conventional art shown in Fig. 1 an anode end plate 2 defines the left portion of a fuel cell stack 1. Hydrogen fuel is channeled through the flow plates to the anode on one side of the fuel cell, while oxygen is channeled to the cathode on the other side of the cell. The catalyst on the anode end plate 2 causes the hydrogen to split into positive hydrogen ions (protons) and negatively charged electrons. The hydrogen ions migrate through a membrane, which allows only the positively charged ions to pass through it, to the cathode end plate 14, where the cathode end plate 14 catalyst causes the combination of the hydrogen ions, electrons and oxygen to produce water. The negatively charged electrons travel along external circuit 16 to the cathode, generating an electric current. [0009] 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). [0010] 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. [0011] 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. [0012] 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. [0013] 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. [0014] U.S. Patent 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.

SUMMARY OF THE INVENTION [0015] 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. [0016] 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. [0017] 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.

BRIEF DESCRIPTION OF THE DRAWINGS [0018] 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. [0019] 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: [0020] Fig. 1 is an exemplary diagram of a fuel cell stack. [0021] Fig. 2 is an exemplary diagram of an inertial switch. [0022] Fig. 3 is an exemplary diagram of a polymer electrolyte membrane battery

(PEMERY). DETAILED DESCRIPTION OF THE INVENTION [0023] 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 r iniature 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. [0024] The present invention, in one exemplary embodiment, may include a fuel cell.

Current polymer electrolyte membrane (PEM) fuel cells have produced cells of .2 millimeters in thickness that can produce better tbtan .5 ampere of cureent per square centimeter at .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. [0025] 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. [0026] 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. [0027] 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." [0028] In this embodiment, such small blocks of material are infiltrated with micro channels, cavities, passages, sinuses or nano-runnels 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 bea.cons as used in downed aircraft as a few non-limiting examples. [0029] 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. [0030] 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. [0031] An inertial switch is shown in Fig. 2. In this embodiment, two miniature, sharp, hollow probes 24 and 26 are positioned above and/or adjacent to membrane 28, located so as to separate a fuel cell (not pictured) from hydrogen receiver 28 and oxygen receiver 30. [0032] When sufficient G forces, for example, o 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 furtriter described in Fig. 3 below. [0033] Each of these probes (24 and 26) is covrnterbalanced 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 axid equivalent means to generally and continuously (for long periods of time) maintain a first position adjacent, yet apart, from a respective membrane. [0034] More recently, delicate, micro-inertia swatches 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. [0035] 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. [0036] 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. [0037] In the inventive assembly described and illustrated in Fig. 3, the components that run the device and generate electricity, when needed, are separated by physical barriers. This figure shows a PEMERY 40 with hydrogen storage tank 42 and the oxygen storage tank 44 as sealed by membranes 43 and 45, respectively. Inertial switch 46 is positioned beneath membranes 43 and 45. When activated, inertial switch 4<5 will rupture membranes 43 and 45, allowing the hydrogen from storage tank 42 and the ocygen from storage tank 44 to flow through inertial switch 46 and into fuel cell 48. The hydrogen and oxygen undergo an electrochemical reaction in fuel cell 48, as previously described with respect to Fig. 1, allowing the conversion into electrical energy, represent&d by DC current 50. [0038] Because the barriers discussed with respect to Fig. 3 are generally stable by design, the shelf life of the PEMERY unit is inherently very long. A life period of fifty to sixty years, or even twice that period, is not unreasonable. Thus, the limitations of the fuel cell would be reduced to those associated with the materials utilized in building the fuel cell itself. [0039] 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. [0040] 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. [0041] 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. [0042] 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. [0043] 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. [0044] In another embodiment of the invention, the fuel cell and inertia-! 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 crasfaes. [0045] 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. [0046] 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, sucfc as on remote missions, i.e., arctic exploration or space travel in which devices activated upon, landing. [0047] While the invention has been particularly shown and described ^with reference to a prefened 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.

Claims

What is claimed is:

1. A method of storing energy, comprising: storing hydrogen and oxygen in first and second storage tanks, positioning an inertial switch in close proximity to the at least one membrane, rupturing at least one membrane with the switch activated by inertia; and mixing the hydrogen and oxygen in a fuel cell.

2. The method of claim 1, wherein the mixing of hydrogen and oxygen generates and electric cunent.

3. The method of claim 2, wherein the mixing of the hydrogen and oxygen in the fuel cell acts as a triggering mechanism.

4. The method of claim 1, wherein the rupturing of the at least one membrane is a result of an external force.

5. The method of claim 4, wherein the rupturing of the at least one membrane is a result of G forces.

6. The method of claim 1, wherein the mixing of the hydrogen and oxygen is done in a nano- sized fuel cell.

7. An apparatus for storing energy, comprising: a fuel cell; a first storage tank for a first fuel; a second storage tank for a second fuel; an inertial switch in close proximity to a membrane having a rest position and a disturbed position; and the first and second fuels are combined in the fuel cell following the moving of the switch to the disturbed position.

8. The apparatus of claim 7, wherein the inertial switch comprises probes that act to penetrate the membrane separating the first fuel and the second fuel when in the disturbed position.

9. The apparatus of claim 8, wherein the probes of the inertial switch are hollow.

10. The apparatus of claim 9, wherein the first fuel and the second fuel flow through the hollow probes of the inertial switch from the storage tanks to the fuel cell.

11. The apparatus of claim 8, wherein the inertial switch is activated by G-forces.

12. The apparatus of claim 8, wherein the inertial switch is activated by centrifugal force.

13. The apparatus of claim 8, wherein the inertial switch is activated by an external force.

14. The apparatus of claim 7, wherein the fuel cell is nano-sized.

15. The apparatus of claim 7, wherein the fuel cell has a thickness of approximately 0.2mm.

16. The apparatus of claim 7, wherein the fuel cell and inertial switch is used in ordnance.

17. The apparatus of claim 7, wherein the first fuel is hydrogen and the second fuel is oxygen.

18. The apparatus of claim 7, wherein the first fuel is hydrogen and the second fuel is- air.