ELECTROCHEMICAL PRIME MOVER

Abstract: A prime mover or motor having a single compartment in which pressure variations are produced by transporting molecules into and/or out of the compartment by means of an electrolytic membrane (310). A device is disclosed for converting the pressure changes to mechanical motion without adversely affecting the sealed condition of the compartment. The mechanical motion produced by the apparatus is typically reciprocating linear motion. Disposed within the compartment is an electrochemical­ ly active material that can exist in the gaseous phase and that can enter into an oxidation/reduction reaction in order to form ions that move across the electrolytic membrane (310) so as to increase or decrease pressure in the compartment in response to application of a voltage gradient of proper duration and polarity across the membrane. Hydrogen and oxygen are suitable materials for use in the apparatus.

Description: This invention relates to a prime mover and more particularly to a prime mover which exploits pressure increases and decreases induced by converting molecules of electrochemically active material to ions, transporting the ions through an electrolytic membrane and reconverting the ions to molecules. U.S. Patent No. 3,489,670 discloses a process for gas purification in which a gas composed of hydrogen and various contaminants is introduced into a chamber bounded by an ion exchange membrane. A voltage gradient is established across the membrane, and the hydrogen molecules within the gas are ionized so that they pass through the membrane and are extracted from the opposite side of the membrane. The contaminants are not ionized and therefore do not pass through the membrane. The process can also be employed in providing hydrogen for a fuel cell. U.S. Patent No. 4,118,299 discloses an electrochemical water desalination process in which water containing salt and other contaminants is mixed with hydrogen gas. The mixture is introduced into a chamber bounded by an ion exchange membrane across which a voltage gradient is established. The hydrogen molecules are ionized and pass through the membrane. During passage of the hydrogen ions through the membrane, water is entrained with the ions so that at the opposite side of the membrane, hydrogen and pure water are produced. The hydrogen in gaseous form is pumped back for reuse. U.S. Patent No. 4 118 299 discloses that the hydrogen ions under the influence of the voltage gradient will be transported from a low pressure environment on one side of the membrane to a high pressure environment on the other side of the membrane. An article entitled "Hydrogen Electrolysis Cell" by Sedlak et al, International Journal of Hydrogen Energy, Volume 6, pp 45-51, Pergamon Press, Ltd., 1981, makes reference to the above cited U.S. Patents and describes experiments in recovering hydrogen from water by employment of an electrolytic cell that includes an ion exchange membrane. Although the above cited prior art references disclose passage of hydrogen ion through a membrane a cross which a voltage gradient is established, none utilizes the pressure changes caused by depletion or increase of hydrogen molecules on respective sides of the membrane to perform mechanical work. EP A 82591 by the same present inventor Henri Maget discloses an electrochemical prime mover device in which two compartments are provided between which is a membrane having a first pervious surface bounding one compartment and a second pervious surface bounding the other compartment, both compartments contain an electrochemically active medium and ions are caused by a voltage applied to the membrane to pass from one compartment to the other which results in a pressure differential between the compartments. The pressure differential is conducted by means of a conduit from each compartment to a bellows from which a reciprocating drive may be taken. This is a complex construction and furthermore the drive is indirect so that inaccuracies between the application of the voltage and the final drive may develop. According to the present invention, there is provided a prime mover comprising a single gas-tight chamber, an electrolytic membrane disposed in said chamber, said membrane having a first surface and a second surface spaced from said first surface in substantial parallelism thereto, said membrane being fixed within said chamber so as to form a single compartment bounded in part by said first surface, a first pervious electrode disposed on said first surface and a second pervious electrode disposed on said second surface, said compartment containing an electrochemically active material capable of existing in a gaseous phase and being electrochemically reversibly active so as to enter into a reduction/oxidation reaction at said electrodes and produce ions that are transportable through said membrane, means connected to said electrodes for establishing a voltage gradient across said membrane so as to ionize said electrochemically active material at one said electrode and transport ions through said membrane from said second surface to said compartment thereby effecting a pressure increase in said compartment, and converting means operatively associated with said compartment for converting the pressure change therein to mechanical motion, said converting means including a hollow tubular member fixed to said chamber and having an inner end communicating with said compartment and an outer end exterior of said compartment, a sealed movable wall member transversely spanning said tubular member and forming a fluid enclosing volume remote from said inner end, said movable wall moving away from said inner end in response to pressure increase in said compartment and said tubular member having an outlet orifice remote from said compartment to afford ejection of fluid from said fluid enclosing volume in response to increase of pressure in said compartment, characterised in that said single compartment is the only compartment formed by said membrane. An advantage over the prior art is that the simple construction of the prime mover of the present invention enables a very accurate response from the single compartment arrangement which controls the fluid filler hollow tubular member to eject an amount of fluid in response to a specific electrical signal causing increased pressure in the single compartment. The amount of fluid ejected is related accurately to the electrical signal. Because electrolytic membranes are available in extremely thin structures, the voltage necessary to activate a prime mover according to the invention is extremely small so that a prime mover incorporating the invention can be powered by conventional dry batteries and therefore provide a high degree of portability. A feature and advantage of the invention is that the increase and/or decrease of pressure in the compartment is accomplished without moving parts to the end that no friction losses are present and substantial longevity is achieved. For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawing, in which:- Figure 1 is a side view in section of a prime mover which provides reciprocating mechanical motion, portions being shown out of scale for clarity, and Figure 2 is a cross sectional view taken along line 2-2 of Figure 1. The drawing shows an impervious, cylindrical shell or wall 300. The wall is formed of metal but can be of any other suitable material such as plastics, glass or like gas-tight material. There is a closure wall 302 centrally of which is a cylindrical, tubular extension 304. The end of the extension 304 remote from the wall 300 is closed by an end wall 306. Opposite to the closure wall 302 is an electrolytic membrane 310 which spans the circular opening defined by the cylindrical wall 300 and has an inner surface on which is disposed a gas-pervious electrode 308. The membrane also has an outer surface, typically parallel to the inner surface, on which is disposed a gas-pervious conductive electrode 312. The electrode 312 is exposed to the ambient enviroment. Means for applying a voltage differential across the membrane is exemplified by a controller 314 powered by a battery 316. The controller 314 typically includes an on/off switch and components for controlling the magnitude and time pattern of current and voltage applied to the membrane 310. The specific construction of electrolytic membrane 310 depends upon the electrochemically active material that is employed in the device. The device can operate on any redox couple that contains material capable of existing in a gaseous phase and that is electrochemically reversibly active so as to react at one of the electrodes 308, 312 to produce ions which can migrate across the electrolytic membrane and be reconverted at the opposite electrode into a molecular state. One example of a suitable redox couple is wherein both species of the couple are molecular hydrogen (H₂ / H₂) in gaseous form. The process by which hydrogen molecules are moved through the membrane 310 is well described in the above cited prior art references. If, for example, controller 314 establishes electrode 312 at a potential that is higher than electrode 308, electrode 308 functions as a cathode and electrode 312 functions as an anode. At electrode 308, a cathodic reaction represented by the following equation occurs: 2H⁺ + 2e⁻ → H₂ Other suitable redox couples are oxygen and water (O₂/H₂O), chlorine and hydrochloric acid (Cl₂/HCl), bromine and hydrobromic acid (Br₂/HBr), iodine and hydriodic acid (I₂/HI), and chlorine and lithium chloride (Li/LiCl). The electrodes can be formed of a titanium-palladium alloy in the form of a mesh, palladium black in the form of a thin coating on the respective surfaces of membrane 310 or any other material that is electrically conductive and acts as a catalyst in converting molecules of the electrolytic material in shell 300 to ions in response to a voltage gradient applied across membrane 310. Disposed in the tubular extension 304 in communication with the compartment bounded by the wall 300, membrane 310 and closure wall 302, is a moveable wall member spanning the inside of the tubular extension and exemplified in Figure 1 by a piston 318. An O-ring seal 320 provides a seal between the outer surface of the piston 318 and the inner surface of the tubular extension 304, so that the portion of the volume interior of the tubular extension remote from the membrane 310 is sealed from the compartment. A pharmaceutical or like fluid material can be disposed within the volume. The end wall 306 is provided with a fitting 322 which defines an outlet orifice for fluid within the volume defined at the right-hand side of the piston 318. In a typical example, during fabrication a small quantity of water W is placed within the compartment between the membrane 310 and the piston 318. After fabrication, the fluid material is placed within the volume to the right of the piston 318, and the battery 314 is connected with the switch 316 in an opened position. To the left of the piston 318 within the volume formed by the cylindrical wall 300 there is air and a small quantity of water. Typically air is present at the exterior of the device and specifically adjacent to the left-hand or outer surface of the membrane 308. A typical application is a device to administer pharmaceuticals to a human body over a substantial period of time at a sustained very low rate. The size of the device can be about 1 centimetre in diameter or even less. When it is desired to dispense or eject the liquid material from the volume within the tubular extension 304, a suitable outlet conduit is connected to the fitting 322 and the controller 314 is activated, thus establishing a voltage gradient across the membrane 310. The oxygen in the air constitutes the electrochemically active material. Under the influence of the voltage gradient across the membrane, oxygen molecules are introduced into the compartment to the right of the membrane 310 and cause a pressure increase in the compartment. The pressure increase is converted to mechanical motion by moving the piston 318 rightward and expels the fluid through the outlet orifice in the fitting 322. A typical repetition rate for the controller 314 provides for one second of a voltage gradient across the membrane 310 of one polarity followed by a one second interval of a voltage gradient of opposite polarity. The electrodes 308 and 312 have a thickness of about .002 - .003 inches (0,05 - 0,076 mm), membrane 310 has a thickness of about .010 inches (0,25 mm) and the electrodes have a cross-sectional area of about one square centimetre. A voltage of about .1 volt causes a current flow through the membrane of about one ampere and at a rate of about one polarity reversal per second; the device having a membrane area of about one square centimetre can pump about 400 cubic centimetres of hydrogen per hour. In such exemplary system, the pressure in the compartment can vary from about one atmosphere to about three atmospheres. At the surface of the membrane 310 on which the electrode 312 is disposed, a reaction takes place in which oxygen from the ambient air is consumed and water is produced. The reaction is described by this equation: O₂ + H⁺ + 4e → H₂O At the opposite surface of the membrane 310, the surface on which the electrode 308 is disposed, oxygen is produced and water is consumed. The reaction is described by this equation: H₂O → O₂ + 4H⁺ + 4e. The oxygen molecules produced by the reaction at the right-hand surface of the membrane 310 causes the pressure increase within the compartment. In certain applications it is desirable to fill the compartment with substantially pure hydrogen. In other cases where depletion of hydrogen from the compartment would produce unacceptably low pressures, the hydrogen can be mixed with an inert gas to which the membrane is impervious, nitrogen exemplifying a suitable gas for the purpose. Thus, in a system where a hydrogen-nitrogen mixture is employed, the nitrogen remains in the compartment in which it is placed thereby providing a preselected residual pressure even when all hydrogen is depleted from the compartment. The prime mover can be constructed in a wide range of sizes from an extremely small device having a cross sectional area of about one centimetre to devices substantially larger. Because the device affords implementation in such a miniature device utilizing battery power sources, it lends itself to implantation or installation at inaccessible locations. Similar devices, but not in accordance with the present invention, are shown and described in co-pending patent application EP-A- 0082591, published on 29.6.83, to which reference is accordingly directed.

Claims: A prime mover comprising a single gas-tight chamber, an electrolytic membrane (310) disposed in said chamber, said membrane having a first surface and a second surface spaced from said first surface in substantial parallelism thereto, said membrane being fixed within said chamber so as to form a single compartment bounded in part by said first surface, a first pervious electrode (308) disposed on said first surface and a second pervious electrode (312) disposed on said second surface, said compartment containing an electrochemically active material capable of existing in a gaseous phase and being electrochemically reversibly active so as to enter into a reduction/oxidation reaction at said electrodes and produce ions that are transportable through said membrane, means connected to said electrodes for establishing a voltage gradient across said membrane so as to ionize said electrochemically active material at one said electrode and transport ions through said membrane from said second surface to said compartment thereby effecting a pressure increase in said compartment, and converting means (304, 318) operatively associated with said compartment for converting the pressure change therein to mechanical motion, said converting means including a hollow tubular member (304) fixed to said chamber and having an inner end communicating with said compartment and an outer end (306) exterior of said compartment, a sealed movable wall member (318) transversely spanning said tubular member and forming a fluid enclosing volume remote from said inner end, said movable wall moving away from said inner end in response to pressure increase in said compartment and said tubular member having an outlet orifice (332) remote from said compartment to afford ejection of fluid from said fluid enclosing volume in response to increase of pressure in said compartment, characterised in that said single compartment is the only compartment formed by said membrane. A prime mover according to claim 1, wherein said electrochemically active material is oxygen-containing air. A prime mover according to claim 1 or 2, wherein said sealed movable wall member includes a piston slidably disposed in said hollow tubular member for movement toward and away from said compartment, and a sealing ring (320) circumscribing said piston between the exterior of said piston and the interior of said hollow tubular member for effecting a seal therebetween.

Inventors: MAGET, HENRI J.R.
Applicants: MAGET, HENRI J.R.
Application year: 1985
Main classification: F04B17
IPC codes: F04B17