Electrochemical hydrogen pump and uses thereof for heat...

Refrigeration – Refrigeration producer – Sorbent type

Utility Patent

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Details

C062S003100, C062S259200

Utility Patent

active

06167721

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to a hydrogen pump, more particularly to a hydrogen pump which includes a proton exchange membrane and even more particularly to a heat exchange system which utilizes an electrochemical hydrogen pump which includes symmetrical hydrogen electrodes and a proton exchange membrane.
BACKGROUND OF THE INVENTION
Electrochemical cells in which a chemical reaction is forced by adding electrical energy are called electrolytic cells. Central to the operation of any cell is the occurrence of oxidation and reduction reactions which produce or consume electrons. These reactions generally take place at electrode/solution interfaces, where the electrodes must be good electronic conductors and the solution should have high ion conductivity. In operation, a cell is connected to an external voltage source, and electric charge is transferred by electrons between the anode and the cathode through the external circuit. To complete the electric circuit through the cell, an additional mechanism must exist for internal charge transfer. This is provided by one or more electrolytes, which support charge transfer by ionic conduction.
The simplest electrochemical cell consists of at least two electrodes and one or more electrolytes. The electrode at which the electron producing oxidation reaction occurs is the anode. The electrode at which an electron consuming reduction reaction occurs is called the cathode. The direction of the electron flow in the external circuit is always from anode to cathode. In order to drive the electrolysis reaction, it is necessary to apply electric power to the cell electrodes. The electrodes are connected through the electrical leads to an external source of electric power with the polarity being selected to induce the electrolyte anion flow to the anode and the cation flow to the cathode.
Generally speaking, the anode and cathode are made of a substrate material, such as titanium, graphite, or the like, coated with a catalyst such as lead dioxide or other known materials. The selection of a substrate and catalyst is determined by the particular electrode reactions which are to be optimized in a given situation. As a rule a cathode and an anode produce different products. Classically, these products are hydrogen and oxygen.
Generally, the electrolyte is a liquid which is conductive of ions. The most common applications are fuel cells. In fuel cells, proton exchange membranes are used as electrolytic and catalyst support for providing a reaction of hydrogen oxidation on the one side of membrane and oxygen reduction on the other side. This combination of membrane and electrodes can be called a Membrane Electrode Assembly (MEA).
Cooling of electronic devices utilizing a vapor compression refrigeration cycle known in the art. Vapor compression cooling uses the thermodynamic principles associated with phase transfer, specifically the latent heat of vaporization and the entropy of evaporization of a working fluid. Compression of a vaporous working fluid can occur through mechanical or electrochemical means. Mechanical compression requires a relatively large, heavy, mechanical compressor having a great number of parts which are often bulky and susceptible to wear. Electrochemical compressors have been proposed to drive Joule-Thomson refrigeration cycles. (See, for example, U.S. Pat. No. 4,593,534 which is hereby incorporated by reference in its entirety.) This type of compressor is preferred since it has no moving parts, is vibration free, and has the potential for long life and reliability.
As described in U.S. Pat. No. 4,523,635, which is hereby expressly incorporated by reference in its entirety herein, it is known that certain metals and alloys exothermically occlude hydrogen to form a metal hydride and the metal hydride reversibly releases hydrogen. Such a heat pump can be constructed by providing a first metal hydride (M
1
H) and a second metal hydride (M
2
H) which have different equilibrium dissociation pressures at the same temperature, in closed receptacles capable of effecting heat exchange with a heat medium, and connecting these receptacles with a common gas space conduit so as to permit transfer of hydrogen therebetween. However, these type of heat exchange devices rely on differences in equilibrium dissociation pressures of the respective metal hydrides. The metal hydrides utilized must be able to occlude and release hydrogen at very substantial rates, and metal hydrides of this type are very expensive to manufacture and utilize. Additionally, it is difficult to efficiently control the production and consumption of hydrogen during operation of the heat exchanger using principles of disassociation of hydrogen from metal hydrides.
U.S. Pat. Nos. 5,768,906 and 5,746,064 which are both owned by Applicant and are both incorporated herein by reference thereto teach an electrochemical heat exchanger which utilizes hydrogen production and consumption to effectuate heat transfer. These electrodes connected with a power supply produce and consume hydrogen depending on the power supply's polarity. Hydrogen can provide heat exchange itself, but in general the hydrogen gas pushes liquid causing it to move back and forth. This electrochemical “pump,” although very effective, has certain disadvantages for heat exchanging function. These disadvantages relate to the need for undesirable electrolyte in the electrochemical cell, relatively low rate of hydrogen production and consumption, and relatively short cycle life.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided an electrochemical heat exchanger which contains one or more electrochemical cells which produce and consume hydrogen gas in a common gas space within a closed receptacle or sealed chamber, the gas space being capable of effecting heat exchange with an element to be temperature regulated and a gas or liquid contained within the chamber. Preferably, the electrochemical heat exchanger is comprised of an electrochemical cell(s) which include an anode and a cathode sharing a common gas space. It is preferable that the cell include a proton exchange membrane preferably situated between the anode and cathode and it is more preferable to utilize hydrogen electrodes as both the cathode and anode. Hydrogen electrodes are capable of both generating and consuming hydrogen.
The reactions which occur at the hydrogen cathode:
2H
+
+2
e

→H
2
  (1)
And at the hydrogen anode:
H
2
→2H
+
+2
e

  (2)
The net product of the overall reaction is heat. Hydrogen is produced at the cathode and hydrogen is consumed at the anode.
Applications of the presently disclosed heat exchanger include cooling electrical machines or devices such as electrical generators and transformers, and the refrigeration art wherein metal hydrides having different dissociation constants are used to transfer hydrogen between cells. By way of example only U.S. Pat. Nos. 4,523,635 and 5,445,217, both of which are hereby expressly incorporated by reference in their entireties provide possible applications of the present invention.
Hydrogen as discussed herein is very useful as a cooling agent. Hydrogen has a thermoconductivity value seventeen times that of air. However, hydrogen does have some limitations when compared to liquid cooling agents. For example, hydrogen has a low magnitude of specific capacity which may make it less appealing for larger volume applications. For larger volume applications it may be more energy efficient to use hydrogen as a pump or as a means to move a liquid cooling agent.
The present invention may utilize hydrogen produced during charging of a cell to regulate the temperature of an element to be temperature regulated such as a microchip. When using the hydrogen gas produced as a cooling agent it is preferable to “move” and replenish the gas so that it transfers heat absorbed to the environment and maintains an ambient temperature, therefore, utilizing the hydrogen produced to create a p

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