US3433675A - Air-operated electrolytic cell - Google Patents

Description

March 18, 1969 D. MCLEOD MOULTON 3,433,675

AIR-OPERATED ELECTROLYTIC CELL Filed Feb. 25, 1965 8 4 a EXHAUST 00 L REMOVER 3 I cow 1 HEAT LOAD EXCHANGE/F 6 v HOT M A? VE/VT DAVID McLEOD MOULTON, INVENTOR BY (MA-62.

ATTORNEYS United States Patent 3,433,675 AIR-OPERATED ELECTROLYTIC CELL David McLeod Moulton, Scituate, Mass., assignor to Prototech Incorporated, Cambridge, Mass., 21 corporation of Massachusettts Filed Feb. 25, 1965, Ser. No. 435,130 US. Cl. 136--86 Int. Cl. H01m 27/02 6 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to electrolytic cells and, more particularly, to cells of the fuel-cell variety in which fuel is applied to an anode or fuel electrode disposed within an electrolytic medium and oxidant is applied in the vicinity of a cathode or oxidant electrode in order to generate between the electrodes an output current as a result of the electrochemical action within the cell.

In copending application, Ser. No. 376,916, entitled Fuel Cell Apparatus and Method, filed June 22, 1964, now abandoned, in the name of the present applicant and others, alkali metal hydroxide molten electrolytic media are disclosed for use in fuel cells, with air employed as an oxidant for enabling the production of peroxide or superoxide in'the vicinity of the cathode that provides for the electrochemical operation of the cell.

Some electrolytic media, such as the molten-electrolyte alkali metal hydroxides and others, are, however, sensitive to the CO present in the introduced air, even though the percentage of CO carried by the air is only about 0.03%. It is thus desirable to remove the CO from the introduced air so as to avoid the deleterious effects of insoluble carbonate production within the cell when such Co -sensitive electrolytic media are employed. On the other hand, as explained in the said copending application, it is important to apply an excess of air in the vicinity of the cathodic oxidant electrode to insure sufficient generation of peroxide or superoxide and, by blowing or other forceful introduction of the air, to agitate or stir the electrolytic medium in the vicinity of the oxidant electrode to insure adequate presentation of the formed peroxide in the vicinity of the cathode and to assist in the acceleration of such formation of peroxide. The introduction of an excess quantity of air, however, inherently means the introduction of CO thus imposing the added burden of CO removal apparatus of substantial size.

It is to the problem of limiting the amount of air that must be applied to the cell in order to limit the size of the CO removal apparatus, while insuring an excess of air agitating the electrolytic medium in the vicinity of the oxidant electrode, that the present invention is primarily directed; it being an object of the invention to attain such result together with an efiicient technique for heating the air so as to permit appropriate operation within the elevated temperature electrolytic medium of the cell.

A further object is to provide a new and improved 3,433,675 Patented Mar. 18, 1969 electrolytic cell of more general utility and applicability, as Well.

Other and further objects will be explained hereinafter and will be more particularly pointed out in connection with the appended claims. In summary, however, from one point of view, the invention relates to elevated temperature electrolytic cells containing an electrolytic medium sensitive to CO and in which air is introduced near the oxidant electrode. Means is provided for circulating and recirculating the introduced air in the vicinity of the oxidant electrode to accelerate and insure adequate peroxide formation, with a portion of the recirculated air being vented; and, in one embodiment, used for heat exchange purposes with the introduced air. In accordance with the present invention, by limiting the quantity of introduced and vented air to substantially stoichiometric proportions, the quantity of CO that must be removed from the introduced air is limited, while enabling the maintenance of the required excess of heated air at the oxidant electrode for the peroxide formation and operation above discussed. Preferred constructional details will be hereinafter set forth.

The invention will now be described in connection with the accompanying drawing, the single figure of which is a schematic diagram of a fuel cell constructed in accordance with a preferred embodiment.

Within a housing 1, there is shown disposed an electrolytic medium 3, such as a molten alkali metal hydroxide or mixture of hydroxides, among other electrolytic media that, as before described, is sensitive to the presence of C0 The electrolytic medium is maintained at an elevated temperature by conventional means, not shown; for example, in the neighborhood of 400-450 C. and certainly in excess of 300 C., but generally not more than approximately 700 C. Disposed within the electrolytic medium 3 is an appropriate fuel anode 2 which may, for example, assume the form of a Ag-Pd tube that is permeable to hydrogen or other hydrogen-containing fuel. The fuel may be introduced through an appropriate inlet in the cover of the housing 1, as schematically shown by the arrow 2. Air may be similarly introduced in the vicinity of the cathode or oxidant electrode 4, the cathode being also disposed within the electrolytic medium 3 and shown containing at least a pair of end-communicating chambers 4 and 4" within which electrolytic medium may flow. In accordance with one feature of the invention, the electrolyte is caused to circulate along a circuitous path between the chambers 4' and 4" by virtue of air introduced through a tubular inlet 4" or conduit means in the direction of the arrow. The cathode structure 4 may embody a corrugated or other geometrically large-area construction, as illustrated to the left of the chamber 4, being preferably solid to enable the bubbling air to circulate or pump the electrolytic medium between chambers 4 and 4", as indicated by the arrows, and thus expose the surfaces of the cathode 4 to the required peroxide or superoxide as well as assisting in the acceleration of the peroxide formation.

Further in accordance with the invention, the air introduced at its source 6 is passed through a C0 remover cartridge 8, such as a cartridge containing C210, and may then be applied to a circulating pump 10 for forcing the air, with CO removed, into the cathode inlet 4", as before described. It has been found that by limiting the quantity of the introduced air, as by the valve control 6, considered in the light of the air that is vented from the cell at 12, to substantially stoichiometric proportions, the before-described desirable end of introducing a minimal quantity of air (and thus requiring minimal-size CO removing apparatus 8) while maintaining a great excess of air circulating in the vicinity of the cathodic oxidant electrode 4, can be attained. The introduced air may be heated as a result of exchange with the molten elevated temperature electrolytic medium 3. A portion of the heated vented air may also or alternatively be fed at 12 along path 12 to a conventional heat exchanger 14 into which the output of the CO -removal apparatus 8 may be applied, as at 8'. This enables heat exchange between the introduced and vented air. Part of the heated air within the cell 1 may also be fed back, as shown at 13, into the circulating pump 10 to effect recirculation of the air circulated in the vicinity of the cathode 4 in order to enable the maintenance of excess agitating air thereat, as previously described. The pump 10 need not, of course, be within the housing 1, though it may be desirable to mount it within the housing to minimize heat loss.

The output current may be taken through leads 20 and 40 for applying the generated electric current to any desired load L, as is well known.

As an illustration, a 1500 watt electrical output cell may require 2115 amps at 0.71 volts. Such a cell requires stoichiometric air at the rate of 35.1 liters/minute, such air containing 0.021 grams/minute of CO For the CO removal process at 8, this would require the use of 0.026 grams of CaO per minute and further require 72 calories/ minute of heat for an 84% efficient heat exchanger, assuming air flow in both directions and neglecting the removed oxygen. If, as an illustration, five times of air excess is desirable at the cathode 4, this would require 0.13 grams/minute of CaO to be consumed at the apparatus 8, and 360 calories/minute of heat. By the recirculating technique above described, however, only stoichiometric air is introduced requiring only the 0.026 grams of CaO per minute and only the 72 calories/ minute of heat.

A suitable cell for operation in this manner may employ a Ag-Pd tubular anode 2, a solid nickel cathode 4, and a fused KOH electrolytic medium 3 maintained at a temperature of approximately 400 C. Under such circumstances, sutficient tubing 2 would be used to provide an area of about 20 ft. of anode and approximately the same area of cathode 4 to generate the approximately 100 ma./cm. required.

Further modifications will occur to those skilled in the art and all such are considered to fall within the spirit and scope of the invention as defined in the ap- 4 pended claims.

What is claimed is:

1. In an elevated temperature electrolytic cell provided with an oxidant electrode disposed Within an electrolytic medium sensitive to CO and which forms peroxide when air is introduced therein, means for introducing air into the electrolytic medium near the electrode, means for removing the CO content of the air prior to its introduction into the cell, means including conduit means defining a circuitous path for circulating and recirculating the introduced air in the vicinity of the electrode to accelerate and insure adequate peroxide formation thereat, means for venting a portion of the recirculated air, and means for limiting the quantity of introduced and vented air to substantially stoichiometric proportions to limit the quantity of CO that must be removed while maintaining an excess of heated air at the said electrode.

2. An electrolytic cell as claimed in claim 1 and in which means is provided for exchanging heat between the introduced and vented air.

3. An electrolytic cell as claimed in claim 1 and in which the electrode comprises communicating chambers for enabling the introduced air to circulate the electrolyte between the chambers.

4. An electrolytic cell as claimed in claim 3 and in which at least one of the said chambers is provided with a solid electrode surface.

5. An electrolytic cell as claimed in claim 1 and in which a fuel electrode is provided within the said medium, and an output current is connected between the electrodes.

6. An electrolytic cell as claimed in claim 5 and in which the fuel and oxidant electrodes are respectively palladiumand nickel-containing.

References Cited UNITED STATES PATENTS 2,384,463 9/1945 Gunn et al. 136-86 2,901,524 8/1959 Gorin et a1. l3686 3,068,311 12/1962 Chambers et a1. l3686 3,239,383 3/1966 Hauel l3686 3,288,644 11/1966 Delfino l3686 3,259,524 7/1966 Fay et al 136-86 FOREIGN PATENTS 12,676 5/1919 Great Britain.

ALLEN B. CURTIS, Primary Examiner.

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