Electrolysis cell system including recirculating product gas stream for cooling the cell

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ELECTROLYSIS (CEELL SYSTEM INCLUDING to remove waste heat therefrom. Also, moisture is RECIRCULATING PRODUCT GAS STREAM FOR added to the air entering the cathode side of the fuel COBOLING THE CELL cell to provide a positive means of fuel cell water bal BACKGROUND OF THE INVENTION ance control over the range of ambient temperature 1. Field of the invention and humidity expected. In an electrolysis cell water is continuously being used up and must therefore be con

This invention relates to electrolysis cells and more tinuously supplied. Of course, if an electrolysis cell sys particularly to a compact electrolysis cell system. tem used a cell constructed similar to the cell of FIG. 2. Description of the Prior Art 2 in Sanderson there would not be the usual circulating it is well known that it is possible to operate fuel cells O electrolyte for water addition. In Sanderson water is in a reverse mode so that they generate hydrogen and brought into the cell in the incoming air stream. But, in oxygen when supplied with liquid water and electric an electrolysis cell system the electrolysis cell produces power. Cells that operate in that manner are referred oxygen and hydrogen and thus there would be no in to as electrolysis cells. In one common type of electrol coming reactant gas stream for carrying water vapor to ysis cell two solid electrodes which may, for example, 5 the cell as there is in Sanderson. In any event, Sander be made from nickel, are spaced apart in a free liquid son adds water merely to prevent dryout of the electro electrolyte and a potential is applied across the elec lyte matrix near the inlet thus providing for more uni trodes. Water in the electrolyte is electrolyzed liberat form water removal. There is no means for providing ing hydrogen and oxygen into the electrolyte in the the proper amount of water input if the Sanderson sys form of gas bubbles. The water used is replenished by 20 tem were an electrolysis system using up water. adding it directly to the liquid electrolyte between the electrodes. Generally the electrolyte is also used to SUMMARY OF THE INVENTION cool the cell; for example, a recirculating loop of elec One object of the present invention is an electrolysis trolyte picks up waste heat from the cell, rejects this cell system using an electrolysis cell having an electro heat outside the cell, and then returns to the cell, 25 lyte trapped in a matrix between a pair of gas porous makeup water being added somewhere in the loop. An electrodes.

other type of cell called the Bacon Cell utilizes two A further object of the present invention is a simpli spaced apart dual porosity electrodes enclosing a free fied electrolysis cell system wherein the cell is fed with liquid electrolyte trapped in a sealed compartment. water and cooled by a single recirculating fluid stream. These electrodes may, for example, be made of sin 30 Yet another object of the present invention is an tered nickel. However, since both sides of the elec electrolysis cell system wherein the circulation require trodes are metallic, electrolysis can occur in the elec ment for the cooling fluid is minimized thereby reduc trolyte as well as on the gas side of the electrode. If this ing the size of the pumps used to circulate the cooling cell were to operate in a zero gravity environment, such fluid.

as in a space craft, the gas in the electrolyte would have 35 Accordingly, the present invention is an electrolysis to be removed such as by the use of a liquid-gas vortex cell system including an electrolyte matrix sandwiched separator, thus complicating the design. between a pair of gas porous electrodes wherein one of Although these electrodes could be modified so as to the products of electrolysis recirculates through the be made of inert material on the fine pore side exposed cell and has water added thereto for cooling the cell. to the electrolyte to prevent gas formation within the 40 The water added also replenishes the water used, and bulk of the electrolyte, this type of cell would have to the amount added is controlled to maintain a constant operate at relatively high temperatures. In either of the temperature of the recirculating stream as it exits from foregoing systems, wherein the electrolyte is a circulat the cell, having picked up waste heat therefrom and es ing or noncirculating free liquid disposed between or tablished a temperature gradient thereacross. Means around the electrodes, and is not held within a matrix, 45 are also included in the system for establishing the de each cell within a stack of cells would necessarily have sired partial pressure of water vapor in the recirculating to be fairly thick in order to either permit electrolyte product gas entering the cell. Thus, water supply and to flow or to prevent the electrodes from touching. heat removal are accomplished with a single recirculat It is often desirable that an electrolysis cell be as 50 ing product gas loop and one pump. compact as possible. Thus, it would be desirable to use, The subject matter of this application is related to the as an electrolysis cell, a fuel cell similar to the type subject matter of a commonly assigned application ti shown in FIG. 2 of Sanderson U.S. Pat. No. 3,507,702 tled “Electrolysis Cell System" by R. Sanderson, M. or Bushnell et al U.S. Pat. No. 3,779,811, both of com Katz and J. Hirschenhofer filed on even date herewith. mon assignee with the present application. In the type 55 The foregoing and other objects, features and advan of cell shown in Sanderson the electrolyte is held in a tages of the present invention will become more appar matrix trapped between partially hydrophobic partially ent in the light of the following detailed description of hydrophilic gas diffusion electrodes; a gas space is preferred embodiments thereof as illustrated in the ac formed on the nonelectrolyte side of each electrode for companying drawing.

carrying the oxidant and fuel. The matrix is usually of very fine pore structure with a high resistance to bubble BRIEF DESCRIPTION OF THE DRAWING formation in the electrolyte. This type of cell is very The sole FIGURE is a schematic of an electrolysis thin compared to the earlier mentioned types since cell system according to the present invention. there is no requirement that the electrolyte must be pumped through the system, and therefore the elec DESCRIPTION OF THE PREFERRED trodes may bc spaced very close to each other. In the 65 EMBODIMENTS fuel cell system of Sanderson there is a separate coolant Referring to FIG. I, an electrolysis cell system 10 ac loop for carrying a liquid coolant through the fuel cell cording to a preferred embodiment of the subject in

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vention is shown. The system 10 comprises an electrol 24 and reenters the cell at the entrance 38 to the ther. ysis cell 12. Only one cell is shown, however, any num mal exchange portion 22. It leaves the cell again ber of cells may be combined to form a multi-cell stack through the exit 40 of the thermal exchange portion 22 which could be used in this system. The cell 12 is repre and reenters once again at the inlet 42 of the gas space sented schematically as comprising a cathode 14, an 24. Although in this embodiment hydrogen is recircu anode 16, a porous matrix 18 sandwiched therebe lated, it should be apparent to persons with ordinary tween and filled with an aqueous electrolyte, a porous skill in the art that the oxygen could be recirculated in backup plate 20 adjacent the anode 16, and a thermal stead.

exchange portion 22. The cell also includes gas spaces Water from a pressurized water supply 44 is intro 24, 26 on the nonelectrolyte side of the cathode and duced into the recirculating hydrogen stream through anode, respectively. The thermal exchange portion 22 a water sprayer 46 immediately upstream of the en may be of any well known construction suitable for trance 28 so that it enters the thermal exchange portion passing a cooling fluid therethrough for removing heat 22 in droplet form. Droplets are desirable because they from the cell 2. For example, it may be a plate having vaporize much more easily and therefore cool the cell cooling fluid passages therethrough. The plate with its 15 much more efficiently, minimizing the pumping re attendant passages would be configured and arranged quirement for the recirculating gas stream and the so that heat generated in the cell during operation amount of water required. Although in this embodi thereof is transferred to the fluid passing through the ment the water is added to the recirculating stream pre passages in a manner well known to those skilled in the cisely at the location of the sprayer 46, it may instead art. The porous backup plate 20 serves as an electrolyte be added elsewhere, such as between the condenser 52 reservoir, in a manner well known to those skilled in and the pump separator 60. The sprayer 46 or other the art, thereby allowing large variations in the electro means would still be desirable to convert the water into lyte volume without flooding or drying of the elec droplet form as it enters the thermal exchange portion trodes. If the electrolysis cell system 10 were required 22.

to operate in only a narrow power range then a porous 25 A temperature sensor 48 is positioned downstream of backup plate 20, which is also sometimes known as an the exit 40 to measure the temperature of the recircu electrolyte storage matrix, may not be required. lating hydrogen stream emerging from the thermal ex In this embodiment a base electrolyte such as KOH change portion 22. A control valve 50 is responsive to is contemplated although it should be apparent to per the temperature sensor 48 and controls the amount of sons with ordinary skill in the art that the system of the water added to the recirculating hydrogen stream so present invention is equally as applicable to acid cells. that the temperature of the stream emerging from the It is also contemplated that the electrodes are of the gas thermal exchange portion 22 is maintained at a prede porous type and may comprise, for example, a metal termined value which may be different for various cell. support screen or mesh in intimate contact with a cata operating conditions, such as for high power operation lyst layer preferably comprising an admixture of cata 35 and for low power operation. As the mixture of hydro lyst and hydrophobic polymer binder. Although the gen gas and water droplets pass through the thermal ex specific material of which the electrodes are made and change portion 22 of the cell 12 the water droplets their construction is not considered critical to the pres evaporate, absorbing heat and locally raising the partial ent invention, it is required that the electrodes be gas 40 pressure of water vapor in the stream. Near the exit 40 porous so that product gas bubbles are not retained in the increased partial pressure of water vapor causes the the electrolyte and so that process water may be added water droplets to evaporate at a higher temperature in vapor form from the nonelectrolyte side of the elec thus providing a temperature gradient across the cell. trodes. Electrodes of this type are commonly referred Since the exit 40 is on the same side of the cell as the to as gas diffusion electrodes, and are suitable for either inlet 42 to the gas space 24 the temperature of the cell terrestrial or zero-gravity operation. A cell of the type 45 12 at the inlet 42 will be higher than the temperature just described and which may be used in the system 10 of the cell at the outlet 32. This is the preferred (al of the present invention is shown in FIG. 1 of Bushnell though not required) direction for the temperature gra et al U.S. Pat. No. 3,779,811 and is incorporated herein dient as will hereinafter be explained. by reference, although the present invention is not lim The system 10 also automatically adds makeup water ited to that precise configuration. into the stream. For example, as water is used up by the During operation an electric potential is applied by electrolysis cell 12 there will thus be less water passing a power source 30 causing electrolysis of the water through the water sprayer 46. Thus, less heat will be re fraction of the electrolyte within the matrix 18 and lib moved from the cell causing the exit temperature erating oxygen from the gas space 26 on the anode side sensed by the thermal sensor 48 to increase. When the of the cell and hydrogen from the outlet 32 of the gas 55 temperature sensed increases the valve 50 opens allow space 24 on the cathode side of the cell. In this embodi ing additional water to be introduced through the ment all of the oxygen and a portion of the hydrogen sprayer 46 into the recirculating hydrogen stream until is removed from the cell for either storage or immedi the temperature goes down to a predetermined value ate use through conduits 34, 36, respectively. These 60 whereupon the valve 50 closes. Thus the system tends product gases pass through pressure regulating means to keep a constant volume of water recirculating and 37 for maintaining substantially equivalent pressures automatically compensates for water leaving the sys within the gas spaces 24 and 26 which is usually neces tem with the product gas streams as well as for high and sary for proper operation of the cell as is well known low power operation wherein the amount of water elec in the art. A portion of the hydrogen produced is recir 65 trolyzed varies.

culated through the cell and is the vehicle for carrying The recirculating stream as it emerges from the ther a coolant fluid through the cell. The recirculating hy mal exchange portion 22 includes water in both vapor drogen leaves the cell at the outlet 32 of the gas space and liquid form. The stream thereupon passes through

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S 6 a condenser 52 where at least a portion of the water . Although the invention has been shown and de vapor is changed back to liquid water. Heat which was scribed with respect to a preferred embodiment thereof picked up in the cell may also be rejected from the it should be understood by those skilled in the art that stream at this point. In this embodiment a coolant is cir various changes and omissions in the form and detail culated through the condenser by means of a conduit thereof may be made therein without departing from 54 and a pump 56 to remove heat therefrom and the spirit and the scope of the invention. thereby condense the water vapor in the recirculating Having thus described typical embodiments of our gas stream. The coolant passes through a radiator 58 invention, that which we claim as new and desire to se which may, for example, reject the heat to the sur cure by Letters Patent of the United States is: rounding environment. It should be apparent to one O 1. An electrolysis cell system for producing oxygen with ordinary skill in the art that any of many well and hydrogen comprising:

known means for condensing water vapor and remov an electrolysis cell including a pair of gas diffusion ing heat from the recirculating gas stream may be uti electrodes spaced apart, aqueous electrolyte ma lized in the system 10 of the subject invention. Upon trix means in the space between said electrodes, leaving the condenser 52 the gas stream, which still has 15 means forming a gas space on the nonelectrolyte water in both vapor and liquid form, passes into a pump side of each electrode, one of said gas spaces in separator 60 which separates the liquid water from the cluding inlet means and outlet means, said cell also water vapor. The hydrogen gas and remaining water including a thermal exchange portion having en vapor leave the pump separator 60 and reenter the fuel trance means and exit means; cell 12 at the inlet 42. The separated liquid water leaves means for recirculating a portion of one of said prod the pump 60 by means of conduit 62 and is bypassed uct gases from said outlet means, through said ther around the cell 12 and is reintroduced into the circulat mal exchange portion, to said inlet means and back ing hydrogen stream in droplet form through the water through said gas space;

sprayer 46. means for introducing sufficient water into said recir It is desirable to control the partial pressure of water 25 culating product gas to maintain the temperature vapor in the gas stream entering the inlet 42 so that it of said gas exiting from said thermal exchange por is equivalent to the equilibrium partial pressure of tion exit means at a predetermined first tempera water over the electrolyte. If the partial pressure of ture;

water vapor in the gas stream at the inlet 42 is too high condenser means disposed in said recirculating gas the matrix 18 may become flooded despite the porous stream between said thermal exchange portion exit backup plate 20; or, if the partial pressure of water means and said gas space inlet means for removing vapor is too low the matrix may dry out. In this embodi heat from said recirculating gas stream exiting from ment the partial pressure of the water vapor in the gas said thermal exchange portion and for condensing stream at the inlet 42 is established by controlling the 35 vaporized water entrained within said recirculating temperature of the gas stream leaving the condenser gas; and 52. A temperature sensor 64 is located in the gas means for establishing a desired partial pressure of stream immediately downstream of the condenser 52. water vapor in said recirculating gas reentering said The conduit 54 for carrying the coolant through the gas space inlet means.

condenser 52 includes a bypass conduit 66 for bypass 40 2. The electrolysis cell system according to claim 1 ing coolant around the condenser 52. The amount of lating including means causing the water within said recircu coolant bypassed is controlled by a bypass valve 68. gas to enter said thermal exchange portion in The bypass valve 68 operates in response to the tem droplet said cell.

form to create a temperature gradient across perature sensed by the temperature sensor 64 to main 3. The electrolysis cell system according to claim 2 tain the temperature 64 within a predetermined tem 45 wherein said electrolysis cell system is arranged and perature range so that the partial pressure of water constructed vapor at the inlet 42 is a satisfactory level which insures creases fromsosaid that the temperature of said cell de inlet means to said outlet means neither flooding nor drying out of the matrix 18. across said cell, and wherein said means for establish As heretofore mentioned it is desirable that the tem perature of the cell 12 decrease from the inlet 42 to the circulating gas entering said of 50 ing a desired partial pressure gas water vapor in said re inlet means includes outlet 32. This will be the case in the embodiment

(A) thermal sensing means shown since the exit 40 of the thermal exchange por perature of said recirculating gas leaving for sensing a second tem tion 22 is on the same side of the cell as the inlet 42 to said con denser, and (B) means responsive to the gas space 24. Thus the coolant (i.e., water in drop 55 ing means for maintaining said second temperature said thermal sens let form) flows through the thermal exchange portion within a range which will result in the desired partial 22 counter to the hydrogen gas entering the gas space pressure of water vapor in said recirculating gas enter 24. As the moist hydrogen stream enters the inlet 42 ing said inlet means.

and moves past the cathode more and more water is re 4. The electrolysis cell system according to claim 3 moved from the stream resulting in a decrease in the wherein said condenser means includes means for car water partial pressure of the gas stream from the hot rying a coolant into indirect heat exchange relationship inlet 42 to the cool exit 32. The fact that the equilib with said recirculating gas and wherein said means re rium partial pressure of water vapor over the electro sponsive to said thermal sensing means for maintaining lyte and partial pressure of water vapor in the gas said second temperature within a range which will re stream both decrease from the inlet 42 to the outlet 32 sult in the desired partial pressure of water vapor in helps to maintain, as close as possible, an even concen 65 said recirculating gas as it reenters said inlet means in tration of electrolyte across the cell for most efficient cludes (A) bypass means for bypassing said coolant cell operation. around said condenser means, and (B) bypass valve

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means responsive to said thermal sensing means for introduced in an amount sufficient to maintain the controlling the proportion of flow of coolant through temperature of said stream exiting from said ther said condenser means and said bypass means. mal exchange portion at a predetermined tempera 5. The electrolysis cell system according to claim 4 ture, including pump separator means in said recirculating 5 condensing vaporized water entrained within said re gas stream said condenser means and said gas space circulating gas after it exits from said thermal ex inlet means for separating out liquid water entrained in change portion and prior to its being reintroduced said recirculating gas, and means in operable relation into said gas space for removing heat therefrom; ship with said pump separator means for taking said and separated liquid water out of said recirculating gas and establishing a desired partial pressure of water vapor reintroducing it into said recirculating gas between said in said recirculating gas as it reenters said gas gas space outlet means and said thermal exchange por Space.

tion entrance means. 11. The process according to claim 10 including the 6. The electrolysis cell system according to claim 2 step of causing the water within said recirculating gas wherein said means for introducing water includes first 15 to enter said.thermal exchange portion in droplet form thermal sensing means for sensing the temperature of to create a temperature gradient across said cell. the recirculating gas exiting from said thermal ex 12. The process according to claim 11 wherein said change portion exit means, pressurized water supply step of recirculating a portion of one of said product means, first control valve means responsive to said first gases includes flowing said product gas through said thermal sensing means for permitting the proper 20 thermal exchange portion in a direction counter to the amount of water to pass from said supply means into flow of said recirculating gas through its respective gas said recirculating gas to maintain the temperature of space so that the temperature of said cell decreases said recirculating gas exiting from said thermal ex across said cell in the direction of the flow of said recir change portion exit means at said predetermined first culating gas through its respective gas space. temperature. 25 13. The process according to claim 12 wherein said 7. The electrolysis cell system according to claim 6 step of establishing a desired partial pressure of water wherein said recirculating product gas is hydrogen and vapor in said recirculating gas as it reenters said gas said electrolysis cell is a base cell. space includes the step of maintaining the temperature 8. The electrolysis cell system according to claim 6 of said recirculating gas as it reenters said gas space wherein said electrolysis cell system is arranged and 30 within a range which will result in said desired partial constructed so that the temperature of said cell de pressure of water vapor.

creases from said inlet means to said outlet means 14. The process according to claim 13 wherein said across said cell, and wherein said means for establish step of condensing includes the step of carrying a cool ing a desired partial pressure of water vapor in said re ant through a heat exchanger into indirect heat ex circulating gas as it enters said gas inlet means includes 35 change relationship with said recirculating gas. (A) second thermal sensing means for sensing a second 15. The process according to claim 14 wherein said temperature of said recirculating gas leaving said con step of maintaining said desired partial pressure of denser, and (B) means responsive to said second ther water vapor in said recirculating gas as it reenters said mal sensing means for maintaining said second temper gas space includes bypassing an appropriate portion of ature within a range which will result in the desired par 40 said recirculating gas around said indirect heat ex tial pressure of water vapor in said recirculating gas as changer thereby removing less heat from said recircu it enters said inlet means. lating gas.

9. The electrolysis cell system according to claim 7 16. The process according to claim 5 including including pump separator means in said recirculating maintaining substantially equivalent product gas pres gas stream between said condenser means and said gas 45 sures in said gas spaces of said cell and wherein said space inlet means for separating out liquid water en step of recirculating a portion of one of said product trained in said recirculating gas, and means in operable gases includes recirculating a portion of said hydrogen relationship with said pump separator means for taking produced by said cell.

said separated liquid water out of said recirculating gas 17. The process according to claim 12 including the and reintroducing it into said recirculating gas between 50 step of separating the condensed liquid water entrained said gas space outlet means and said thermal exchange in the recirculating gas from the water in vapor form portion entrance means. prior to said gas reentering said gas space, bypassing 10. In the process of generating hydrogen gas and OX said separated liquid water around said gas space, and ygen gas in an electrolysis cell wherein the cell includes reintroducing it into said recirculating gas before said a pair of gas diffusion electrodes spaced apart, matrix recirculating gas enters said thermal exchange portion. means for retaining an aqueous electrolyte in the space 18. The process according to claim 11 wherein said between said electrodes, means forming a hydrogen gas step of recirculating a portion of one of said product space on the nonelectrolyte side of one of said pair of gases includes recirculating a portion of said hydrogen electrodes and an oxygen gas space on the nonelectro produced by said cell.

lyte side of the other of said pair of electrodes, and a 19. The process according to claim 11 wherein the thermal exchange portion, the steps of: step of causing the water to enter said thermal ex supplying current to said cell; change portion in droplet form includes passing all liq recirculating a portion of one of said product gases uid water within said recirculating gas and water added from its respective gas space through said thermal to Said recirculating gas through a sprayer positioned exchange portion and back through said gas space; 65 immediately upstream of said thermal exchange por introducing water into said recirculating product gas t1Con.

for removing heat from said cell, said water being

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UNITED STATES PATENT OFFICE

CERTIFICATE OF CORRECTION

INVENTOR(S) : Edmund K. Parenti, Jr. et all it is Certified that error appears in the above-identified patent and that said Letters Patent are hereby COrrected as shown below:

Column 7, 1ine 6: after the word 'stream' insert --between--. Column 8, 1ine 4:3: "including' should read --including--.

eigned and Sealed this second Day of December 1975

SEAL

Attest.

Attesting Officer Connaissioner of Patents and Trideroarris