Operation method for combined electrolysis device and fuel cell using molten salt to produce power by thermoelectric regeneration mechanis

Greenberg, J.

Thaller, L. H.

English

NASA Technical Reports Server

REPLY TO 
A I T N O F  GP 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON, D.C. 20546 
March 27, 1971. 
TO : USI/Scientific & Technical Information Division 
Attention: Miss Winnie M. Morgan 
FROM: GP/Office of Assistant General 
Counsel for Patent Matters 
SUBJECT: Announcement of NASA-Owned 
U,S, Patents in STAR 
In accordance with the procedures contained in the Code GP 
to Code US1 memorandum on this subject, dated June 8, 1970, 
the attached NASA-owned U.S. patent is being forwarded for 
abstracting and announcement in NASA STAR. 
The following information is provided: 
U,S. Patent No. : 3,357,862 
Corporate Source : Lewis Research Center 
Supplementary 
Corporate Source 
NASA Patent Case No.: 
Gayle Parker 
Enclosure: 
Copy of Patent 
=E-01645 
N 
9 0 ( A C C E S S I O T U M B E R )  (THRU) 
(CODE) 
(92 
03 
(CATEGORY) 
u- : 
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$ ( N A S A  CR O R  T M X  O R  A D  NUMBER) 
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NASA-HQ 
https://ntrs.nasa.gov/search.jsp?R=19710011429 2020-03-17T02:55:20+00:00Z
J. GREENBERG E T A L  3,357,862 
COMBINED ELECTROLYSIS UEVICE A N D  FUEL CELL 
AND METHOD OF OPERATION 
Dec. 12, 1967 
Filed Feb. 4, 1964 
- 
30 / 5 *  -37 44 1.
-32 
-- 46 
60 FIG. 2 
BY 
t 
INVENTORS 
JACOB GREENBERG 
LAWRENCE H. THALLER ab-\ 
3,357,862 
Patented Dec. 12, 1967 
1 
3.357.862 
COMBINED ELECTROLYSIS-DEVICE AND FUEL 
CELL AND METHOD OF OPERATION 
Jacob Greenbera. Parkview. and Lawrence H. Thsller, 
Cleveland, Ohio, assignors to the United States of 
America as represented by the Administrator of the Na- 
tibnal Aeronautics and Space Administration 
Filed Feb. 4$ 1964, Ser, No. 342,574 
9 Claims. (Cl. 136-86) 
The invenion described herein may be manufactured 
and"used by or for the Government of the United States 
of America for Government purposes without the pay- 
ment of any royalties thereon or therefor. 
The present invention relates, generally to fuel cells 
and, more particularly, to  a process and apparatus that 
utilizes a molten salt to produce useful power by a thermo- 
e!edric-regeneration mechanism. 
Power-producing electrochemical devices may be di- 
vided generally into three broad categories; these are 
static battery cells, dynamic reserve cells, and fuel cells. 
However, each of these broad categories suffers from a 
number of deficiencies. For example, the operating life 
of a static battery cell or dynamic reserve cell is limited 
by virtue of the fixed amounts of the active electrode com- 
ponents present in the batteries, Thus, in order to meet 
large and sustained power demands, batteries of these 
two types impose large weight penalties on any system 
in which they are employed. On the other hand, fuel cells 
which produce electricity directly from the oxidation of 
fuel are normally provided with fuel from an outside 
tank or with means for regeneration of the fuel constit- 
uents and therefore impose a lesser weight penalty for 
power generation. Heretofore, however, fuel cells utilizing 
regeneration have depended on the use of extremely high 
heat inpu?s and operating temperatures to physically 
break down and decompose the cell constituents to there- 
by provide for continued operation of the fuel cell. 
If the regeneration could be accomplished by elec- 
trolysis, a much lower heat input would be required than 
if the compound were decomposed by purely thermal 
means. 
Further, some of the useful power could be obtained 
from the regeneration cycle by utilizing a portion of the 
current generated during electrolysis. Molten salts have 
been discovered to be the best thermoelectric materials 
for this use because of their relatively good values of 
figures of merit, their chemical stability, their long liquid 
range, and the additional fact that they can be designed 
to operate in conjunction with a nuclear reactor producing 
heat. 
However, when fused salts are utilized as electrolytic 
conductors for the passage of an electric current, there is 
a transport of materials and a subsequent decomposition 
and provision must be made for the removal of these 
decomposed materials so that they are available for use 
in the fuel cell section in ordcr for the system to operate 
effectively. 
Accordingly, it i s  an object of this invention to provide 
an apparatus combining a thermoelectric regenerator and 
fuel cell. 
It is an additional object of the invention to provide 
a method for producing power by a thermoelectric- 
regeneration mechanism. 
It is still another object of the invention to provide 
a fuel cell utilizing the decomposition products of a mol- 
ten salt as the reactants. 
It is yet another object of the invention to  provide a fuel 
cell and regeneration system which does not requite 
extremely high thermal energy inputs or  operating tem- 
peratures to provide for regeneration of the fuel Celt 
reactants. 
5 
10 
15 
2 
A more complete appreciation of the invention and 
many attendant advantages thereof will be readily ap. 
parent as the same becomes better understood by refer. 
ence to the following detailed description when consid- 
ered in connection with the accompanying drawing 
wherein: 
FIG. 1 is a schematic illustration of one form of ap- 
ratus utilizing thermoelectric regeneration; 
FIG. 2 is a schematic illustaation of another form of 
apparatus utilizing the novel method of the invention. 
According to the present invention, the foregoing and 
other objects are obtained by providing a novel method 
for fuel cell and regenerator operation and apparatus to 
perform this function. In particular, the invention in- 
cludes the use of a molten salt capable of an electrolytic 
conduction, the imposition of a temperature gradient 
upon the molten fused salt, decomposition of the molten 
salt into its constituents by electrolysis and the use of 
these constituents in a fuel cell to uroduce useful flower. 
20 Apparatus is provided for performing this method-which 
includes a thermoelectric regenerative section, a fuel cell 
section, means for supplying the decomposed molten salt 
constituents to the fuel cell section and means for re- 
turning the fused salt to the regenerator section. 
From what has been said, it i s  apparent that practice 
of the invention involves temperature cycles in which 
electricity is produced in the fuel cell a t  a relatively low - 
temperature (sufficient to keep the salt molten) while 
sonic useful electricity is produced in the thermoelectric 
30 regenerator at a slightly higher average temperature (the 
average temperature of the regenerator, advantageously, 
bciiig maintai!ied at between 50" C. and 200" C. above 
the melting point of the salt). Of course, the actual op- 
erating temperatures of the cell and the average operating 
36 temperature of the regenerator depend upon the particu- 
lar molten salt utilized as the electrolyte conductor. 
Examination of some salt systems indicates that the 
polaiity of the thermopotential at the hot junction of the 
regenerator can be either positive or negative with respect 
40 to the cooler electrode depending upon the salt used, the 
gas constituent always being generated at the negative 
electrode. The polarities of some of the salts found useful 
in the practice of the instant invention are given in the 
table below: 
46 Polarity at 
Salt: hqt junction 
CdBr, ___________________-_______________ - 
FbBr2 _______________________-_____---___- - 
PbCi2 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  - _ _ _ _  - 
ZnBrz ____________________________________ -
ZnCla _________________________c__________ -
_I ________--___ _ _ _  _ _ _  -- ___-_-____ - + AgCl __________________-_---_-_---__----_ 
4- AgBr ____-____I__________________________ 
3. Agi _________-__________________c________ 
3. SnCI, ____________________________________ 
The electrodes utilized for both the regenerator and 
60 fuel cell sections must, of course, be inert to permit 
proper decomposition and recombination. Tungsten and 
platinum electrodes have been satisfactorily utilized in 
the practice of this process, both these materials being 
inert and not reversible in the presence of the aforemsn- 
65 timed fused salts. Additionally, the melting point of the 
metal constituent of the metalljc salt must be within the 
liquidus operating range of molten salt while the boiling 
point of the metal must be below this range for proper 
operation to take place. Advantageously, also the metal 
70 constituent should be relatively insoluble in the melt to 
permit proper separation from the thermocell electrode 
and transport to the fuel cell electrode for electrochemi- 
g6 
CdC12-----________-__,,_-__--_-__-,-_-,_- - 
60 
AgNOs 
3,357,862 
3 
cal recombination with the gas constituent. Exemplary of 
one salt having these requirements is zinc chloride. This 
salt is especially useful in the practice of the process 
since zinc is very insoluble in zinc chloride and the pre- 
cipated metal may then easily be made to react with the 
released chlorine gas. 
Referring now to the drawing wherein like numerals are 
utilized to indicate like parts throughout the figures, there 
is shown in FIG. 1 a combined fuel cell and regenerator 
10, which comprises a container 12 that completely sur- 
rounds and encloses the molten salt 13, for example, zinc 
chloride and its disassociated metal and gaseous con- 
stituents 14 and 16, respectively. Mounted within the con- 
tainer are a pair of upper electrodes 18 and 20 that are 
immersed therein and insulated from the container 12. 
Heat is applied to the fuel cell and regenerator 10 con- 
tiguous to the electrode 18 so that it is maintained at a 
higher temperature than the electrode 20, the electrode 
18 forming, in the case of zinc chloride, the cathode and 
the electrode 20 forming the anode. 
Advantageously, the electrode 18 is provided with an 
extended surface 22 having for example, dimples or in- 
dented portions 24 so as to provide an additional area of 
contact between it and the molten salt. In a similar man- 
ner, the electrode 20 is provided with dimpled or in- 
dented portions 26 and also includes finned section 28 
to provide a radiating or conducting surface for heat 
flow to thereby aid in maintaining the required tempera- 
ture gradient across the molten salt. Electrodes 18 and 
20 are externally short-circuited by a wire 30 so that this 
temperature gradient imposed across the molten salt 13 
will, since the salt is an electrolytic conductor, cause a 
passage of electric current and a consequent decomposi- 
tion of the zinc chloride at the electrodes 18 and 20 to 
liberate the gaseous constituent at the negative electrode 
and the metallic constituent a t  the positive electrode. 
Adjacent to and above the cathode 18 a bell-shaped or 
the like gas collector 32 is disposed, this bell-shaped device 
serving as a collector or catch basin for the gas con- 
stituent formed at electrode 18. Attached to and in com- 
munication with the gas collector 32 is a conduit 34 
which leads the gaseous constituent of decomposition 
downwardly and discharges it through a bell-shaped or 
the like gas dispenser 35. Situated above gas dispenser 
35 and directly below anode 20 is a porous electrode 36. 
This electrode, in conjunction with a wire screen elec- 
trode 38 that is disposed above it, form cell section 
within the container 12. Generated power is tapped from 
the fuel cell through leads 40 and 42 connected to the 
electrodes 36 and 38 respectively. 
The electrode reactions are as follows. 
I. Cathode electrode 18: 
11. Anode electrode 20: 
JII. Porous electrode 36: 
N. Metal screen electrode 38: 
2G-+Gat+2e- 
2e-+M+++ M.l 
Ga+2e-+2G- 
M-, M+++2e- 
where M is the metallic constituent of the fused salt (e.g., 
zinc chloride) and G is the gaseous Constituent thereof. 
In operation, the imposition of a temperature gradient 
across electrodes 18 and 20 causes electrolysis of the 
molten salt to occur and a decomposition of the salt 
into its gaseous and metallic constituents. The gaseous 
constituent is formed at  the cathode 18 which may be 
either the hot or cold electrode depending upon the pa-  
ticular salt utilized and collected by collector 32 and then 
led to the porous electrode 36 through conduit 34, the 
generated gas pressure being sufficient to insure proper 
circulation. The gas percolate3 through this electrode and 
4 
combines with the metal constituent of the salt which 
forms at the anode 20 and, in turn, settles or sinks through 
the molten salt bath. passing through wire screen elec- 
trode 38. Combination of these constituents, as detailed 
5 above, generates electrical power which may be utilized 
in any desired manner. 
Turning now to the alternate embodiment of the in- 
vention illustrated in FIG. 2, there is shown a further 
concept of the invention wherein the fuel cell and re- 
generator sections are physically isolated from each other. 
Cathode 18 and anode 20, similar to the first embodiment, 
are immersed in the molten salt 13 such as  zinc chloride 
and provided with extended surfaces by the use of a ph- 
rality of indented portions such as dimples 24 and 26, 
15 respectively. However, as clearly seen in FIG. 2, these 
electrodes are housed in a separate regenerator section 44 
formed by container 46. 
A bell-shaped or the like gas collector 32 is disposed 
above hot electrode 18 and is in communication with fuel 
20 cell section 48 by means of a conduit 50 which provides 
passage for the gas constituent to the fuel cell section. 
Conduit 52 is also in communication with the regenerator 
and fuel cell section 48 to provide passage for 
the metallic constituent of the molten salt. This conduit 
25 has attached to the top thereof a dished portion or section 
54 to collect the metal constituent formed at the cold elec- 
trode 20 and a pump 56 is provided to insure flow of the 
molten metal constituent in the conduit 52. 
The fuel cell section 45 is enclosed in container 58 and 
30 has disposed therein a porous electrode 36 and a wire 
screen electrode 38, with the screen electrode disposed 
above the porous electrode in B manner similar to the 
first illustrated embodiment so that the gas constituent 
percolates upwardly as the metal constituent passes 
35 through the wire screen electrode to recombine there- 
between and produce electric power which is passed to 
a load through leads 40 and 42. 
The recombined molten salt is returned to the regenera- 
tor section 44 through return conduit 60 provided with 
40 pump 62 which overcomes any difference in head between 
the separated regenerator and fuel sections. 
It will be understood, of course, that the output of cells 
made pursuant to this invention is dependent upon a 
number of factors other than that determined by the se- 
45 lection of the particular salt to be utilized as the elec- 
trolytic conductor, of course the salt selected governs 
whether the cathode gas-producing electrode is the hot 
or cold side of the regenerator section. 
For cells producing a high rate of current, it is desir- 
60 able that the electrodes in the regenerator and fuel cell 
sections be as closely spaced as possible and the selected 
electrolyte have a low value of resistance to  the fiow of 
current. Further, high current rates are best obtained by 
utilizing the highest temperature gradient possible con- 
Obviously, many modifications and variations of the 
present invention are possible in the light of the above 
teachings. It is therefore, to be understood that within 
the scope of the appended claims, the invention may be 
What is claimed is: 
1. A fuel cell and regenerator system comprising: a 
first and second pair of electrodes; said first pair of elec- 
trodes disposed in spaced relation in a molten electrolytic 
65 salt; a wire externally shorting said first pair of electrodes; 
a gas conducting conduit disposed adjacent to and in 
communication with said first pair of electrodes and lead- 
ing to said second pair of electrodes, whereby electrolysis 
of 'said salt at said first pair of electrodes provides de. 
composed constituents for recombination at said second 
pair of electrodes. 
2. The fuel cell and regenerator system according to 
claim I wherein a container is provided; said container 
55 sistant with the particular fused salt selected. 
60 practiced other than as specifically described. 
75 enclosing said first and second pair of electrodes. 
3,3 57,862 
5 6 
3. The fuel cell and regenerator system according to constituent of electrolysis is separated from the molten 
claim 2 wherein said second pair of electrodes are dis- salt by the force of gravity. 
posed beneath said first pair of electrodes. 7. An apparatus for the production of power compris- 
4. A fuel cell and regenerator system comprising: a ing: a container holding a molten salt electrolyte; means 
container for holding a molten salt selected from the 5 for imposing a temperature gradient upon said molten 
group consisting of cadmium bromide, cadmium chloride, salt; a first pair of electrodes disposed in said container 
lead chloride, zinc chloride, lead bromide, zinc bromide, in spaced relation and immersed in said molten salt to 
silver nitrate, silver chloride, silver bromide, silver iodide thereby provide an anode and a cathode; an external wire 
and stannous chloride; a pair of space electrically con- electrically shorting said first pair of electrodes; a second 
nected electrodes disposed in the upper portion of said pair of electrodes disposed in spaced relation in said con- 
container and in contact with said molten salt; a gas col- tainer beneath said anode; and a conduit communicating 
lecting baffle disposed above one of said pair of electrodes; between said cathode and said second pair of electrodes 
a second pair of spaced electrodes disposed within said whereby electrolysis of said molten salt at said first pair 
container and immersed in said molten salt bath beneath of electrodes produces an electric current at said second 
the other of said first pair of electrodes; a conduit leading 15 pair of electrodes. 
from said gas collecting baffle to one of said second pair 8. The apparatus according to claim 7 wherein said 
of electrodes whereby a heat gradient imposed across said second Pair of electrodes comprises a wire screen elec- 
first pair of electrodes produces power at  said second pair trode and a porous electrode. 
of electrodes. 9. The apparatus according to claim 8 wherein said 
5. A method of producing electric current comprising: ZO Wire screen electrode is disposed above said porous 
providing a cell containing a fused salt electrolyte selected 
from the group consisting of cadmium bromide, cadmium 
chloride, lead chloride, zinc chloride, lead bromide, zinc 
bromide, silver nitrate, silver chloride, silver bromide, 25 1,545,385 711925 Ashcroft _ _ _ _ _ _ _ _ _ _ _ _  204-66 
silver iodide and stannous chloride; heating said fused 1,588,608 611926 Oppenheim _ _ _ _ _ _ _ _ _ _  136-86 
salt above its melting point; imposing a temperature 2,384,463 911945 Gunn et al. _ _ _ _ _ _ _ _ _ _  136-86 
gradient across said salt; providing an external electrical 2,980,749 411961 Broers --____________ 136-86 
short-circuit connection between the hot and cold portions 3,256,504 611966 Fidelman -_-___I_- 204-150 X 
of said salt to decompose said salt into its constituents by 30 
References Cited 
UNITED STATES PATENTS 
FOREIGN PATENTS 
electrolysis; and recombining the constituents to provide 1,266,037 511961 France. 
an electric current. 
6. The method according to claim 5 wherein the metal /&,LEN B. CURTIS, Primary Examiner. 


Combined electrolysis device and fuel cell and method of operation Patent

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