Inorganic ion exchange membrane electrolytes for fuel cell us

Arrance, F. C.

Soltis, D. G.

English

NASA Technical Reports Server

Jan. 14, 1969 JAMES E. WEBB 3,42 1,948 
ADMINISTRATOR OF THE NATIONAL AERONAUTICS 
AND SPACE ADMINISTRATION 
METHOD OF MAKING MEMBRANES 
Filed April 13, 1965 Sheet 1 of 2 
https://ntrs.nasa.gov/search.jsp?R=19690011975 2020-03-16T18:19:12+00:00Z
Jan. 24, 1969 JAMES E. WEBB 3,421,948 
ADMINISTRATOR OF THE NATIONAL AERONAUTICS 
A N D  SPACE ADMINISTRATION 
METHOD OF MAKING MEMBRANES 
Fi l ed  April 13, 1965 Sheet 2 o f  2 
PREVIOUS METHOD 
> W E T  MIX 15 MINS. 
DRY 40 HRS. 'i3 14OoC. 
PHOSPWORIC 
33% % BY WT: 33% % B Y  WT. 
3,42 1,948 United States Patent Office patented Jan. 14, 1969 
a 2 
stronger membrane than previously could be produced, 
3,421,945 and that can therefore withstand greater shock, vibration 
METHOD OF MAKING MEMBRANES and other adverse physical conditions than could be tol- 
James E. Webb, Administrator of the National Aero- erated in the past. 
nautics and Space Administration with respect to an in- Another object of this invention is to provide a new 
vention of Prank C. Arrance, Costa Mesa, Calif., land ’ method of making a physically stronger membrane than 
Daniel G. Soltis, West ]Richfield, QMo previously could be made, yet requires substantially less 
time to make the membrane than formerly required. 
Another object of this invention is to provide a new 
1o method of making a physically stronger membrane than 
previously could be made, yet requires less steps than 
formerly necessary. 
Summary of the invention 
Filed Apr. 13, 1945, Ser. No. 447,933 
US. CI. 136-144 
Int. 4311. HOlm 3/02 
2 Claims 
ABSTRACT OF THE DISCLOSURE 
This invention teaches an improved method of making Essentially this invention teaches that a stronger mem- 
an inorganic membrane suited for fuel cell use. Zeolite 15 brane will result if conditions during manufacture are 
and a binder, such as zirconium phosphate, are used. Es- controlled SO that the bond forming reaction between 
sentially, a mixture of zirconium oxide, phosphoric acid, the zeolite mineral and the binder is inhibited until sub- 
and zeolite is formed under conditions (such as low teni- stantially all the physical working of the mixture is sub- 
€’erature and that stantially complete. The technical reasons as to why this 
inhibit bond formation until substantially all physical 20 should produce a stronger membrane are given later. 
working of the membrane is complete. Then it is sintered IJowever, to accomplish the above, such things as control 
to form the bonds. The resulting membrane is strong, con- of the amount of water, as well as temperatures as low 
tinuous, flexible, can withstand high temperatures, is un- as practicable are used in the new method to inhibit bond 
affected by radiation, can be hydrated and dehydrated formation. Further, some additional advantages in carry- 
without ill effect, and has good dimensional stability. 25 ing out the improved method are that less steps are re- 
quired, and less time is required in making the membrane. 
Brief description of drawings 
Origin of invention 
Other objects and advantages will appear from the speci- 
The invention described herein was made in the per- 30 fication and claims taken in connection with the accom- 
formance of work under a NASA contract and is subject 
to the provisions of Section 305 of the National Aero- FIGURE 1 is a cross sectional view of a fuel cell uti- 
nautics and Space Act of 1958, Public Law 85-568 (72 
Stat. 435; 42 USC 2457). FIGURE 2 is a flow diagram of a previous method of 
Background of the invention 
FIGURE 3 is a flow diagram of the improved method 
to a membrane that can be of making the zeolite membrane structure according to the 
used as an electrolyte in a fuel cell. More particularly this present invention. 
invention relates to an improved method of increasing the 
physical strength of “solid” inorganic ion exchange mem- 40 Description of preferred embodiment 
brane of the type shown in the US. patent application of Referring to FIGURE 1, there is illustrated a fuel cell 
A. Levy-Pascal, titled “Zeolite Electrolitic Membranes for 2 as background, to show how a “soli#’ ion exchange 
Fuel Sells,” Ser. NO. 447,587, filed Apr. 12, 1965; and membrane made according to this invention can be used. 
assigned to the same assignee as this invention. In general, fuel cell 2 may contain a gas permeable 
One of the things that is taught by the above Patent 45 anode electrode 4 and a gas permeable cathode electrode 
aPPlication, is how to make an inorganic membrane. An 6. These may be made of porous stainless steel for ex- 
inorganic membrane has many desirable features when ample. An electrolyte in the form of a “solid” inorganic 
compared to an organic membrane. It is not subject to ion exchange membrane 8, containing a compacted hydrate 
swelling, has good dimensional stability, has excellent re- form of the mineral zeolite, is positioned between and in 
sistance to oxidation, radiation, and due to its high energy 60 direct contact with anode electrode 4 and cathode electrode 
of adsorption can withstand higher temperatures. It also 6. 
can be cycled between complete dehydration followed by Means 10 are provided for supplying fuel, as for exam- 
hydration without ill effect. ple hydrogen, to anode electrode 4. And, means 12 are 
As taught by the above application, a membrane may provided for supplying oxidant, as for example oxygen, to 
be made out of zeolite powders and a binder of Zirconium 55 cathode electrode 6. A load p4 is electrically connected 
phosphate. The binder acts to securely hold the zeolite between electrodes 4 and 6.  
powders together, so that they can be formed into a wafer Generally, the fuel cell operates when hydrogen gas is 
that has sufficient physical strength to permit its use as a fed to anode electrode side 4 of membrane 8 where it is 
membrane. catalytically decomposed into hydrogen ions and its elec- 
Physical strength is very important in the use of a 60 trons transferred to the anode and travel through the out- 
membrane. Just as an example, a fuel cell employing a side load 14 where they perform work, and then to the 
membrane electrolyte, may be used in a vehicle adapted cathode electrode 6. 
for land, underwater Or even Space travel. The fuel cell The hydrogen ions are transported as hydromiurn ions 
may be subjected to all types of shocks and vibrations in by a cation exchange mechanism through the width of 
use. It is therefore necessary that the membrane have 65 membrane 8 toward the cathode. 
sufficient physical strength to withstand shock, vibration Meanwhile, oxygen gas is fed to porous cathode 6 where 
and even high “ G  forces without cracking, falling apart it is picked UP by the electrons coming from the anode 
or shorting in use. and combined with the hydrogen ions at the catalyst- 
It follows that the stronger a membrane can be made, zeolite interphase to form water. 
the more suited it is for use under adverse conditions. The water produced is eliminated from the cell by dif- 
In view of the above, it is therefore an object of this fusion through the cathode and evaporation to the outside, 
invention to provide a new method of making a physically or by a wick (not shown) connected to its outer surface. 
Of the amount Of water 
panying drawings wherein: 
lizing a lnembrane electrolyte; 
35 making the zeolite membrane structure; and 
This invention 
70 
3,421,948 
3 4 
As mentioned above, menbrane 8 is made in the form As mentioned in the above patent application and as 
of wafer containing a compacted hydrate form of the repeated here, it is very important to note that when niak- 
mineral zeolite. In zeolite crystals, the lallice structure is ilig the membrane, the zeolite should not be heated above 
such that the water of hydration or adsorbate is primaiily its heat stabilization temperature. At the heat stabilization 
located inside a regular inlraciqstalline three dimensional temperature, the ion exchange properties of the zeolite are 
cavity network. This permits the crystals to retain their ti destroyed and ionization will no longer take place. With- 
water of hydration under circumstances wherein other ma- out ionization, the membrane cannot function as an elec- 
terials would become dehydrated. For example one type tiolyte. 
of synthetic zeolite can retair, 60% of its water of hy- With respect to the new method, an example of the 
dration at 250” C. when the waier vapor pressure is kept steps that result in a much stionger membrane is illus- 
at 50 mm. Hg. trated in FIGURE 3 and are as follow. 
Neiv inethod With respect to zeolites, about forty different natural 
crystalline zeolites are known. Also, a number of synthetic 
zeolites have been developed that possess higher adsorp- Zirconium oside - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  33% % by weight. 
tion and ion exchange capabilities than the nztural occur- Phosphoric acid --------------_--_ 33% % by weight. 
ring zeolites. Additionally these synthetic zeolites can be A hydiogen form Of zeolite _ _ _ _ _ _ _ _ _  33% % by weight. 
modified to a degree, to meet particular needs. See for ex- Mi% dry for 1.5 minutes. 
ample U.S. Patent 2,852,243 to R. M. Milton setting forth Air dry 1.5 hours at 25”  C. 
various types of zeolites, including hydrogen forms. Gen- Fcrm at 3-4 tons p.s.i. into wafer shape. 
erally, the formula for zeolites is M2klsSi40096.24H20 2o Sinter 500” for 15 hours. 
where M may be a metal or hydrogen. It will be noted that in comparing the new with the old Some of the present manufacturers of synthetic zeolites method, that the step of adding water has been eliminated. are the Davison Chemical Division of W. R. Grace Co. It will be further noted that the mixture is air dried for (by the name of “Microtraps”) Linde Division of Union as little as 15 hours a t  a relatively low temperature of Carbide Corporation (by the name of “Molecular Sieves”) and the Norton co. (by the name of ~czeolon Synthetic 25 2.5’ C. (aproximately room temperature). In the previous 
method, the mixture was dried for 40 hours at 140” C. Zeolites”). In an attempt to technically cxplain why the membrane As pointed out in the previously cited patent applica- has increased strength when made by the new method, tion, one problem in the use of zeolites per se is that they 
lack strength and cannot be formed into a strong, con- the following is suggested: During the original wet mix- 
use. I-Iowever, a can be made w i t h  sufficient tion of the zeolite crystals and binder would react to 
zeolite particles together. the following forming step, many of the bonds were physi- 33 callY broken apart due to the later working. As a result, 
by the above patent application are: that  it is nn inorgailic these bonds were “lost” and not available to be formed 
material, will securely hold the zeolite particles together, during the sintering step. 
and will pass ions. The above may be likened to making a cracker. Before 
of a very satisfactory inorganic binder that a cracker is bakcd, the dou$ can be worked without 
will pass ions as described in the above *O decreasing the strength of the cracker. However, if the 
is zirconium phosphate. This is formed by reaction of cracker is partially baked, any later working will destroy 
zirconium oxide, phosphoric acid and the zeolite crystals. Gr weaken the cracker. 
Inorganic polymer bonds are formed that bind the zeolite The new method operates to control conditions so as 
crystals together. These bonds */ill be referred to later on to inhibit the amount of reaction taking place until after 
in discussing the new method. 45 the mechanical working of the mixture is complete. Thus 
To aid in understanding the present invention, reference many of the bonds that were Previously broken apart 
will first be made to the previous method of nIa!;ing a due to later working O f  the mixture are saved. These 
membrane, so that the difference between the new and bmds  are now formed after the mixture has been shaped 
previous method will be more readily apparent. into finished form and working of the mixture is substan- 
An example of the previous method of prepa~ing a 80 tially complete. These bonds are now available to be 
membrane as set forth in the above auDlication and as il- formed during the Sintering Step. Thus a much stronger 
tinuous and flexible membrane. If they were formed into 30 ing and 
a membrane, they would fall apart, crack 2nd short in 
physical strength if a binder is used to hold the 
temprature drying steps of the previous 
a large par- 
folnl the organic poly111er bonds. However, because of 
conditions were produced 
Some of the characteristics of a good binder as 
* _  
lustrated in FIGURE 2, is as follows. 
Previoris method 
Zirconium oxide _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  
Phosphoric acid _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  
A hydrogen form of zeolite (such as 
Zelon H made by Norton Co., or 
Linde A made by Union Carbide 
CO.) ........................... 
Water__________-_________________ 
Wet mix _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  
Dry 40 hours at 140” C. 
Form at 3-4 tons p.s.i. into wafer shape. 
Sinter 15 hours at 500” C. 
membrane can be made. This is borne out by the in- 
creased transverse strength of membranes made by the 
new method-3770 p.s.i., as compared to 2400 p.s.i. pre- 
viously-well over a 50% increase in strength. 
In  summary this invention teaches how to make a mem- 
brane that is stronger than previous membranes, requires 
less time to make the membrane, and is less complicated 
than previous methods. 
The membrane made by the new method has a trans- 
verse strength of approximately 3770 p.s.i., as compared 
to a transverse strength of approximately 2400 p.s.i. when 
made with the previous method. This is well over a 50% 
increase in strength of the membrane. 
The new method eliminates a step (adding water) and 
uses lower temperatures, it is more simple. Also, an ini. 
portant advantage in the new method is that over a day 
is saved ( 2 5  hours) in the drying step. The drying step 
having been reduced to approximately 15 hours, as com- 
70 pared to the 40 hours previously required. 
33% by weight. 
33% by weigllt. 
60 
33% by weight. 
Sufficient to aid 
15 minutes. 
in mixing. 65 
. -  
A membrane made by the above method has a trans- 
verse strength of approximately 2400 pounds per square 
inch. The resultant membrane is comparatively strong, 
continuous and flexible so that it can be used in a fuel 
cell. 
I t  is noted that while specific proportions, temperatures, 
pressures, and types of materials are set forth, these are 
by way of example only, and that it would be apparent 
to one skilled in the art that variations can be made with- 
75 out departing from the teachings of this invention. 
3,421,948 
6 
dry mixing said mixture for approximately 15 minutes; 
heating said mixture for approximately 
15 hours at approximately 25" C.; 
shaping said mixture into wafer form under 
approximately 3 tons pressure per square inch; 
sintering said shaped mixture at approximately 500" 
5 
It should be understood that it is not intended to limit 
the invention to the herein disclosed form, but that the 
invention includes such other forms or modifications as 
are embraced by the scope of the appended claims. 
What is claimed is: 
1. An improved method of making an inorganic mem- 
providing a mixture of zeolite, zirconium oxide and 
phosphoric acid; 
physically working said mixture dry and at approxi- 
mately room temperature, to inhibit the reaction of 
said resultant mixture until shaping of said mixture 
is substantially complete; and then 3,266,940 8/1966 Caesar _ _ _ _ _ _ _ _ _ _ _ _ _ _  136-86 
sintering said mixture. 3,298,839 1/1967 Troell _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  106-57 
2. An improved method of making an inorganic mem- 15 
providing a mixture of approximately 
33% % by weight zeolite; 
33% % by weight zirconium oxide: 
33% % by weight phosphoric acid; 
5 
and 
brane comprising the steps of: 
C. for approximately 15 hours. 
References Cited 
UNITED STATES PATENTS 
10 
brane for use as an electrolyte in a fuel cell, comprising 
the steps of: 
WINSTON A. DOUGLAS, primary ~ ~ ~ ~ i , ~ ~ ~ .  
DONALD L. WALTON, Assistant Examiner. 
US. C1. X.R. 
'* 136-153; 106-57; 252-449; 2 6 L 5 6  


Method of making membranes

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