An improved system for interconnects in a fuel cell. In one embodiment, the membranes are located in parallel with one another, and current flow between them is facilitated by interconnects. In another embodiment, all of the current flow is through the interconnects which are located on the membranes. The interconnects are located between two electrodes

Clara, Filiberto

Narayanan, Sekharipuram R.

Valdez, Thomas I.

NASA Technical Reports Server

(12) United States Patent 
Narayanan et al. 
(54) ELECTRODE AND INTERCONNECT FOR 
MINIATURE FUEL CELLS USING DIRECT 
METHANOL FEED 
(75) Inventors: Sekharipuram R. Narayanan, Arcadia, 
CA (US); Thomas I. Valdez, Covina, 
CA (US); Filiberto Clara, Prosser, WA 
(US) 
(73) Assignee: California Institute of Technology, 
Pasadena, CA (US) 
Subject to any disclaimer, the term of this 
patent is extended or adjusted under 35 
U.S.C. 154(b) by 0 days. 
( * ) Notice: 
(21) Appl. No.: 09/994,907 
(22) Filed: Nov. 26, 2001 
(65) Prior Publication Data 
US 200210102449 A1 Aug. 1, 2002 
Related U.S. Application Data 
(60) Provisional application No. 601253,423, filed on Nov. 27, 
2000. 
(51) Int. C1.7 ............................ HOlM 8/10; HOlM 8124 
(52) U.S. C1. ............................ 429/32; 4271115; 429134 
(58) Field of Search .............................. 429130, 32, 34, 
429138, 39; 4271115; 291623.5 
(56) References Cited 
U.S. PATENT DOCUMENTS 
4,450,212 A 511984 Feigenbaum et al. 
(io) Patent No.: 
(45) Date of Patent: 
US 6,756,145 B2 
Jun. 29,2004 
4,537,840 A 811985 Tsukui et al. 
5,108,849 A 411992 Watkins et al. 
5,230,849 A 711993 Hsu 
5,393,619 A 211995 Mayer et al. 
6,127,059 A * 1012000 Kat0 .......................... 2041283 
6,146,781 A 1112000 Surampudi et al. 
FOREIGN PATENT DOCUMENTS 
DE 19624887 A1 * 111997 
JP 59-73852 411984 
OTHER PUBLICATIONS 
U.S. patent application publication No. 200210058175 Al, 
published May 16, 2002. 
* cited by examiner 
Primary Examineraruce F. Bell 
Assistant Examiner-Jonathan Crepeau 
(74) Attorney, Agent, or F i r m C i s h  & Richardson P.C. 
(57) ABSTRACT 
An improved system for interconnects in a fuel cell. In one 
embodiment, the membranes are located in parallel with one 
another, and current flow between them is facilitated by 
interconnects. In another embodiment, all of the current flow 
is through the interconnects which are located on the mem- 
branes. The interconnects are located between two elec- 
trodes. 
14 Claims, 1 Drawing Sheet 
https://ntrs.nasa.gov/search.jsp?R=20080005182 2019-08-30T03:04:06+00:00Z
U S .  Patent Jun. 29,2004 US 6,756, 
CURRENT HOW 
145 B2 
IMfRCONNECl 
FIG. 2 
US 6,756,145 B2 
1 2 
ELECTRODE AND INTERCONNECT FOR 
MINIATURE FUEL CELLS USING DIRECT 
METHANOL FEED 
CROSS-REFERENCE TO RELATED 
APPLICATIONS 
resistance of a flat pack may be an important part of 
increasing power density of the direct methanol fed fuel cell. 
The present application teaches a flat pack design which 
reduces the path length for the current flow, and increases 
5 the area of the interconnect. By carrying out both of these 
objectives substantially simultaneously, the internal resis- 
tance may be reduced. 
The electrodes of the first embodiment may allow current 
to flow along the length of the electrodes. The effective path 
10 length for the current flow may be given by one arbitrary 
unit for each 1 cmxl cm section of the electrode. Thirty units 
of path length may be used for the six cell pack. For 
The invention described herein was made in the Perfor- example, all the current through the cells passes through an 
mance of Work under a NASA 7-1407 contract, and is interconnect area of approximately 0.15 cm’. The ratio of 
subject to the Provisions of Public Law 96-517 (35 UsC 15 the interconnect area to the electrode area is approximately 
202) in which the Contractor has elected to retain title. 0.03. Moreover, the pack has a resistance of about 9.6 ohms. 
In the FIG. 1 embodiment, the current flow from a first 
unit 100 occurs in the direction of the arrow 102. In the 
embodiment, a COmmOn membrane may be used, Or mem- 
A number of separate cells are formed, each having 
electrodes with different parts. Interconnects operate to 
connect between the respective interconnects. For example, 
interconnect 118 connects between the cell including mem- 
ne electrode configuration of these devices may form a 2s brane 110 and the cell including membrane 112. Similarly, 
a second interconnect 122 connects between the cell includ- 
this embodiment, the cells are connected through the mem- 
brane interconnect. The current flows along the length of the 
30 cells from one interconnect to the other. Overall current 
flows from the cathode 99 to the anode 107, 
A second embodiment is shown in FIG, 2, In this 
embodiment, larger area interconnects are used with parallel 
current paths. In this embodiment, the current flows in 
parallel through the width of the cell, along and through the 
membranes and the interconnects. This system may use a 
catalyst layer coating and membrane electrode assembly 
formation of a type which has been known in the art. 
arrent flow passes through the membrane. An is 
associated with the membrane. Interconnect 202 is similarly 
planar, and associated with the electrode and membrane. 
Similarly, a second membrane 210 is connected using a 
second interconnect 212. This effectively forms a strip cell 
Methanol fuel cells may be Constructed as described in 4s in which current flows through the width of the cells, and the 
cells are connected through the interconnect along almost 
the entire area of the cell. For example, the interconnect may 
be Over 90 percent of the area of the membrane, 
The methanol may be fed to the fuel cells using a wicking 
part 290 which feeds methanol from a methanol fuel supply 
208 to edges of the membranes of the electrochemical cells. 
~n advantage of this system is that the current flows 
the pack, The effective path length is approximate~y 
5s 615 units, because there are five parallel segments of 
resistance, each about equal to six arbitrary units of length. 
The ratio between the interconnect area and the electrode 
area is approximately 0.2. Also, the pack has an internal 
resistance of about three ohms. 
In order to formulate this new layout and interconnect, the 
system uses new types of masks for appropriately overlap- 
ping electrodes and interconnects. The interconnect materi- 
als which are used are of a type that retain their form prior 
to curing. In addition, the interconnect material is applied in 
The masks may be formed of Kapton materials that are 
3-5 mils thick. The electrodes are sized appropriately to fit 
This application claims priority from Provisional appli- 
cation No. 601253,423 filed Nov. 27, 2000. 
STATEMENT AS TO FEDERKLY-SPONSORED 
RESEARCH 
BACKGROUND 
Direct methanol fed fuel cells may be used as energy 
sources. Miniaturization of these devices may allow the 2o brane Parts may be connected. 
devices to replace rechargeable batteries in certain applica- 
tions. Such applications may include, for example, cellular 
telephones, laptop computers, and other small portable elec- 
tronic devices. 
critical factor about the performance of such fuel cells, 
Resistance between interconnects may also form a factor. ing membrane 112 and the membrane l14. In 
SUMMARY 
The present application teaches an electrode and inter- 
connect technique which may be more efficient than previ- 
ous techniques, as well as enabling reduction of size. 
BRIEF DESCRIPTION OF THE DRAWINGS 3s 
These and other aspects will now be described in detail 
FIG. 1 shows a first interconnect technique; and 
with reference to the accompanying drawings, wherein: 
FIG, 2 shows a second interconnect technique, in which 40 A first membrane 200 is planar, as conventional, and the 
the current passes through the membranes and the intercon- 
nects. 
DETAILED DESCRIPTION 
Pat. No. 631463781. However, these Often use 
bipolar Plates, often called ‘‘biplates”, between the stacks. 
These bipolar plates may be too large for effective minia- 
turization. 
A flat Pack design has been disclosed. This flat Pack 
technique may operate WithoutbiPlates. Instead, the cells are 
connected in series on a common membrane plane, using 
electrical interconnects which are formed through the mem- 
brane. 
This technique, although compact and lightweight, may 
result in a higher internal resistance than that of the bipolar 
cell, which would have the same active electrode areas and 
the same number of cells. 
The higher internal resistance may lower the power 60 
density and also lower the efficiency. 
Power density that has been attained with a first genera- 
tion flat pack was in the range of 2-3 mw per centimeter 
squared. However, it may be desirable to increase that power 
density, for example to as high as a 8-10 mwicm’, in order 6s a controlled manner, as a 1 mm wide line segment. 
to meet requirements of portable power source applications. 
The inventors accordingly realized that the high internal 
so 
US 6,756,145 B2 
3 4 
the masks. An interconnect paste is formulated from a high 
graphite and that he curing binder in the weight ratio 20:l. 
Isopropanol is added in small amounts to the paste in order 
to achieve appropriate consistency. This formation tech- 
nique results in formable interconnects which do not flow 
excessively, and which their retain their connection, allow 
optimum electrode alignment prior to membrane electrode 
assemblies being hot pressed. The system may be applied 
using a hypodermic syringe loaded with interconnect paste i o  
of an appropriate consistency. 
Although only a few modifications have been disclosed in 
detail above, other modifications are possible. All such 
modifications are intended to be encompassed within the 
following claims. 
6. A fuel cell, comprising: 
surface area conducting carbon material such as Astbury a plurality of membrane assemblies, arranged substan- 
tially adjacent to one another, each membrane assembly 
being electrochemically active to produce a voltage 
when an electrochemical reaction occurs; 
a plurality of electrodes, in contact with said membrane 
assemblies; 
a plurality of interconnects, located between adjacent 
ones of said electrodes, wherein a ratio of an area of an 
interconnect to an area of the electrode is at least 0.2; 
a methanol fed part that feeds methanol to said plurality 
of membrane assemblies; and 
wherein said membrane assemblies are rectangular with 
flat faces facing against one another, and edge portions 
between the faces, and said edge portions extremely 
substantially perpendicular to said face, said methanol 
feed part is a wicking part which feeds methanol to only 
said edge portion of membranes within said membrane 
assemblies. 
7. A fuel cell as in claim 6, wherein said ratio is substan- 
8. A fuel cell as in claim 6, wherein said interconnects are 
9. A fuel cell as in claim 8, wherein said paste includes 
10. A fuel cell as in claim 8, wherein said paste includes 
11. A fuel cell as in claim 6, wherein said membrane 
5 
What is claimed is: 
1. A fuel cell, comprising: 
a plurality of electrochemical cells, each including a 
plurality of electrodes, associated with the electro- 
chemical cells including an electrochemical anode, an 2o 
electrochemical cathode and a membrane, said plurality 
of electrochemical cells arranged in series such that 
current flows across said membranes; 
a plurality of interconnects, between two adjacent 2s 
electrodes, and wherein each interconnect is at least 20 
percent of an area of at least one of said electrodes; 
a methanol feed part that feeds methanol to said plurality 
of electrochemical cells; and 
against one another, and edge portions between the 
perpendicular to said face, said methanol feed part is a 
wicking part which feeds methanol to only said edge 
portion of said membranes of said electrochemical 3s 
cells. 
tially 0.2, 
formed of a paste. 
graphite therein. 
graphite herein and a heat curing binder. 
wherein said cells are rectangular with flat faces facing 30 each an anode part, a cathode part, and 
a membrane part, between said anode and cathode. 
faces, and said edge portions extremely 12. A as in 11, wherein said membrane 
produce a a length Of the mem- 
brane 
13. A fuel cell as in claim 11, wherein said membrane 
assemblies produce a voltage along a width of the membrane 
14. A method Of forming a as in 6 2  
forming a plurality of assemblies which are substantially 
coating said membranes with a catalyst layer coating; 
forming interconnects of a paste with a heat curing binder 
therein, between electrodes associated with said mem- 
branes; and 
hot pressing, wherein said heat curing binder is heated 
during said hot pressing said electrodes to form a 
membrane electrode assembly. 
2. A fuel cell as in claim 1, wherein said membranes are 
formed of a planar structure, and said interconnects are also 
formed of planar structures of substantially the same size as 
said electrochemical cells. 
3. A fuel cell as in claim 1, wherein said electrochemical 
cells are arranged such that an anode of one of said elec- 
trochemical cells contacts a cathode of another of said 
electrochemical cells. 
cells produce a current which travels along a length of the 
cell. 
5. A fuel cell as in claim 3, wherein said electrochemical 
cells produce a current which travels along a width of the 
cell. * * * * *  
comprising: 
4o 
adjacent with one another; 
4. A fuel cell as in claim 3, wherein said electrochemical 4s 


Electrode and interconnect for miniature fuel cells using direct methanol feed

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