Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2002-07-26
2004-11-09
Alejandro, Raymond (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S010000, C340S659000, C702S064000
Reexamination Certificate
active
06815107
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to gas leak detection methods for fuel cells, and particularly relates to a gas leak detection method for leaks due to damage or deterioration of solid polymer electrolyte membranes.
2. Description of Related Art
For a fuel cell which is carried in a fuel cell vehicle, for example, there is a fuel cell in which a solid polymer electrolyte membrane made from solid polymer ion exchange membrane is sandwiched between an anode and a cathode horizontally, and sandwiching outside of the anode and cathode is a pair of separators to form a fuel cell unit, and a stack is formed by stacking a plurality of fuel cell units each of which is provided with a hydrogen gas flow passage to which a hydrogen gas is supplied as a fuel gas, an air flow passage to which air including oxygen as an oxidizing gas is supplied, and a coolant liquid flow passage to which coolant liquid is supplied. Hereinafter, a fuel gas and an oxidizing gas may be called “reaction gases” in generally. In a fuel cell, a hydrogen ion which is generated in an anode by a catalytic reaction moves to a cathode after passing a solid polymer electrolyte membrane and generates electric current by having electrochemical reaction with oxygen in a cathode. After that, heat which is generated during electric current generation is removed by a coolant liquid in a coolant liquid flow passage so as to cool down a fuel cell.
In this fuel cell, the solid polymer electrolyte membrane has a function of allowing permeation of a hydrogen ions as an electrolyte, and a function to act as a partition wall so as to separate a hydrogen gas in a hydrogen gas flow passage and an oxidizing gas (air) in an air flow passage. Therefore, if this solid polymer electrolyte membrane has small holes, a hydrogen gas in a hydrogen gas flow passage leaks to an air flow passage.
Also, a hydrogen has high permeability, and even in a solid polymer electrolyte membrane which does not have a small hole, a hydrogen permeates (gas cross leak) a solid polymer electrolyte membrane in a molecular form. When a thickness of a solid polymer electrolyte membrane becomes reduced due to change over time, the amount of hydrogen permeation increases.
Here, as a root cause of thinning and damage of a solid polymer electrolyte membrane, damage to a fuel cells due to operating conditions for generating electric current such as low humidity, high temperature, and high work load, and damage caused by dynamic influences such as pressure differences between an anode and a cathode can be named.
In this way, when a hydrogen gas leaks to an air flow passage in a fuel cell, a hydrogen reacts with oxygen in the air in the air flow passage and heat is generated because hydrogen is a combustible gas; thus, there is a concern that a fuel cell may be adversely affected. Therefore, in a fuel cell, it is necessary to find leaks of hydrogen due to damage to a membrane or a thinning of solid polymer electrolyte membrane so as to deal with such a situation by replacing the solid polymer electrolyte membrane.
Conventionally, a method for a gas leak detection method in a fuel cell has been suggested as follows.
In a gas leak detection method which is disclosed in a Published Japanese Translation No. 2000-513134 of a PCT International Publication, an anode and a cathode of a fuel cell are purged by a nitride gas, a nitride gas is exhausted, and furthermore hydrogen is supplied to an anode while oxygen is supplied to a cathode, and the pressure of the gas at the cathode is made greater than the pressure of the gas at the anode keeping a reaction gas flow passage. In this state, an output voltage without electric current flow passages being closed such as an open circuit voltage (OCV) is measured so as to detect the gas leak by utilizing a detecting principle that an OCV decreases rapidly when a gas leak exists.
Also, in a gas leak detection method which is disclosed in a Japanese Unexamined Patent Application, First Publication No. Hei 5-205762, the existence of gas leak and the size of the gas leak are detected by closing a reaction gas flow passage of a fuel cell, supplying a nitrogen gas to an anode of the closed flow passage so as to generate a predetermined pressure difference between an anode and a cathode, and measuring the amount of nitrogen gas which leaks to a cathode.
Also, in a gas leak detection method which is disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 9-27336, an anode and a cathode of a fuel cell are purged by a nitride gas, an electric current to a fuel cell is stopped, and furthermore hydrogen is supplied to an anode while an oxygen containing gas is supplied to a cathode, output voltage of a fuel cell is measured while reducing the supply amount of an oxygen containing gas to a cathode gradually so as to detect the gas leak by utilizing a detecting principle that the output voltage decreases rapidly when a gas leak exists.
Furthermore, in a method and apparatus for detecting a leak within a fuel cell which is disclosed in International Publication No. WO 00/39870, a gas leak in a fuel cell and the existence of a gas leak from an electrolyte membrane are detected by supplying a tracer gas which is an inert gas such as helium, argon, carbon dioxide, and nitrogen to one reaction gas which is supplied to a fuel cell, and measuring the concentration of tracer gas in another reaction gas.
Also, in a method and apparatus for detecting a gas leak which is disclosed in International Publication No. WO 98/13890, a gas leak is detected by detecting heat with an infrared ray camera caused by a reaction between an oxygen and a hydrogen due to a gas leak.
In a gas leak detection method which is disclosed in Published Japanese Translation No. 2000-513134 of a PCT International Publication, a gas leak is detected by making a pressure of gas in a cathode greater than a pressure of gas in an anode so as to monitor OCV when an oxygen in a cathode permeates a solid polymer electrolyte membrane and reaches an anode. However, an oxygen molecule is too big to permeate a solid polymer electrolyte membrane. Therefore, the OCV dispersion is small, and it was a problem in that detecting accuracy is not reliable. Also, in such a detection method, OCV change is monitored while closing a reaction gas flow passage. However, it is difficult to distribute a reaction gas uniformly in each cell in a stack. Therefore, the OCV dispersion is large, and there was a disadvantage in that the gas leak detecting accuracy became unreliable.
Also, in a gas leak detection method which is disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 5-205762, a sensor which detects a nitrogen gas is necessary; thus, there was a problem in that the entire system became complicated. Furthermore, in such a detection method, although it is possible to detect a gas leak when a solid polymer electrolyte membrane has small holes, it is difficult to detect an increase of amount of gas permeation (gas leak) due to thinning of a membrane.
Also, in a gas leak detection method which is disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 9-27336, an output voltage of a fuel cell is measured while reducing a supplying amount of an oxygen containing gas to a cathode gradually. However, there was a problem in that the detecting accuracy is unreliable because variance of the output voltage according to a change of the supplying amount of an oxygen containing gas is small.
In a method and apparatus for detecting a leak within a fuel cell which is disclosed in International Publication No. WO 00/39870, a tracer gas supplying device is necessary, and a sensor for measuring density of a tracer gas is also necessary. Therefore, there was a problem in that the overall system became complicated. Also, in such a detection method, although it is possible to detect a gas leak when a solid polymer electrolyte membrane has small holes, it is difficult to detect an increase of gas permeation (gas
Fujii Yosuke
Hayashi Katsumi
Inai Shigeru
Koshinuma Minoru
Alejandro Raymond
Honda Giken Kogyo Kabushiki Kaisha
Lahive & Cockfield LLP
Laurentano, Esq. Anthony A.
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