Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2000-11-30
2003-01-28
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S006000
Reexamination Certificate
active
06511765
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a fuel cell system and more particularly to a fuel cell system using a proton exchange membrane as an electrolyte.
DESCRIPTION OF THE PRIOR ART
A proton exchange membrane fuel cell comprises a proton exchange membrane (PEM) between two electrodes that is a cathode to which an oxidizing gas is supplied and an anode to which fuel gas is supplied. PEM acts as an electrolyte and transports therethrough hydrogen ions obtained at the anode of the fuel cell toward the cathode in the form of proton (H
+
). Each of the electrodes comprises a catalyst layer deposited on a porous base member through which the reactant gas is supplied. Mounted externally of each electrode is a separator or connector plate with grooves permitting the reactant gas to be introduced into the electrode at a constant flow rate. Excess gas which has not been consumed by the fuel cell reaction is exhausted to the open air through the grooved separator. The electricity generated by the energy conversion reaction at the anode is collected at the electrode porous base member and transported to the outside of the fuel cell system through the separator. In actual application, the system includes a plurality of fuel cells which are stacked in series with the separator being interposed between adjacent fuel cells.
Since the fuel cell generates heat in correspondence to the electric power generated, a fuel cell stack usually includes cooling plates between fuel cells at predetermined intervals. Each cooling plate has a passage of a cooling medium such as air and water to prevent overheating of fuel cells in operation.
Protons are hydrated in transfer through the PEM electrolyte, so that the PEM tends to become dehydrated as the fuel cell reaction proceeds. The PEM must always be properly humidified to prevent decrease of ion-conductivity and energy conversion efficiency. In the conventional designs, hydrogen gas is humidified by suitable means which, in turn, humidify the PEM when it is supplied to the anode.
Various attempts have also been proposed to humidify the air supplied to the cathode. Since the cathode of the fuel cell operates at 80° C., for example, the air of a normal temperature should be preheated by a humidifier so that its saturated vapor becomes consistent with the ambient vapor condition of the cathode. Such a humidifier that is required to have both a water supplying function and an air preheating function can not be simple in construction.
In Japanese patent un-examined publication No. 7-14599, there is provided a water injection nozzle to inject a necessary quantity of water into an air introducing pipe through which air is supplied to the cathode of the PEM fuel cell. Since the nozzle is located upstream of a compressor, liquid water injected from the nozzle is evaporated by the heat generated by the compressor. Thus, the cathode is humidified by vapor, not by liquid water.
In the fuel cell system of Japanese patent un-examined publication No. 9-266004, a discharge gas from the anode containing hydrogen gas which has not been consumed during the anodic reaction is introduced into the cathode where the unconsumed hydrogen gas in the discharge gas is combusted with oxygen to generate water, which well humidifies the PEM electrolyte. In this system, there is no need to install a humidifier for humidifying the air supplied to the cathode.
During operation of the fuel cell system, electrons produced at the anode move to the cathode where they react with oxygen in the air or any other oxidizing gas supplied thereto to produce water. Accordingly, in accordance with the conventional practice in the art, there is a greater need to humidify hydrogen gas to be supplied to the anode, than at the cathode where supply of water is at least partially self-sustaining.
As a result of the inventors' repeated tests and investigation, however, it has been found that water produced at the cathode permeates through the PEM electrolyte toward the anode, which makes it unnecessary to humidify hydrogen gas to be supplied to the anode. On the other hand, the quantity of water in the PEM electrolyte at the cathode tends to be decreased by the air flow to the cathode. Such finding is contradictory to the conventional understanding and has been first recognized by the present inventors.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a fuel cell system, based on the above-described finding, which is capable of maintaining a proton exchange membrane in a suitably moist condition.
Another object of the present invention is to provide a fuel cell system which is simple in construction, small in size, easy to install and, therefore, particularly suitable to be mounted on a vehicle.
Still another object of the present invention is to smoothly and effectively humidify an electrolyte membrane in a fuel cell system during the start-up operation of the system.
Accordingly, the present invention provides a fuel cell system in which water is supplied to the surface of the cathode, not in a vapor state, but in a liquid state. Thus, the fuel cell system of the present invention comprises one or more fuel cells each having an anode, a cathode and an electrolyte membrane interposed between the anode and the cathode; first gas supplying means for supplying a first gas including fuel gas to the anode; second gas supplying means for supplying a second gas including oxygen to the cathode; liquid water supplying means for supplying liquid water to the surface of the cathode; and control means for controlling operation of the second gas supplying means and the liquid water supplying means such that, when the system starts up, the cathode first receives supply of the second gas, followed by supply of the liquid water. Liquid water supplied onto the surface of the cathode may preferentially take latent heat from the air around the cathode to prevent water evaporation from the electrolyte membrane which, therefore, remains in a suitably and evenly moist condition. This contributes to improvement of capacity and durability of the fuel cell system. Supply of the liquid water is also effective to cool the cathode which would otherwise become overheated to an excessive temperature, which means that the temperature of the fuel cell of the present invention may be controlled without need to use cooling plates.
In accordance with the above aspect of the present invention, the liquid water supplying means may supply the liquid water continuously during start-up operation of the system. In a modified application, the liquid water supplying means supplies the liquid water for a predetermined period during start-up operation of the system. Accordingly, the electrolyte membrane, which could have become too dry to provide its original performance after a long time interval from the last operation of the fuel cell system, is readily humidified. The liquid water supplied by the liquid water supplying means is well dispersed onto the surface of the cathode by the flow of the first gas such as the air supplied by the second gas supplying means.
In accordance with another aspect of the present invention, there is provided a fuel cell system comprising one or more of fuel cells each having an anode, a cathode and an electrolyte membrane interposed between the anode and the cathode; first gas supplying means for supplying a first gas including fuel gas to the anode; second gas supplying means for supplying a second gas including oxygen to the cathode; liquid water supplying means for supplying liquid water onto the surface of the cathode; sensor means for detecting water supply capacity of the liquid water supplying means at least when the system starts up; and control means for discontinuing or interrupting operation of the system when the sensor means detects that water supply capacity of the liquid water supplying means has decreased to below a predetermined minimum level. In a preferred embodiment, the liquid water supplying means includes a water tank, the sensor means com
Horiguchi Munehisa
Kato Kenji
Takada Noriyuki
Ueno Masataka
Alejandro R.
Kabusikikaisha Equos Research
Lorusso & Loud
LandOfFree
Fuel cell system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fuel cell system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fuel cell system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3031555