Fuel cell apparatus

Details Fuel cell apparatus Fuel cell apparatus

2000-10-05

2003-11-25

Gulakowski, Randy (Department: 1746)

Chemistry: electrical current producing apparatus, product, and

With pressure equalizing means for liquid immersion operation

C429S006000, C429S006000

Reexamination Certificate

active

06653008

ABSTRACT:

INCORPORATION BY REFERENCE
The disclosures of Japanese Patent Application No. HEI 11-287517 filed on Oct. 8, 1999 and No. HEI 11-334100 filed on Nov. 25, 1999 including the specification, drawings and abstract are incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuel cell having an anode and a cathode that sandwich a hydrogen ion-permeable electrolyte layer and, more particularly, to a technology for reducing the size of a fuel cell stack.
2. Description of the Related Art
A fuel cell has an anode and a cathode that sandwich a hydrogen ion-permeable electrolyte layer, and generates an electromotive force by causing reactions as in equations (1), (2) on the anode and the cathode, respectively.
Anode:
H
2
→2H
+
+2
e
−
  (1)
Cathode:
(1/2)O
2
+2H
+
+2
e
31
→H
2
O  (2)
Various types of fuel cells based on different kinds of electrolyte layers, for example, a phosphoric acid fuel cell, a molten carbonate fuel cell, a electrolyte fuel cell, an alkaline fuel cell, etc., have been proposed. Recently, a polymer electrolyte fuel cell adopting a hydrogen ion-conductive polymer membrane as an electrolyte layer is receiving attention because of, for example, its high output density and size reduction potentiality. With regard to the polymer electrolyte fuel cells, various improvements have been and are being considered.
In any of the aforementioned types of fuel cells, the theoretical electromotive force per unit cell is about 1.23 V. Therefore, a desired voltage is achieved by stacking a plurality of cells. A unit formed by stacking cells and securing them through the use of a case is termed stack. In a typical stack, the cell stacking precision appears as an internal resistance. Therefore, if an extremely great number of cells are stacked, the internal resistance becomes large and the fuel cell efficiency decreases. Furthermore, stacking an extremely large number of cells makes it difficult to equally supply fuel gas to the cells. For these reasons, it is a normal practice to avoid constructing a fuel cell apparatus by using a single stack in which cells are stacked to a number that substantially achieves a desired voltage. Instead, plurality of divided fuel cell stacks are connected in series so as to achieve a desired voltage.
As a technology related to this invention, a fuel cell apparatus employing a plurality of stacks is proposed in Japanese Patent Application Laid-Open No. HEI 8-171926. This fuel cell apparatus is able to equally supply fuel to the individual stacks, and allows a size reduction of the entire apparatus. The fuel cell apparatus has a construction in which four stacks are connected via supply/discharge members.
However, it has been found that when fuel cell stacks are to be installed in various appliances, such as vehicles and the like, there are various problems as mentioned below, in addition to the problems in supplying and discharging fuel. According to the conventional art, size reduction of fuel cells is not sufficiently considered in means for solving problems as mentioned above. Therefore, a solution to a problem as mentioned above often gives rise to a problem of a size increase of a fuel cell. In other words, preferable means for solving the below-mentioned problems haven not been thoroughly considered.
A first problem with the fuel cell stack is one attributed to cooling. Fuel cells are cooled by cooling water which flows in cooling water channels formed in each separator that defines gas channels of the corresponding cell. A typical separator is formed by an electrically conductive member. Therefore, due to contact with the electrically conductive separators during the process of cooling cells, cooling water is electrified in accordance with the electric potentials of the electrodes. In a construction having a water-supplying opening for supplying cooling water into a stack and a water-discharging opening for discharging cooling water from the stack, there is a potential difference near the openings. In such a case, the electric potential difference may cause detrimental effects such as galvanic corrosion at the water-supplying and water-discharging openings and the like.
To avoid such detrimental effects, it may be conceivable to, for example, cover the water-supplying and water-discharging openings with an electrically insulating material, or the like. However, this measure results in an increased size of the stack. Particularly in a construction in which a plurality of stacks are connected, the potential difference between the water-supplying and water-discharging openings is as high as several hundred volts. Therefore, in such a construction, it becomes necessary to increase the size of an insulating coating member, so that the effect of the insulating coating members on the size of the apparatus becomes great.
As another measure, it may be conceivable to provide a water-supplying opening and a water-discharging opening at a site where there is no electric potential difference. However, since this measure increases the restrictions regarding the sites of provision of the water-supplying and water-discharging openings, the freedom in designing cooling water channels decreases, thereby impeding the size reduction of the apparatus.
A second problem regarding the stack is attributed to the discharge of water produced by the reactions. As indicated in equations (1), (2), a fuel cell produces water (H
2
O) through the reactions therein. Water produced in each cell is transported along with gas flows through a manifold for supplying gases to the stack, to a gas-discharging opening. In a polymer electrolyte fuel cell, water for moisturizing the electrolyte membranes is also transported to the gas-discharging opening via the same route as mentioned above. If the amount of water transported to the gas-discharging opening increases, a phenomenon generally termed flooding may occur, causing unstable operation of the fuel cell. More specifically, condensed water droplets formed within the gas-discharging opening reduce the sectional area of the gas-discharging opening and thereby impede gas flow, so that supply of gas to each cell is impeded. This results in unstable power generation.
To avoid such a problem, Japanese Patent Application Laid-Open No. HEI 11-204126 proposes a construction in which a stack is provided with a drain port. However, since this construction includes the drain port and a drain valve provided outside the stack, there is a problem of a great size increase of the stack construction and therefore a great size increase of the entire fuel cell construction. Furthermore, in a fuel cell construction having a plurality of stacks, it is necessary to provide drain mechanisms separately for the individual stacks, so that the size increase of the fuel cell construction becomes even greater.
A third problem regarding the stack is attributed to the cell insulating characteristic. A stack is formed by securing stacked cells in such a manner that the cells do not separate from one another in the stacking direction. An external structure for securing the cells is herein referred to as “stack case.” Since the stacked cells are a set of electrodes, it is necessary to insulate the stack case and the stacked cells from each other if a stack is constructed as described above. In a stack related to this invention, an insulator, such as a silicone rubber or the like, is inserted between the stacked cells and the stack case to provide insulation therebetween. However, if the insulation between the stack case and the stacked cells is to be achieved by the above-described construction, the stack production process must include a step of inserting an insulator, so that productivity may decrease. Since in the process of forming a stack by stacking cells, precision related to internal resistance is required, the addition of the insulator inserting step greatly reduces the productivity in some cases. Furthermore, sinc

Affiliated with

Also associated with

Rating

Fuel cell apparatus 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 apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fuel cell apparatus will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3134523