Fuel cell system

Abstract

A fuel cell system includes a fuel cell stack which is composed of an assembly of fuel cells, each of which is provided with an anode that is supplied with fuel and a cathode that is supplied with oxygen. The fuel cell system further includes an air duct for supplying oxygen, which is disposed along the fuel cell stack, and at least a fuel tank and a recovery tank unit of a gas-liquid separator, namely, a tank for supplying water to be mixed with fuel, which both are disposed on a side opposite to the fuel cell stack with the air duct interposed therebetween. Accordingly, vaporization of fuel due to heat generated in the fuel cell stack which is the power generating section is suppressed, and a deterioration of generating characteristics attributable to insufficient fuel supply is prevented.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematically illustrating one embodiment of a fuel cell system according to the present invention; and

FIG. 2 is a block diagram schematically illustrating a conventional fuel cell system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a fuel cell system according to an embodiment of the present invention will be described with reference to FIG. 1.

In FIG. 1, reference numeral 1 designates a fuel cell stack that is composed of a plurality of layered fuel cells where a membrane electrode assembly (MEA) is disposed counter to a separator channel surface. Reference numeral 2 designates a fuel tank that stores a fuel such as methanol or dimethyl ether of a predetermined concentration. Reference numeral 3 designates a gas-liquid separator that separates vapor and liquid from discharges from the anode and the cathode of the fuel cell stack 1 and recovers the liquid, and reference numeral 3a designates a recovery tank unit that stores water thus separated and recovered. The vapor separated by this gas-liquid separator 3, or equivalently, carbon dioxide generated during power generation and remaining air except oxygen consumed are discharged to the atmosphere, and water generated during power generation is recovered to the recovery tank unit 3a. The gas-liquid separator 3 is preferably made of a gas-liquid separating membrane because of its compactness in structure.

A fuel in the fuel tank 2 and water in the recovery tank unit 3a are fed into a mixing tank 6 at predetermined flow rates by a first pump 5 with valves 4a and 4b being switched appropriately, thereby diluting the fuel to a predetermined concentration. Then, the fuel evenly diluted to a predetermined concentration in the mixing tank 6 is supplied to the anode of the fuel cell stack 1 by a second pump 8 through a valve 7. Furthermore, air is supplied to the cathode of the fuel cell stack 1 by a fan 9 through an air duct 10.

Accordingly, the fuel diluted to a predetermined concentration and air are supplied to the anode and the cathode, respectively, of the fuel cell stack 1, and the before-mentioned reactions of Equations (1) and (2) take place at each fuel cell in the fuel cell stack 1, generating electricity between the anode and the cathode. Power generated in all the fuel cells is then sent out as an output from an output terminal of the fuel cell stack 1.

In the present embodiment, with the fuel cell system having the above-mentioned structure, the air duct 10 is disposed along and adjacent to the fuel cell stack 1, and the fuel tank 2 and the recovery tank unit 3a of the gas-liquid separator 3 are disposed on the side opposite to the fuel cell stack 1 with the air duct 10 interposed therebetween. In addition to this, thermal insulators may be provided in the vicinities of the inlet and the outlet of the anode of the fuel cell stack 1 so that it prevents heat from the fuel cell stack 1 from reaching the fuel supply system or the gas-liquid separator 3.

According to the structure of the present embodiment, since the air duct 10 is present between the fuel cell stack 1 which is the power generating section as well as the heat generating section, and the fuel tank 2 and the recovery tank unit 3a of the gas-liquid separator 3, the fuel or a mixture of the fuel and water is prevented from being heated to high temperatures due to the heat generated at the fuel cell stack 1. This prevents the fuel that would otherwise be of high temperatures by being directly subjected to heat or by being mixed with high temperature water from being vaporized when it is being fed to the fuel cell stack 1, thereby suppressing the risk of insufficient fuel supply to the fuel cell stack 1. It further prevents elution of a ruthenium catalyst or corrosion of carbon, which is attributable to the insufficient fuel supply to the fuel cell stack 1. A deterioration of generation characteristics due to reduction in CO poisoning resistance, reduction in utilization efficiency of a platinum catalyst, missing MPL structure of the diffusion layer, or the like is also prevented. Vaporization of water is also prevented, and therefore an amount of water required for power generation is secured.

Furthermore, since air supplied to the fuel cell stack 1 is warmed up in advance by heat from the fuel cell stack 1 when it passes through the air duct 10, a temperature difference between the inlet and the outlet of the cathode becomes small, and the uniformity of in-plane generating capability within the fuel cell stack 1 is ensured, thereby improving power generation efficiency.

Furthermore, since the recovery tank unit 3a of the gas-liquid separator 3 does not become too hot, the separating capability of the gas-liquid separator 3 is in turn improved, and recovered water can be counted in when securing an amount of water required for power generation. Though, in the present embodiment, the recovery tank unit 3a of the gas-liquid separator 3 is used as a tank for supplying water to be mixed with a fuel, the present invention is not limited to this configuration. Even in the case where a separate water tank is provided, water in such a tank is prevented from being heated to high temperature due to the heat from the fuel cell stack 1, thereby obtaining similar function and effect.

In the fuel cell system of the present invention, methanol, dimethyl ether, or the like is directly used as a fuel without reforming to obtain hydrogen. Furthermore, by suppressing vaporization of fuel due to heat generated in the fuel cell stack, a deterioration of generating characteristics attributable to insufficient fuel supply is prevented. Therefore, the present invention is useful not only as a power source for mobile electronic equipment such as mobile phones or personal data assistants (PDA), notebook computers, video cameras, and the like but also as a power source for electric scooters, automobiles, or the like.

While preferred embodiments of the invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.

Claims

1. A fuel cell system comprising: a fuel cell stack which is composed of an assembly of fuel cells each of which includes an anode which is supplied with a fuel and a cathode which is supplied with oxygen;an air duct for supplying oxygen, which is disposed along the fuel cell stack; andat least a fuel tank and a tank for supplying water to be mixed with the fuel which both are disposed on a side opposite to the fuel cell stack with the air duct interposed therebetween.

2. The fuel cell system according to claim 1, further comprising a gas-liquid separator having a recovery tank unit, and wherein the recovery tank unit serves as the tank for supplying water.