Conventionally in a fuel cell device, a humidifier is arranged in an air supply system, and a moisture condition of a solid electrolyte membrane and a reaction layer (hereinafter may be referred to as “membrane electrode assembly”) is regulated by adjusting humidity of process air. However, from the viewpoint of improvement in efficiency required for current fuel cells, auxiliaries such as the humidifier tend to be removed from the fuel cell device. In that case, the moisture condition of the membrane electrode assembly may not be able to be always maintained at an appropriate level corresponding to an operating environment of the fuel cell.
For example, when the fuel cell is operated under a low humidified environment, the membrane electrode assembly is placed in a dry condition to have a reduced proton conductivity, and thereby cannot exhibit a sufficient power generation property. By contrast, when the fuel cell is operated under a highly humidified environment, so-called flooding occurs to degrade the power generation property.
In order to avoid such phenomena, there is proposed a technology in which a reaction layer has a two-layer structure, and a first layer on the side of a solid electrolyte membrane has a high moisture retention capacity whereas a second layer on the side of a diffusion layer has a low moisture retention capacity (high water discharge capacity and high air permeability) (refer to Patent Document 1).
With this arrangement, the first layer is maintained in a wet condition even under the low humidified environment, and water accumulated under the highly humidified environment is efficiently discharged from the second layer.
Refer to Patent Documents 2 to 5 as documents introducing technologies related to the present invention.