Development of 1 kW Class PEFC Stack System with Variable Gas Flow Channel

Polymer electrolyte fuel cell (PEFC) is considered to be a promising candidate of clean power source for electric vehicles or stationary systems because of its high energy conversion efficiency. The stable and efficient operation of PEFC at various loads has been strongly required for the practical use. There needs, for example of electric vehicle, the minimum power for idling step and the maximum for accelerating step, respectively. Two main problems were observed in such a wide load operation. One is a flooding phenomenon caused by insufficient gas flow velocity enough to expel the remained water within gas flow channels, resulting in the remarkable voltage drop under the low power operation when the gas utilization is same as the case of high power. The other is an increase of pressure loss through gas flow channels caused by the increase of amount of fed gas to meet its corresponding electrochemical reaction, resulting in the extra energy of auxiliary systems such as a gas feed pump and so on. We have proposed the variable gas flow channel of which function is to solve these problems by switching the connection of gas flow channels in series or parallel. The beneficial function will be discussed in more detail for the 1 kW class PEFC stack system.