A liquid water management strategy for PEM fuel cell stacks

Gas and water management are key to achieving good performance from a PEM fuel cell stack. Previous experimentation had found, and this experimentation confirms, that one very effective method of achieving proper gas and water management is the use of an Interdigitated flow field design. However, the results of a single fuel cell with an Interdigitated flow field could not be extended to a multi-cell stack because of the inability to establish uniform gas flow to each individual cell. Since the interdigitated flow field uses the flow of gas for excess water removal, a deficient flow of gas causes the cell to become flooded. To alleviate this problem of unequal gas distribution, a method of sequentially exhausting each individual cell was developed. This method controls each cell’s exhaust so that only one cell at any given time has an open exhaust port, thereby, ensuring gas will flow through that cell. By sequentially exhausting each cell, it will be ensured that the gas will flow to each cell and provide the water management necessary to achieve good performance. This was demonstrated in a three-cell PEM stack with interdigitated flow fields operating at ambient pressure and temperature on neat hydrogen and oxygen. The results showed that the use of sequential exhaust control improved the peak power from 0.26 W/cm2 per cell without exhaust control to 0.50 W/cm2 per cell, a doubling of the power density.