Detection of Liquid Water in PEM Fuel Cells' Channels: Design and Validation of a Microsensor

Suitable water management is a critical issue to reach the full potential of PEM fuel cells: whereas the membrane must be hydrated enough, liquid droplets formed by water in excess can block the flow in the gas distribution channels and hinder the fuel cell performance. In order to detect the presence of droplets in cathode flow channel, an electrochemical sensor has been developed and tested in a dedicated emulation cell. It is based on the widely used principle of two-electrode cells for conductivity measurements; the collected signal is converted to impedance values. The sensor, mounted in a gas flow channel grooved in a graphite plate, reacts to the passage of water droplets, either being injected into the continuous air stream or produced by condensation of humidified air at the graphite plate. The time variation of the electrical impedance could be correlated to the observations allowed by the high-speed digital camera. Water droplets separated from each other by less than a second can be distinguished by the sensor, which is of a sufficient rapidity.