Spatially resolved optical measurements of water partial pressure and temperature in a PEM fuel cell under dynamic operating conditions

In situ non-intrusive measurements of water vapor partial pressure and temperature were performed simultaneously along two gas channels on he cathode side of a PEM fuel cell using tunable diode laser absorption spectroscopy. This measurement technique developed by us was utilized arlier to make measurements in a single bipolar plate channel of a prototype PEM fuel cell. The current study examines the variation of water partial ressure and temperature near the flow inlet and outlet during operation under both steady state and time-varying load conditions. For steady-state peration, an increase in the water vapor partial pressure was observed with increasing current density due to electrochemical production of water. s expected, the measurement channel near the inlet of the flow path showed a lower water vapor partial pressure than the outlet under identical oad conditions; however, the quantitative distribution of water content across the cell is important to understanding operational behavior of a EM fuel cell. These quantitative water concentration differences between two measurement channels are reported with variations in cell load and emperature. Temperature in the gas phase remained constant due to thermal equilibrium of the fuel cell. For time varying operation, no phase lag as observed between the load and the water vapor partial pressure. The outlet measurement channel showed higher partial pressure than the inlet ith larger differences for increasing cell load. The transient data matched the steady-state measurements at the same conditions. A temperature ise from the controlled value was observed at high current densities for the unsteady operation; thus, the temperature did not equilibrate on the ame time scale as the water partial pressure. 2006 Elsevier B.V. All rights reserved.