IN-SITU OPTICAL DIAGNOSTICS FOR MEASUREMENTS OF WATER VAPOR CONCENTRATION IN A PEM FUEL CELL

摘要

A fiber optic coupled diode laser sensor has been constructed for in-situ measurements of water vapor concentration in active proton-exchange membrane (PEM) fuel cell systems. The bipolar plate of a PEM device was modified to allow for transmission of a laser beam through the flow channels on either the fuel or oxidizer side of its membrane-electrode assembly. The laser wavelength was scanned over several water rovibrational transitions and the light absorption was detected by measuring the transmitted laser power through the device. The intensity and line shape of the measured transition was used to extract path-averaged values for the water vapor partial pressure. Measurements were initially taken in a non-operating fuel cell with known temperature and humidity input gas streams to calibrate and test the optical device. A technique for rapid recovery of the water concentration was conceived. The optical technique is applicable over the entire temperature and humidity operating range of a PEM fuel cell. Measurement technique was subsequently applied to an operating PEM fuel cell system to examine the effects of incoming gas humidity and load on the local water vapor concentrations.