Quantitative Evaluation of Liquid Water at Cathode Interface of Polymer Electrolyte Fuel Cell Using Near-Infrared Reflectance Spectroscopy

Abstract

Water management in cathode electrode of polymer electrolyte fuel cells (PEFCs) is essential for achieving high performance operation, because excessive liquid water accumulated in cathode catalyst layer (CL) and gas diffusion layer (GDL) blocks oxygen transport to active reaction sites. In this study, the liquid water accumulated at the CL|GDL interface of a PEFC was quantitatively evaluated by using near-infrared reflectance spectroscopy (NIRS), and the effects of operating conditions and GDL properties on the liquid water transport in the cathode electrode were investigated. NIRS is a non-invasive optical measurement technique for quantitatively estimating the amount and concentration of water. In this experiment, the thickness of liquid water film at the cathode CL|GDL interface of the fuel cell can be determined by detecting the water absorbance of the NIR light reflected from the CL surface. It was found that the cell voltage drops down to zero when the thickness of liquid film at the cathode CL|GDL interface reaches more than 30 μm. Furthermore, the liquid water accumulation at the cathode CL|GDL interface is affected by hydrophobic treatment of GDL and compression pressure of assembled fuel cell. When the PTFE content inside the cathode GDL increases from 5 to 15 wt%, the amount of liquid water at the cathode CL|GDL interface increases, because the highly hydrophobic treatment of GDL suppresses the liquid water influx into the cathode GDL. The thickness of liquid water film at the CL|GDL interface decreases remarkably with an increase in compression pressure of the assembled cell. The addition of microporous layer (MPL) at the cathode is effective in decreasing the liquid water accumulation at the CL|GDL interface and preventing water flooding.