Analysis of performance characteristics and internal phenomena of PEFC with porous flow field

Abstract

A polymer electrolyte membrane fuel cell (PEFC) with a porous-flow-field separator has been proposed as an alternative to cells with gas flow channels. In this study, basic characteristics of a PEFC with porous flow field were identified using a cell allowing local current density measurement and direct observation of the condensed water at the surface of porous material. It was shown that a stable operation can be maintained under conditions at high current density and low stoichiometric ratio of cathode air, but an operation with low relative humidity of reaction gases is difficult with the porous type separator. To clarify the detailed causes of these characteristics, the internal phenomena were investigated using a cell specially made for the cross-sectional observation of the separator or the temperature distribution measurement. The direct observations of the condensed water at the cross-section of porous flow field showed that the porous type cell is superior in drainage performance of the condensed water from the surface of gas diffusion layer (GDL), and the hydrophilic property of the porous material is important for better cell performance under high current density conditions. The measurements of temperature distribution on the anode GDL surface indicated that the increase in temperature near the reaction area tends to be larger in the porous type cell than in channel type due to the lower thermal conductivity of the porous media, and this resulted in the unstable operation with low relative humidity conditions. © 2012 The Japan Society of Mechanical Engineers.