Effect of Ionomer Content and Relative Humidity on IT-PEMFC Performances at 120 oc

Abstract

Due to its higher operating temperature (100 -120oC), intermediate temperature PEMFC (IT-PEMFC) is expected to provide improved heat and water management, CO tolerance, and electrode reaction kinetics. The previous researches regarding IT–PEMFCs have been focused on the material developments: proton exchange membranes and electrocatalysts, to achieve high performance and durability at elevated temperatures. Maintaining hydration of membrane electrode assemblies (MEAs) to provide sufficient conductivity is one of the key issues in IT-PEMFC operation. When pressurized air feed is supplied with low humidity and high temperature, the sulfonated polymer membranes can be easily dried and, as a result, cell performances can be decreased severely. Therefore, the optimization of catalyst layer would be also very important, in order to achieve acceptable performances under unique operation conditions of IT-PEMFCs. However, there have been only reports regarding catalyst optimization of IT-PEMFC (1) (2). For conventional PEMFCs (~ 80oC), various groups have reported the effect of ionomer content (3), catalyst loading (4) and electrode thickness (5); but these results cannot be directly utilized to IT-PEMFCs that have much more severe drying problem. In this study, the effect of ionomer content and relative humidity (RH) of inlet gas on single cell performance are examined under various RHs(10 ~ 35%). For this, MEAs were fabricated with ionomer content from 20 to 40 wt%. The cell performances were characterized through constant current operation and i-V polarization. In addition, impedance analysis was carried out in order to monitor the variation of ohmic resistances under various operating conditions.