The effects of relative humidity on the performances of PEMFC MEAs with various Nafion (R) ionomer contents

Abstract

For PEMFC operation water management is very important to provide both sufficient proton conductivity and mass transport Therefore in this study the effect of the relative humidity (38-87%) on cell performance is examined for PEMFC MEAs with various Nafion ionomer contents The MEAs were fabricated using a CCM (catalyst coated membrane) spraying method As the relative humidity of the cathodes (RHC) increases the cell volt ages at 04 and 1 2 A/cm(2) increased for a MEA with 20 wt% ionomer This can be explained in terms of the expansion of active sites with enhanced ionic conductivity (activation overpotential) In contrast with a higher RHC value the cell voltages for 35 wt% ionomer (more hydrophilic) gradually decreased as a result of slower gas transport (concentration overpotential) For MEAs with intermediate ionomer contents 25 and 30 wt%, the cell voltages at 04 A/cm2 showed maximum values at a RHC of 67% at which point the mass transport begins to be the more dominant factor The highest unit cell performance was observed in a MEA with an ionomer content of 25 wt% at a RHC of 59% and in a MEA at 20 wt% ionomer content at a higher humidity of 87%.