PEMFC Cathode Contamination Mechanisms for Several VOCs - Acetonitrile, Acetylene, Bromomethane, Iso-Propanol, Methyl Methacrylate, Naphthalene and Propene

Abstract

The behavior of PEMFCs exposed to airborne contaminants was characterized in 2 stages. In the first stage, impedance spectroscopy was used to identify resistance loss types. In the second stage, other ex situ and in situ characterization methods were employed to obtain more detailed information about observed resistance loss types: rotating ring/disc electrode, membrane conductivity cell, tracer based method for residence time distribution measurements, segmented cell, and fuel cell coupled with a gas chromatograph/mass spectrograph. All 7 VOCs led to kinetic and mass transfer resistance changes. Only acetonitrile led to an ohmic resistance change. A decrease in catalyst active area (7 to >90 %) and increase in H2O2 side reaction product (18 to 1027 %) accounts for the smaller oxygen reduction current (12 to 100 %). An acetonitrile decomposition product is presumed to be responsible for the observed in situ ohmic loss because acetonitrile did not show an effect in the conductivity cell. Modest current redistributions were noted (<19 % on an absolute and dimensionless basis) but acetylene also initially showed a strong transient effect (≤100 % on an absolute and dimensionless basis) attributed to a gradual contamination along the flow field length. Only the unaffected contaminant species, CO2 and CO were detected at the cathode outlet. Contaminant conversion increased at higher cell voltages (62 to 332 % V-1) indicative of electrochemical oxidation. An acetylene contamination mechanism is proposed.