The Impact of Fuel Impurities on Pemfcs Using a Hydrogen Fuel Re-Circulation System

Abstract

Research has shown that contaminants in the hydrogen fuel stream have an impact on Polymer Electrolyte Membrane Fuel Cells (PEMFCs) performance that is influenced by the platinum loading, membrane thickness, the impurity, its concentration and PEMFC operating conditions such as cell temperature, relative humidity, and back pressure. A significant portion of previous reported results were conducted with the fuel cell being operated in single-pass mode where the exhaust hydrogen is vented from the fuel cell. While these findings have proven useful in improving the fundamental understanding of the poisoning mechanisms of non-hydrogen species (contaminants) in operating single fuel cells; the question remains whether or not these findings correlate to PEMFC systems that use a re-circulating fuel stream as being designed by the OEMs. Some advantages of re-circulating the anode exhaust gas back into the anode inlet are: 1) the anode outlet water is returned into the dry H2 fuel stream to obtain proper humidification and also 2) the excess H2 fuel is returned to enhance fuel utilization. While these advantages are attractive, there are some inherent challenges that are introduced in fuel re-circulation mode. Two of the more notable drawbacks involve inert gas build-up due to crossover and the accumulation of contaminants in the anode. In this study, we focus our efforts on correlating the impact of CO and H2S on fuel cell performance in H2 single-pass versus H2 re-circulation mode using the SAE J27191 and ISO 14687-2 Hydrogen Fuel Product Specification2 limits (4 ppb H2S and 200 ppb CO). This study was conducted on Membrane Electrode Assemblies (MEAs) at the 2015 DOE target loadings for platinum (anode: 0.05 mg/cm2 and cathode: 0.1 mg/cm2).