Potential of Proton-Exchange Membrane Fuel-Cell System with On-Board O2-Enriched Air Generation

Abstract

Hydrogen fuel-cell systems are one of the alternatives for the decarbonization of the transportation sector. In such systems, the usage of O2-enriched air has the potential to improve fuel cell performance as well as to reduce degradation phenomena linked to local O2 starvation. However, the production of an O2-enriched air stream implies energy consumption that needs to be evaluated in the overall system efficiency. In this study, the potential of a system including polymeric membranes for O2-N2 separation to produce O2-enriched air was evaluated theoretically. First, the balance of plant, including the O2-N2 separation membrane and a two-stage boosting system, was considered. Two sources of energy recovery were identified: a high-pressure H2 stream and retentate flow (N2-rich) at the outlet of the separation membrane. Then, the efficiency of the system was evaluated for different levels of O2 enrichment, with sensitivities to the main operational and design parameters, i.e., cathode excess O2 ratio, turbomachinery efficiency, essure ratios. The results show the potential for an O2-enriched system if the energy recovered reaches approximately 25% of the additional power consumption induced by the separation membrane.