Performance degradation generated by reverse current flow during fuel cell shut-down/start-up is a big challenge for commercialization of polymer electrolyte membrane fuel cells in automobile applications. Under transient operating conditions, the formation of H2/O2 boundaries on Pt surfaces and the occurrence of undesired oxygen reduction reaction (ORR) in an anode cause severe degradation of carbon supports and Pt catalysts in a cathode because of an increase of the cathode potential up to ∼1.5 V. Herein, to directly prevent the formation of H2/O2 boundaries in the anode, we propose a unique metal-carbon hybrid core-shell anode catalyst having Pt nanoparticles encapsulated in nanoporous carbon shells for selective H2 permeation. This hybrid catalyst exhibits high hydrogen oxidation reaction (HOR) selectivity along with fully subdued ORR activity during long-term operation because of the excellent stability of the carbon molecular sieves. Furthermore, the HOR-selective catalyst effectively suppresses the reverse current flow in a single cell under shut-down/start-up conditions.
Keywords: durability; hydrogen oxidation reaction; polymer electrolyte membrane fuel cells; reverse current; selectivity.