Analysis of operational characteristics of polymer electrolyte fuel cell with expanded graphite flow-field plates via electrochemical impedance investigation

Expanded graphite was investigated as a material for flow-field plates in PEFCs (polymer electrolyte fuel cells). Because expanded graphite is flexible but has similar material properties with normal graphite, channels on flow-field plates were designed to have single channel in order to compare operational characteristics including diffusion of reactants through ribs by comparing polarization curves and electrochemical impedance spectra between PEFCs with expanded graphite and graphite flow-field plates. As a result, PEFC with the expanded graphite flow-field plates has comparable open-circuit voltage to that with the graphite flow-field plates. However, PEFC with the expanded graphite plates had higher ohmic resistance than that with the graphite plates due to higher electrical resistance of the expanded graphite than that of the graphite. It was also found from faradaic resistances that the diffusion of the reactants through GDLs (gas diffusion layers) is disturbed in the case of the expanded graphite flow-field plates because the GDL is compressed excessively due to its flexibility.