Impact of flow rates and electrode specifications on degradations during repeated startups and shutdowns in polymer-electrolyte membrane fuel cells

Separate testing protocols for fuel cell startup (SU) and shutdown (SD) are developed to distinguish between the effects of SU and SD on performance degradation. The internal currents during SU and SD operation are measured in a segmented cell to evaluate the charge exchanged between the active (H-2/Air) and passive (Air/Air) portions of the cell. Cells with different membrane-electrode assemblies (MEAs) are subjected to SU or SD sequences to evaluate the time evolution of spatially resolved decrease of performance and electrochemical active surface area (ECSA). We examine the influence of the cathode and anode Pt loading, and the type of carbon for cathode catalyst support. Both the CO2 emissions and the charges exchanged increase with the common residence time of air and hydrogen in the anode compartment. However, the evolved CO2 accounts for less than 25% of the total exchanged charge. Startups are consistently more damaging than the shutdowns, evidenced by more evolved CO2 and charge exchanged, severe ECSA decrease, and higher performance losses. (C) 2013 Elsevier B.V. All rights reserved.