The operating mode dependence on electrochemical performance degradation of direct methanol fuel cells

Comprehensive and systematic direct methanol fuel cell (DMFC) membrane electrode assembly (MEA) lifetime tests are presented under a wide range of operating conditions including constant voltage, constant current, constant power, and cyclic voltage loading. In this work, the characteristics of the MEA lifetime are strongly dependent on how the DMFC system is managed in a certain operation mode. The degradation ratio of MEAs is strongly dependent on the set voltage/current level in the constant operation mode. In the case of the DMFC constant power operation mode, the trend of MEA performance degradation shows the combined effect of both constant voltage and constant current operation mode, due to the required current increases to maintain the specified power output with time, while the voltage has the downward tendency from the initial value. The DMFC performance degradation under cyclic voltage loading (on-off) mode is much more severe than that of continuous voltage and current operation, while there is little difference between continuous voltage and current mode designs. The potential degradation mechanisms are proposed at each operating condition and demonstrated by using various electrochemical analysis techniques including impedance spectroscopy and polarization curves for improving long-term operational stability through mitigating such deterioration mechanisms of MEAs. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.