Degradation of DMFC using a New Long-Term Stability Cycle

Abstract

The understanding of the degradation mechanisms involved in the performance of direct methanol fuel cells (DMFCs), constitute important matter for the future implementation of this technology. In this context, it is necessary to develop new and reliable analysis tools to simulate realistic operating conditions. To reflect these, the present study used a “start-run-stop-run’” (SRSR’) test in three different characteristic voltages (at open-circuit potential (OCP), 0.3, and 0.1 V). The electrical loss performance at different operating times (0, 22, 40, and 60 h) working under SRSR’ test was followed by analysis of polarization curves and electrochemical impedance spectroscopy (EIS). The results reveal a decrease of 65% in the maximum density power, 30 mW/cm², with a degradation rate of 1.2 mV/h at 50 mA/cm². In addition, the contribution to the overall loss of fuel-cell performance was observed to follow the order: anode reaction > cathode reaction > IR resistance. Ex situ characterizations confirm this reduced activity due to catalyst agglomeration and the dissolution of the anode cocatalyst (Ru). Finally, X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed 20.8% and 24.2% losses of specific surface area for the anode and cathode, respectively. The performance losses of the fuel cell by the new SRSR’ cycle and constant voltage (CV) were compared. The results show that the CV test is significantly more aggressive than the SRSR’, following the order cathode reaction > anode reaction > IR resistance to the overall performance losses.

Keywords:

• DMFC
• Cycling test
• Start-run-stop-run
• Performance degradation
• EIS
• Catalyst agglomeration

Acknowledgments

The authors would like to acknowledge to MICINN for funding the projects with reference CTQ2010-17338. Project S2009/ENE-1743 (RESTOENE) and MAT2010-19837-C06-01 are also acknowledged.