Current density dependence on performance degradation of direct methanol fuel cells

Abstract

A stability test on direct methanol fuel cells (DMFCs) was carried out at current densities of 100, 150, and 200 mA cm −2. Each test lasted for 145 h in the three cases. X-ray diffraction, energy dispersive spectroscopy, and scanning electron microscopy were used for analysis of the membrane electrode assemblies (MEAs). The maximum power densities were 93.9, 79.9, and 55.1% of the initial value after operation at 100, 150, and 200 mA cm −2, respectively. A PtRu black catalyst with an original particle size of 3.3 nm was used for the anode electrode. For the MEAs operated at 100, 150, and 200 mA cm −2, the PtRu particle sizes increased from the original size to 3.4, 3.9, and 4.2 nm, respectively, while a Pt black catalyst used for the cathode electrode did not change in size. Dissolution of the Ru was observed, and the ratio of (Pt:Ru) changed from (53:47) in the case of the fresh MEA, to (54:46), (56:44), and (73:27) for the MEAs after operation at 100, 150, and 200 mA cm −2, respectively. The equivalent weight of the Nafion TM membrane increased from a weight of 1264 g for a fresh membrane, to a weight of 1322, 1500, and 1945 g with the increases in operating current density to 100, 150, and 200 mA cm −2, respectively.