Investigation on the durability of direct methanol fuel cells

This study addresses the durability of direct methanol fuel cells (DMFCs). Three performance indices including permanent degradation, temporary degradation and voltage fluctuation are proposed to qualify the durability of DMFC. The decay rate, associated with permanent degradation, follows from such failure mechanisms as dissolution, growth and poisoning of the catalyst, while temporary degradation reflects the elimination of the hydrophobic property of the gas diffusion layer (GDL). However, voltage fluctuations reveal different results which cannot stand for degradation phenomenon exactly. In this investigation, such methods of examination as scanning electron microscope (SEM), and X-ray diffraction (XRD) are employed to check the increase in the mean particle size in the anode and cathode catalysts, and the degree is higher in the cathode. The Ru content in the anode catalyst and the specific surface area (SSA) of the anode and cathode catalysts decrease after long-term operation. Moreover, the crossover of Ru from the anode side to the cathode side is revealed by energy dispersive X-ray (EDX) analysis. Electro-catalytic activity towards the methanol oxidation reaction (MOR) at the anode is verified to be weaker after durability test by cyclic voltammetry (CV). Also, the electrochemical areas (ECAs) of the anode and cathode catalysts are evaluated by hydrogen-desorption. SSA loss simply because of agglomeration and growth of the catalyst particles, of course, is lower than ECA loss. The observations will help to elucidate the failure mechanism of membrane electrode assembly (MEA) in durability tests, and thus help to prolong the lifetime of DMFC.