Investigation of the performance decay of anodic PtRu catalyst with working time of direct methanol fuel cells

Life tests of direct methanol fuel cells (DMFC) were carried out with three individual single cells at a current density of 100 mA cm^-2 for three different times under ambient pressure and at a cell temperature of 60 °C. X-ray diffraction (XRD) and X-ray photoelectron spectra (XPS) were used to characterize the anodic PtRu catalysts before and after the life tests. XRD results showed that the particle sizes of anodic catalysts increased from an original value of 2.8 to 3.0, 3.2, and 3.3 nm, whereas their lattice parameters first increased and then decreased from an original value of 3.8761 to 3.8879, 3.8777, and 3.8739 Å before and after 117, 210, and 312 working hours, respectively. XPS results indicated that during cells' working the contents of Pt and Ru oxides in anodic catalysts increased, but the metal content gradually decreased with test times. Polarization curves, power density curves, and in situ CO-stripping cyclic voltammetric (CV) curves were also plotted to evaluate the performances of fuel cells and electrochemically active surface areas (S_EAS) of anodic catalysts before and after life tests. After different time tests, the performances of DMFC lowered to different extents and could not recover their initial performances. The S_EAS of anodic catalyst decreased slightly by 4.78 and 9.03 m² g^-1 after 117 and 312 working hours, respectively. The utilization of anodic catalysts lowered slightly. This indicates that the change of (S_EAS) and utilization of anodic catalysts are not the main factors affecting the performance degradation of DMFC. The dissolution of Ru metal from anodic catalysts surface could be one of the main factors for the performance degradation of the PtRu black catalyst.