Thermally induced changes in the structure and ethanol oxidation activity of Pt0.25Mn0.75/C

Abstract Decreasing the cost associated with platinum based catalysts along with improving catalytic properties is a major challenge for commercial direct alcohol fuel cells (DAFC). In this work, Pt/C and Pt–Mn/C alloys have been synthesized and the impact of heat treatment on the structure and electrochemical properties of these catalysts was investigated. The structure, composition and thermal properties of the samples were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). TGA and XRD data showed the Pt–Mn deposits did not have a uniform structure. Several phase transitions occurred upon heat treatment of the catalysts at temperatures between 500 and 950 °C. Cyclic and linear sweep voltammetry illustrated that the ethanol oxidation reaction (EOR) activity of pure Pt and Pt–Mn alloy catalysts was altered significantly by heat treatment. The highest EOR activity was achieved with a Pt–Mn alloy that was annealed at 700 °C for 4 h, exceeding the EOR activity of the pure Pt and untreated Pt–Mn alloy catalysts. XRD analysis indicated that at 700 °C an ordered PtMn intermetallic phase was formed and that these highly alloyed particles were the reasons for the enhanced EOR activity.