Growth Characteristics of Self-Assembled Mesoporous Nanospheres of Platinum and Platinum-Ruthenium
- PDF / 131,325 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 64 Downloads / 164 Views
R12.7.1
Growth Characteristics of Self-Assembled Mesoporous Nanospheres of Platinum and Platinum-Ruthenium Trevor L. Knutson, Kimberly A. Haglund, William H. Smyrl Corrosion Research Center Chemical Engineering and Materials Science, University of Minnesota Minneapolis, MN, 55422, U.S.A. ABSTRACT Self assembled spheres of both Pt and Pt/Ru have been electrodeposited in a matrix of carbon black on a gold electrode. The spheres are roughly 200nm in diameter and have a high degree of surface porosity. As a fuel cell catalyst, the activity of the Pt/Ru toward methanol oxidation is the primary indication of performance. Catalysts deposited in the current limiting regime (i.e. low metal ion concentrations or more negative deposition potentials) show markedly higher oxidation current at 4.8-5.5mA as measured at +0.2V vs. saturated calomel electrode. Pt only deposits were also made and show identical morphology to Pt/Ru deposits. Surface area analysis of the Pt deposits correlate well with the oxidation activity of the Pt/Ru deposits, at similar deposition conditions. The maximum specific surface area measured for Pt, based on 100% coulombic efficiency, was about 35m2/g. INTRODUCTION Since its introduction in the mid 1960s by Petrii1 and Adlhart2, bi-metallic platinumruthenium has remained the premier choice for use as a poison-tolerant direct methanol fuel cell (DMFC) catalyst. Researchers have long sought to develop a high activity, stable and inexpensive alternative to platinum-based alloys, however only modest progress has been made due to insufficient oxidation activity compared to platinum analogs. Alternatively, application of standard reaction engineering techniques to Pt/Ru such as increasing specific surface area, using supported catalysts, and creating morphologies that have higher specific activity toward methanol oxidation have dramatically reduced the required loadings (and associated costs), while increasing performance. Morphological engineering of catalyst nano-structures holds promise on two fronts: higher specific surface area and increased oxidation activity. Liu, et. al.3 have developed both supported and unsupported nanoparticles of Pt and Pt/Ru from colloid precursors that exhibit relatively high specific activity and surface area. Other efforts to develop nanostructures include microemulsions4, microwave irradiation5, sonochemistry6 and sol-gel7 processes. More recently, Liang, et. al.8 have developed hollow nanospheres of platinum that are made by a red-ox replacement reaction of Pt onto Co nanospheres. High surface area mesoporous microspheres of Pt/Ru are also reported by Jiang and Kucernak9 in which a surfactant template is used with electro co-reduction of the two precursor salts. This work focuses on the activity and characterization of a self-assembled array of mesoporous nanospheres of either Pt or Pt/Ru grown by electro-reduction within a conductive carbon matrix. Sphere diameters are nominally 200nm with a low size distribution. Additionally, the catalyst shows some degree of porosity as e
Data Loading...
