Marco Lopez

Deposition of continuous platinum shells on gold nanoparticles by chemical precipitation

Continuous platinum shells consisting of ~5 atomic layers were deposited onto preformed gold seeds in aqueous medium by reducing hexachloroplatinic acid with ascorbic acid. By controlling the reduction kinetics of Pt(IV) species and the properties of the substrate, it was possible to ensure a slow and controlled deposition of platinum atoms onto the gold cores. Electrochemical evaluations revealed the presence of a compact platinum shell. The mass specific oxygen reduction activity of platinum in the AuPt core-shell nanoparticles was found to be four times higher than that of platinum black and comparable to that of polycrystalline bulk metal.

A spectroscopic proton-exchange membrane fuel cell test setup allowing fluorescence x-ray absorption spectroscopy measurements during state-of-the-art cell tests.

A test setup for membrane-electrode-assemblies (MEAs) of proton exchange membrane fuel cells which allows in situ fluorescence x-ray absorption spectroscopy studies of one electrode with safe exclusion of contributions from the counter electrode is described. Interference by the counter electrode is excluded by a geometry including a small angle of incidence (< 6°) between primary beam and electrode layer. The cell has been constructed by introducing just minor modifications to an electrochemical state-of-the-art MEA test setup, which ensures realistic electrochemical test conditions. This is at the expense of significant intensity losses in the path of the incident beam, which calls for the brilliance of third-generation synchrotrons to provide meaningful data. In measurements on Pt∕C and Pt-Co∕C cathodes combined with Pt-C anodes (H(2)/O(2) feed), good data quality was demonstrated both for the majority element Pt as well as for Co despite of a low areal Co density in the order of 0.02 mg/cm(2).