Event Details

In this talk, microstructural, chemical, and electrochemical property measurements, for (111) crystallographically oriented Pt100-xMx (M = Zr, V) sputtered thin films are presented, together with some preliminary electronic structure calculations. These platinum-group-metal (PGM), valve metal based alloys are used as model surfaces to determine how the electrochemical properties evolve with changing chemical composition, and the moiety of the alloy constituents. The variation of the electronic structure is key design parameter, as the position of the Fermi Energy, Ef, dictates in part the voltage overpotential required to efficiently catalyze the oxygen-reduction-reaction (ORR) at the PEMFC cathode. The role of the valve-metal moiety, M = Zr, V, is of importance, in that the presence of the valve metal constituent may introduce a bi-functional character to the surface, to increase the normally sluggish ORR reaction kinetics, which typically limit the over-all cell performance (ORR current density). The influence of the alloy composition, and constituent moiety, was also examined for the other fuel cell reaction of interest, specifically the hydrogen-oxidation-reaction (HOR), operant at the PEMFC anode. While the kinetically fast HOR reaction does not typically limit the PEMFC performance, efforts to reduce the over-all PGM content would be enabled, if the new Pt100-xMx alloy surfaces exhibited a larger HOR active area, even though alloying reduces the number of platinum active surface sites. These results will aid in the development of candidate alloys, with even further reduced PGM contents, for use as the electrode materials in H2-Air polymer-electrolyte-membrane fuel cells (PEMFCs). This work is a continuation of research sponsored by the US Department of Energy, Office of Energy Efficiency & Renewable Energy (DOE-EERE), and was initially conducted at the California Institute of Technology's Jet Propulsion Laboratory (JPL), in Pasadena, California.