Oxygen Reduction Kinetics on Electrodeposited Pt, Pt100-xNix, and Pt100-xCox

The kinetics of the oxygen reduction reaction (ORR) on a series of electrodeposited Pt100-xNix and Pt100-xCox alloy films were examined in comparison to electrodeposited Pt and mechanically polished polycrystalline Pt. The alloys were electrodeposited at potentials positive of that required to grow the pure iron group metal. The growth process is ascribed to strong bonding enthalpy between Pt and the iron group metals that can be envisioned as iron-group underpotential deposition (upd) on Pt surface sites coupled with ongoing Pt overpotential electrodeposition. Rotating disk electrode measurements of the ORR kinetics, normalized for the H upd electroactive area, indicate a approximate to 1.9 to 2.7-fold catalytic enhancement on Pt100-xCox and Pt100-xNix, when x is in the range of 25-35, as compared to electrodeposited Pt films grown under similar conditions. An even greater ORR enhancement factor, between 3 and 4.8, was noted for dealloyed transition metal-rich (x > 75) films. Different schemes for integrating the electrodeposition (and dealloying) process into the fabrication of fuel cell membrane electrode array are also briefly discussed. (C) 2008 The Electrochemical Society.