Acid Stability and Oxygen Reduction Activity of Magnetron-Sputtered Pt[sub 1−x]Ta[sub x] (0≤x≤1) Films

Pt 1 − x Ta x ( 0 ≤ x ≤ 1 ) thin-film libraries were prepared using combinatorial dc magnetron sputtering on a variety of substrates. For x < 0.5 , the materials adopted a face-centered cubic structure and for x 0.5 a nanocrystalline phase of Pt 1 − x Ta x was observed. The bulk composition of the films obtained by electron microprobe before and after treatment in 0.5 M H 2 SO 4 at 80°C showed no detectable dissolution of Ta at any x in Pt 1 − x Ta x . X-ray photoelectron spectroscopy of acid-treated samples revealed that for regions with high Ta content ( x 0.5 ) , full oxidation of surface Ta had occurred. The samples, when used as oxygen-reduction electrocatalysts, also showed corrosion stability; however, the addition of Ta significantly lowered the activity towards oxygen reduction reaction for x 0.1 in Pt 1 − x Ta x .