Oxygen Reduction Kinetics on Electrodeposited PtCo as a Model Catalyst for Proton Exchange Membrane Fuel Cell Cathodes: Stability as a Function of PtCo Composition

PtCo catalysts with composition varying between Pt 80 Co 20 and Pt 10 Co 90 were prepared by electrochemical underpotential codeposition. The bimetallic catalysts were subjected to 1000 electrochemical cycles in 0.5 M HClO 4 at room temperature. The activity and stability of these electrodes for oxygen reduction was determined, in conjunction with the characterization of these catalysts with energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. Although Pt-rich electrodes had better activity in the initial stages of potential cycling, higher Co atomic ratios led to higher stability and higher oxygen reduction reaction (ORR) activity after electrochemical cycling. Pt 10 Co 90 turned out to be the best electrode among the alloys considered, in terms of ORR activity and stability, which is linked to a higher concentration of Co on the surface.