Platinum submonolayer-monolayer electrocatalysis: An electrochemical and X-ray absorption spectroscopy study

Abstract

A new Pt monolayer electrocatalyst concept is described and the results of electrochemical and X-ray absorption spectroscopy (XAS) studies are presented. Two new methods that facilitate the application of this concept in obtaining ultra-low-Pt-content electrocatalysts have been developed. One is the electroless (spontaneous) deposition of a Pt submonolayer on Ru nanoparticles, and the other is a deposition of a Pt monolayer on Pd nanoparticles by redox displacement of a Cu adlayer. The Pt submonolayer on Ru (PtRu20) electrocatalyst demonstrated higher CO tolerance than commercial catalysts under conditions of rotating disk experiments. The long-term stability test showed no loss in performance over 870 h using a fuel cell operating under real conditions, even though the Pt loading was approximately 10% of that of the standard Pt loading. In situ XAS indicated an increase in d-band vacancy of deposited Pt, which may facilitate partly the reduced susceptibility to CO poisoning for this catalyst. The kinetics of O2 reduction on a Pt monolayer on Pd nanoparticles showed a small enhancement in comparison with that from a Pt nanoparticle electrocatalyst. The increase in catalytic activity is partly attributed to decreased formation of PtOH, as shown by XAS experiments.