Platinum monolayer electrocatalysts for oxygen reduction: Effect of substrates, and long-term stability

We describe a novel concept for a Pt monolayer electrocatalyst and present the results of our electrochemical, X-ray absorption spectroscopy, and scanning tunneling microscopy studies. The electrocatalysts were prepared by a new method for depositing Pt monolayers involving the galvanic displacement by Pt of an underpotentially depos- ited Cu monolayer on substrates of Au (111), Ir(111), Pd(111), Rh(111) and Ru(0001) single crylstals, and Pd nanoparticles. The kinetics of O2 reduction showed significant enhancement with Pt monolayers on Pd(111) and Pd nanoparticle surfaces in compari- son with the reaction on Pt(111) and Pt nanoparticles, respectively. This increase in cata- lytic activity is attributed partly to the decreased formation of PtOH, as shown by in situ X-ray absorption spectroscopy. The results illustrate that placing a Pt monolayer on a suitable substrate of metal nanoparticles is an attractive way of designing better O 2 re- duction electrocatalysts with very low Pt contents.