文摘
Novel electrocatalysts based on Pt submonolayer deposits on Ru and Au nanoparticles, and on a Au(111) surface, have been prepared by two new methods for noble metal monolayer deposition. These were tested for H2 and H2/CO oxidation and O2 reduction kinetics. Our recently reported methods for controlled submonolayer-to-multilayer deposition of Pt involve spontaneous deposition of Pt on Ru and Pt deposition by redox replacement of a Cu upd monolayer on Au. The Pt mass-specific activity for H2 oxidation of the PtRu20 electrocatalyst was found to be three to four times higher than that of commercial catalysts at 25°C. The CO tolerance appears to be also higher than those of commercial catalysts under conditions of rotating disk experiments. Fuel cell tests at 80°C have shown practically the same activity of the PtRu20 electrocatalyst for H2 oxidation as that of the catalyst containing a 10× larger Pt loading. Extended X-ray absorption fine structure spectroscopy measurements showed that Pt is coordinated with three to four Ru atoms in this catalyst, with a bond length of 2.68 Å between Pt and Ru as in PtRu alloys. A Pt0.75Pd0.25 monolayer on Au/C is a very active electrocatalyst for O2 reduction that equals the activity of a Pt/C catalyst with a 2.5 times larger Pt loading. The activity of a Pt monolayer on Au(111) is also considerable. A single Tafel slope of −110 mV for the Pt0.75Pd0.25/Au/C catalyst, and a −120 mV for Au(111), may indicate a smaller adsorption of OH on Pt and Pt0.75Pd0.25 on Au in comparison with bulk or nano Pt. Further work utilizing a Pt monolayer on metal nanoparticles seems to be a promising approach for both reduction of noble metal loading and designing electrocatalysts with improved properties.