Pd 3Fe and Pt monolayer-modified Pd 3Fe electrocatalysts for oxygen reduction

In a search for electrocatalysts based on other metals with comparable attributes to very scarce and expensive Pt, we studied the kinetics of the oxygen reduction reaction (ORR) on carbon-supported Pd 3Fe alloy nanoparticles in HClO 4 and NaOH solutions. In acid solution, the electrocatalyst's activity for the ORR is slightly higher than that of commercial Pt/C. The reaction kinetics involves predominantly a four-electron reduction with the first charge-transfer step being the rate-determining one. The synthesis of a Pd overlayer on the Pd 3Fe alloy's surface at elevated temperatures is due to strong segregation effects. The major cause of this electrocatalyst's high activity appears to be the downshifting of the d-band center of Pd overlayer, resulting in a weaker interaction between the oxygen-containing species and the Pd surface. We demonstrated a further enhancement of the ORR kinetics with a Pt monolayer-covered Pd 3Fe/C electrocatalyst. In HClO 4 solution, the mass-specific activity of Pt/Pd 3Fe/C was about five times higher than that of commercial Pt/C, surpassing the Pt/Pd/C. In situ XANES data indicate that this elevated ORR activity may be due to the decreased formation of PtOH, and weaker oxygen adsorption on Pt/Pd 3Fe/C. © by Oldenbourg Wissenschaftsverlag