Enhanced Intrinsic Activity and Stability of Au-Rh Bimetallic Nanostructures as a Supportless Cathode Electrocatalyst for Oxygen Reduction in Alkaline Fuel Cells

Abstract

The electroreduction of dioxygen on supportless Au-Rh bimetallic nanostructures (Au-Rh NSs) synthesized by a surfactant template-free, single step chemical reduction method occurred with high intrinsic activity in an alkaline medium. Cyclic voltammetry and linear scan voltammetry together with X-ray diffraction and high-resolution electron microscopy showed that the improved performance of the Au-Rh NSs toward dioxygen reduction could be due to the synergistic electronic effects of nanobimetallic combination and its clusterlike morphology. The electrochemically active surface area (ECSA) was estimated to be 37.2 m(2) g(-1) for supportless Au-Rh NS with a 3:1 atomic composition, which was higher than that reported for Ag-based nanocatalysts. The intrinsic activities (IA) of the supportless and carbon supported Au-Rh (3:1) NSs were 3.2S and 3.0 mA/cm(2), respectively, which were higher than those of the standard Pt/C (0.1 mA/cm(2))(45) Au/C catalysts for the oxygen reduction reaction (ORR). Oxygen reduction on both catalysts followed a direct four electron pathway. The accelerated durability test carried out by continuous potential cycling showed that the 3:1 ratio of Au-Rh nanostructures had excellent stability with a 20% increase in ECSA after 10 000 potential cycles, highlighting their potential application for real systems.