Enhanced electrocatalytic activity on gold nanocrystals enclosed by high-index facets for oxygen reduction

The physical nature (e.g. crystal size or surface atomic arrangement) of an electrocatalyst is central to the performance of electrochemical devices such as fuel cells and lithium-air batteries. This is particularly true in electrodes for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which involve multiple elementary steps and a substantial energy barrier. As a result, OER and ORR generally are rate-limiting step in electrode reactions. Here, we show Au nanocrystals enclosed by high-index facets (e.g. (310)) are more energetically and kinetically favorable than (111) facets for oxygen reduction in both lithium-air battery and fuel cell conditions. In both systems, the electric potential for oxygen reduction was reduced by 60-160 mV and the current increases by more than five times if high-index Au nanocrystals were utilized. These Au nanocrystals were synthesized at a temperature greater than the boiling point of ethylene glycol, the solvent used in this work. This synthetic approach opens a new reproducible route to synthesize nanocrystals with high-index facets because it is facile, rapid, and results in a large-quantity of nanocrystals with control over the size and morphology. (C) 2014 Published by Elsevier Ltd.