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 60–160mV 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.