Well-defined Pt nanocubes (Pt-NCs) with mean diameters of 6.2 nm are synthesized successfully by a diethylene glycol (DEG) reduction route with the assistance of 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) ionic liquid. The structure, size, morphology and composition of Pt-NCs are characterized by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy, etc. Experimental characterization shows DEG serves as a reducing agent whereas [Bmim]BF4 acts as a stabilizer and structure direct agent during the synthesis of Pt-NCs. Due to the crystal facets effect, the as-prepared Pt-NCs exhibit significantly enhanced electrocatalytic activity and anti poisoning capability for the ammonia oxidation reaction in alkaline media. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.