The platinum (Pt) particle electrocatalysts were fabricated by a surfactant-free, electro-deposition technique in the cyclic voltammetric mode for electro-oxidation of ammonia in aqueous solutions. The hierarchical Pt nanoparticles with various morphologies, including sheet-, flower-, prickly sphere- and cauliflower-like shapes, were obtained by controlling the electrodepositing parameters. The amount of Pt loading was determined by an inductively coupled plasma method, and the electrocatalytic activity of the prepared nano-Pt electrocatalysts for the ammonia oxidation was characterized by cyclic voltammetry. The results showed that there is a remarkable effect of the surface morphology of Pt particles on the electrocatalytic activity. In particular, the hierarchical Pt particles have a much higher electrocatalytic activity for the ammonia oxidation than the smooth, spherical Pt particles. The improved electrocatalytic activity is attributed not only to the large electrochemically active surface area (ECSA) achieved, but also to the high electrocatalytic activity per unit ECSA. Electro-deposition technique provides a promising alternative to fabricate high-performance electrocatalysts for oxidation of ammonia in aqueous solutions. (C) 2012 Elsevier B.V. All rights reserved.