A template-free, surfactant-free, simple electrochemical approach has been developed to prepare well-dispersed platinum (Pt) nanosheets. By simply changing the anions from SO42- to Cl- in the electrodeposition solution, the formed Pt deposits is changed from flower-like Pt particles consisting of aggregated Pt nanosheets to well-dispersed Pt nanosheets. The surface morphology and structure of the Pt particles/nanosheets were investigated by the scanning electron microscopy and X-ray diffraction. The amount of the Pt loading was measured by an inductively coupled plasma method. The electrocatalytic activity of the prepared Pt electrocatalysts for ammonia oxidation was characterized by cyclic voltammetry. The result showed that the well-dispersed Pt nanosheets exhibits 112% and 89% increase in the mass activity (MA) for the ammonia oxidation compared with the flower-like Pt particles and commercial Pt/C catalyst, respectively. The much improved MA of the well-dispersed Pt nanosheets is attributed to not only the increased electrochemically active surface area (ECSA), but also the specific activity (SA). For example, the well-dispersed Pt nanosheets shows 88% increase in the SA compared with the commercial Pt/C catalyst. (C) 2013 Elsevier Ltd. All rights reserved.