Platinum nanoparticles (PtNPs) were successfully synthesized using a liquid plasma system with 1-butyl-3-methylimidazolium tetrafluoroborate under atmospheric pressure. The PtNPs with a size of 3 nm were uniformly distributed on the surface of a copper grid. The particle size, shape and crystallinity of the Pt were further controlled by a mixture of hydrogen and argon gases, stabilizers and plasma reduction time. Furthermore, a smaller particle size had a better forward sweep of catalytic performance in oxidation of methanol while the cube-like structure was better for backward sweep of the electrochemical catalyst. (C) 2014 Elsevier Ltd. All rights reserved.