Monodispersed cobalt-boron spherical nanoparticles have been prepared through solution plasma processing in the presence of hexadecyltrimethyl ammonium bromide for the first time. The particle size of cobalt-boron can be adjusted by changing either the plasma time or the concentration of hexadecyltrimethyl ammonium bromide. The samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. During the decomposition of hydrous hydrazine, the obtained monodispersed cobalt-boron spherical nanoparticles exhibit higher catalytic activity and hydrogen selectivity than regular cobalt-boron prepared by direct reduction of Co(2+) with BH(4)(-). The experimental investigations indicate that hydrous hydrazine along with the monodispersed cobalt-boron spherical nanoparticles may find application in small-scale on-board hydrogen storage and supply. (C) 2009 Elsevier Ltd. All rights reserved.