Electrochemical generation of transition metal nanoparticles
The electrochemical reduction of cobalt(II), nickel(II), and iron(II) ions in the presence of small amounts of 2,2’-bipyridine (10-50 mol %) stabilizes the reduced metal(0) forms in the homogeneous state and prevents the electrochemical deposition of reduced forms and the formation of insoluble metal associates. The stabilization of electroreduced forms of cobalt(II), nickel(II) and iron(II) involves not only the formation of complexes of these metals with 2,2’-bipyridine but also the formation of metal nanoparticles that requires much lower ligand concentrations. Thereby we have developed a new method for generation of nanosized particles of cobalt, nickel and iron by the electrochemical reduction of coordination-unsaturated metal(II) complexes. The mechanism of electrochemical generation of metal nanoparticles includes the stage of electrochemical reduction of metal(II) complexes followed by disproportionation of [М0(bpy)] complexes coordinatively unsaturated by 2,2’-bipyridine. It was found that the formation of nanoparticles in solution is possible only for metal complexes coordinatively unsaturated with respect to 2,2’-bipyridine, whereas no formation of nanoparticles was observed in the presence of the excess of bpy ligand due high stability of bis- and tris- chelate bpy-metal(0) complexes.