Platinum nanoparticles have here been synthesized via the microemulsion method that isolates the reactive species from the whole medium into compartmentalized nanoreactors. Such synthesized Pt nanoparticles have diam. included in the 2-5 nm range domain with narrow size distribution. It was also shown that, when deposited on Boron-Doped Diamond electrode and stabilized by a Nafion adlayer, microemulsion-synthesized Pt nanoparticles can be activated by OH radicals electrogenerated on BDD at high overpotentials. Activated nanoparticles has exhibited higher activity towards methanol electrooxidn., due to both addnl. cleaning of the surface and participation of the radicals to the oxidn. process. [on SciFinder (R)]