Platinum nanoparticles spontaneously formed on HOPG

Abstract Spontaneous deposition of platinum was observed when a piece of highly orientated pyrolytic graphite (HOPG) was immersed in acetonitrile containing PtCl62−. The non-uniform and disordered Pt particles spontaneously formed could be reconstructed to more uniform and smaller nanoparticles by negatively charging the sample with a microsecond scale current pulse. Expectedly, the negative charges may be used to neutralize the residue positive charges on HOPG resulting from the spontaneous chemical redox deposition reaction. Changes in the double layer arrangement, hydrophobicity, and other interfacial properties such as surface tension could also contribute to the reconstruction. Within a range of negative charges passed, the nanoparticles became smaller in diameters but taller. Pre-treating the HOPG with a voltage of 1.0 V (Ag|AgCl) can eliminate the spontaneous deposition.