Supporting Electrolyte and Solvent Effects on Single-Electron Double Layer Capacitance Charging of Hexanethiolate-Coated Au140 Nanoparticles
journal contributionposted on 15.04.2005, 00:00 by Rui Guo, Dimitra Georganopoulou, Stephen W. Feldberg, Robert Donkers, Royce W. Murray
Sequential injections of single electrons (or holes) into the cores of Au140 hexanethiolate monolayer-protected clusters (MPCs) occur at measurably different electrochemical potentials owing to the extremely small (subattofarad) values of the single MPC capacitance (CMPC) of the nanoparticle. The potential increment for each sequential injection is ΔV = e/CMPC. The dependence of ΔV on the concentration of supporting electrolyte (from 1 to 100 mM), measured using square wave voltammetry, is shown to be caused, primarily, by changes in the diffuse double layer component (CDIFFUSE) of CMPC. The dependence of CDIFFUSE on rcore, the radius of the nanoparticle, is considered. Additionally, significant changes in the magnitude of the compact double layer component (CCOMPACT, equivalent to the Stern layer) of CMPC were induced by adding hydrophobic solvent components such as hexane or dodecane or by introducing hydrophobic electrolyte ions (tetrabutyl-, tetrahexyl-, and tetraoctylammonium, perchlorate, and tetraphenylborate). These changes are interpreted as specific solvation and ion penetration of the hexanethiolate monolayer. For brevity we will refer to these phenomena as solvation/penetration phenomena.