Supporting electrolyte and solvent effects on single-electron double layer capacitance charging of hexanethiolate-coated Au140 nanoparticles

Sequential injections of single electrons (or holes) into the cores of Au-140 hexanethiolate monolayer-protected clusters (MPCs) occur at measurably different electrochemical potentials owing to the extremely small (subattofarad) values of the single MPC capacitance (C-MPC) of the nanoparticle. The potential increment for each sequential injection is Delta V = e/C-MPC. The dependence of AV on the concentration of supporting electrolyte (from I to 100 mM), measured using square wave voltammetry, is shown to be caused, primarily, by changes in the diffuse double layer component (C-DIFFUSE) of C-MPC. The dependence of C-DIFFUSE on r(core), the radius of the nanoparticle, is conresidered. Additionally, significant changes in the magnitude of the compact double layer component (C-COMPACT, equivalent to the Stem layer) of C-MPC were induced by adding hydrophobic solvent components such as hexane or dodecane or by introducing hydrophobic electrolyte ions (tebrabutyl-, 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.