Ionic-Ligand-Mediated Electrochemical Charging of Anionic Gold Nanoparticle Films and Anionic−Cationic Gold Nanoparticle Bilayers

Abstract

Gold nanoparticles ∼2 nm in diameter were synthesized with, on average, between 0 and ∼5.4 anionic thiols per particle. An electrochemical quartz-crystal microbalance was used to monitor the motion of ions and electrons during redox cycling (charging) of thin films of these nanoparticles. When the electrochemistry was performed using a polyanion electrolyte too large to penetrate the nanoparticle film, the degree of oxidation that was possible was found to be dictated by the average number of anionic ligands on the particle surface available for charge compensation. These anionic nanoparticle thin films were combined with previously reported/synthesized cationic nanoparticles into solution-processed nanoparticle film bilayers. We demonstrate using these bilayers that the control over charge compensation kinetics afforded by the use of a polyelectrolyte supporting electrolyte in conjunction with ionic surface functionalization allows for the selective charging of one layer of nanoparticles over the other a...