The Surface Potential of Zero Charge Controls the Kinetics of Diazonium Salts Electropolymerization

Abstract

AbstractOne of the central fundamental properties of solid/liquid interfaces is the potential of zero charge (pzc), where no excess charge prevails at the electrode surface. Applying potential on either side of the pzc can control adsorption of molecules on surfaces and is paramount for any interfacial process. However, the impact of pzc on electrode processes has been only demonstrated for reactions involving the adsorption of inorganic ions and gases. Here, the direct relationship between the pzc and electropolymerization rate of a small organic molecule was reported. The electrochemical reduction of diazonium salts, which are the most commonly used molecules to form thin films of molecules on electrode surfaces, was tested. The kinetics of the surface reaction and the reduction potential in electrochemical measurements depended on the pzc of the surface following the order of gold>platinum>carbon>indium‐tin‐oxide>fluorine‐doped tin‐oxide>silicon hydride. The immediate consequence of this finding was that the concentration of the diazonium salt molecules became critical in defining the electrochemical reduction mechanism. At higher concentrations, the mechanism was pzc‐controlled adsorption‐dominated inner‐sphere electron transfer whereas at lower concentrations, diffusion‐based outer‐sphere electron transfer dominated.