Electrochemical Ce3+/Ce4+ and Eu2+/Eu3+ interconversion, complexation, and electrochemical CO2 reduction on thio-terpyridyl-derivatized Au electrodes

Abstract

Thio-terpyridyl derivatized Au electrodes (Au-STpy) were first employed to understand electrochemical redox behaviors of Ce3+/Ce4+ and Eu2+/Eu3+ ions by cyclic voltammetry (CV). For Ce3+/Ce4+ ions in H2SO4 electrolyte, real-time amperometry and fluorescence spectroscopy revealed that the reduction process was more facile than the oxidation process, and the functionalized Au showed enhanced redox rates. CV and amperometry of Eu2+/Eu3+ ions were performed in KCl electrolyte. X-ray photoelectron spectroscopy (XPS) and fluorescence data confirmed Eu3+ state for electrodeposited Eu complexes. Density functional theory was employed for optimized geometry, electronic energy levels and thermodynamics of the complexation of thio-terpyridyl-functionalized Au with Ce3+/Ce4+ and Eu2+/Eu3+ ions. The role of functionalization was also shown in electrochemical CO2 reduction with major products of CO and H2. Ultraviolet photoelectron spectroscopy revealed the newly aligned energy level at the interface of Au and STpy. The present unique results provide deeper information on functionalized Au for electrochemical applications to the treatment/recycling of lanthanide elements, in addition to catalysts, displays, and metal-organic complexes.