Cerium Ion Adsorption to Fluorine-Doped Tin Oxide Electrodes

Abstract

The f-elements are critical in many technologies including electronics, catalysis, magnetics, and clean energy. Additionally, these elements occur in very low abundance worldwide. Research has therefore been motivated in the detection, quantification, and reclamation of these elements from waste streams. In this presentation we explore the use of fluorine-doped tin oxide (FTO) electrodes as sensitive and cost-effective electrochemical sensors for cerium ions. We demonstrate that cerium adsorbs reversibly to bare FTO surfaces with a dependence on pH. Through voltammetry and XPS characterization, we demonstrate that the adsorbed cerium, which can undergo the quasi-reversible CeIV/CeIII redox transition, exists in more than one chemical environment. Based on these data, we posit that these different environments are due to the buildup of multiple layers of cerium ions on the FTO surfaces. At lower concentrations (< ca. 100 uM), we can use voltammetry to quantify the cerium adsorbed to the FTO and relate it to the concentration of cerium in solution, with a lower detection limit of about 10-6 M. The data fits to a pseudo second order rate law with a rate constant on the order of 107 (cm2 mol-1)2 s-1. The adsorption fits well to the Freundlich model, but we are working towards finding a non-empirical adsorption model than provide the equilibrium constant for the adsorption reaction.