Interrogation of Anodic Stripping Voltammetry Peaks of Metals for the Determination of Electrochemical Reaction Parameters

The aim of this study was to develop a method for the analysis of peaks obtained during anodic stripping voltammetry (ASV) at silver-based mercury film electrodes (SBMFE) in the presence of transition and rare earth metals. Such stripping peaks may originate from reversible or irreversible electrochemical processes, with a plethora of unknown parameters, such as number of electrons involved, electrochemical rate constant, formal potential, charge transfer coefficient, and metal concentration (in the film and/or solution). In particular, we were interested in the concentration of transition metals and rare earth elements deposited simultaneously in the mercury film during ASV in order to quantify the electrochemical amalgamation of each species and their rates of deposition. Herein, we studied the concurrent ASV of multiple metals using a mercury film electrode as part of the development of the OREATE (Oxide Reduction by Electrochemical Amalgamation and Thermal Extraction) process. Certain of these species generate electrochemically irreversible processes, while others produce reversible ones. In addition, the reduction of most rare earth metals into the mercury film occurs well below the onset of the hydrogen evolution reaction, preventing us from probing these reduction processes. For example, the reduction of cerium(III) (an electrochemically irreversible process) occurs at a formal potential of −1.64 V vs. Ag/AgCl (3 M KCl). Furthermore, the presence of multiple metals in solution can lead to overlapping stripping peaks and mask these oxidative processes. For instance, the irreversible oxidative stripping of cerium (−0.75 V vs. Ag/AgCl (3 M KCl)) from the mercury film can obscure the reversible stripping of zinc (−0.95 V vs. Ag/AgCl (3 M KCl)). In this talk, we describe the use of thin layer electrochemistry equations to extract electrochemical parameters from the ASV at a mercury film electrode. This electroanalytical method enables investigation of processes that are otherwise obscured by the hydrogen evolution reaction, as well as resolution of overlapping stripping processes. This permits the determination of the concentration of each metal deposited in the film during the electrochemical amalgamation. By summing the thin layer electrochemical equations for reversible and irreversible processes, we were able to extract the number of electrons involved, the electrochemical rate constants, and the charge transfer coefficients for simultaneous oxidative processes. Finally, we were able to obtain the concentrations of multiple species in the mercury film and their rates of deposition. In conclusion, we have established a protocol for the interrogation of electrochemical reaction parameters in anodic stripping voltammetry of mixed-metal systems. Moreover, we demonstrated an electrochemical method to quantitatively separate overlapping peaks for the determination of the species’ concentrations, all based on the principles of thin layer behavior.