Electrochemical and Photoelectrochemical Oxidation of Americium(III) and Cerium(III) at Ligand Modified Mesoporous Indium Tin-Doped Oxide

Authors

Jeffrey R. McLachlan, Florida International UniversityFollow

Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

Chemistry

First Advisor's Name

Christopher Dares

First Advisor's Committee Title

Committee chair

Second Advisor's Name

Konstantinos Kavallieratos

Second Advisor's Committee Title

Committee member

Third Advisor's Name

Alexander Mebel

Third Advisor's Committee Title

Committee member

Fourth Advisor's Name

David Chatfield

Fourth Advisor's Committee Title

Committee member

Fifth Advisor's Name

Anthony McGoron

Fifth Advisor's Committee Title

Committee member

Keywords

Electrochemistry, Photochemistry, Radiation Chemistry, Americium, Cerium, Polyoxometalate, Polyphosphate, Surface Modification, Metal Oxide

Date of Defense

11-3-2022

Abstract

The efficient recycling of actinides from used nuclear fuel (UNF) is of utmost importance to maximize the energy obtained from mined uranium ore while minimizing the volume and heat load of UNF placed in repositories. The partitioning of hexavalent actinides from UNF may be readily achieved as they are vastly different from the mixture’s other components. However, americium exists in the trivalent state (Am³⁺) and its oxidation to higher valence is hindered by its high one-electron oxidation potential, E_Am(IV/III) = 2.38 V vs SCE. Demonstrating a simple and clean method to oxidize Am³⁺ to its hexavalent state (AmO₂²⁺) will facilitate the scientific community’s ability to study this rare species and provide new avenues to its efficient partitioning from UNF for future energy use. Herein, we report the radiolytic stability of mesoporous indium tin-doped oxide (nITO) electrodes, the preparation of phosphate and polyoxometalate modified nITO electrodes, the electrochemical behavior of cerium at bare and modified nITO electrodes, and the novel quantitative electrochemical and photoelectrochemical oxidation of Am³⁺ to AmO₂⁺ and AmO₂²⁺ without the use of solution based complexants or oxidizing agents. nITO electrodes were found to be stable in intense gamma radiation fields, retaining their electrochemical and photoelectrochemical properties after accumulating high absorbed doses (100 kGy). In Am(III) surrogate studies, we found that electrochemically generated Ce(IV) spontaneously condensed to nITO electrodes in acidic media with pH as low as 1. Additionally, tripolyphosphate and lacunary polyoxometalate modified nITO electrodes catalyzed the oxidation and deposition of cerium to the substrate. The electrochemical oxidation of Am(III) was accomplished at tripolyphosphate and lacunary polyoxometalate modified nITO electrodes which stabilized the highly reactive intermediate tetravalent species (Am⁴⁺). Consequently, oxidation past Am⁴⁺ was achieved at potentials as low as 1.75 V vs SCE, a half volt less than the standard potential. The novel photoelectrochemical oxidation of Am³⁺ was accomplished by irradiating Ti|TiO₂ or nITO electrodes with 375 nm light while applying a potential of 1.55 V and 1.62 V vs SCE, respectively. These findings provide the scientific community with clean and simple means to generate and study high-valent americium chemistry in both academic and applied settings.

Identifier

FIDC010878

ORCID

0000-0001-6944-3377

Previously Published In

ACS Appl. Mater. Interfaces 2021, 13, 33, 40127– 40133

ACS Appl. Energy Mater. 2021, 4, 10, 11854–11857.

Recommended Citation

McLachlan, Jeffrey R., "Electrochemical and Photoelectrochemical Oxidation of Americium(III) and Cerium(III) at Ligand Modified Mesoporous Indium Tin-Doped Oxide" (2022). FIU Electronic Theses and Dissertations. 5200.
https://digitalcommons.fiu.edu/etd/5200