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Cyclic Voltammetric Experiment-Simulation Comparisons of the Complex Zr4+to Zr0Reduction Mechanism at a Molybdenum Electrode in LiF-CaF2Eutectic Molten Salt
Journal of the Electrochemical Society Số 3, năm 2022 (Tập 169, trang -)
ISSN: 134651
ISSN: 134651
DOI:
Tài liệu thuộc danh mục:
Article
English
Từ khóa: Cyclic voltammetry; Electrolytic reduction; Fission products; Fluorspar; Lithium compounds; Molten materials; Molten salt reactor; Molybdenum; Nuclear fuels; Nuclear reactions; Nucleation; Sols; Zirconium; Zirconium compounds; % reductions; Cyclic voltammetric; Electrochemical reductions; Eutectic molten salt; Irradiated fuels; Molybdenum electrodes; Reduction mechanisms; Simulation comparison; Square-wave; Voltammetric experiments; Fused salts
Tóm tắt tiếng anh
Nuclear energy represents an important option for generating largely clean CO2-free electricity. Zirconium is a fission product in the nuclear reaction that needs to be extracted from irradiated fuels used in Gen-IV molten salt reactors. The present investigation addresses the electrochemical reduction of solution soluble Zr4+(soln) to surface confined Zro(s-c) at a molybdenum electrode in a LiF-CaF2 eutectic molten salt at 840 °C using DC cyclic, square-wave and AC voltammetry. Cyclic voltammograms simulated by the reaction scheme: Zr4+(soln) + 4e- → Zro(soln); Zro(soln) ↔ Zr∗(s-c); Zr∗(s-c) → Zr4+∗(s-c) + 4e-; Zr4+∗(s-c) → Zr4+(soln); Zr∗(s-c) + Zr4+(soln) ↔ 2Zr2+(soln); Zr2+(soln) ↔ Zr2+∗(s-c) and Zr2+∗(s-c) → Zr4+∗(s-c) + 2e- provided excellent agreement with experimental data over the scan rate range of 50 to 500 mV s-1. The interpretation of the simulation is that the reduction of Zr4+(soln) to Zro(metal) takes place via a transiently soluble Zro(soln) in an overall 4-electron essentially reversible diffusion-controlled process having a reversible formal potential (Eof) of -1.22 V (vs Pt). A minor oxidation process observed at -0.455 V (vs Pt) on the reversing the potential scan direction is simulated via the reaction step Zr(s-c) + Zr4+(soln) ↔ 2Zr2+(s-c) followed by Zr2+(s-c) → Zr4+(sol) + 2e-. The sharply rising initial component where reduction of Zr4+(sol) commences, contains evidence of a nucleation-growth mechanism associated with the electrocrystallisation of zirconium metal. This initial rapid growth of current is not fully accommodated in the simulations, but all features found beyond the peak potential are supported by the theory. A comparison with theory based on a direct reduction of Zr4+(soln) to the metallic state having unit activity is provided. It is proposed that an analogous mechanism applies at a Ni electrode, except that a Ni-Zr alloy formation occurs instead of Zr metal. © 2022 The Electrochemical Society ("ECS").
