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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Unraveling Na and F coupling effects in stabilizing Li, Mn-rich layered oxide cathodes via local ordering modification

Regardless of the prevailing capacity and energy density of lithium, manganese-rich layered oxide (LMR-NMC) cathodes, continuous decay of voltage and overall energy density during cycling hinders this material from commercialization in Li-ion batteries. Although significant work focuses on single doping of Na and F, analysis in portraying the benefit of these ions in diminishing the structural distortion during activation cycle is in doubt. In this study, the effects of co-doping Na and F into the LMR-NMC structure in stabilizing the structure and mitigating oxygen loss during the first cycle are closely examined via in situ x-ray measurements. Na and F co-doping shows a 30% lower degree of Li + /Ni 2+ mixing in the Li layer (C2/m structure), 50% reduced Debye-Waller factor of Mn-O bonding, increase reversible TM migration, and faster Li diffusion relative to the pristine material. Due to the utilization of Ni redox chemistry below 4.4 V, less oxygen redox is required for charge compensation at high voltage. This study offers the first instance to quantitatively evaluate the effects of co-doping Na and F in LMR-NMC cathode in order to minimize voltage degradation by altering the local ordering of O3-type structure, which may rationalize strategies to overcome the issues of the material.

25 ENERGY STORAGE↗
DOE OSTI2021

The influence of LiH and TiH 2 on hydrogen storage in MgB 2 II. XPS study of surface and near-surface phenomena

We report that Mg(BH 4 ) 2 is a promising solid-state hydrogen storage material, releasing 14.9 wt% hydrogen upon conversion to MgB 2 . The rehydrogenation of MgB 2 is particularly challenging, requiring prolonged exposure to high pressures of hydrogen at high temperature. Here we report an XPS study probing the influence of LiH and TiH 2 on the hydrogen storage properties of MgB 2 in the surface and near-surface regions, as a complementary investigation to a preceding study of the bulk properties. Surface and near-surface properties are important considerations for nanoscale and bulk hydrogen storage materials. If there are reactions occurring at the surface that modify the chemical composition in the near-surface region, species diffusion can alter the chemical composition even deep into the bulk of the material. For LiH/MgB 2 , metastable LiH–B and LiH–Mg species are produced that are more reactive than Bulk MgB 2 . With prolonged glovebox storage, the LiH/MgB 2 material shows increased reactivity towards O and C and enriched levels of Li and B in the near-surface region. In addition, Li induces the growth of Li 2 CO 3 in the surface and near surface regions. Exposing LiH/MgB 2 to hydrogen at 700 bar and 280 °C for 24 h produces borohydride at a temperature 100 °C below the threshold for bulk MgB 2 hydrogenation. In a specifically surface process with macroscopic implications, the hydrogenation conditions also cause Li 2 CO 3 to react with boron hydroxide in the sample to form a Li-deficient glassy lithium borate melt at the interfaces of the particles, bonding them together. Subsequent heating to 380 °C dehydrogenates the borohydride and eliminates the Li-deficient glassy lithium borate. The LiH/MgB 2 material is not reversible because desorption does not lead back to LiH/MgB 2 , but rather to elemental B and Mg metal in the near-surface region. In contrast to LiH, TiH 2 does not react with MgB 2 , despite the favorable thermodynamics for destabilization via TiB 2 formation. Furthermore, high pressure hydrogenation yields only unreacted TiH 2 and MgB 2 in the surface and near-surface regions. Thus, added TiH 2 provides no benefit to MgB 2 hydrogenation, in agreement with the findings of the preceding bulk study.

08 HYDROGEN↗
DOE OSTI2021

Selenium infiltrated hierarchical hollow carbon spheres display rapid kinetics and extended cycling as lithium metal battery (LMB) cathodes

Lithium metal–selenium (Li–Se) batteries offer high volumetric energy but are limited in their cycling life and fast charge characteristics. Here a facile approach is demonstrated to synthesize hierarchically porous hollow carbon spheres that host Se (Se@HHCS) and allow for state-of-the-art electrochemical performance in a standard carbonate electrolyte (1 M LiPF 6 in 1:1 EC:DEC). The Se@HHCS electrodes display among the most favorable fast charge and cycling behavior reported. For example, they deliver specific capacities of 442 and 357 mA h g -1 after 1500 and 2000 cycles at 5C and 10C, respectively. At 2C, Se@HHCS delivers 558 mA h g -1 after 500 cycles, with cycling coulombic efficiency of 99.9%. Post-mortem microstructural analysis indicates that the structures remain intact during extended cycling. Per GITT analysis, Se@HHCS possesses significantly higher diffusion coefficients in both lithiation and delithiation processes as compared to the baseline. Furthermore, the superior performance of Se@HHCS is directly linked to its macroscopic and nanoscale pore structure: the hollow carbon sphere morphology as well as the remnant open nanoporosity accommodates the 69% volume expansion of the Li to Li 2 Se transformation, with the nanopores also providing a complementary fast ion diffusion path.

25 ENERGY STORAGE↗
NASA NTRS2018

Exploring Li-Air Batteries for High Specific Energy and High Power Applications: A Simulation Study

Commercialization of lithium-air batteries face many challenges, such as electrolyte decomposition, short cycle life, low energy efficiency, low power density, etc. However, commercialization of Li-air batteries for mass sensitive applications such as electric vehicles, portable power source, and drones is more challenging due to additional constraints of safety, electrolyte evaporation, high specific energy requirements, and reliable discharge times. In this presentation, we will present our finite element simulation results comparing Li-O2 and Li-air batteries using power density, energy density, specific power, and discharge times as metrics to evaluate different electrolytes and electrode geometry to reduce total mass and maximize discharge current. We use a finite element model and a discharge product model developed in which is based on porous electrode and concentrated electrolyte theories and the discharge product is modeled using quantum tunneling; for reaction kinetics and oxygen diffusion, an improved model was used. The electrolyte properties such as ion conductivity and ion diffusion were obtained from Molecular Dynamics (MD) simulations while the other parameters for the finite element model were calibrated to match experiments at high discharge current densities (>1.5 mA/cm2). The mass densities of different electrolytes were computed using MD simulations as well. For this presentation, we examine the practical electrochemical mass of a system at different current ratings, the sensitivity of mass to the use of ambient air as compared to pure oxygen as well as the electrolyte, which affects maximum current density and the total mass associated with the electrolyte (which includes the mass of additional components), and, the optimization of battery geometry for total discharge time, average discharge voltage, maximum discharge current, and minimum electrochemical mass.

Mehta, M.↗
DOE OSTI2021

Structural Evolution of Layered Manganese Oxysulfides during Reversible Electrochemical Lithium Insertion and Copper Extrusion

The electrochemical lithiation and delithiation of the layered oxysulfide Sr 2 MnO 2 Cu 4-δ S 3 has been investigated by using a combination of in situ powder X-ray diffraction and ex situ neutron powder diffraction, X-ray absorption and 7 Li NMR spectroscopy, together with a range of electrochemical experiments. Sr 2 MnO 2 Cu 4-δ S 3 consists of [Sr 2 MnO 2 ] perovskite-type cationic layers alternating with highly defective antifluorite-type [Cu 4-δ S 3 ] (δ ≈ 0.5) anionic layers. It undergoes a combined displacement/intercalation (CDI) mechanism on reaction with Li, where the inserted Li replaces Cu, forming Li 4 S 3 slabs and Cu + is reduced and extruded as metallic particles. For the initial 2-3% of the first discharge process, the vacant sites in the sulfide layer are filled by Li; Cu extrusion then accompanies further insertion of Li. Mn 2.5+ is reduced to Mn 2+ during the first half of the discharge. The overall charging process involves the removal of Li and re-insertion of Cu into the sulfide layers with re-oxidation of Mn 2+ to Mn 2.5+ . However, due to the different diffusivities of Li and Cu, the processes operating on charge are quite different from those operating during the first discharge: charging to 2.75 V results in the removal of most of the Li, little reinsertion of Cu, and good capacity retention. A charge to 3.75 V is required to fully reinsert Cu, which results in significant changes to the sulfide sublattice during the following discharge and poor capacity retention. This detailed structure-property investigation will promote the design of new functional electrodes with improved device performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Enabling practical nanoparticle electrodeposition from aqueous nanodroplets

The rapid rise of technology in the modern world has led to an increased demand for energy. Consequently, it is essential to increase the efficiency of current energy-producing systems due to the poor activity of their catalysts. Nanoparticles play a significant role in energy storage and conversion; however, electrodeposition of nanoparticles is difficult to achieve due to surface heterogeneities, nanoparticle diffusion layer overlap, and the inability to electrodeposit multi-metallic nanoparticles with stoichiometric control. These problems can be solved through nanodroplet-mediated electrodeposition, a technique where water nanodroplets are filled with metal salt precursors that form stable nanoparticles when they collide with a negatively-biased electrode. Further, this method has demonstrated control over nanoparticle size and morphology, displaying a wide variety of applications for the generation of materials with excellent catalytic properties. Historically, the cost of nanodroplet-mediated electrodeposition experimentation is prohibitive because practitioners use 0.1 M to 0.5 M tetrabutylammonium perchlorate (TBAP) dissolved in the oil phase (∼10 mL). Such high concentrations of electrolytes have been used to lower ohmic drop and provide ions to maintain charge balance during electrodeposition. Here, we show that supporting electrolyte is not necessary for the oil phase. In fact, one can use a suitable salt (such as lithium perchlorate) in the aqueous phase to achieve nanoparticle electrodeposition. This simple change, grounded in an understanding of ion transfer, drives down the cost per experiment by nearly three orders of magnitude, representing a necessary step forward in enabling practical nanoparticle electrodeposition from water nanodroplets. This approach is a promising procedure for future cost-effective energy conversion systems relying on electrocatalytic nanoparticles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Physics-informed machine learning exploration of Na storage mechanisms in disordered carbon

Sodium-ion batteries are a cost-effective, sustainable alternative to lithium-ion systems for large-scale energy storage. However, optimizing sodium storage in carbon-based anodes with microstructural complexity and atomic disorder remains a major challenge. The intrinsic inhomogeneity of these materials produces diverse local environments, making it difficult for conventional methods to predict and control ion dynamics. Hard carbon (HC) anodes, composed of ranges of ordered-to-disordered graphitic and amorphous nanodomains, offer tunable ion storage and rate capacity, yet rationale design remains a challenge due to poorly understood correlation between local atomic feature and ion transport mechanism. Here, to address this challenge, we introduce a data-driven framework that integrates validated machine-learned interatomic potentials, large-scale molecular dynamics simulations, and machine learning to elucidate sodium transport mechanisms as a function of carbon and sodium loading densities. By computing per-ion structural descriptors and applying unsupervised learning, we identify distinct diffusion modes governed by microscopic features. Supervised analysis and correlation mapping then establish quantitative links between these transport regimes and processing variables such as bulk carbon density and sodium content. This physics-informed approach establishes quantitative structure–transport relationships and offers actionable design principles for engineering high-performance HC anodes.

Data-driven framework↗
DOE OSTI2024

Effects of irradiation temperature on the microstructure and deuterium retention in γ-LiAlO 2 pellets

This report presents the experimental findings obtained from November 2023 to September 2024. The study aims to investigate the effects of temperature on the microstructure, deuterium (D) retention, and lithium (Li) loss in γ-LiAlO 2 pellets subjected to sequential He + and D + ion irradiation to a high dose. Sequential ion irradiation has been a key method in our previous studies to simulate the behavior of γ-LiAlO 2 under neutron irradiation. In addition to dose and dose rate, irradiation temperature is a critical factor influencing microstructural and compositional changes. LiAl 5 O 8 precipitates have been observed in γ-LiAlO 2 pellets irradiated with reactor neutrons at ~300°C. These precipitates also form during ion irradiation at an elevated temperature of 500°C, but not at 300°C. In our ion irradiation experiments, the dose rate is typically three orders of magnitude higher than that of neutron irradiation, leading to a more rapid damage production. To better emulate the microstructural features in neutron-irradiated pellets using ion irradiation, a higher irradiation temperature is needed to accelerate the diffusion of point defects and enhance defect recovery rates, thereby compensating for the effects of the higher dose rate. The microstructural changes observed are the result of competing processes occurring during ion irradiation.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Effect of Zwitterionic Additives on Solvation and Transport of Sodium and Potassium Cations in (Ethylene Oxide)10: A Molecular Dynamics Simulation Study

Sodium- (Na + ) and potassium- (K + ) ion batteries are cost-effective alternatives to lithium-ion (Li + ) batteries due to the abundant sodium and potassium resources. Solid polymer electrolytes (SPEs) are essential for safer and more efficient Na + and K + batteries because they often exhibit low ionic conductivity at room temperature. While zwitterionic (ZW) materials enhance Li+ battery conductivity, their potential for Na + and K + transport in batteries remains unexplored. In this study, we investigated the effect of three ZW molecules (ChoPO4, i.e., 2-methacryloyloxyethyl phosphorylcholine, ImSO3, i.e., sulfobetaine ethylimidazole, and ImCO2, i.e., carboxybetaine ethylimidazole) on the dissociation of Na + and K + coordination with ethylene oxide (EO) chains in EO-based electrolytes through molecular dynamics simulations. Our results showed that ChoPO4 possessed the highest cation–EO10 dissociation ability, while ImSO3 exhibited the lowest. Such dissociation ability correlated with the cation–ZW molecule coordination strength: ChoPO4 and ImSO3 showed the strongest and the weakest coordination with cations. However, the cation–ZW molecule coordination could slow the cationic diffusion. The competition of these effects resulted in accelerating or decelerating cationic diffusion. Our simulated results showed that ImCO2 enhanced Na + diffusion by 20%, while ChoPO4 and ImSO3 led to a 10% reduction. For K + , ChoPO4 reduced its diffusion by 40%, while ImCO2 and ImSO3 caused a similar decrease of 15%. These findings suggest that the ZW structure and the cationic size play an important role in the ionic dissociation effect of ZW materials.

25 ENERGY STORAGE↗
DOE OSTI2022

Single‐Crystal LiNi x Mn y Co 1− x − y O 2 Cathodes for Extreme Fast Charging

Abstract Ni‐rich layered LiNi x Mn y Co 1− x − y O 2 (NMCs, x ≥ 0.8) are poised to be the dominating cathode materials for lithium‐ion batteries for the foreseeable future. Conventional polycrystalline NMCs, however, suffer from severe cracking along the grain boundaries of primary particles and capacity loss under high charge and/or discharge rates, hindering their implementation in fast‐charging electric vehicular (EV) batteries. Single‐crystal (SC) NMCs are attractive alternatives as they eliminate intergranular cracking and allow for grain‐level surface optimization for fast Li transport. In the present study, the authors report synthetic approaches to produce SC LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NMC811) samples with different morphologies: Oct‐SC811 with predominating (012)‐family surface and Poly‐SC811 with predominating (104)‐family surface. Poly‐SC811, representing the first experimentally synthesized NMC811 single crystals with (104) surface, delivers superior performance even at the ultra‐high rate of 6 C. Through detailed X‐ray analysis and electron microscopy characterization, it is shown that the enhanced performance originates from better chemical and structural stabilities, faster Li + diffusion kinetics, suppressed side reactions with electrolyte, and excellent cracking resistance. These insights provide important design guidelines in the future development of fast‐charging NMC‐type cathode materials.

Lu, Yanying↗
NASA NTRS2019

A Multi-Physics Study on High-Specific Power Li-O2 Batteries for Electric Aircraft

Commercialization of lithium-air batteries faces many challenges, such as electrolyte decomposition, short cycle life, low energy and power density, etc. However, commercialization of Li-O2 batteries for aeronautics is much more challenging due to additional safety constraints on cyclability and performance (high specific power and specific energy). For this presentation, we will discuss inter-related aspects of physics-based modeling of a pack: cell and battery model calibration. In addition, we will evaluate and present optimal battery designs for high discharge current density, high discharge time, and low battery mass using simulation-based optimization.The Finite Element Model (FEM) used to simulate a Li-O2 cell is based on the work of Bevara [1]. The different aspects of the model are based on: porous electrode theory and concentrated electrolyte theory; quantum tunneling model for the resistance of conformal layer of discharge product (Li2O2) [1]; Butler-Volmer kinetics for electrochemical reaction; Fick's diffusion for oxygen transport; and an oxygen dissolution model is applied at the air/electrolyte interface [2]. The electrolyte properties such as ion conductivity, ion diffusion, oxygen diffusion, and mass density of the electrolyte were taken from Molecular Dynamics (MD) simulations [3]; while the other model parameters, which includes mass of cell components, were calibrated to match experiments at high discharge current densities. The cell mass includes the anode, cathode, separator, electrolyte, and other components (such as current collector). This calibrated model is used to perform parametric studies on cathode thickness, porosity, tortuosity, carbon particle size, electrolyte transport and material properties, partial pressure of oxygen, discharge time, and discharge current density to study optimal designs for high specific power and energy. References:1. Bevara, V. & Andrei, P. (2014), J. Electrochem. Soc. 161 (14), A2068-A2079.2.Mehta, M. & Andrei, P. (2015), J. Power Sources. 286, 299-308.3.Liyana-Arachchi, T.; Haskins, J.; Burke, C.; Diederichsen, K.; McCloskey, B.; & Lawson, J. (2018), J. Phys. Chem. B. 122 (36), 8548 - 8559.4.Choi, W.; Kikumoto, H.; Choudhary, R. & Ooka, R. (2018), Applied Energy, 209, 306-321.

Mehta, Mohit↗
DOE OSTI2025

Using Light to Enhance Charge Transfer in Battery Materials: Increasing Charging Rates in LiNi 0.5 Mn 1.5 O 4

Electrochemical, spectroscopic, and computational studies on the interplay between light perturbation and coupled electron and Li-ion transfer in LiNi 0.5 Mn 1.5 O 4 (LNMO) cathodes identify that photon perturbation moves the system out of equilibrium, increases entropy, lowers the impedance of the battery, and increases the charging capacity by at least 15% during fast charging by promoting the oxidation of Ni 3+ to Ni 4+ . Here, the correlation with density functional theory calculations points out that oxidation of Ni 3+ faces a 30% higher barrier compared with the oxidation of Ni 2+ and hence exhibits greater responses to the energy transferred from photons. Structural analysis elucidates that photon energy also assists the transition of LNMO from the Jahn−Teller distorted asymmetric lattice with Ni 3+ to the nondistorted Ni 4+ . Synergistically, photons energize the removal of electrons from Ni 3+ and create photoinduced Ni 4+ intermediates, followed by the removal of Li + with almost two times faster diffusion rates.

5 V spinel↗
DOE OSTI2023

Role of Intra-Domain Heterogeneity on Ion and Polymer Dynamics in Block Polymer Electrolytes: An Approach for Spatially Resolving Dynamics and Ion Transport

The design of safe and high-performance, nanostructured, block polymer (BP) electrolytes for lithium-ion batteries requires a thorough understanding of the key parameters that govern local structure and dynamics. Yet, the interfaces between microphase separated domains can introduce complexities in this local behavior that can be challenging to quantify. Herein, the local polymer, cation (Li + ), and anion dynamics were described in salt-doped polystyrene block poly(oligo-oxyethylene methyl ether methacrylate) (PS-b-POEM) through a quantitative framework that considered the effects of polymer architecture, segmental mixing, chain stretching, and confinement on polymer mobility and ion transport. This framework was validated through nuclear magnetic resonance (NMR) spectroscopy measurements on solid (dry) polymer electrolyte samples. Notably, a mobility transition temperature (T mobility ) was identified through NMR spectroscopy that captured the local dynamics more accurately than the thermal glass transition temperature. Additionally, the approach quantitatively described the mobility gradient across a domain when segmental mixing effects were combined with chain stretching and confinement information, especially at higher segregation strengths – facilitating the assessment of local ion diffusion and conductivity. As a result, spatially averaged local ion diffusion predictions quantitatively matched NMR-measured ion diffusivities in the BP samples, while spatially summed ionic conductivity predictions across a domain qualitatively captured trends in the measured ionic conductivities.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Tetrahedral Zn 2+ doping LiNi 0.6 Mn 0.2 Co 0.2 O 2 improves discharge capacity retention by altering surface Ni valence during cycling and preventing oxygen evolution

5 mol-% Zn 2+ was added to the co-precipitation synthesis of LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) to understand Zn's effect on the structural and electronic properties of NMC622. Zn is determined to successfully dope into the NMC crystal lattice as there is an increase in d-spacing along the [003], [104], and [110] directions and an increase in molar volume (100.75 cm 3 mol -1 for NMC622 and 101.00 cm 3 mol -1 for Zn-NMC). Through XPS, Zn is determined to dope on the tetrahedral 6c Wyckoff site in the NMC structure and TEM-EDS reveals that despite a slight ZnO impurity phase, 1.4 mol-% Zn successfully dopes into the crystal structure. Furthermore, cyclic voltammetry shows a suppressed anodic wave associated with oxygen evolution and EIS demonstrates that Zn-doped NMC decreases charge transfer resistance and increases Li diffusion by an order of magnitude. After the formation cycles, NMC has a higher 1 C accessible capacity, 141 mAh/g, over Zn-NMC (132 mAh/g), but after long term cycling Zn-NMC has a higher accessible capacity (117 mAh/g compared to 96 mAh/g for NMC) and increases discharge capacity retention by 18% leading to longer cycle life.

Electrochemistry↗
DOE OSTI2025

Nanoscopic strain evolution in single-crystal battery positive electrodes

Single-crystal Ni-rich layered oxides (SC-NMC) with a grain-boundary-free configuration have effectively addressed the long-standing cracking issue of conventional polycrystalline Ni-rich materials (PC-NMC) in lithium-ion batteries, prompting a shift in optimization strategies. However, continued reliance on anisotropic lattice volume change—a well-established failure indicator in PC-NMC—as a metric for understanding strain and guiding compositional design for SC-NMC becomes controversial. Here, in this study, by leveraging multiscale diagnostic techniques, we unravelled the distinct nanoscopic strain evolution in SC-NMC during battery operation, challenging the conventional composition-driven strategies and mechanical degradation indicators used for PC-NMC. Through particle-level chemomechanical analysis, we reveal a decoupling between mechanical stability and lattice volume change in SC-NMC, identifying that structural instability in SC materials is primarily driven by multidimensional lattice distortions induced by kinetics-driven reaction heterogeneity and progressively deactivating chemical phases. Using this mechanical failure mode, we redefine the roles of cobalt and manganese in maintaining mechanical stability. Unlike cobalt’s detrimental role in PC-NMC, we find cobalt to be critical in enhancing the longevity of SC-NMC by mitigating localized strain along the extended diffusion pathway, whereas manganese exacerbates mechanical degradation.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Highly-Cyclable Room-Temperature Phosphorene Polymer Electrolyte Composites for Li Metal Batteries

Despite significant interest toward solid-state electrolytes owing to their superior safety in comparison to liquid-based electrolytes, sluggish ion diffusion and high interfacial resistance limit their application in durable and high-power density batteries. Here, a novel quasi-solid Li + ion conductive nanocomposite polymer electrolyte containing black phosphorous (BP) nanosheets is reported. The developed electrolyte is successfully cycled against Li metal (over 550 h cycling) at 1 mA cm -2 at room temperature. The cycling overpotential is dropped by 75% in comparison to BP-free polymer composite electrolyte indicating lower interfacial resistance at the electrode/electrolyte interfaces. Molecular dynamics simulations reveal that the coordination number of Li + ions around (trifluoromethanesulfonyl)imide (TFSI - ) pairs and ethylene-oxide chains decreases at the Li metal/electrolyte interface, which facilitates the Li + transport through the polymer host. Here, density functional theory calculations confirm that the adsorption of the LiTFSI molecules at the BP surface leads to the weakening of N and Li atomic bonding and enhances the dissociation of Li + ions. This work offers a new potential mechanism to tune the bulk and interfacial ionic conductivity of solid-state electrolytes that may lead to a new generation of lithium polymer batteries with high ionic conduction kinetics and stable long-life cycling.

2D materials↗
DOE OSTI2025

Electrochemical Characterization of Dissolved Oxides in Molten FLiNaK

Molten fluoride salts have long been the subject of investigation given their application in a variety of industrial processes. Oxides are a common exogeneous impurity within these systems, and can lead to many operational and regulatory concerns. In recent studies, the electro-oxidation of dissolved metallic oxides has been attributed to a single step oxygen evolution reaction despite voltametric evidence suggesting otherwise. Here, we first use square wave voltammetry to confirm that the oxidation of dissolved oxides in fluorides proceeds via a two-electron transfer reaction and then demonstrate that the presence of a peroxide-mediated redox reaction better explains the electrochemical data. Numerical simulations were then used to support the determination of improved diffusion coefficients to enable electroanalytical measurements of the oxide concentration across at a variety of temperatures. A linear Arrhenius relationship was observed when the experimental data was corrected for ohmic resistance effects. Concentration measurements using the corrected square wave voltammetry data demonstrated high accuracy across a large range of concentrations, while the uncorrected data showed plateauing and high errors. In total, this work serves to rectify previously misconstrued electrochemical data of oxides in molten salts and demonstrate how accurate, in situ concentration measurements can be achieved in real-world systems.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗