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DOE OSTI2024

Controlling the Phase Transformation of Alumina for Enhanced Stability and Catalytic Properties

Current transition alumina catalysts require the presence of significant amounts of toxic, environmentally deleterious dopants for their stabilization. Herein, we report a simple and novel strategy to engineer transition aluminas to withstand aging temperatures up to 1200 °C without inducing the transformation to low-surface-area α-Al 2 O 3 and without requiring dopants. By judiciously optimizing the abundance of dominant facets and the interparticle distance, we can control the temperature of the phase transformation from θ-Al 2 O 3 to α-Al 2 O 3 and the specific surface sites on the latter. These specific surface sites provide favorable interactions with supported metal catalysts, leading to improved metal dispersion and greatly enhanced catalytic activity for hydrocarbon oxidation. Further, the results presented herein not only provide molecular-level insights into the critical factors causing deactivation and phase transformation of aluminas but also pave the way for the development of catalysts with improved activity for catalytic hydrocarbon oxidation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Direct computation of magnetic surfaces in Boozer coordinates and coil optimization for quasisymmetry

We propose a new method to compute magnetic surfaces that are parametrized in Boozer coordinates for vacuum magnetic fields. We also propose a measure for quasisymmetry on the computed surfaces and use it to design coils that generate a magnetic field that is quasisymmetric on those surfaces. The rotational transform of the field and complexity measures for the coils are also controlled in the design problem. Using an adjoint approach, we are able to obtain analytic derivatives for this optimization problem, yielding an efficient gradient-based algorithm. Starting from an initial coil set that presents nested magnetic surfaces for a large fraction of the volume, our method converges rapidly to coil systems generating fields with excellent quasisymmetry and low particle losses. In particular for low complexity coils, we are able to significantly improve the performance compared with coils obtained from the standard two-stage approach, e.g. reduce losses of fusion-produced alpha particles born at half-radius from $17.7\,\%$ to $6.6\,\%$ . We also demonstrate 16-coil configurations with alpha loss ${<}1\,\%$ and neoclassical transport magnitude $\epsilon _{\text {eff}}^{3/2}$ less than approximately $5\times 10^{-9}$ .

Physics↗

DOE OSTI2023

First-Principles Examination of Multiple Criteria of Organic Solvent Oxidative Stability in Batteries

Oxidative instability of the liquid electrolyte at or near battery cathode oxide surfaces has significant detrimental effects on batteries. Organic solvent molecules are often the fuel and precursors of such degradation processes, releasing electrons and protons that react with cathode oxides and electrolyte anions. These reactions contribute to cathode–electrolyte interphase (CEI) film formation, transition-metal ion dissolution, and phase transformation of the surface regions of the cathode. Here we apply density functional theory calculations to examine four criteria of oxidative stability (oxidation potential, hydrogen removal energies, and initial reactivity on two types of oxide facets) using four different solvent/additive molecules (ethylene carbonate, fluoroethylene carbonate, 1,3-dioxolane, and dimethyl ether). The ranking of molecular stability differs with each criterion. Surprisingly, the all-oxygen-terminated basal planes of layered oxides exhibit lower reaction barriers than spinel surface facets with exposed transition-metal cations, especially for ether solvents; the calculations also suggest basal planes contribute to the dissolution of transition-metal ions. Further, the structure–degradation relation complexity underscores the challenge of understanding the function of the CEI but also offers a guide to future degradation-mitigation strategies including facet engineering. Our predictions and models help establish a framework for future studies relevant to high-voltage conditions.

25 ENERGY STORAGE↗

DOE OSTI2020

New Synthesis Strategies to Improve Co-Free LiNi0.5Mn0.5O2 Cathodes: Early Transition Metal d0 Dopants and Manganese Pyrophosphate Coating

In this work, we report solution-based doping and coating strategies to improve the electrochemical performance of the Co-free layered oxide cathode LiNi0.5Mn0.5O2 (LNMO). Small amounts of d0 dopants (e.g., Mo6+and Ti4+, 0.5-1 at. %) increase the cathode’s specific capacity, cycling stability, and rate capability. More specifically, a Mo-doped cathode with the nominal composition LiNi0.495Mn0.495Mo0.01O2 achieves a high reversible capacity of 180 mAh/g at 20 mA/g with good retention at higher rates (e.g., 120 mAh/g at 100 mA/g). Effects of 1 at.% Mo dopant on the cathode structure were studied using a suite of characterization tools including X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). These measurements demonstrate that Mo6+ reduces Li+/Ni2+cation mixing and mitigates undesirable phase transformations near the cathode surface during cycling. This work also reports the use of an inorganic Mn2P2O7 coating which enhances cycling stability, presumably through formation of a stable cathode electrolyte interphase (CEI) layer. Overall, the synthesis approaches reported herein are quite general and can potentially be expanded to other high voltage LIB cathodes.

Co-free cathodes, d0 cation, pyrophosphate coating↗

DOE OSTI2024

Recycled graphite enabled superior performance for lithium ion batteries

Recycling graphite attracts growing attention since cumulative amount of spent Li-ion batteries and the shortage of graphite supply chain. Although various recycling methods have been reported, the recycled graphite cannot reach the strict commercial standards of purity, scalability, efficiency, and capacity, preventing it from battery manufacturing. Herein, the important roles of defects and functional groups on the graphite surface are deeply studied, and a closed-loop graphite recycling process with the surface recovery and modification for the graphite from the end-of-life batteries is demonstrated. The recovered graphite delivers a purity of over 99.9 % and an average initial coulombic efficiency of 91.5 %. Compared with commercial graphite in industrial standard battery testing parameters, full cells with recovered graphite possess enhanced rate reversibility, doubled cycle life, over 10 % higher capacity along with half anode material cost. In conclusion, these impressive results not only underscore the transformative potential of surface reconstruction and modification in graphite recycling, but also present economic feasibility and sustainable pathway for significantly improving battery performance and addressing global resource challenges via integration with the hydrometallurgical recycling process.

25 ENERGY STORAGE↗

DOE OSTI2021

Solid phase characterization and transformation of illite mineral with gas-phase ammonia treatment

In situ remediation applications of ammonia (NH 3 ) gas have potential for sequestration of subsurface contamination. Ammonia gas injections initially increase the pore water pH leading to mineral dissolution followed by formation of secondary precipitates as the pH is neutralized. However, there is a lack of understanding of fundamental alteration processes due to NH 3 treatment. In these batch studies, phyllosilicate minerals (illite and montmorillonite) were exposed to NH 3 gas with subsequent aeration to simulate in situ remediation. Following treatments, solids were characterized using a variety of techniques, including X-ray diffraction, N 2 adsorption-desorption analysis for surface area, Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), and microscopy methods to investigate physicochemical transformations. The results of this study indicate that, at high pH, the clays are altered as observed by differences in morphology and particle size via microscopy. However, the two clays interact differently with NH 3 . While montmorillonite interlayers collapsed due to intercalation, illite layers were unaffected as confirmed by FTIR analysis. Further, structural changes in silicate ([SiO 4 ] n- ) and aluminol (Al-OH) groups were identified by NMR and FTIR. This research showed that mineral alteration processes occur during and after NH 3 gas treatment which may be used to remove radionuclides from the aqueous phase through sorption, co-precipitation, and coating with secondary phyllosilicate alteration products.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

Activating magnetite ores for aqueous ironmaking at high current densities

Low-temperature electrochemical cells reducing iron oxides to metal in alkaline electrolytes can support fully electrified steelmaking processes. Previous studies on these cells have primarily focused on high-surface-area hematite, Fe 2 O 3 , reactants whereas attempts to reduce suspensions of magnetite, Fe 3 O 4 —one of the two feedstocks for existing ironmaking reactors—have generally been limited to low rates of reaction (<30 mA cm −2 ). Here, in this study, we control the crystalline domain size of Fe 2 O 3 and Fe 3 O 4 particles in 10 M NaOH electrolytes to study how the nanoscale morphology of oxides controls the rate of electrochemical ironmaking. Rotating-ring disk electrode measurements of Fe 2+ , in situ Raman spectroscopy of the electrode surface, and ex situ electron microscopy were consistent with a hypothesized passivation process at Fe 3 O 4 surfaces that may prevent the continuous formation of soluble intermediates. Sufficiently small (<100 nm diameter) oxide particles yielded Fe partial current densities >160 mA cm −2 , a fivefold increase relative to previously reported rates for Fe 3 O 4 suspensions and comparable to active Fe 2 O 3 . Electron microscopy revealed that electrodeposited films were composed of micron-scale crystalline Fe domains with a porous film of Fe 3 O 4 nanoparticles and supports a model where Fe is grown primarily from soluble Fe 2+ intermediates. Based on these insights, inactive blast-furnace-grade iron-oxides were transformed into high surface area nanoparticles (1.6 to 229.2 m 2 g −1 ) via reprecipitation, leading to a ninefold enhancement in faradaic efficiency and an Fe partial current density of 120 mA cm −2 . When integrated with chlor-iron cells producing reagents for reprecipitation, this approach could lead to a cost-competitive process for electrochemical ironmaking from industrially relevant feedstocks.

TEM↗

DOE OSTI2022

Effects of physical, chemical, and biological ageing on the mineralization of pine wood biochar by a Streptomyces isolate

If biochar is to be used for carbon (C) management, we must understand how weathering or ageing affects biochar C mineralization. Here, we incubated aged and unaged eastern white pine wood biochar produced at 350 and 550°C with a Streptomyces isolate, a putative biochar-decomposing microbe. Ageing was accelerated via three different processes, namely, (a) physical ageing–subjecting biochar to alternating freeze-thaw and wet-dry cycles, (b) chemical ageing–treating biochar with concentrated hydrogen peroxide and (c) biological ageing–incubating biochar in the presence of nutrients and microorganisms. Elemental composition and surface chemistry (Fourier Transform Infrared spectroscopy) of biochar samples were compared before and after ageing. Biochar C mineralization between ageing treatments was significantly different in the case of 350°C biochar ( p value = 0.03). Among the 350°C biochars, physical ageing resulted in the greatest increase (by 103%) in biochar C mineralization ( p value = 0.05). However, in the case of 550°C biochar, ageing did not result in a significant change in biochar C mineralization ( p value = 0.40). Biochar C mineralization was positively correlated with an increase in O/C ratio post-ageing ( r s = 0.86, p value = 0.01). In the case of 350°C biochar, surface oxidation during ageing enhanced biochar degradation by the isolate. For 550°C biochar, however, ageing did not significantly increase biochar C mineralization, likely due to high condensed aromatic C content and lower surface oxidation during ageing. The results from our study suggest that low temperature aged biochar is more susceptible to biological degradation by soil microbes. These findings have implications for the use of biochar for long term C storage in soils.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2025

Advancing Sodium-Ion Battery Cathodes: A Low-Cost, Eco-Friendly Mechanofusion Route from TiO 2 Coating to Ti 4+ Doping

Layered oxide battery cathodes often require extra stabilization strategies, such as surface coating or doping, to mitigate side reactions and enhance longevity. Conventional methods such as aqueous deposition and atomic layer deposition are costly and environmentally unfriendly and even damage the original structure, especially for air-sensitive sodium-ion battery (SIB) cathodes. Herein, we introduce an all-dry mechanofusion technique that modifies hydroxide precursors with TiO 2 coating before sintering with a sodium source. Using advanced characterizations including X-ray diffraction, neutron diffraction, and solid-state nuclear magnetic resonance for structural insights, X-ray absorption spectroscopy to study metal valence states, and transmission X-ray microscopy for nanoscale visualization of nickel oxidation states, we verified that postsintering transforms TiO 2 surface coating into Ti doping, leading to improved Ni-oxidation homogeneity, modified charge compensation, and enhanced thermal stability. Electrochemical tests reveal superior performance in capacity retention, rate capability, and air stability for these modified cathodes, with pouch cells maintaining over 85% capacity after 650 cycles. This method presents a sustainable, cost-effective route for advanced SIB cathode development.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Effects of Surface Orientation and Termination Plane on Glass‐to‐Crystal Transformation of Lithium Disilicate by Molecular Dynamics Simulations

Glass‐to‐crystal transformation of lithium disilicate is studied using molecular dynamics simulations using an effective partial charge potential. The structural evolution of the interface between glassy and crystalline lithium disilicate is analyzed to simulate crystallization of glass on pre‐existing crystal seeds. Besides previously used atomic number density, the distribution of Q n species (Si tetrahedra with n bridging oxygen) is shown to be an effective parameter for following this transformation quantitatively. The early stages of crystal growth are significantly affected by the orientation and termination of the surface of adjacent crystal, as indicated by calculated atomic density, partial ordering, atomic segregation, and an increase in Q 3 concentration. In particular, under‐coordinated Si within the outer crystal layer is found to be most effective in transforming the amorphous structure toward crystallinity. The increase in Q 3 in the glass close to interface region most clearly shows the initial stage of lithium disilicate crystal growth.

Sun, Wei↗

DOE OSTI2025

Mechanistic Transformation of CuI Nanoparticles Into Oxidation‐Resistant 2D Copper Nanoplates

Unconventional phase transformations reveal new crystallization mechanisms, yet direct observation of such pathways during nanoscale solution-phase synthesis remains challenging. This study uncovers an atypical growth process in which thermodynamically stable CuI nanoparticles (NPs) transform into high-energy 2D Cu plates. Using a combination of in situ transmission electron microscopy, ex situ structural analysis, and density functional theory calculations shows that the formation of structural defects induced by hexadecylamine and chloride ions facilitates the transformation by promoting surface iodine vacancies. The resulting Cu{111} nanoplates, with ultrathin thicknesses (≈4 nm) and exceptionally high aspect ratios (≈450), display enhanced oxidation resistance and long-term stability under ambient conditions. This resistance is attributed to the close-packed {111} facets, which suppress chemical oxidation even after extended exposure to air over 100 days. These findings provide new insights into non-classical crystallization pathways in metal nanomaterials and suggest a versatile approach for preparing oxidation-resistant, structurally defined Cu nanostructures.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Photoinduced Electron and Energy Transfer Pathways and Photocatalytic Mechanisms in Hybrid Plasmonic Photocatalysis

Hybrid plasmonic nanostructures are built on plasmonic metalnanostructures surrounded by catalytic metals or metal oxides. We report that recent studies have shown that hybrid plasmonic nanocatalysts can concurrently utilize thermal energy and photon stimuli and exhibit high catalytic activity, selectivity, and stability that are not attainable in conventional purely thermally activated catalytic processes. The hybrid plasmonic photocatalytic approach has recently emerged as an attractive concept for the conversion of solar energy into chemical energy, the distributed synthesis of valuable chemicals such as ammonia with little to no requirement of external heating, and the development of coke-resistant and selective catalytic processes. The field of hybrid plasmonic photocatalysis has grown tremendously in the last decade. In this review article, the advantages of visible-light-augmented hybrid plasmonic photocatalysis over conventional pure thermally activated heterogeneous catalysis are discussed. Fundamental insights are provided into photocatalytic mechanisms by which the photoexcited charge carriers (electrons and holes) are formed and transferred to adsorbates triggering chemical transformations on the surface of hybrid plasmonic nanocatalysts. Computational modeling used for predicting and understanding the photocatalytic activity and selectivity on hybrid plasmonic nanostructures is also reviewed. The review closes with a discussion of the current challenges, new opportunities, and future outlook for hybrid plasmonic photocatalysis.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Electron energy levels determining cathode electrolyte interphase formation

Cathode electrolyte interphase (CEI) has a significant impact on the performance of rechargeable batteries and is gaining increasing attention. Understanding the fundamental and detailed CEI formation mechanism is of critical importance for battery chemistry. Herein, a diverse of characterization tools are utilized to comprehensively analyze the composition of the CEI layer as well as its formation mechanism by LiCoO 2 (LCO) cathode. We reveal that CEI is mainly composed of the reduction products of electrolyte and it only parasitizes the degraded LCO surface which has transformed into a disordered spinel structure due to oxygen loss and lithium depletion. Based on the energy diagram and the chemical potential analysis, the CEI formation process has been well explained, and the proposed CEI formation mechanism is further experimentally validated. This work highlights that the CEI formation process is nearly identical to that of the anode-electrolyte-interphase, both of which are generated due to the electrolyte directly in contact with the low chemical potential electrode material. This work can deepen and refresh our understanding of CEI.

LiCoO2↗

DOE OSTI2023

Evidence of plasma‐driven decomposition of common plastics exposed to an atmospheric nonthermal discharge

Abstract A nonthermal, pulsed spark discharge is applied to three polymer powders in Ar and Ar– gas mixtures. Hydrogen is introduced to assess plasma‐driven decomposition. Gaseous decomposition products, including methane, acetylene, and ethylene, are observed with Fourier‐transform infrared (FTIR). Surface modifications are observed on the residual polymer via attenuated total internal reflection‐FTIR. Time‐averaged rotational, vibrational, and excitation temperatures are characterized in the discharge. The plasma density is found to be around , with rotational and vibrational temperatures ranging from 1500 to 2200 K and an excitation temperature of 1–2 eV. While spark properties did not change with either gas composition or polymer composition, it was determined that the addition of hydrogen promoted higher concentrations of gaseous phase products (promoting hydrogenolysis).

36 MATERIALS SCIENCE↗

DOE OSTI2024

Catalytic Resonance Theory: Forecasting the Flow of Programmable Catalytic Loops

Chemical transformations on catalyst surfaces occur through series and parallel reaction pathways. These complex networks and their behavior can be most simply evaluated through a three-species surface reaction loop (A* to B* to C* to A*) that is internal to the overall chemical reaction. Application of an oscillating dynamic catalyst to this reactive loop has been shown to exhibit one of three types of behavior: (1) a positive net flux of molecules about the loop in the clockwise direction, (2) a negative net flux of molecules about the loop in the counterclockwise direction, or (3) negligible flux of molecules about the loop at the limit cycle of reaction. Three-species surface loops were simulated with microkinetic modeling to assess the reaction loop behavior resulting from a catalytic surface oscillating between two or more catalyst surface energy states. Selected input parameters for the simulations spanned an 11-dimensional parameter space using 127 688 different parameter combinations. Their converged limit cycle solutions were analyzed for their loop turnover frequencies, the majority of which were found to be approximately zero. Classification and regression machine learning models were trained to predict the sign and magnitude of the loop turnover frequency and successfully performed above accessible baselines. Notably, the classification models exhibited a baseline weighted F1 score of 0.49, whereas trained models achieved weighted F1 scores of 0.94 and 0.96 when trained on the parameters used to define the simulations and derived rate constants, respectively. The trained models successfully predicted catalytic loop behavior, and interpretation of these models revealed all input parameters to be important for the prediction and performance of each model.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

From material properties to multiscale modeling to improve lithium-ion energy storage safety

Energy storage using lithium-ion cells dominates consumer electronics and is rapidly becoming predominant in electric vehicles and grid-scale energy storage, but the high energy densities attained lead to the potential for release of this stored chemical energy. This article introduces some of the paths by which this energy might be unintentionally released, relating cell material properties to the physical processes associated with this potential release. The selected paths focus on the anode–electrolyte and cathode–electrolyte interactions that are of typical concern for current and near-future systems. Relevant material processes include bulk phase transformations, bulk diffusion, surface reactions, transport limitations across insulating passivation layers, and the potential for more complex material structures to enhance safety. We also discuss the development, parameterization, and application of predictive models for this energy release and give examples of the application of these models to gain further insight into the development of safer energy storage systems.

25 ENERGY STORAGE↗

DOE OSTI2022

Value Proposition of UV-Absorbers in PV Module Encapsulation

Various common crystalline silicon cell technologies were exposed to UVA radiation (1.24 Wm-2 nm-1 at 340 nm peak) on the front and back faces at 45 degrees Celsius for periods up to 3000 h, representing about 3 y of solar exposure in Phoenix, Arizona, USA. The resulting degradation of the open-circuit voltage and short-circuit current is presented. Of the various cell types examined, significant levels of degradation were seen in all cases. Less degradation was generally found after UV irradiation of cell fronts and older cell types, whereas a bifacial PERC type exposed on the rear showed about 25% degradation in short circuit current, attributable to lack of a diffused surface field. Selected cells were exposed to UV irradiation with the addition of long pass UV filters to replicate UV-absorbers in encapsulants. Modern cell designs are sensitive to UV-ID because of reduced or eliminated front and back surface field and increased dependence on high quality surface passivation. Single transformation of the independent variable (t, kW h/m^2) could be used to achieve a linear model of the data to extrapolate to 50 y. Solar Advisor Model (SAM) shows appropriate filtering of UV-irradiation can improve LCOE and net present value of plant. Some advanced cell types are seen to be UV-resistant (cell level solutions also exist). Solutions therefore exist on the cell, glass, and encapsulant level. Changes over time in each of these would also need to be considered (solarization, encapsulant browning...).

ENGINEERING,SOLAR ENERGY↗

DOE OSTI2025

Computational Modeling of Molten Salt Infiltration and Oxidation in Nuclear Graphite

Graphite is utilized as a moderator and reflector in advanced nuclear reactor designs due to its high thermal conductivity, neutron moderation properties, and resistance to radiation damage. However, its longterm performance and reliability are challenged by degradation mechanisms such as molten salt infiltration in molten salt reactors (MSRs) and oxidation in gas-cooled reactors (GCRs). These mechanisms can compromise the structural integrity and operational lifetime of graphite components, necessitating a more detailed assessment of their physical behavior. This report focuses on the development of computational models for molten salt infiltration and oxidation of graphite to aid the design and performance analysis of graphite components. For molten salt infiltration, a computational framework is developed that couples incompressible Navier-Stokes and phase-field model to simulate the penetration of molten salt into graphite?s interconnected pore structure. Initial model verification is performed using two-phase flows in two dimensions, demonstrating the models ability to capture fundamental physical behavior and agree with analytical solution. This framework is then applied to a realistic IG110 nuclear graphite , where a computed tomography extracted pore geometry is used to analyse the infiltration behavior of FLiNaK molten salt. This model provides insights into how the microstructure and other relevant parameters influence the transport pathways of molten salt into graphite, potentially offering a means to rapidly evaluate a graphite grade?s resistance to infiltration. For oxidation, the report details pore-scale mass and heat transport models, describing the diffusion of gases, reaction kinetics, and thermal effects. Additionally, this report highlights inconsistencies in the existing volume-averaged macroscopic model, particularly in upscaling of reaction kinetics and flux terms, and surface to volume transformations. These inconsistencies suggest that current formulations may not accurately capture the experimentally observed graphite oxidation process, highlighting the need for improved model development. This work advances the development of physics-based computational models for graphite degradation, contributing to improved predictive models for next-generation nuclear reactor designs. Future efforts will focus on refining the infiltration model to address non-physical behaviors and enhance its robustness. Additionally, for oxidation, further studies will employ the principles of volume averaging to rigorously derive the upscaled equations, potentially in collaboration with subject matter experts.

Computational Modeling of Molten Salt Infiltration↗