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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Fluoride-Catalyzed Siloxane Exchange as a Robust Dynamic Chemistry for High-Performance Vitrimers

Sustainable development of new technologies requires materials having advanced physical and chemical properties while maintaining reprocessability and recyclability. Vitrimers are designed for this purpose; however, their dynamic covalent chemistries often have drawbacks or are limited to specialized polymers. Here, fluoride-catalyzed siloxane exchange is reported as an exceptionally robust chemistry for scalable production of high-performance vitrimers through industrial processing of commodity polymers such as poly(methyl methacrylate), polyethylene, and polypropylene. The vitrimers show improved resistance to creep, heat, oxidation, and hydrolysis, while maintaining excellent melt flow for processing and recycling. Furthermore, the siloxane exchange between different vitrimers during mechanical blending results in self-compatibilized blends without any compatibilizers. In conclusion, this offers a general, scalable method for producing sustainable high-performance vitrimers and a new strategy for recycling mixed plastic wastes.

36 MATERIALS SCIENCE↗
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 OSTI2026

Atomic Layer Deposition (ALD) of Metal and Metal Oxide Films: A Surface Science Study (Final Report)

This is the final report for this project. The long-term objective of our project is to develop a general molecular-level picture of the surface chemistry associated with ALD processes. Our central hypothesis is that the chemistry of ALD precursors can differ significantly from that seen in solution. Awareness of such differences should provide general guidelines on what to watch for when synthesizing new ALD precursors and designing and optimizing new ALD processes, especially in terms of minimizing the incorporation of impurities in the growing films and of carrying out depositions under mild pressure and temperature conditions. The main objective of our research project has been to advance the fundamental knowledge of the surface chemistry of ALD precursors needed for the design and optimization of film deposition processes. A modern surface-science approach has been implemented to both elucidate the mechanism of the reactions of the precursors on the surface and characterize the composition and morphology of the growing films. In general, emphasis is being placed on: • Identifying the primary reactions that may lead to the deposition of clean films; •Identifying the secondary reactions that may help the ALD process, by, for instance, helping with the reduction (or oxidation) of the metal atom; • Identifying the secondary reactions that may lead to the deposition of undesirable impurities in the growing films; • Determining the kinetic parameters of the relevant surface reactions in order to define the optimum conditions for film deposition and to minimize impurity deposition. • Characterizing the nature of the resulting films, with focus on their stoichiometry and on the final oxidation states of the constituent elements; and • Using the information obtained to propose better precursors for given ALD processes.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Oxide layer delamination: An energy dissipation mechanism during high-velocity microparticle impacts

The break-up of microparticle surface oxides is needed to generate a clean metal-metal contact for metallurgical bonding during impact events such as seen in cold-spray. However, the mechanism by which this occurs is not clear. Here, using a laser-induced particle impact tester, we conduct site-specific experiment of single Cu microparticle impacts on a polished Cu substrate and characterize the impact sites. We observe that oxide layers on the particles begin to delaminate at velocities high enough to cause jetting of the substrate around the periphery of the impact site. We show that the energy cost of such delamination is ~30% of the energy needed to slow and stop particle as it bonds to the substrate, with the remainder being associated with the jetting process and bonding itself. At higher velocities, the oxide barrier is broken up to permit metallurgical bonding. Closer to the particle south-pole where hoop strain is low, oxide layers break up with few gaps and thus no metallurgical bonding is observed. Away from the south-pole where larger strains develop, oxide breakup permits intermittent bonding by the extrusion of bare metal into the gaps between oxide islands. These observations provide new insights towards understanding impact-induced metallurgical bonding during cold-spray process.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Confocal Raman Microscopy for Measuring In Situ Temperature-Dependent Structural Changes in Poly(Ethylene Oxide) Thin Films

Crystallization from the melt is a critical process governing the properties of semi-crystalline polymeric materials. While structural analyses of melting and crystallization transitions in bulk polymers have been widely reported, in contrast, those in thin polymer films on solid supports have been underexplored. Herein, in situ Raman microscopy and self-modeling curve resolution (SMCR) analysis are applied to investigate the temperature-dependent structural changes in poly(ethylene oxide) (PEO) films during melting and crystallization phase transitions. By resolving complex overlapping sets of spectra, SMCR analysis reveals that the thermal transitions of 50 µm thick PEO films comprise two structural phases: an ordered crystalline phase and a disordered amorphous phase. The ordered structure of the crystalline PEO film entirely disappears as the polymer is heated; conversely, the disordered structure of the amorphous PEO film reverts to the ordered structure as the polymer is cooled. Broadening of the Raman bands was observed in PEO films above the melting temperature (67 °C), while sharpening of bands was observed below the crystallization temperature (45 °C). The temperatures at which these spectral changes occurred were in good agreement with differential scanning calorimetry (DSC) measurements, especially during the melting transition. The results illustrate that in situ Raman microscopy coupled with SMCR analysis is a powerful approach for unraveling complex structural changes in thin polymer films during melting and crystallization processes. Furthermore, we show that confocal Raman microscopy opens opportunities to apply the methodology to interrogate the structural features of PEO or other surface-supported polymer films as thin as 2 µm, a thickness regime beyond the reach of conventional thermal analysis techniques.

Koh, Miharu [Department of Chemistry, University o↗
DOE OSTI2020

Mechanisms of Plutonium Redox Reactions in Nitric Acid Solutions

Plutonium (Pu) exhibits a complex redox behavior in acidic solutions due to its ability to adapt a wide range of oxidation states typically from +3 to +6 and the tendency for dynamic interconversion between the oxidation states that depends upon electrochemical potential, acid concentration and coordination environments. In particular, the accurate redox speciation of Pu in nitric acid solutions and mapping the interconversion between the various oxidation states mechanistically is challenging due to overlapping chemical and electrochemical reactions leading to significant experimental uncertainties. The last several decades have seen the extensive use of spectroscopic methods to identify and characterize Pu solution species in the various oxidation states. However, dynamic redox mobility of Pu has led to discrepancies among the relevant spectral databases for Pu in nitric acid solutions. This work utilizes a combination of voltammetry and controlled-potential in-situ vis–NIR spectroelectrochemistry to overcome these challenges, and map the interconversion between Pu species in +3, +4, and +6 oxidation states. This allowed elucidation of the mechanisms of the involved redox reactions and an in-depth understanding of the relative stability of the Pu oxidation states through mapping of the Pu redox processes as a function of redox potentials and nitric acid concentrations. The NIR-spectroelectrochemistry studies used to spectroscopically map the redox speciation of Pu as a function of oxidation potentials with varying HNO3 concentrations allows a new perspective into the plutonium redox transformations.

Chatterjee, Sayandev↗
DOE OSTI2022

Temperature-dependence of oxidation and carburization of Grade 91 steel in CO 2 containing impurities

Future CO 2 based power systems require steels resistant to corrosion in high-temperature CO 2 -rich environments. Candidate 9Cr ferritic-martensitic steels degrade by surface oxidation and substrate carburization, both of which can be strongly affected by impurities in the CO 2 . In this study we examined Grade 91 steel exposed to 95%CO 2 -4%H 2 O-1%O 2 with/without 0.1% SO 2 at 1 atm and 550, 600, 650° C for up to 3000 h to establish the temperature-dependence of these processes. SO 2 showed little effect on oxidation at 550-600° C but reduced carburization, while the combination of SO 2 and faster alloy diffusion at 650° C resulted in significant reduction in both oxidation and carburization.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Long-Lived Triplet Excited State in a Heterogeneous Modified Carbon Nitride Photocatalyst

Heterogeneous carbon nitrides have numerous advantages as photocatalysts, including strong light absorption, tunable band edges, and scalability, but their performance and continued development are limited by fast charge recombination and an under-developed mechanistic understanding of photodriven interfacial electron transfer. These shortcomings are a result of complex photophysics, leading to rate asynchrony between oxidation and reduction, as well as redox processes driven out of electronic trap states rather than excited states. We show that a well-defined triplet excited state in cyanamide-modified carbon nitride is realized with appropriately sized particles. The utility of this long-lived excited state is demonstrated by its ability to drive a hydroamidation photoredox cycle. By the tuning of the particle size of CN x , the oxidation–reduction photochemistry of carbon nitride may be balanced to achieve a redox-neutral closed photocatalytic cycle. Here, these results uncover a triplet excited state chemistry for appropriately sized CNx particles that preludes a rich energy and electron transfer photochemistry for these materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

FCET Solid Oxide Fuel Cell Testing and Development: CRADA 526 [Abstract only]

The purpose of the proposed project is for PNNL to test the performance of prototype solid oxide fuel cells (SOFCs) created by FCET. Such testing will provide FCET with independent performance data that can be communicated to potential clients and/or investors. Additionally, PNNL will collaborate with FCET on design changes to improve fuel cell performance. Intellectual property developed in this way will benefit FCET with improved products to market, and PNNL through royalty revenue. The key technology held by FCET is a process to deposit extremely thin layers of oxide materials, from 10-50 nm in thickness. The range of possible materials that can be deposited with their method is broad, but this project will focus on the yttria-stabilized zirconia (YSZ) electrolytes for SOFCs. Thin, gas tight YSZ membranes have been a long-sought target in SOFC research. The thinner the YSZ, the lower the cell resistance, and the higher performance of the cell (or the lower the operating temperature). 10-50 nm would be a major step change in YSZ thickness from the state of the art. PNNL can team with FCET on future R&D projects and push this technology forward to improve energy efficiency and reduce carbon emissions.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2020

Estimating the cost and energy demand of producing lithium manganese oxide for Li-ion batteries

Lithium Manganese Oxide (LMO) is one of the important cathode active materials used in lithium ion batteries of several electric vehicles. In this paper, the production of LMO cathode material for use in lithium-ion batteries is studied. Spreadsheet-based process models have been set up to estimate and analyze the factors affecting the cost of manufacturing, the energy demand, and the environmental impact. Two processes based on the solid-state synthesis method and a sol-gel method have been explored. Results show that the solid-state process is more cost-effective because of its lower cost of raw materials. The production cost for a solid-state process is $7 kg -1 and requires 6 kWh·kg -1 of energy. The pack level cost of electric vehicle battery using LMO as a primary active material is studied as a function of LMO production cost and other parameters. The potential for reducing the cost of automotive batteries to $100 per kWh is explored in terms of LMO price and plant production volume (economy of scale), using Argonne’s BatPaC spreadsheet tool.

25 ENERGY STORAGE↗
DOE OSTI2020

Enabling Efficiencies > 22.5% with Metal Oxide Passivating Contacts using Low-Cost Spatial Atomic Layer Deposition (Final Technical Report)

In this project, the University of Central Florida (UCF) worked to both increase module efficiency and reduce manufacturing cost by driving demonstrated lab-scale passivating contact technology using materials and processes compatible with high-volume manufacturing for crystalline silicon (c-Si) photovoltaic (PV) cells. Passivating contacts have garnered significant attention in recent years. They provide a means of suppressing contact recombination, a loss mechanism that limits the performance of industrially relevant cell architectures like Al back surface field (Al-BSF) cells and passivated emitter and rear cells (PERC). Most of the development of passivating contact technology has focused on the use of doped amorphous silicon or doped polysilicon contacts, but both suffer from parasitic optical absorption amongst other issues. Our team developed fully transparent hole-selective heterojunctions, deposited using atomic layer deposition (ALD), and showed how they could be incorporated into c-Si PV cells. The team conducted experiments to understand the process-structure-property relationship of hole-selective oxides, surface passivation oxide materials, and transparent conductive oxides deposited by ALD, and use that understanding to reduce contact recombination, contact resistivity, and parasitic optical absorption within c-Si PV cells. Before getting into the details of the report, we would like to note that COVID-19 has made it more challenging to conduct experimental research at UCF. UCF has a number of mandatory policies in place to ensure social distancing, testing, and contact tracing are all carried out in day-to-day operations. Despite these challenges, we worked diligently to make progress on this project in a manner that was as safe as possible. Over the course of the project, the UCF team and its collaborators have made the following discoveries and developments.

14 SOLAR ENERGY↗
DOE OSTI2024

Unraveling the Structure and Composition of Li 4 Mn 2 O 4.5 (Li 2 O·Li 0.667 Mn 1.333 O 2 ) Electrodes for Lithium Batteries Using a High-Temperature Synthesis Approach

This paper addresses the debate about the composition and structure of a lithium-rich manganese oxide electrode with a fully disordered rock salt component, Li 4 Mn 2 O 5 (or Li 2 O·2LiMnO 2 ), first reported by Freire et al. in 2016; it is typically prepared by a high-energy ball milling procedure. It has now been demonstrated that, when prepared at 800°C, the formula of this compound is Li 4 Mn 2 O 4.5 , alternatively Li 2 O·Li 0.667 Mn 1.333 O 2 , or close thereto. The cubic, disordered Li 0.667 Mn 1.333 O 2 (or Li 0.333 Mn 0.667 O) rock salt component, in which the manganese ions adopt an average oxidation state of 2.5+, transforms to a clearly-defined spinel configuration during electrochemical cycling. The electrochemical activation process that occurs during the initial charge reaction includes the oxidation of the manganese ions by oxygen released by the Li 2 O component between 4.5 and 4.6 V. In complete contrast, nickel- and nickel-cobalt-substituted electrodes, such as Li 2 O·2LiMn 0.5 Ni 0.5 O 2 (Li 4 MnNiO 5 ) and Li 2 O·2LiMn 0.475 Ni 0.475 Co 0.050 O 2 (Li 4 Mn 0.95 Ni 0.95 Co 0.10 O 5 ), in which the manganese ions adopt a tetravalent state, have completely disordered rock salt components that are electrochemically inactive.

25 ENERGY STORAGE↗
DOE OSTI2020

DFT and microkinetic comparison of Pt, Pd and Rh-catalyzed ammonia oxidation

Ammonia oxidation is the heart of the Ostwald process and is important in emissions control. Catalytic behaviors are a function of conditions and are observed to vary across the platinum group metals (PGMs) Pt, Pd, Rh. Here, we combine density functional theory computations and microkinetic modeling to rationalize these dependencies. We compute reactions over model (2 1 1) and (1 1 1) surfaces of PGMs. Binding energies are similar on Pd and Pt and generally greater on Rh, while activation energies vary across all metals. Rates on (2 1 1) surfaces are greater than (1 1 1) surfaces. Additionally, the stepped Pt is most active and stepped Rh most selective to N 2 at ammonia slip conditions, while at Ostwald process conditions, stepped Pd is most active and stepped Pt most selective to NO. Degree of rate and selectivity control analysis provides insights into the reactions limiting performance of PGMs. Both activation barriers and surface coverages influence rates and selectivities.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Electrochemical Routes for the Valorization of Biomass-Derived Feedstocks: From Chemistry to Application

The drive to reduce consumption of fossil resources, coupled with expanding capacity for renewable electricity, invites the exploration of new routes to utilize this energy for the sustainable production of fuels, chemicals, and materials. Biomass represents a possible source of platform precursors for such commodities due to its inherent ability to fix CO2 in the form of multi-carbon organic molecules. Electrochemical methods for the valorization of biomass are thus intriguing, but there is a need to objectively evaluate this field and define the opportunity space by identifying pathways suited to electrochemistry. In this contribution we offer a comprehensive, critical review of recent advances in low-temperature (liquid phase), electrochemical reduction and oxidation of biomass-derived intermediates (polyols, furans, carboxylic acids, amino acids, and lignin), with emphasis on identifying the state-of-the-art for each documented reaction. Progress in computational modeling is also reviewed. We further suggest a number of possible reactions that have not yet been explored but which are expected to proceed based on established routes to transform specific functional groups. We conclude with a critical discussion of technological challenges for scale-up, fundamental research needs, process intensification opportunities (e.g., by pairing compatible oxidations and reductions), and new benchmarking standards that will be necessary to accelerate progress toward application in this still-nascent field.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Stability of Mn-Doped TiO 2 Thin-Film Anodes during Water Oxidation Reactions

Incorporating manganese atoms into TiO 2 has been shown to improve its activity for water oxidation. However, its activity has been observed to steadily degrade under constant applied potential, especially at more oxidizing applied potentials. Here, the compositional profile and electrochemical stability of Mn-doped TiO 2 (Mn:TiO 2 ) thin-film electrodes precisely fabricated by atomic layer deposition (ALD) were evaluated to elucidate the mechanisms of electrode degradation. Although ALD enables the deposition of Mn dopants throughout the film thickness, only Mn within 1.5 nm of the surface was observed to be redox active. Annealing Mn:TiO 2 films in air leads to the diffusion of Mn toward the electrode surface and oxidation of the Mn and alters the redox behavior. Annealing endows greater stability to Mn redox behavior but does not fully stabilize the water oxidation current, suggesting that the two electrochemical processes are not precisely correlated. In situ inductively coupled plasma mass spectrometry reveals that Mn is lost from Mn:TiO 2 films at potentials greater than 1.8 V vs RHE. However, the initial Mn loss is equivalent to less than a single ALD layer of MnO x . Longer-term constant potential experiments suggest that Mn is lost from up to 1 nm of the electrode surface but that this loss may account for only a portion of the diminished water oxidation activity.

atomic layer deposition↗
DOE OSTI2022

Activation of Transition Metal (Fe, Co and Ni)-Oxide Nanoclusters by Nitrogen Defects in Carbon Nanotube for Selective CO 2 Reduction Reaction

The electrochemical carbon dioxide reduction reaction (CO2RR), which can produce value-added chemical feedstocks, is a proton-coupled-electron process with sluggish kinetics. Thus, highly efficient, cheap catalysts are urgently required. Transition metal oxides such as CoO x , FeO x , and NiO x are low-cost, low toxicity, and abundant materials for a wide range of electrochemical reactions, but are almost inert for CO 2 RR. Here, we report for the first time that nitrogen doped carbon nanotubes (N-CNT) have a surprising activation effect on the activity and selectivity of transition metal-oxide (MO x where M = Fe, Ni, and Co) nanoclusters for CO 2 RR. MO x supported on N-CNT, MOx/N-CNT, achieves a CO yield of 2.6–2.8 mmol cm -2 min -1 at an overpotential of -0.55V, which is two orders of magnitude higher than MO x supported on acid treated CNTs (MOx/O-CNT) and four times higher than pristine N-CNT. The faraday efficiency for electrochemical CO 2 -to-CO conversion is as high as 90.3% at overpotential of 0.44V. Both in-situ XAS measurements and DFT calculations disclose that MO x nanoclusters can be hydrated in CO 2 saturated KHCO 3 , and the N defects of N-CNT effectively stabilize these metal hydroxyl species under carbon dioxide reduction reaction conditions, which can split the water molecules and provide local protons to inhibit the poisoning of active sites under carbon dioxide reduction reaction conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Incorporation of Oxygen Carrier Recycle into Large-Scale Production of Cu-Based Oxygen Carriers

One of the greatest challenges in the chemical looping combustion (CLC) of solid fuels is developing an oxygen carrier material that is reactive and attrition resistant and can be prepared at a reasonable cost. Recent efforts in oxygen carrier development have followed two primary approaches: (1) using natural ores, such as ilmenite, or (2) developing highly attrition-resistant and reactive synthetic materials. Both approaches have shortcomings, namely, the low reactivity and incompatibility of ores with solid fuel CLC and the high cost and low durability of synthetic materials. Here, a different approach is taken where attrition is assumed inevitable and the recycling of spent oxygen carrier materials is incorporated into oxygen carrier manufacture. For solid fuel CLC, Cu-based oxygen carriers are attrited and are collected with fly ash. Copper oxides are more reactive with nitric acid than most ash materials, meaning that a copper-nitrate-rich leachate can be generated. This copper nitrate stream could then be reused in oxygen carrier synthesis by impregnation. For proof of concept, leaching experiments were conducted to verify that copper oxides are selectively leached from ash-containing spent oxygen carriers. Several cases for process design are proposed based on the composition of spent materials, as the degree of copper oxidation and type of solid fuel dictate leaching residence times and general processing intensity. The four stages proposed here include impurity removal, copper leaching and recovery, solid–liquid separation, and evaporation/concentrating. The resulting process should be able to recover up to 95% of copper while minimizing inclusion of undesirable ash-based impurities.

anions↗