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Results for “Oxide Reduction”

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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Metal-Centered Photoredox Catalysis using d 6 Transition Metal-based Chromophores

Controlling excited-state reactivity in transition metal chromophores is central to light-driven chemistry, with applications spanning from solar energy conversion to photoredox catalysis. Ru(II) and Ir(III) chromophores currently dominate applications within this field due to their long-lived charge-transfer (CT) excited states, which support bimolecular electron transfer chemistry. However, their elemental scarcity and relative lack of selectivity for differentiating oxidative versus reductive pathways has in part motivated the exploration of alternative platforms that could, in principle, offer distinct mechanistic opportunities. Earth-abundant, valence-isoelectronic 3d 6 complexes of Fe(II) and Co(III) have attracted significant attention due to their electronic similarity to Ru(II) and Ir(III), suggesting the potential for complementary photophysical behavior. In contrast to their heavier congeners, however, the weaker ligand fields of first-row transition metals promote rapid relaxation from initially populated CT states to low-lying metal-centered (MC) excited states, typically of 5 T 2 or 3 T 1 character. Because these MC states involve redistribution of electron density within MC d-orbitals rather than charge separation between metal and ligand orbitals, they were historically considered poor candidates for use in photochemical transformations.

Charge transfer↗
DOE OSTI2020

Combined Experimental and Theoretical Investigations of n-Type BiFeO 3 for Use as a Photoanode in a Photoelectrochemical Cell

Combined experimental and theoretical investigations were performed to evaluate the potential of n-type BiFeO 3 as a photoanode. While previous experimental and theoretical studies on BiFeO 3 mainly focused on its ferroelectric properties, several studies have reported the advantages of BiFeO 3 as a photoelectrode for solar water splitting (e.g. bandgap energy and band edge positions relative to water reduction and oxidation potentials). However, the photoelectrochemical properties of n-type BiFeO 3 have not yet been thoroughly investigated. In our experimental investigation, we developed an electrodeposition-based synthesis to prepare uniform n-type BiFeO 3 thin-film electrodes. Furthermore, using a heat treatment under a N 2 environment, we intentionally introduced additional oxygen vacancies into the pristine n-type BiFeO 3 electrodes to increase the majority carrier density. The bandgaps, flatband potentials, photocurrent onset potentials, photocurrent generation, and photoelectrochemical stabilities of the pristine and N 2 -treated BiFeO 3 photoanodes were investigated comparatively to improve our understanding of BiFeO 3 photoanodes and to examine the effect of oxygen vacancies on the photoelectrochemical properties of BiFeO 3 . In our theoretical investigation, we performed first-principles calculations and demonstrated the formation of a small polaron when an extra electron was introduced into the BiFeO 3 lattice. Changes in electronic states cause by the small polaron formation were carefully investigated. We also examined the effects of oxygen vacancies on electron polaron formation and carrier concentration in BiFeO 3 . Using charge formation energy calculations and referencing charge transition levels to the free electron polaron level instead of to the conduction band minimum, we showed that the oxygen vacancy is capable of serving as a donor to enhance the carrier concentration of BiFeO 3 . Furthermore, our theoretical results agree well with our experimental findings. Together, the new experimental and theoretical results and discussion provided in this study have considerably improved our understanding of n-type BiFeO 3 as a photoanode.

25 ENERGY STORAGE↗
DOE OSTI2023

Electronic and Magnetic Properties of Oligomers and Chains of Poly(benzodifurandione) (PBDF), A Highly Conducting n-Type Polymer

The seminal development of highly electrically conducting polyacetylene via oxidative or reductive treatment (“doping”) has continuously inspired the search for other conducting π-conjugated polymers. Recently, poly(benzodifurandione), PBDF, was reported to have unexpected solubility given the absence of side chains and to exhibit an unprecedented, high electrical conductivity upon reduction (“n-doping”), with protons acting as counterions. Here, we theoretically investigate the electronic and magnetic properties of PBDF by taking long oligomers and one-dimensional (1D) periodic chains as model systems. With the oligomer models, we characterize the formation of polarons and bipolarons in n-doped PBDF. Our results indicate that singlet bipolarons tend to be the energetically most favorable species when protons bind to two closely located carbonyl groups in nearest-neighbor benzodifurandione moieties. The calculations on the 1D periodic chain models show that the positions of the protonated carbonyl groups determine the metallic, semiconducting, or insulating nature of a PBDF chain. When the protonated carbonyl groups are all situated on the same side of a PBDF chain, a stable helical chain configuration is found that exhibits ferromagnetic behavior. Our findings elucidate the mechanism of polaron and bipolaron formation in long oligomers of n-doped PBDF and highlight the fascinating electronic and magnetic properties of periodic 1D chains. Furthermore, these studies also provide a stepping stone for investigations of PBDF thin films, for which two- and three-dimensional structures must be considered.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Review on Preprocessing Strategies, Deactivation, Thermal Safety, and Future Perspectives in Lithium-Ion Battery Recycling

The rapid growth in the use of lithium-ion batteries (LIBs) in electric vehicles, consumer electronics, and renewable energy storage has made effective end-of-life management essential. Recycling LIBs is critical not only for resource recovery and environmental protection but also for ensuring safety and economic viability. This review focuses on the preprocessing technologies that precede typical recovery processes, including disassembly, sorting, discharging, electrolyte removal, dismantling, thermal treatment, separation, and flotation. These steps play a foundational role in determining the efficiency, safety, and environmental impact of LIB recycling. LIBs pose substantial fire and explosion risks due to residual charge, flammable electrolytes, and reactive materials. The conditions and successive progression of the exothermic reactions which lead to thermal runaway has been discussed. It also explores secure deactivation techniques such as external circuit discharge, saline immersion, and thermomechanical methods, alongside fire prevention strategies including the use of flame retardants, elimination of oxidants, and reduction of heat generation and accumulation. Challenges and future directions are outlined, highlighting the need for standardized designs, automation, and safer, more sustainable recycling infrastructure. Furthermore, this review is distinguished by its focused analysis of preprocessing and deactivation steps, with particular attention to the thermal safety engineering aspects of LIB recycling.

Battery deactivation↗
DOE OSTI2021

Elucidating the Role of Single-Atom Pd for Electrocatalytic Hydrodechlorination

In this study, we loaded Pd catalysts onto a reduced graphene oxide (rGO) support in an atomically dispersed fashion [i.e., Pd single-atom catalysts (SACs) on rGO or Pd 1 /rGO] via a facile and scalable synthesis based on anchor-site and photoreduction techniques. The as-synthesized Pd 1 /rGO significantly outperformed the Pd nanoparticle (Pdnano) counterparts in the electrocatalytic hydrodechlorination of chlorinated phenols. Downsizing Pd nano to Pd 1 leads to a substantially higher Pd atomic efficiency (14 times that of Pdnano), remarkably reducing the cost for practical applications. The unique single-atom architecture of Pd 1 additionally affects the desorption energy of the intermediate, suppressing the catalyst poisoning by Cl – , which is a prevalent challenge with Pdnano. Characterization and experimental results demonstrate that the superior performance of Pd 1 /rGO originates from (1) enhanced interfacial electron transfer through Pd–O bonds due to the electronic metal–support interaction and (2) increased atomic H (H*) utilization efficiency by inhibiting H 2 evolution on Pd 1 . Furthermore, this work presents an important example of how the unique geometric and electronic structure of SACs can tune their catalytic performance toward beneficial use in environmental remediation applications.

36 MATERIALS SCIENCE↗
DOE OSTI2023

In Situ Attenuated Total Reflectance Infrared Spectroelectrochemistry (ATR-IR-SEC) for the Characterization of Molecular Redox Processes on Surface-Proximal Doped Silicon ATR Crystal Working Electrodes

In situ mid-infrared spectroscopy is a powerful technique for understanding the mechanism of CO 2 reduction (CO 2 R) catalysts because it enables the direct detection of catalytic intermediates and products. Moreover, spectroelectrochemistry (SEC), the coupling of spectroscopy with electrochemistry, allows spectroscopic changes to be correlated with applied potentials to reveal potential-dependent intermediates that are often relevant to photoelectrochemical reactions. Hybrid photoelectrodes, comprised of a narrow bandgap semiconductor, like silicon (Si), with a covalently-linked molecular catalyst, are a promising platform for sunlight-driven catalysis, but characterization of the catalytic mechanism(s) is challenging under photoelectrochemical conditions, particularly when the catalyst is present in monolayer or less concentrations. Here, we have developed a new strategy to use multiple-reflection attenuated total reflectance IR spectroscopy (ATR-IR) coupled with electrochemistry to characterize catalysts directly integrated with a semiconductor surface under applied potential. We show that by surface-proximal n-type or p-type doping of the top ~100-200 nm of the crystal surface, Si ATR crystals can be used simultaneously as the internal reflection element and semiconductor working electrode for ATR-IR-SEC measurements. The surface-proximal doping strategy yields a quasi-equipotential surface with excellent infrared transparency that would have been compromised by free carrier absorption if the crystal was uniformly doped. This approach permits the catalytically-active functionalized surface to be directly probed without modification and overcomes signal-to-noise limitations of other strategies that use separately deposited working electrodes on Si ATR crystals. Proof-of-concept ATR-IR-SEC spectra were collected during the reduction and oxidation of monolayers of Re- and Ru-based transition metal carbonyl complexes, respectively, verifying the viability of the technique to probe redox processes associated with CO 2 R catalysts on Si electrode surfaces with high sensitivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Effect of Ligand Chemistry on the Electronic Properties and Reactivity of Cobalt Acetate Autoxidation Catalysts

Autoxidation chemistry catalyzed by cobalt(II) acetate is an industrial pathway for converting hydrocarbons into oxygenated compounds and has promising potential applications in plastic waste deconstruction. However, the chemical properties of the Co acetate-based catalysts and their roles in the reaction mechanism are poorly understood, and as a result, attempts to redesign the autoxidation chemical process for novel applications lack clear direction. In this work, we investigate the structure and electronic properties of a series of multinuclear Co(III) compounds that have been proposed as active participants in catalytic autoxidation. Through a combination of X-ray spectroscopic measurements [Co K-edge X-ray absorption spectroscopy (XAS), extended X-ray absorption fine structure (EXAFS), Kβ X-ray emission spectroscopy (XES), and high-energy resolution fluorescence detection (HERFD) XAS] and theoretical methods, we characterize the interactions of Co with acetate and hydroxyl ligands in these compounds. Here we show that the substitution of acetate ligands with hydroxyls in these compounds causes an increase in the electron density on Co, driven by the loss of a π back-bonding interaction between Co and acetate and an increase in electron donation to Co from the hydroxyl ligands. We further classify the bonding between Co and acetate based on the orbital overlap and show that the experimental absorption and emission spectra are well-described by the resulting molecular orbitals. Finally, we predict the impacts of acetate/hydroxyl ligand exchange on autoxidation catalytic properties, showing that the reaction free energies for key Co oxidation and reduction steps are extremely sensitive to metal-ligand bonding interactions and thus have meaningful impacts on overall reactivity. The results of this study constitute an important set of design criteria for developing novel homogeneous autoxidation catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Untapped Potential of Fluoride Ions in Maximizing the Electrochemical Stability of Deep Eutectic Solvents

Advancing the batteries is pivotal to propelling our society toward a sustainable, electrified future. The stability of electrolytes forms the backbone of energy storage systems. This is particularly the case for redox flow batteries (RFBs). Their deployability depends on their longevity and dependability. The presence of unstable electrolytes can trigger undesirable reactions, degrade performance, and lead to battery failure. Aqueous electrolytes, with limited electrochemical stability window (ESW), are prone to hydrogen and oxygen evolution. Conversely, non-aqueous electrolytes offer enhanced stability. In this study, we unveil the ESW of a non-aqueous eutectic solvent, comprising choline fluoride and ethylene glycol—a composition that has eluded experimental investigation until now. Our findings show that the stability window, reduction and oxidation potential limits of deep eutectic solvents, are sensitive to variations in the halide component of the ammonium salt. Furthermore, this work not only highlights the benefits of novel deep eutectic solvents but also sets the stage for their strategic use in future battery electrolytes.

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

Understanding Electrochemical Sulfur-Based Phase Evolution via Complementary Insight from Operando Spatially Resolved X-ray Diffraction and X-ray Absorption Spectroscopy

Lithium/sulfur batteries are emerging as promising candidates for use in large-scale energy storage, but practical challenges, including insufficient power density and polysulfide shuttling, remain. Here, this work presents the first use of operando energy dispersive X-ray diffraction (EDXRD) to monitor Li/S electrochemistry within a liquid electrolyte. Complementary operando synchrotron-based EDXRD, X-ray absorption spectroscopy (XAS), X-ray powder diffraction (XPD), and ex situ laboratory Raman analysis provide evidence for α-S 8 conversion upon discharge into Li 2 S x polysulfide phases and conversion into β-S 8 during charge. Understanding the underlying mechanisms of sulfur reduction and oxidation within thick electrodes will enable advances in next-generation Li/S batteries and material design.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Bulk vs Intrinsic Activity of NiFeO x Electrocatalysts in the Oxygen Evolution Reaction: The Influence of Catalyst Loading, Morphology, and Support Material

We used a combination of ultrahigh vacuum surface science techniques, X-ray spectroscopy, electrochemistry, and density functional theory (DFT), to characterize the influence of catalyst morphology, loading/coverage, and substrate material on the bulk (all atoms) and intrinsic (electrochemically accessible atoms) activity of NiFeO x electrocatalysts in the oxygen evolution reaction (OER). NiFeO x catalysts were grown on both Au(111) and highly oriented pyrolytic graphite (HOPG) electrodes. DFT predicted Fe edge-site atoms at the NiFeO x /Au(111) interface to be the most thermodynamically favorable reaction center, and X-ray absorption spectroscopy data indicated small NiFeO x catalyst particles on Au(111) contained a high population of OER active Fe edge-site atoms. However, restructuring of the Au(111) surface due to repeated oxidation and reduction cycles of the OER CV measurements encapsulated small NiFeO x nanoparticles at catalyst loadings below ~1.5 nmol metal /cm 2 , passivated catalyst edges and reduced bulk OER activity of Au-supported NiFeO x compared with HOPG-supported ones. Analysis of intrinsic activity revealed that the Au(111) support strongly benefited electrochemically accessible NiFeO x atoms, and we observed a 2–3 fold activity enhancement compared with HOPG-supported catalysts for loadings above ~1 nmol metal /cm 2 . Overall, evaluating bulk vs intrinsic activity and identifying loading/coverage-dependent support effects is important for accurately probing fundamental interfacial chemistry, choosing suitable catalyst loadings and supports, and optimizing system parameters to maximize the performance of electrocatalyst systems.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Advances in Polymerizations Modulated by External Stimuli

Synthetic polymer chemistry endeavors to imitate the spatial and temporal control exhibited within biological systems to obtain well-defined polymeric materials with unique structures, properties, and applications. This is often approached through the development of dynamic catalyst (or initiator) systems that use external stimuli to elicit discrete, site specific transformations that impact the polymerization. In this work, we highlight developments in polymerizations that are modulated by external stimuli, with particular focus on those systems that enable notable changes in kinetics, monomer selectivity, polymer architecture, or tacticity. Examples of external stimuli include chemical oxidants or reductants, light, applied voltage, and mechanical force.

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

Shining a Light on Some Fundamental Research Opportunities in Semiconductor Photoelectrochemistry

Decades of research in semiconductor photoelectrochemistry have yielded a deep understanding of charge transfer, energetics, and stability at solid−liquid interfaces. Theoretical frameworks developed by Gerischer and contemporaries, together with extensive experimental validation, have clarified the key principles affecting the interfacial kinetics and energetics of semiconductor photoelectrodes. Nevertheless, significant opportunities remain for advances in fundamental understanding of semiconductor photoelectrochemistry. Exciting opportunities include exploiting advances in theory, synthesis, and instrumentation to determine the chemical identity and reactivity of surface states; exerting control of band-edge energetics through molecular-level surface modification processes; and systematically improving emerging photoelectrode protection strategies to enable long-term photoelectrode operation under both oxidative and reductive conditions. Advanced morphologies, such as nanowire and microwire arrays, present new pathways to combine efficient light absorption with effective charge collection and catalyst integration. Unique light−matter interactions during photoelectrochemical deposition of p-type semiconductors readily allow preparation at scale of complex 3D morphologies that are difficult, if not impossible, to access by other methods. Continued exploration of these avenues will expand the fundamental understanding of semiconductor−liquid interfaces and could additionally advance the realization of efficient, stable, and scalable systems for solar fuel generation and other emerging photoelectrochemical applications.

Bean, Paul J. L. [California Institute of Technolo↗
DOE OSTI2020

Reversible Oxidation Quantified by Optical Properties in Epitaxial Fe2CrO4+d Films on (001) MgAl2O4

We report on the structural and optical properties of Fe2CrO4+d epitaxial films grown by molecular beam epitaxy on MgAl2O4 (001) as a function of ?. The average Fe valence can be correlated with the out-of-plane lattice parameter and the extent of light absorption in the infrared spectral region. Over-oxidized films (0 < d < 0.5) exhibit reduced lattice parameters and suppressed infrared absorption. We discuss the behavior of a novel infrared transition at ~0.6 eV in stoichiometric Fe2CrO4 films deposited on MgAl2O4 (MAO) at or above 400 °C. This research provides new insight into the atomic structure, optical processes, oxidation states, electronic structure, and application potentials of Fe2CrO4+d.

ellipsometry, Epitaxy, thin film, oxidation, reduc↗
DOE OSTI2020

Realizing Metal-Free Carbene-Catalyzed Carbonylation Reactions with CO

Many organic and main group compounds, usually acids or bases, can accelerate chemical reactions when used in substoichiometric quantities, a process known as organocatalysis. In marked contrast, very few of these compounds are able to activate carbon monoxide and, until now, none of them catalyze its chemical transformation, a classical task for transition metals. In this work, we report that a stable singlet ambiphilic carbene activates CO and catalytically promotes the carbonylation of an ortho -quinone into a cyclic carbonate. These findings pave the way for the discovery of metal-free catalyzed carbonylation reactions.

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

A Donor–Acceptor [2]Catenane for Visible Light Photocatalysis

Colored charge-transfer complexes can be formed by the association between electron-rich donor and electron-deficient acceptor molecules, bringing about the narrowing of HOMO–LUMO energy gaps so that they become capable of harnessing visible light. In an effort to facilitate the use of these widespread, but nonetheless weak, interactions for visible light photocatalysis, it is important to render the interactions strong and robust. Furthermore, we employ a well-known donor–acceptor [2]catenane—formed by the mechanical interlocking of cyclobis(paraquat-p-phenylene) and 1,5-dinaphtho[38]crown-10—in which the charge-transfer interactions between two 4,4'-bipyridinium and two 1,5-dioxynaphthalene units are enhanced by mechanical bonding, leading to increased absorption of visible light, even at low concentrations in solution. As a result, since this [2]catenane can generate persistent bipyridinium radical cations under continuous visible-light irradiation without the need for additional photosensitizers, it can display good catalytic activity in both photo-reductions and -oxidations, as demonstrated by hydrogen production—in the presence of platinum nanoparticles—and aerobic oxidation of organic sulfides, such as l-methionine, respectively. This research, which highlights the usefulness of nanoconfinement present in mechanically interlocked molecules for the reinforcement of weak interactions, can not only expand the potential of charge-transfer interactions in solar energy conversion and synthetic photocatalysis but also open up new possibilities for the development of active artificial molecular shuttles, switches, and machines.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗