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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Solvent-free synthesis of Co single atom and nanocluster decorated N-doped carbon for efficient oxygen reduction

The advancement of efficient, cheap, and durable catalysts for oxygen reduction reaction (ORR) to substitute Pt/C in metal-air batteries is of paramount importance. However, traditional solvent-based methods fall short in terms of environmental benign and scalability. Herein, a solvent-free organic-inorganic self-assembly approach is explored to construct cobalt single atom and cobalt nanocluster decorated nitrogen-doped porous carbon spheres (Co-SA/NC@NCS). The solvent-free synthesis demonstrates an impressively high yield (282 g/L) and the resultant Co-SA/NC@NCS possesses a high N content (6.9 wt%). Density functional theory calculations disclose that the Co-SAs and Co-NCs are able to optimize the surface oxygen adsorption capability and enhance the conductivity of the NCS, thereby facilitating the ORR performance. Here, the solvent-free synthesis is also feasible for the synthesis of other non-noble metal element (Fe, Ni, and Zn) decorated nitrogen-doped porous carbon spheres.

Nitrogen-doped carbon↗
DOE OSTI2025

Fermi Level Equilibration and Charge Transfer at the Exsolved Metal-Oxide Interface

Exsolution is a promising approach for fabricating oxide-supported metal nanocatalysts through redox-driven metal precipitation. A defining feature of exsolved nanocatalysts is their anchored metal-oxide interface, which exhibits exceptional structural stability in (electro)catalysis. However, the electronic interactions at this unique interface remain unclear, despite their known impact on catalytic performance. In this study, we confirm charge transfer between the host oxide and the exsolved metal by demonstrating a two-stage Fermi level ( E F ) evolution on SrTi 0.65 Fe 0.35 O 3−δ (STF) during metallic iron (Fe 0 ) exsolution. Combining ambient pressure X-ray photoelectron spectroscopy with theoretical analysis, we show that E F initially rises due to electron doping from oxygen vacancy formation in STF. Subsequently, upon Fe 0 precipitation, E F stabilizes and becomes insensitive to further oxygen release in STF, driven by E F equilibration and charge transfer between STF and the exsolved Fe 0 . In conclusion, these findings highlight the importance of considering electronic metal–support interactions when optimizing exsolved nanocatalysts.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Identification of In Situ Generated High-Spin Fe(II)-N 4 Active Sites for Acidic Oxygen Reduction Reaction via Operando 57 Fe Mössbauer Spectroscopy

Iron-nitrogen-carbon (FeNC) catalysts are considered among the most promising alternative to Pt catalysts in acidic oxygen reduction reaction (ORR), yet the geometric and electronic structures of the true active site under reaction conditions have not been clearly elucidated. Herein, we synthesized a representative FeNC catalyst by pyrolyzing Fe 3+ absorbed on ZIF-8-derived N-doped carbon at a mild temperature under the H 2 /Ar atmosphere, where a formation mechanism of FeN 4 sites through a Zn-mediated Fe nanoparticle atomization process was proposed. The resulting FeNC-750 catalyst shows high acidic ORR activity with a half-wave potential of 0.838 V and a peak power density of 1 W cm -2 in proton-exchange membrane fuel cell (PEMFC). By using operando 57 Fe Mössbauer spectroscopy on FeNC-750, it was revealed that the pyrrolic N-coordinated high-spin Fe 2+ N 4 sites, which are in situ generated from high-spin Fe 3+ N 4 during ORR, are identified as catalytic active states. Density functional theory calculations further verified that, compared to the pyridinic N-coordinated low-spin Fe 2+ N 4 , the pyrrolic N-coordinated high-spin Fe 2+ exhibits optimized adsorption energy for reaction intermediates, thereby lowering the energy barrier of the rate-determining step (RDS) and facilitating OH* desorption. In conclusion, this work provides both experimental and theoretical evidence of the true active site in the FeNC during acidic ORR, offering significant insights for the rational design of high-performance materials for acidic fuel cells.

FeNC catalyst↗
DOE OSTI2024

Understanding vortex dynamics in CaK(Fe,Ni) 4 As 4 and Ba(Fe,Co) 2 As 2 single crystals under the influence of random point disorder

We report on the influence of doping on vortex dynamics in 3 MeV proton-irradiated single crystals of CaK(Fe 1–x Ni x ) 4 As 4 (1144, x = 0.015, 0.025, and 0.03) and Ba(Fe 1–x Co x ) 2 As 2 (x = 0.04, 0.062, 0.066 and 0.074). Non-irradiated crystals of the 1144 system display superconducting critical temperatures ranging from 31 K for x = 0.015–20.5 K, as doping increases to 0.03. On the other hand, pristine crystals of the 122 system show T c values between 14.6 and 23.6 K, with the maximum T c occurring at intermediate doping levels. The fluence was set at 3 × 10 16 p cm –2 , resulting in a decrease in the T c by around 1.5 K for all samples and significantly affecting the vortex dynamics by reducing the flux creep relaxation compared to previously reported values for unirradiated crystals. Parameters such as vortex pinning energy U 0 and the glassy exponent μ dependencies on doping and magnetic field strength are identified. For the 1144 system, U 0 reaches values approaching 500 K for small fields in samples with T c = 29.3 K (x = 0.015), systematically decreasing to around 200 K as T c falls below 20 K. Furthermore, U 0 decreases as the field increases to 3 T for the same sample, varying from approximately 250 K to 100 K as T c decreases. These changes are typically accompanied by modifications in μ, gradually increasing from values around 1 towards 1.5, corresponding to small bundle relaxation in the collective creep theory. Despite differences in the substitutional disorder and magnetic phase diagram with respect to the 1144 system, the results for 122 single crystals follow a similar tendency in which U 0 usually reduces and μ increase rise as the applied magnetic field is increased. Due to moderate U 0 in these systems (few hundreds of kelvins), the resulting decay of persistent current at liquid helium temperatures is primarily determined by a balance between U 0 and bundle size contribution. Furthermore, these findings provide valuable insights for potential applications of these systems, particularly in the context of intrinsic superconducting parameters and the resulting pinning landscape.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Heterogeneous Fe-N-C Catalyst for Aerobic Dehydrogenation of Hydrazones to Diazo Compounds Used for Carbene Transfer

Organic diazo compounds are versatile reagents in chemical synthesis and would benefit from improved synthetic accessibility, especially for larger scale applications. Here, we report a mild method for the synthesis of diazo compounds from hydrazones using a heterogeneous Fe-N-C catalyst, which has Fe ions dispersed within a graphitic nitrogen-doped carbon support. The reactions proceed readily at room temperature using O 2 (1 atm) as the oxidant. Aryl diazoesters, ketones, and amides are accessible, in addition to less stable diaryl diazo compounds. Initial-rate data show that the Fe-N-C catalyst achieves faster rates than a heterogeneous Pt/C catalyst. The oxidative dehydrogenation of hydrazones may be performed in tandem with Rh-catalyzed enantioselective C–H insertion and cyclopropanation of alkenes, without requiring isolation of the diazo intermediate. Furthermore, this sequence is showcased by using a flow reactor for continuous synthesis of diazo compounds.

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

Ion-Selective Scattering Studied Using the Variable-Energy Electron Irradiation in the Ba 0.2 K 0.8 Fe 2 As 2 Superconductor

Low-temperature variable-energy electron irradiation was used to induce non-magnetic disorder in a single crystal of a hole-doped iron-based superconductor, Ba $1-x$ K $x$ Fe 2 As 2 , $x$ = 0.80. To avoid systematic errors, the beam energy was adjusted non-consequently for five values between 1.0 and 2.5 MeV when sample resistance was measured in situ at 22 K. For all energies, the resistivity raises linearly with the irradiation fluence suggesting the creation of uncorrelated dilute point-like disorder (confirmed by simulations). The rate of the resistivity increase peaks at energies below 1.5 MeV. Comparison with calculated partial cross-sections points to the predominant creation of defects in the iron sublattice. Simultaneously, superconducting $T_c$, measured separately between the irradiation runs, is monotonically suppressed as expected, since it depends on the total scattering rate, hence on the total cross-section, which is a monotonically increasing function of the energy. Our work experimentally confirms an often-made assumption of the dominant role of the iron sub-lattice in iron-based superconductors.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Transition metal elements as donor dopants in CdO

CdO has been shown to achieve a high electron concentration N (> 10 21 cm -3 ) and at the same time a high mobility μ (> 100cm 2 /V s) when doped with conventional shallow dopants (In or Ga), and consequently making it a transparent conducting oxide with very low resistivity ρ <10 -4 $\Omega$ cm. In this work, the properties of CdO thin films doped with a series of transition metal elements (CdO:TM) with partially filled 3d and 4d shells, including Sc, Ti, V, Cr, Fe, Y, Mo, and W, were investigated. We find that doping with these TM elements can effectively increase the N in CdO to a maximum N (N max ) of ~(7-12)×10 20 cm -3 with a dopant concentration x max of 4-7 %. However, unlike CdO:In, the μ of CdO:TM films drops rapidly from > 100 to < 10cm 2 /Vs as the dopant concentration x increases, so that they can only achieve a minimum ρ of ~ (1-2) × 10 -4 $\Omega$ cm, ~ a factor of 2-3 higher than that in CdO:In. As a result, free-carrier absorption and plasma reflection effects limit their optical transparency to <1200 nm. For most 3d TM dopants, a qualitatively higher d-donor level E d,donor gives rise to higher E F,max or a higher N max . Although at low x, the optical band gap E opt of CdO:TM follows the calculated values due to free-carrier effects, as x increases, E opt values are significantly higher than the calculated values. This is believed to be an effect of the anticrossing interaction of the localized d-levels and the extended CdO conduction-band (CB) states, giving rise to a lower occupied E - and an upper unoccupied E + subband. In conclusion, the restructured CBs have much flatter dispersion, which also results in a much higher effective mass $m^{\star}_{e}$, hence it can also explain the much lower μ of CdO:TM films with high N.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Resilience of the Aurivillius structure upon La and Cr doping in a Bi 5 Ti 3 FeO 15 multiferroic

Here, combining the experimental techniques of high-resolution X-ray diffraction, magnetometry, specific heat measurement, and X-ray photoelectron, Raman and dielectric spectroscopy techniques, we have studied the influence of La and Cr doping on the crystal structure and magnetism of the room temperature Aurivillius multiferroic Bi 5 Ti 3 FeO 15 by investigating the physical properties of (Bi 4 La)Ti 3 FeO 15 and Bi 5 Ti 3 (Fe 0.5 Cr 0.5 )O 15 . The parent (Bi 5 Ti 3 FeO 15 ) and the doped ((Bi 4 La)Ti 3 FeO 15 and Bi 5 Ti 3 (Fe 0.5 Cr 0.5 )O 15 ) compounds crystallize in the A2 1 am space group, which is confirmed through our analysis of high-resolution synchrotron X-ray diffraction data obtained on phase-pure polycrystalline powders. We determined the oxidation states of the metal atoms in the studied compounds as Fe 3+ , Ti 4+ , Cr 3+ , and La 3+ through the analysis of X-ray photoelectron spectroscopy data. The magnetic susceptibilities of the three compounds are marked by the absence of a long-range ordered ground state, but dominated by superparamagnetic clusters with dominant antiferromagnetic interactions. This signature of short-range magnetism is also seen in specific heat as a low temperature enhancement which is suppressed upon the application of external magnetic fields up to 8 T. Our dielectric spectroscopy experiments showed that the three studied compounds display similar features in the dielectric constant measured as a function of frequency. However, upon doping La at the Bi site, the width of the ferroelectric hysteresis loop increases for (Bi 4 La)Ti 3 FeO 15 compared to that of the parent compound Bi 5 Ti 3 FeO 15 , and with Cr doping, Bi 5 Ti 3 (Fe 0.5 Cr 0.5 )O 15 becomes a leaky dielectric. The resilience of the Aurivillius crystal structure towards doping of La at the Bi site and Cr at the Fe site is clearly seen in the bulk properties of magnetic susceptibility, specific heat and the average crystal structure. The relevance of changes in the local structure is evident from our Raman spectroscopy and X-ray pair distribution function studies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Single‐Atom Electrocatalysts from Multivariate Metal–Organic Frameworks for Highly Selective Reduction of CO 2 at Low Pressures

Abstract Single‐atom catalysts (SACs) are of great interest because of their ultrahigh activity and selectivity. However, it is difficult to construct model SACs according to a general synthetic method, and therefore, discerning differences in activity of diverse single‐atom catalysts is not straightforward. Herein, a general strategy for synthesis of single‐atom metals implanted in N‐doped carbon (M 1 ‐N‐C; M=Fe, Co, Ni and Cu) has been developed starting from multivariate metal–organic frameworks (MOFs). The M 1 ‐N‐C catalysts, featuring identical chemical environments and supports, provided an ideal platform for differentiating the activity of single‐atom metal species. When employed in electrocatalytic CO 2 reduction, Ni 1 ‐N‐C exhibited a very high CO Faradaic efficiency (FE) up to 96.8 % that far surpassed Fe 1 ‐, Co 1 ‐ and Cu 1 ‐N‐C. Remarkably, the best‐performer, Ni 1 ‐N‐C, even demonstrated excellent CO FE at low CO 2 pressures, thereby representing a promising opportunity for the direct use of dilute CO 2 feedstock.

Jiao, Long↗
DOE OSTI2024

Revealing Structural Evolution of Single Atom Catalysts during Electrochemical CO 2 Reduction by in Situ X-ray Absorption Spectroscopy

Investigating the structural variation of single-atom catalysts (SACs) is crucial to reveal the reaction mechanism under working conditions. Different in situ techniques, especially X-ray absorption spectroscopy (XAS), have been reported to study the structural changes in active sites. However, a systematic study of the relationship between the coordination environment and the catalytic ability of different kinds of SACs is still lacking. Herein, we established isolated transition metal atoms (Fe, Co, Ni, Cu) on N-doped carbon (M-N-C) and employed them in electrocatalytic CO 2 reduction reaction (CO 2 RR). Significantly, Ni-N-C exhibits the highest selectivity (similar to 97.9%) toward CO at -0.8 V vs RHE. In situ XAS characterization discloses the coordination number dependent catalytic performance. Further, the decreased average coordination number of Ni in Ni-N-C at the voltage point with maximum Faradaic efficiency was observed. Density functional theory further provides the possible mechanism of CO 2 -to-CO over the undercoordinated Ni-N-C structure.

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

Magnetostrictive materials for enhanced sensors and electronic components

Magnetostriction is a property of magnetic materials that causes them to change their shape or dimensions when their magnetization changes. Low-cost, mechanically robust magnetostrictive sensors would be valuable for a wide range of applications addressing DOE's energy, environmental, and national security missions. Several examples include monitoring internal conditions of pipelines, enhancing implantable systems for the human body, and improving the electrical grid by providing real time sensors for detecting high impedance faults that may act as ignition sources for forest fires. Historically, magnetostrictive materials tended to be expensive and mechanically brittle, but recent developments in iron-based alloys, especially those that include dilute solutions of rare earth elements, have demonstrated useful magnetostriction values, mechanical robustness, and low costs. This project investigated addition of dilute cerium doping on the magnetostrictive properties of Fe-Ga and Fe-Al alloys. Advanced manufacturing techniques were applied to these materials to take advantage of rapid cooling of the alloy to stabilize desired phases and to make near net shape coupons. These coupons develop significant texturing, offering a route to target microstructures with exceptional performance.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Probing putative orbital differentiation effects via Eu 2+ spin dynamics in Sr 1-x Eu x Fe 2 As 2

Here, in this work, we report x-ray powder diffraction, elemental analysis, electrical resistivity, magnetic susceptibility, specific heat, and electron spin resonance (ESR) in single crystals of Sr 1-x Eu x Fe 2 As 2 . We observed a breakdown of the previously reported scaling between the Eu 2+ Korringa relaxation rate obtained from ESR and the spin density wave temperature evolution for Sr-rich samples. This result suggests a distinct evolution of the orbital differentiation of the Fe 3d bands along the Sr-based series when compared to the Ba counterpart. We argue that this difference is related to a larger splitting between the structural (tetragonal-to-orthorhombic) and the Fe-driven spin density wave transitions induced by Eu doping in this series. In fact, our results indicate that the two transitions follow an opposite x-Eu dependence for Sr-concentrated samples. Our work shows that Sr 1-x Eu x Fe 2 As 2 series and the comparison with their Ba-based counterparts are exciting platforms to be explored for understanding the interplay among orbital differentiation, magnetism, and structural distortions in the iron pnictides

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

22 K superconductivity in Ba Fe 2 As 2 exposed to F 2

Several previous reports on undoped AEFe 2 As 2 (AE = alkaline earth metal) point to drops in resistivity indicative of possible superconductivity and some degree of Meissner effect in the magnetic susceptibility. Also, based on both resistivity and magnetic susceptibility measurements, controlled exposure to water vapor has been shown to induce superconductivity in AEFe 2 As 2 . In our study, BaFe 2 As 2 single crystals grown using the self-flux method showed a full resistive drop around 22 K and magnetic shielding, when exposed to fluorine gas postgrowth. Our measurements indicate electron (donor) doping via atomic substitution of F for As is concurrent with the observed superconductivity, which sheds light on the likely effect of exposure to water vapor in previous work. Like doping experiments (such as substitution of Co for Fe, P for As, or K for Ba) in AEFe 2 As 2 to date, the present work is consistent with suppression of the spin density wave transition coincident with the appearance of T c . In addition to answering the puzzle of superconductivity in undoped or water vapor exposed AEF 2 As 2 , our results also represent a fast (20 min exposure to 5% F in He) and reliable method suitable for inducing superconductivity in thin films of AEFe 2 As 2 . As a result, some supportive work on BaFe 2 As 2 exposed to Cl 2 is also presented.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Metal ion dopant-induced famatinite to chalcostibite phase transformation of copper antimony sulphide colloidal nanostructures: effect on photophysical and pseudocapacitance properties

Here, the strategic doping of transition metal ions into copper antimony sulphide (CAS) semiconducting nanostructures can significantly influence their photophysical and pseudocapacitive properties, for which there are few reports and therefore is the focus of this study. Accordingly, highly crystalline metal ion (Mn 2+ , Fe 2+ , Co 2+ , Ni 2+ and Zn 2+ ) doped off-stoichiometric copper rich/poor, antimony-rich/poor, and sulphur-poor CAS nanostructures (10–23 nm) were grown via colloidal (hot-injection) synthesis using metal diethyldithiocarbamate precursors. Importantly, metal ion doping significantly influences the structure and composition of the off-stoichiometric CAS nanostructures. Data from powder X-ray diffraction, Raman spectroscopy, high-resolution scanning/transmission electron microscopy, and energy dispersive X-ray spectroscopy confirm that the heavier metal ion dopants induce a novel phase transformation from famatinite (fCAS) to chalcostibite (cCAS) nanostructures. The influence of the metal ion dopants is also observed in the optical properties of as-synthesized nanostructures. This involves blue-shifted ultraviolet-visible absorption, reduced Urbach tailing, and tunable bandgaps between 2.17 and 2.38 eV. Also, the doped nanostructures display broad visible-near infrared photoluminescence via a triple radiative pathway with relatively short decay lifetimes between 0.2 and 6.1 ns. This is mediated by electronic transitions involving intrinsic (copper/antimony/sulphur interstitial) and extrinsic (metal ion interstitial) defect states. Additionally, electrodes prepared from Mn 2+ -doped fCAS nanostructures show enhanced pseudocapacitance via Na+ surface adsorption and intercalation relative to undoped fCAS electrodes, while Zn 2+ -doped cCAS electrodes exhibit pseudocapacitance via a combination of Na+ surface adsorption, intercalation, and redox reactions. These electrodes exhibit reduced charge transfer resistance, improved electronic conductivity and notably enhanced specific capacitance (∼222 F g −1 ), and charge transport, as measured in 1 M Na 2 SO 4 electrolyte via cyclic voltammetry and electrochemical impedance spectroscopy. To this end, the discovery of the metal ion-induced phase transformation presents a new avenue for optimizing the functional properties of fCAS and cCAS nanostructures, highlighting the critical role of metal ion-related defects in controlling the optical and electrochemical properties, towards potential solar absorption and energy storage applications.

25 ENERGY STORAGE↗
DOE OSTI2023

Antiferromagnetic order and its interplay with superconductivity in CaK(Fe$_{1-x}$Mn$_x$) 4 As 4

The magnetic order for several compositions of CaK(Fe$_{1-x}$Mn$_x$) 4 As 4 has been studied by nuclear magnetic resonance (NMR), Mössbauer spectroscopy, and neutron diffraction. Our observations for the Mn-doped 1144 compound are consistent with the hedgehog spin vortex crystal (hSVC) order which has previously been found for Ni-doped CaKFe 4 As 4 . The hSVC state is characterized by the stripe-type propagation vectors $(\pi\,0)$ and $(0\,\pi)$ just as in the doped 122 compounds. The hSVC state preserves tetragonal symmetry at the Fe site, and only this SVC motif with simple antiferromagnetic (AFM) stacking along $\ c$ is consistent with all our observations using NMR Mössbauer spectroscopy, and neutron diffraction. We find that the hSVC state in the Mn-doped 1144 compound coexists with superconductivity (SC), and by combining the neutron scattering and Mössbauer spectroscopy data we can infer a quantum phase transition, hidden under the superconducting dome, associated with the suppression of the AFM transition temperature ($T_N$) to zero for $x$ ≈ 0.01. In addition, unlike several 122 compounds and Ni-doped 1144, the ordered magnetic moment is not observed to decrease at temperatures below the superconducting transition temperature ($T_c$).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Investigating Cu-Site Doped Cu–Sb–S Nanoparticles Using Photoelectron and Electron Paramagnetic Resonance Spectroscopy

Tetrahedrite (Cu 12 Sb 4 S 13 ) and famatinite (Cu 3 SbS 4 ) are good candidates for green energy applications because they possess promising thermoelectric and photovoltaic properties as well as contain earth-abundant and nontoxic constituents. Herein, X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and electron paramagnetic resonance spectroscopy (EPR) methods examined inherent electronic properties and interatomic magnetic interactions of Cu-site doped tetrahedrite and famatinite nanomaterials. An energy-efficient modified polyol method was utilized for the synthesis of tetrahedrite and famatinite nanoparticles doped on the Cu-site with Zn, Fe, Ni, Mn, and Co. This is the first parallel study of tetrahedrite and famatinite nanomaterials with XPS, UPS, and EPR methods alongside a systematic analysis of dopant-dependent effects on the electronic structure and magnetic interactions for each material. XPS showed that the Cu and Sb species in tetrahedrite and famatinite possess different oxidation states, while UPS characterization reveals larger dopant-dependent shifts in the work function for tetrahedrite nanoparticles (4.21 to 4.79 eV) than for famatinite nanoparticles (4.57 to 4.77 eV). Finally, all famatinite nanoparticles display an EPR signal, indicating trace amounts of paramagnetic Cu(II) present below the detection limit of XPS. For tetrahedrite, EPR signatures were observed only for the Zn-doped and Mn-doped nanoparticles, suggesting signal broadening from Cu–Cu spin exchange or spin–lattice relaxation. This study demonstrates the complementary nature of XPS and EPR techniques for studying the oxidation states of metals in solid-state nanomaterials. Comparing the electronic and magnetic properties of tetrahedrite and famatinite while studying the impact of dopant incorporation will guide future endeavors in designing sustainable, high-performance materials for renewable energy applications.

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

Developing a Fundamental Knowledge Base for the Interaction of Ruthenium with Natural and Engineered Iron-Bearing Materials

The intent of this project is to build a fundamental knowledge base concerning the redox coupling between Ru and Fe in heterogeneous systems with predictive applications towards the fate, speciation, and transport of Ru in the environment and its capture using available technologies. RuNOCl 3 and Fe 3+ are redox active over a broad range of pH. Initial assessment of effect of redox coupling between Ru and Fe indicates that Fe(III) in ferrihydrite can oxidize Ru 2+ in RuNOCl3 to Ru(IV) during coprecipitation at ambient conditions and alkaline pH. Further, evidence suggests that Ru(IV) is incorporated in the structure of fh. Likewise, Fe 3+ (aq) also reduces Ru 2+ in RuNOCl 3 in the homogenous system at acidic pH although the kinetics of reaction appear to be slow. Rufh annealed to 500 0C transforms to Ru(III) doped hematite. AIMD informed EXAFS indicates that Ru substitutes for Fe(III) in regular octahedral sites of hematite but requires three distinct configurations involving edge-sharing protonated Fe vacancies and straight substitution with no local defects. Fe 2+ (aq) appears to oxidize at the surface of RuO 2 , but the amount is too low to reasonably expect detectable reduced Ru. Future experiments at higher pH are warranted to make Fe 2+ (aq) less stable (i.e., make more redox active). We also demonstrated that we can functionalize Si aerogels with Fe(II) and Fe(III) but likely need to go to higher T to make Feo nanoparticles.

36 MATERIALS SCIENCE↗