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Results for “heterogeneous doping”

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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Subsurface spectroscopy of heterogeneous materials using optical wavefront shaping

Plastic-bonded explosives and propellants consist of energetic molecular crystals embedded in a polymer matrix that also includes additives, such as taggants, plasticizers, grit, antioxidants, etc. Furthermore, this heterogeneous composition renders these materials optically opaque, limiting optical characterization techniques (e.g., Raman spectroscopy) to probing chemical reactions at the sur-face. However, many reactions of interest are believed to occur inside the material where current optical techniques can not probe. To address this challenge, we have developed a new optical technique that utilizes feedback assisted wavefront shaping (using spatial light modulators) to focus probe light inside a heterogeneous material, such that we can perform subsurface spectroscopy. Recently, we demonstrated this technique by monitoring subsurface photodegradation and thermal degradation of Eu-doped molecular crystals using both fluorescence and Raman spectroscopy. Based off these successes we are now looking into improvements to this technique to allow for greater time resolution, including replacing our spatial light modulators with fast digital mirror devices, using ns optical phase conjugation, and self-healing optical beams.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Mechanically robust high magnetic-performance Sm-Co sintered magnets through microstructure engineering

Samarium-cobalt (Sm-Co) sintered magnets have high magnetic energy densities, great resistance to demagnetization and corrosion, and excellent thermal stability in a wide temperature range (–50–550 °C). However, the utilization of these magnets is restricted by their brittleness. Based on micromechanical and the Zener pinning model, Sm-Co sintered magnets with improved mechanical properties have been designed and fabricated via microstructure engineering. A small amount of fine Sm 2 O 3 particulates (0–3 wt%) has been incorporated into Sm 2 (CoFeCuZr) 17 sintered magnets to refine the grain size by up to approximately 50% (from 45 to 22 µm) and narrow the grain size distribution. Doping with 3 wt% Sm 2 O 3 increased the flexural strength by 62% while maintaining magnetic performance. Both grain-refined unimodal microstructure and heterogeneous laminated coarse/fine grain microstructure were formed by strategically designed assemblies of Sm 2 O 3 -added Sm-Co powder feedstock mixtures. The technology is compatible with existing magnet manufacturing processes. Numerical micromechanics simulation indicates that the fracture is dominated by intragranular mode. The mechanical strength is mainly enhanced by the additive-induced grain refinement, while the small amount of Sm 2 O 3 addition has a small direct positive contribution. Finally, these magnets will be more cost-effective, efficient, and robust for various functional applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Coprecipitation of Fe/Cr Hydroxides at Organic–Water Interfaces: Functional Group Richness and (De)protonation Control Amounts and Compositions of Coprecipitates

Iron/chromium hydroxide coprecipitation controls the fate and transport of toxic chromium (Cr) in many natural and engineered systems. Organic coatings on soil and engineered surfaces are ubiquitous; however, mechanistic controls of these organic coatings over Fe/Cr hydroxide coprecipitation are poorly understood. Here, Fe/Cr hydroxide coprecipitation was conducted on model organic coatings of humic acid (HA), sodium alginate (SA), and bovine serum albumin (BSA). The organics bonded with SiO 2 through ligand exchange with carboxyl (-COOH), and the adsorbed amounts and pK(a) values of -COOH controlled surface charges of coatings. The adsorbed organic films also had different complexation capacities with Fe/Cr ions and Fe/Cr hydroxide particles, resulting in significant differences in both the amount (on HA > SA(-COOH) >> BSA(-NH 2 )) and composition (Cr/Fe molar ratio: on BSA(-NH2) >> HA > SA(-COOH)) of heterogeneous precipitates. Negatively charged -COOH attracted more Fe ions and oligomers of hydrolyzed Fe/Cr species and subsequently promoted heterogeneous precipitation of Fe/Cr hydroxide nanoparticles. Organic coatings containing -NH 2 were positively charged at acidic pH because of the high pK(a) value of the functional group, limiting cation adsorption and formation of coprecipitates. Meanwhile, the higher local pH near the -NH 2 coatings promoted the formation of Cr(OH) 3 . Finally, this study advances fundamental understanding of heterogeneous Fe/Cr hydroxide coprecipitation on organics, which is essential for successful Cr remediation and removal in both natural and engineered settings, as well as the synthesis of Cr-doped iron (oxy)hydroxides for material applications.

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

Construction of Boron- and Nitrogen-Enriched Nanoporous π-Conjugated Networks Towards Enhanced Hydrogen Activation

Boron-enriched scaffolds have demonstrated unique features and promising performance in the field of catalysis towards the activation of small gas molecules. However, there is still a lack of facile approaches capable of achieving high B doping and abundant porous channels in the targeted catalysts. Here, in this paper, construction of boron- and nitrogen-enriched nanoporous π-conjugated networks (BN-NCNs) was achieved via a facile ionothermal polymerization procedure with hexaazatriphenylenehexacarbonitrile [HAT(CN) 6 ] sodium borohydride as the starting materials. The as-produced BN-NCN scaffolds were featured by high heteroatoms doping (B up to 23 wt. % and N: up to 17 wt. %) and permanent porosity (surface area up to 759 m 2 g -1 mainly contributed by micropores). With the unsaturated bonded B species acting as the active Lewis acid sites and defected N species acting as the active Lewis base sites, those BN-NCNs delivered attractive catalytic performance towards H 2 activation/dissociation in both gaseous and liquid phase, acting as efficient metal-free heterogeneous frustrated Lewis pairs (FLPs) catalysts in hydrogenation procedures.

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

The role of the Pt-group dehydrogenation catalyst in alkane metathesis for polyolefin deconstruction

Recent proposed approaches in the depolymerization of waste plastics employ an olefin intermediate to produce alkanes or alkenes using olefin metathesis in tandem chemistry. Here, in this study, we investigated the role of the dehydrogenation catalyst on reaction rate, kinetics, and product distribution in heterogeneous tandem dehydrogenation and olefin metathesis (alkane metathesis) of three different alkane reactants, including polyethylene. We found that many properties to which alkane dehydrogenation rates were sensitive-including metal composition, nanoparticle size, and surface doping of Re species also controlled activity in Tandem D/OM. When comparing Pd, Pt, and Pt 3 Sn 1 , supported Pd in tandem with a Re 2 O 7 olefin metathesis catalyst showed four-fold higher activity (surface area basis) compared to Pt or Pt 3 Sn 1 catalysts on the same support, mainly due to differences in the rate of hydrogenation. Catalyst preparation resulted in metal nanoparticles partially covered by ReO x , as seen from elemental mapping. Co-location of Re 2 O 7 and Pd correlated with increased rates of hydrogenation (i.e., an increase in the rate of alkane formation and simultaneous lowering of the rate of alkene formation), with a reaction order in catalyst study that further supported this conclusion. The Pd and Re 2 O 7 system displayed marked improvement compared to Pt or Pt 3 Sn 1 with Re 2 O 7 , and previous work, in the depolymerization rate of a linear polyethylene feedstock, with over 94 % reduction in polymer molecular weight in 15 h at 190 °C using less catalyst and increased reactant loadings, while keeping solvent to polymer consumption below 2.5.

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

An organic electrochemical transistor for multi-modal sensing, memory and processing

By integrating sensing, memory and processing functionalities, biological nervous systems are energy and area efficient. Emulating such capabilities in artificial systems is, however, challenging and is limited by the device heterogeneity of sensing and processing cores. Here we report an organic electrochemical transistor capable of sensing, memory and processing. The device has a vertical traverse architecture and a crystalline–amorphous channel that can be selectively doped by ions to enable two reconfigurable modes: a volatile receptor and a non-volatile synapse. As a volatile receptor, the device is capable of multi-modal sensing and is responsive to stimuli such as ions and light. As a non-volatile synapse, it is capable of 10-bit analogue states, low switching stochasticity and good state retention. We also show that the homogeneous integration of the devices could provide functions such as conditioned reflexes and could be used for real-time cardiac disease diagnoses via reservoir computing.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2020

Probing Dopant Redistribution, Phase Propagation, and Local Chemical Changes in the Synthesis of Layered Oxide Battery Cathodes

Achieving the targeted control of layered oxide properties calls for more fundamental studies to mechanistically probe their evolution during their synthesis. Herein, dopant distribution, phase propagation, and local chemical changes as well as their interplay in multielement-doped LiNiO 2 materials are investigated using spectroscopic, imaging, and scattering techniques. It is shown that dopants undergo dynamic redistribution in the Ni(OH) 2 host lattice at the early stage of calcination (below 300 °C). Such redistribution behavior exhibits strong dopant-dependent characteristics, allowing for targeted surface and bulk doping control. The Ni oxidation process exhibits depth-dependent characteristics and the most rapid Ni oxidation takes place between 300 and 700 °C. Using Ni oxidation state as the proxy for the phase transformation, the buildup of heterogenous phase propagation in the early stage of calcination is shown, especially along the radial direction of secondary particles. Furthermore, the radial heterogenous phase distribution gradually decreases upon completing the calcination. However, a high degree of mosaic-like heterogeneity may still be present in the final product, departing from the perfect layered oxide. Overall, the present study offers fundamental insights into manipulating multiscale materials properties during calcination for obtaining stable, high-energy layered oxide cathodes.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Visible Light Photolysis at Single Atom Sites in Semiconductor Perovskite Oxides

Designing catalysts with well-defined active sites with chemical functionality responsive to visible light has significant potential for overcoming scaling relations limiting chemical reactions over heterogeneous catalyst surfaces. Visible light can be leveraged to facilitate the removal of strongly bound species from well-defined single cationic sites (Rh) under mild conditions (323 K) when they are incorporated within a photoactive perovskite oxide (Rh-doped SrTiO 3 ). CO, a key intermediate in many chemistries, forms stable geminal dicarbonyl Rh complexes (Rh + (CO) 2 ), that could act as site blockers or poisons during a catalytic cycle. For the first time, we demonstrate that CO removal can occur at mild temperatures (323 K) under low-energy red light (635 nm) irradiation, which is not possible for supported isolated-site Rh catalysts (0.2 wt % Rh/γ-Al 2 O 3 ). Photolysis of supported Rh + (CO) 2 complexes (e.g., 0.2 wt % Rh/γ-Al 2 O 3 ) has been demonstrated but is limited to high energy UV photons. Rigorous kinetic experiments elucidate disparate mechanisms for CO photodepletion from Rh-doped SrTiO 3 and supported isolated site Rh/γ-Al 2 O 3 . CO photodepletion from supported isolated site Rh/γ-Al 2 O 3 involves a direct metal to ligand charge transfer mechanism, whereas Rh-doped SrTiO 3 is governed by electron–hole pair formation in the perovskite. In this work, we show that under visible, low-energy red light, surface Rh species in Rh-doped SrTiO 3 introduce midgap energy states above the valence band that facilitate electronic excitations leading to surface CO removal. Isolated Rh sites in Rh-doped SrTiO 3 also exhibit exceptional stability under multiple CO photodepletion cycles. Overall, incorporating single sites into photoactive perovskite oxides is an effective strategy to influence surface chemistries with visible light.

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

Integrated reactor architecture of conductive network and catalytic nodes to accelerate polysulfide conversion for durable and high-loading Li-S batteries

The development of carbon-based heterogeneous framework host with synergistic catalytic and conductive effects for sulfur cathode is a promising strategy to realize high performance lithium sulfur batteries (LSBs). Here, an integrated reactor architecture with defective carbon nodes (IRA-DC) is designed for serving as high-loading (92.4 wt%) sulfur host. The hierarchical porous IRA-DC consists of untangled conductive carbon nanotube network and Co/N co-doped catalytic nodes with high dispersity. Therein the optimization of electric field distribution and homogenization of adsorption-catalysis sites offer the multi-electron conversion reaction of polysulfides with excellent kinetics and stability. The resultant IRA-DC/S cathode enables a high areal capacity of 8.86 mAh cm -2 under ultra-high sulfur loading (13.1 mg cm -2 ) and lean electrolyte (8 μL mg sulfur -1 ). It also displays a long-term cycling performance (1200 cycles at 1 C) and ultrahigh rate performance up to 20 C (with a capacity of 473.6 mAh g -1 ). In conclusion, this work provides an electrode building strategy by optimizing the environments of heterogeneous electrocatalysis and micro electric field to activate the polysulfide conversion efficiency and utilization of high-loading sulfur in monolithic sulfur-carbon cathodes.

25 ENERGY STORAGE↗
DOE OSTI2020

Gate-Tunable Semiconductor Heterojunctions from 2D/3D van der Waals Interfaces

Van der Waals (vdW) semiconductors are attractive for highly scaled devices and heterogeneous integration since they can be isolated into self-passivated, two-dimensional (2D) layers that enable superior electrostatic control. These attributes have led to numerous demonstrations of field-effect devices ranging from transistors to triodes. By exploiting the controlled, substitutional doping schemes in covalently-bonded, three-dimensional (3D) semiconductors and the passivated surfaces of 2D semiconductors, one can construct devices that can exceed performance metrics of “all-2D” vdW heterojunctions. Here, we demonstrate, 2D/3D semiconductor heterojunctions using MoS2 as the prototypical 2D semiconductor laid upon Si and GaN as the 3D semiconductor layers. By tuning the Fermi levels in MoS2, we demonstrate devices that concurrently exhibit over seven orders of magnitude modulation in rectification ratios and conductance. Our results further suggest that the interface quality does not necessarily affect Fermi-level tuning at the junction opening up possibilities for novel 2D/3D heterojunction device architectures

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Using block-copolymer nanolithography as a tool to sensitively evaluate variation in chemical dry etching rates of semiconductor materials with sub-5 nm resolution

Ion implantation is a robust and established method to customize the electronic properties of Si. However, fabricating doped, ultrafine semiconductor nanostructures can be challenging. Ion implantation has well-established effects on the dry etch rates of Si, which becomes increasingly consequential as the target dimension shrinks below a few tens of nanometers. While dry etching arrays of block copolymer-templated nanoscale holes (pitch = 37.5 nm, diameter ~25 nm) into p-type, n-type, and undoped Si, we observed that the lateral etch rate was notably larger for the n-type regions than p-type or undoped regions. By doing image analyses on high resolution electron micrographs of the nanostructured hole arrays, we were able to extract the porosity and average radii of the holes with subnanometer sensitivity and compare the relative etch rates between different doping conditions. We found that degenerately doped n-type silicon consistently etches between approximately 17% and 27% faster in the lateral direction than p-type Si, resulting in significantly larger porosity and, consequently, less mechanical stability. Here, we demonstrate that top-down dimensional analysis of a densely packed porous nanostructure is a robust method for assessing extremely small differences in the lateral, chemical etch rate of doped Si to a degree of sensitivity that was previously unachievable. The minute, dense-packed nature of block copolymer self-assembled nanostructures is shown to be ideal for this application. This proposed method could be useful for designing fabrication processes for heterogeneous nanostructures, as slight dry etch rate variations that may be within process tolerance at the micrometer-scale appear to have nontrivial consequences at the nanometer scale.

42 ENGINEERING↗
DOE OSTI2023

Role of Intradomain Heterogeneity on Ion and Polymer Dynamics in Block Polymer Electrolytes: Investigating Interfacial Mobility and Ion-Specific Dynamics and Transport

Block polymers show promise as solid-state battery electrolytes due to the optimization of conductive and mechanical properties enabled via tuning of block chemistry and length. We investigate a polystyrene-block-poly(oligo-oxyethylene methacrylate) (PS-b-POEM) electrolyte doped with various lithium salts to investigate the role of molecular structure on ion transport properties and on local ion dynamics and associations. Anion charge becomes more delocalized with increasing size, reducing the coupling between salt ions while increasing coupling between ion and polymer chain motions and creating a more mobile overall environment. We observe support for this ion-polymer coupling via 1 H, 7 Li and 19 F NMR spectroscopy, from which we obtain ion-specific mobility transition temperatures that differ from the polymer glass transition temperature. We also note faster transport and weaker local energetic interactions with anion size using temperature-dependent NMR diffusometry. 1 H NMR spectroscopy further elucidates polymer chain dynamics and enables quantification of the temperature-dependent fraction of the conducting block that is immobile near the PS-POEM domain interface. As a result, NMR thus represents a species-specific and timescale-specific platform to quantify phase and interface behavior, and to correlate ion-specific transport with polymer chain dynamics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Energetic decomposition yields efficient bimetallic Cu MOF-derived catalysts

Metal–organic frameworks (MOFs) have recently emerged as efficient self-sacrificial templates to fabricate porous carbon-supported metal nanoparticles (NPs). Due to observed increased activity, catalysts containing bimetallic NPs represent an active frontier for heterogeneous catalyst development. A strategy to synthesize active catalysts with highly dispersed bimetallic metal/metal oxides within a porous carbon matrix via rapid MOF decomposition using dopants is presented in this paper. A 2,4,6-trinitrotoluene (TNT) additive enhances the rapid thermolysis of the metal-doped Cu-based MOFs to minimize particle aggregation. Catalyst characterization reveals that a secondary metal increases dispersion of both metals over the carbon composite support. The catalyst preparation method influences both the metal particle size and oxidation state. Catalytic performance shows increased rates for 4-nitrophenol reduction even with <1 wt% of added secondary metal. Among the synthesized catalysts, the Ni–CuO@C bimetallic catalyst exhibits outstanding activity. This synthetic strategy is useful for creating highly efficient, robust, non-noble metal catalysts for development of sustainable chemical processes.

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

Mitigation of polysulfide shuttle effect in Li-S batteries through catalytic disproportionation reaction

Polysulfides are poorly retained within porous cathodes and readily diffuse into the electrolyte over time, leading to the well-known shuttle effect that undermines the reversibility of Li-S batteries. Here, in this study, we demonstrate that catalytic disproportionation of polysulfides provides an effective pathway to suppress this process by rapidly converting dissolved species into solid sulfur and sulfides, thereby preventing their migration into the electrolyte. Fundamentally, the sluggish kinetics of sulfur redox reactions are responsible for the accumulation and redistribution of soluble polysulfides in the bulk electrolyte. By accelerating these kinetics, catalyzed disproportionation not only confines sulfur within the conductive cathode matrix but also promotes the homogeneous precipitation of Li₂S₂/Li₂S, which enhances electrochemical reversibility and cycling stability. Using nitrogen-doped carbon (NC800) as a model catalyst, we reveal its ability to drive a pseudo-16-electron reduction pathway, leading to a single dominant Li₂S product and uniform deposition within the porous framework. In contrast, a non-catalytic carbon (KB) yields multiple polysulfide intermediates and heterogeneous deposition. The mechanistic insights provided here highlight the pivotal role of catalytic disproportionation in reshaping sulfur redox pathways and offer a rational strategy for mitigating polysulfide shuttling in practical Li-S pouch cells.

25 ENERGY STORAGE↗
DOE OSTI2024

Atomic-scale identification of active sites of oxygen reduction nanocatalysts

Heterogeneous nanocatalysts play a crucial role in both the chemical and energy industries. Despite substantial advancements in theoretical, computational and experimental studies, identifying their active sites remains a major challenge. Here we utilize atomic electron tomography to determine the three-dimensional atomic structure of PtNi and Mo-doped PtNi nanocatalysts for the electrochemical oxygen reduction reaction. We then employ the experimental atomic structures as input to first-principles-trained machine learning to identify the active sites of the nanocatalysts. Through the analysis of the structure–activity relationships, we formulate an equation termed the local environment descriptor, which balances the strain and ligand effects to provide physical and chemical insights into active sites in the oxygen reduction reaction. The ability to determine the three-dimensional atomic structure and chemical composition of realistic nanoparticles, combined with machine learning, could transform our fundamental understanding of the active sites of catalysts and guide the rational design of optimal nanocatalysts.

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

Faceted NiO(111) nanosheets: morphological and catalytic evolution for the oxygen evolution reaction

The renaissance of the energy system through the use of green hydrogen by water electrolysis lies behind the development of abundant, active, and scalable catalysts for the oxygen evolution reaction (OER). A fundumental understanding of the surface properties for these materials is of vital importance in producing viable heterogenous catalysts. In this feature article, we summarize several years of collaborative work on a uniquely faceted NiO(111) nanosheet possessing hexagonal holes with a focus on understanding how the evolution of the catalyst surface and bulk composition effects OER performance. The importance of surface faceting, morphological evolution, and metal combination by different doping strategies are all analyzed and summarized to further improve the material's performance. Furthermore, microwave and supercritical synthesis processes are utilized to understand how varying wet-chemical techniques effect the formation of the NiO(111) nanosheet and activity of the material. We discuss our chosen strategies and the difficulties encountered with optimizing a catalyst surface for the OER.

08 HYDROGEN↗
NASA NTRS1977

Volatile products from the interaction of KCl(g) with Cr2O3 and LaCrO3 in oxidizing environments

Cooled target collection techniques and high pressure mass spectrometric sampling were used to measure the relative rates of oxidative vaporization and to identify the volatile products emanating from samples of chromia and Mg-doped lanthanum chromite. The materials were exposed to partial pressures of KCl with and without H2O in one atmosphere of slowly flowing oxygen at elevated temperatures. Chromia and fresh samples of lanthanum chromite exhibited enhanced rates of oxidative vaporization upon exposure to these reactants. Mass spectrometric identification showed that the enhancements resulted from the heterogeneous formation of complex molecules of the type KCl sub 1,2,3 CrO3 and KOH sub l,2 CrO3. Lanthanum chromite that had undergone prolonged oxidative vaporization exhibited no enhanced oxidation upon exposure to the reactants.

Kohl, F. J.↗
DOE OSTI2022

High and temperature-insensitive piezoelectric performance in the lead-free Sm-doped BiFeO 3 –BaTiO 3 ceramics with high Curie temperature

Large sensor piezoelectric constant (d 33 = 334 pC/N) and superior actuator piezoelectric constant (d 33 * = 552 pm/V) as well as a high Curie temperature (T C = 454 °C) were obtained simultaneously in the lead-free 0.67Bi 1.03 FeO 3 -0.33Ba 1-x Sm x TiO 3 ceramics. Such an excellent and temperature-insensitive piezoelectric performance with only 10% temperature variation of piezoelectric strain at the range of 25–125 °C is highly desirable for real applications. The structural origin of the enhanced piezoelectric performance is mainly attributed to the morphotropic phase boundary and the highest known tetragonality (c T /a T = 1.02) in such materials. Transmission electron microscopy and electro-mechanical phenomenological theory demonstrate that the superior d 33 and d 33 * are associated with the hybrids nanodomains (60–90 nm) and flattened thermodynamic energy profile owing to the local structure heterogeneity. Furthermore, these results are superior as the piezoelectric properties are temperature-independent and the material has large d 33 *, and high TC compared to other lead-free piezoelectric ceramics.

36 MATERIALS SCIENCE↗