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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 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Surface Passivation by Excess Sulfur for Controlled Synthesis of Large, Thin SnS Flakes

Tin sulfide (SnS) is part of the group IV chalcogenides (SnX, GeX; X: S, Se), a family of anisotropic layered materials considered for thin film photovoltaics, optoelectronics, and valleytronics, and predicted narrow bandgap multiferroic materials. Large ultrathin SnS flakes, suitable for a variety of applications, are challenging to synthesize because of the enhanced surface reactivity due to the open layer structure of SnS which gives rise to a competition between lateral and vertical growth. Here we investigate the effects of added sulfur on passivating the surface and modifying the balance between lateral expansion and thickening of SnS flakes in chemical vapor transport from a SnS precursor. In addition, we investigate the growth of SnS flakes and compare the results of synthesis from a pure SnS precursor with growth, in which a slight excess of sulfur is supplied in different ways. Our results demonstrate that small amounts of excess sulfur can profoundly affect the size and thickness distributions of SnS flakes. The largest and thinnest flakes are obtained if (i) traces of sulfur are added and (ii) the sulfur source consists either of small Sx fragments released at high temperatures from the reactor walls, or atomic S supplied by sublimation from SnS 2 . The likely mechanism for the observed growth modifications is a transient surface passivation of SnS flakes during growth, which reduces the reactivity of the top facet of the flakes, limits vertical growth, and thus gives rise to ensembles with increased lateral size and reduced thickness.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Ion Distribution and Cation Exchange at Mica–Electrolyte Interfaces Probed with Deep Potential Molecular Dynamics

Here, we investigate the Stern layer structure and cation exchange mechanism at muscovite mica-electrolyte interfaces using nanosecond timescale molecular dynamics simulations based on deep neural network interatomic potentials trained on Density Functional Theory (DFT) data. Focusing on mica with exposed surface K + interfaced with aqueous NaCl and mica with surface Na + interfaced with KCl solution, we find that K + remains predominantly in inner-sphere configurations, while Na + exhibits notable populations in outer-sphere states. Most importantly, our simulations show that contact with an electrolyte solution results in the co-adsorption of multiple cation species, making the mica surface locally overcharged and thus reshaping the cation speciation in a manner that enhances the tendency of neighboring surface cations to desorb. These findings are consistent with recent experimental observations that co-adsorption of different cation species induces changes in cation speciation and slow kinetics of cation exchange at the muscovite-water interface, providing a basis for their detailed understanding.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Surface Reorganization Leads to Enhanced Photocatalytic Activity in Defective BiOCl

Introducing defects into semiconductor photocatalysts has been identified as an effective approach to extend the visible-light absorption and achieve high-efficiency solar energy conversion. However, the band gap model system of defect states may not truly describe the evolutions in real materials as the narrower band gap would limit the photocatalytic activity via suppressing the charge separation. We report that reorganizing the surface termination in a defective semiconductor plays a key role in determining the photocatalytic performance. We directly observed that the surface reorganizations are accompanied by the formation of defects in layered structured bismuth oxychloride (BiOCl). Both experimental and theoretical results demonstrate that varying terminations have strong effects on the electronic structure and electron–hole pair recombination, which is shown to be the driving force of the promotion of visible-light photocatalytic activity in BiOCl. We also reveal that the surface reorganization induces a novel transfer path and high-dielectric surface to prevent the trapping of charge carriers, highlighting an efficient way of improving the photocatalytic activity by surface reorganization.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Facile Solvent-Free Synthesis of Manganese Nickel-Layered Double Hydroxide for Sustainable Water-Splitting Applications

The quest for efficient and sustainable water-splitting electrocatalysts has led to the development of a novel bifunctional material, manganese nickel-layered double hydroxide (MnNi-LDH), which demonstrates promising performance for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Although manganese-based materials are less explored than other transition metals, they offer significant potential owing to their widespread availability, affordability, and customizable electronic characteristics. MnNi-LDH exhibits a nanosheet morphology and a layered structure, which collectively provide numerous accessible active sites and facilitate efficient charge transfer and mass transport. Characterization using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy, and transmission electron microscopy reveals the structural and compositional properties of MnNi-LDH. The oxidation states of Mn and Ni, as determined by XPS, play a crucial role in improving the catalytic activity. Notably, MnNi-LDH demonstrates low overpotentials of 187 mV for OER and 225 mV for HER at 10 mA/cm 2 current density comparable to conventional catalysts. Long-term stability tests show minimal degradation in cell performance over 50 h, with a current density drop of only 0.6153% per hour for the OER and 0.37% per hour for the HER. Further, these findings highlight the potential of MnNi-LDH as a promising and environmentally friendly bifunctional electrocatalyst for water splitting, contributing to the advancement of renewable energy sources.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Systematic Doping of Cobalt into Layered Manganese Oxide Sheets Substantially Enhances Water Oxidation Catalysis

The effect on the electrocatalytic oxygen evolution reaction (OER) of cobalt incorporation into the metal oxide sheets of the layered manganese oxide birnessite was investigated. Birnessite and cobalt-doped birnessite were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and conductivity measurements. A cobalt:manganese ratio of 1:2 ended in the most active catalyst for the OER. Specifically, the overpotential (η) for the OER was 420 mV, significantly lower than the η = 780 mV associated with birnessite in the absence of Co. Moreover, the Tafel slope for Co/birnessite was 81 mV/dec, in comparison to a Tafel slope of greater than 200 mV/dec for birnessite. For chemical water oxidation catalysis, an 8-fold turnover number (TON) was achieved (h = 70 mmol of O 2 /mol of metal). Density functional theory (DFT) calculations predict that cobalt modification of birnessite resulted in a raising of the valence band edge and occupation of that edge by holes with enhanced mobility during catalysis. Inclusion of extra cobalt beyond the ideal 1:2 ratio was detrimental to catalysis due to disruption of the layered structure of the birnessite phase.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Insight into SEI Growth in Li-Ion Batteries using Molecular Dynamics and Accelerated Chemical Reactions

The performance of lithium-ion batteries (LIB) using organic electrolytes strongly depends on the formation of a stable solid electrolyte interphase (SEI) film. Elucidating the dynamic evolution and spatial composition of the SEI can be very useful to study the stability of SEI components and help optimize the formation cycles of LIB. We propose a classical molecular dynamics simulation protocol for predicting the first stages of SEI formation using a reaction method involving the decomposition of EC and LiPF 6 molecules in the electrolyte. We accelerate the formation of SEI components near the anode surface by increasing the probability of reactions, implemented through a geometry matching scheme, followed by a force-field reconfiguration. We observe the formation of gases (C 2 H 4 ), inorganic (Li 2 CO 3 and LiF) and organic (LEDC) components. Finally, this protocol shows promise to be able to evaluate the effects of varying electrolyte compositions and additives on SEI layer structure and composition.

25 ENERGY STORAGE↗
DOE OSTI2025

An Atomistic Study of Reactivity in Solid-State Electrolyte Interphase Formation for Li/Li7P3S11

Lithium metal batteries offer superior volumetric and gravimetric specific capacities compared to those based on traditional graphite anodes. Although advancements in solid-state electrolytes address safety concerns, challenges remain, particularly regarding interphase formation in lithium metal anodes. This work presents a computational framework based on high-throughput first-principles density functional theory and machine-learning interatomic potentials (MLIPs) including automated iterative, active learning to enable robust computational exploration of interphase formation between lithium metal anodes and an inorganic solid-state electrolyte. As a demonstration, we apply the framework to a Li/Li7P3S11 interface and find that it accurately identifies the experimentally observed, thermodynamically stable interphase products as well as their overall spatial arrangement within a heterogeneous, amorphous layered structure, with Li2S domains of nanocrystallinity. Our simulations show two stages, a fast and slow diffusion reaction regime, that corroborate the relative phase formation rate of Li x P, Li2S, and Li3P. Using the Onsager transport theory, we capture time-dependent ionic diffusion within the reacting interface, including cross-correlation effects. We found that cross-correlation effects between Li-P and P-S ionic motion significantly influence P-ion diffusion, making it highly sensitive to the local environment and potentially leading to "kinetic trapping" of Li-P phases. The passivation of the interface is shown as the ionic fluxes all approach zero, effectively halting interphase growth.

Diffusion↗
DOE OSTI2018

Competitive Adsorption of H 2 O and CO 2 in 2-Dimensional Nanoconfinement: GCMD Simulations of Cs- and Ca-Hectorites

The intercalation of H 2 O, CO 2 , and other fluid species in expandable clay minerals (smectites) may play a significant role in controlling the behavior of these species in geological carbon sequestration and enhanced petroleum production and has been the subject of intensive study in recent years. This paper reports the results of a computational study of the effects of the properties of the charge-balancing, exchangeable cations on H 2 O and CO 2 intercalation in the smectite mineral, hectorite, in equilibrium with an H 2 O-saturated supercritical CO 2 fluid under reservoir conditions using grand canonical molecular dynamics methods. The results show that the intercalation behavior is greatly different for the cations with relatively low hydration energies and high affinities for CO 2 (here Cs + ) than for cations with higher hydration energies (here Ca 2+ ). With Cs + , CO 2 intercalation occurs in a 1-layer structure and does not require H 2 O intercalation, whereas with Ca 2+ , the presence of a sub-monolayer of H 2 O is required for CO 2 intercalation. The computational results provide a detailed structural, dynamical, and energetic insight into the differences in the intercalation behavior and are in excellent agreement with in situ experimental X-ray diffraction, infrared, quartz crystal microbalance, and nuclear magnetic resonance results for smectite materials obtained under reservoir conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Diffusion Mechanisms of Radiolytic Species in Irradiated Al (Oxy-)Hydroxides

Rare-event simulations (climbing image nudge elastic band and metadynamics) were performed using density functional theory (DFT) and a hybrid exchange-correlation functional to elucidate and quantify the diffusion mechanisms of radiation-induced species (O - , H 0 , and H 2 ) in boehmite (γ-AlOOH) and gibbsite (γ-Al(OH) 3 ). The two Al (oxy-)hydroxide phases are known to have much different radiolytic activities, but the underlying mechanisms remain unknown. The DFT calculations revealed that O - diffusion occurred via proton-coupled hole transfer with high energy barriers in both phases. In contrast, energy barriers for H 0 transfers were generally lower in boehmite than in gibbsite, suggesting a more facile diffusion in boehmite of H radicals to the surface, where H 2 formation can take place. Another key difference was the ability of H 0 and H 2 to diffuse across the structural layers in gibbsite but not in boehmite. Therefore, while the formation of O and H radicals was energetically favored in gibbsite compared to boehmite, the DFT calculations indicated that the mechanisms of diffusion are responsible for the higher H 2 yields measured for boehmite compared to gibbsite

Shen, Zhizhang↗
DOE OSTI2020

Toward Engineering of Solution Microenvironments for the CO 2 Reduction Reaction: Unraveling pH and Voltage Effects from a Combined Density-Functional–Continuum Theory

Engineering the electrolyte microenvironment represents an attractive route to tuning the selectivity of electrocatalytic reactions beyond catalyst composition and morphology. However, harnessing the full potential of this approach requires understanding the interplay between voltage, electrolyte composition, and adsorbate binding within the electrical double layer, which is absent from the usual theoretical approaches. In this study, we apply a recently developed density functional theory (DFT)–continuum approach based on the effective screening medium method and reference interaction site model (ESM–RISM) to explore electrolyte effects with an enhanced description of the electrochemical interface. Furthermore, applying this method to the binding of CO adsorbates in potassium-containing electrolytes on copper, a problem of direct relevance to CO 2 electroreduction to value-added products, we show that the interdependence of voltage and pH leads to an unexpected change in adsorption site preference on Cu(001) terraces. Our findings highlight the often-overlooked importance of the electrical double-layer structure for predicting catalyst operation.

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

Formation of Carbon–Carbon Interlinkage Bonds under High Pressure

The formation of carbon–carbon interlinkage bonds (CCIBs) via the chemical binding of interlayer carbon atoms of many sp 2 -bonded carbon precursors is an essential step for synthesizing various diamond and diamond-like materials. Although the existence of CCIBs may be reasonably assumed under high-pressure conditions, direct experimental evidence has been scarce. Micro-Raman spectroscopy is here employed to track in situ the evolution of C–C bonds in a pressure range from ambient to 54 GPa. A pressure-induced two-stage (polynomial and linear) shift of the G peak and new generation of the CCIB peak at about 1550 cm –1 are observed in multiple types of layer-structured carbon precursors, including glassy carbon, natural graphite, and carbon nanotubes. In conclusion, the experimental discovery of CCIBs holds significance in comprehending phase transitions of sp 2 -bonded carbon materials and has implications for the advancement of novel carbon structures.

Anode materials↗
DOE OSTI2024

Key Experimental Considerations When Evaluating Functional Ionic Liquids for Combined Capture and Electrochemical Conversion of CO 2

Ionic liquids (ILs) are considered functional electrolytes for the electrocatalytic reduction of CO 2 (ECO 2 R) due to their role in the double-layer structure formation and increased CO 2 availability at the electrode surface, which reduces the voltage requirement. However, not all ILs are the same, considering the purity and degree of the functionality of the IL. Further, there are critical experimental factors that impact the evaluation of ILs for ECO 2 R including the reference electrode, working electrode construction, cosolvent selection, cell geometry, and whether the electrochemical cell is a single compartment or a divided cell. Here, we describe improved synthesis methods of imidazolium cyanopyrrolide IL for electrochemical studies in consideration of precursor composition and reaction time. We explored how IL with cosolvents (i.e. acetonitrile, dimethylformamide, dimethyl sulfoxide, propylene carbonate, and n-methyl-2-pyrrolidone) affects conductivity, CO 2 mass transport, and ECO 2 R activation overpotential together with the effects of electrode materials (Sn, Ag, Au, and glassy carbon). Acetonitrile was found to be the best solvent for lowering the onset potential and increasing the catalytic current density for the production of CO owing to the enhanced ion mobility in combination with the silver electrode. Further, the ECO 2 R activity of molecular catalysts Ni(cyclam)Cl 2 and iron tetraphenylsulfonato porphyrin (FeTPPS) on the carbon cloth electrode maintained high Faradaic efficiencies for CO in the presence of the IL. This study presents best practices for examining nontraditional multifunctional electrolytes amenable to integrated CO 2 capture and conversion technologies for homogeneous and heterogeneous ECO 2 R.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Electrochemical Growth of Copper Hydroxy Double Salt Films and Their Conversion to Nanostructured p-Type CuO Photocathodes

New electrochemical synthesis methods were developed to produce copper hydroxy double salts (Cu-HDS) films with four different intercalated anions (NO 3 - , SO 4 2- , Cl - , and dodecyl sulfate (DS)) as pure crystalline films as-deposited (Cu 2 NO 3 (OH) 3 , Cu 4 SO 4 (OH) 6 , Cu 2 Cl(OH) 2 , and Cu 2 DS(OH) 3 ). These methods are based on p-benzoquinone reduction, which increases the local pH at the working electrode and triggers the precipitation of Cu 2+ and appropriate anions as Cu-HDS films on the working electrode. The resulting Cu-HDS films could be converted to crystalline Cu(OH) 2 and CuO films by immersing them in basic solutions. Since Cu-HDS films were composed of 2D crystals due to the atomic level layered structure of HDS, the CuO films prepared from Cu-HDS films have unique low dimensional nanostructures, creating high surface areas, which cannot be obtained by direct deposition of CuO that has a 3D atomic level crystal structure. Here, the resulting nanostructures allowed the CuO films to facilitate electron-hole separation and demonstrate great promise for photocurrent generation when investigated as a photocathode for a water splitting photoelectrochemical cell. Electrochemical synthesis of Cu-HDS films and their facile conversion to CuO films will provide new routes to tune morphologies and properties of the CuO electrodes that may not be possible by other synthesis means.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Role of Periodicity and Acid Chemistry on the Morphological Evolution and Strength in Precise Polyethylenes

We report herein the morphology evolution under tensile deformation for strictly linear polyethylenes with associating functional groups. In situ X-ray scattering measurements during elongation reveal that periodic acid group placement along the backbone is required to form hierarchical layered morphologies that lead to strain hardening. This phenomenon was observed in both semicrystalline and amorphous precise acid polyethylenes with acrylic, geminal acrylic, and phosphonic acids. Polymers with nonperiodic (pseudorandom) acid placement fail to form layered morphologies and instead retain a liquidlike distribution of acid aggregates. Acid chemistry and acid concentration influence morphological evolution in both periodic and nonperiodic polymers predominately through the modification of T g and percent crystallinity, which subsequently impact the mechanical properties. Our results indicate that hierarchical acid-rich layered structures, commensurate with improved mechanical properties, form in polymers with strictly periodic chemical structures and sufficient chain mobility for chain alignment during elongation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Kinetically-Driven Phase Transformation during Lithiation in Copper Sulfide Nanoflakes

Two-dimensional (2D) transition metal chalcogenides have been widely studied and utilized as electrode materials for lithium ion batteries due to their unique layered structures to accommodate reversible lithium insertion. Real-time observation and mechanistic understanding of the phase transformations during lithiation of these materials are critically important for improving battery performance by controlling structures and reaction pathways. Here, we use in situ transmission electron microscopy methods to study the structural, morphological, and chemical evolutions in individual copper sulfide (CuS) nanoflakes during lithiation. We report a highly kinetically driven phase transformation in which lithium ions rapidly intercalate into the 2D van der Waals-stacked interlayers in the initial stage, and further lithiation induces the Cu extrusion via a displacement reaction mechanism that is different from the typical conversion reactions. Density functional theory calculations have confirmed both the thermodynamically favored and the kinetically driven reaction pathways. Lastly, our findings elucidate the reaction pathways of the Li/CuS system under nonequilibrium conditions and provide valuable insight into the atomistic lithiation mechanisms of transition metal sulfides in general.

25 ENERGY STORAGE↗
DOE OSTI2018

Electrochemical Reaction Mechanism of the MoS 2 Electrode in a Lithium-Ion Cell Revealed by in Situ and Operando X-ray Absorption Spectroscopy

As a typical transition metal dichalcogenide, MoS 2 offers numerous advantages for nanoelectronics and electrochemical energy storage due to its unique layered structure and tunable electronic properties. When used as the anode in lithium-ion cells, MoS 2 undergoes intercalation and conversion reactions in sequence upon lithiation, and the reversibility of the conversion reaction is an important but still controversial topic. Here, we clarify unambiguously that the conversion reaction of MoS 2 is not reversible, and the formed Li 2 S is converted to sulfur in the first charge process. Li 2 S/sulfur becomes the main redox couple in the subsequent cycles and the main contributor to the reversible capacity. In addition, due to the insulating nature of both Li 2 S and sulfur, a strong relaxation effect is observed during the cycling process. This study clearly reveals the electrochemical lithiation-delithiation mechanism of MoS 2 , which can facilitate further developments of high-performance MoS 2 -based electrodes.

25 ENERGY STORAGE↗
DOE OSTI2018

Water-Activated VOPO 4 for Magnesium Ion Batteries

Rechargeable Mg batteries, using high capacity and dendrite-free Mg metal anodes, are promising energy storage devices for large scale smart grid due to low cost and high safety. However, the performance of Mg batteries is still plagued by the slow reaction kinetics of their cathode materials. Recent discoveries demonstrate that water in cathode can significantly enhance the Mg-ion diffusion in cathode by an unknown mechanism. Here, we propose the water-activated layered-structure VOPO 4 as a novel cathode material and examine the impact of water in electrode or organic electrolyte on the thermodynamics and kinetics of Mg-ion intercalation/deintercalation in cathodes. Electrochemical measurements verify that water in both VOPO 4 lattice and organic electrolyte can largely activate VOPO 4 cathode. Thermodynamic analysis demonstrates that the water in the electrolyte will equilibrate with the structural water in VOPO 4 lattice, and the water activity in the electrolyte alerts the mechanism and kinetics for electrochemical Mg-ion intercalation in VOPO 4 . Theoretical calculations and experimental results demonstrate that water reduces both the solid-state diffusion barrier in the VOPO 4 electrode and the desolvation penalty at the interface. To achieve fast reaction kinetics, the water activity in the electrolyte should be larger than 10 –2 . The proposed activation mechanism provides guidance for screening and designing novel chemistry for high performance multivalent-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2018

Morphological Engineering of Winged Au@MoS 2 Heterostructures for Electrocatalytic Hydrogen Evolution

Molybdenum disulfide (MoS 2 ) has been recognized as a promising cost-effective catalyst for water-splitting hydrogen production. However, the desired performance of MoS 2 is often limited by insufficient edge-terminated active sites, poor electrical conductivity, and inefficient contact to the supporting substrate. To address these limitations, we developed a unique nanoarchitecture (namely, winged Au@MoS 2 heterostructures enabled by our discovery of the “seeding effect” of Au nanoparticles for the chemical vapor deposition synthesis of vertically aligned few-layer MoS 2 wings). The winged Au@MoS 2 heterostructures provide an abundance of edge-terminated active sites and are found to exhibit dramatically improved electrocatalytic activity for the hydrogen evolution reaction. Theoretical simulations conducted for this unique heterostructure reveal that the hydrogen evolution is dominated by the proton adsorption step, which can be significantly promoted by introducing sufficient edge active sites. Our study introduces a new morphological engineering strategy to make the pristine MoS 2 layered structures highly competitive earth-abundant catalysts for efficient hydrogen production.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗