Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “interfacial energy”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Accelerated Beta Radiation Aging of Interlayer Titanium Nitride in Gallium Nitride Contacts

Research conducted under the Laboratory Directed Research and Development Program at Pacific Northwest National Laboratory, a multiprogram national laboratory operated by Battelle for the U.S. Department of Energy. An NNSS author co-authored this paper, and portions of this work were supported by the Mission Support and Test Services, LLC, under Contract No. DE-NA0003624 with the U.S. Department of Energy, National Nuclear Security Administration, NA-10 USDOE NA Office of Defense Programs (NA-10). PNNL-SA-163618 Currently, there is no good way to determine the influence of radiation on the aging of betavoltaic electrical contacts. This work tested a method to accelerate the aging of the contacts inside a betavoltaic by enhancing energy deposition within the interfacial region of interest. An electrical contact of gold-titanium on gallium nitride was aged by exposure to tritium betas and electrons in a beamline. The interface stoichiometry was compared to the electrical performance of the contact. The method to age the betavoltaic component could help predict the lifetime performance of the internal electrical contacts and provide assurance of deployment reliability.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Self-Propulsion by Directed Explosive Emulsification

An active droplet system, programmed to repeatedly move autonomously at a specific velocity in a well-defined direction, is demonstrated. Coulombic energy is stored in oversaturated interfacial assemblies of charged nanoparticle-surfactants by an applied DC electric field and can be released on demand. Spontaneous emulsification is suppressed by an increase in the stiffness of the oversaturated assemblies. Rapidly removing the field releases the stored energy in an explosive event that propels the droplet, where thousands of charged microdroplets are ballistically ejected from the surface of the parent droplet. The ejection is made directional by a symmetry breaking of the interfacial assembly, and the combined interaction force of the microdroplet plume on one side of the droplet propels the droplet distances tens of times its size, making the droplet active. The propulsion is autonomous, repeatable, and agnostic to the chemical composition of the nanoparticles. The symmetry-breaking in the nanoparticle assembly controls the microdroplet velocity and direction of propulsion. Finally, this mechanism of droplet propulsion will advance soft micro-robotics, establishes a new type of active matter, and introduces new vehicles for compartmentalized delivery.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Insights into solvent and surface charge effects on Volmer step kinetics on Pt (111)

Abstract The mechanism of pH-dependent hydrogen oxidation and evolution kinetics is still a matter of significant debate. To make progress, we study the Volmer step kinetics on platinum (111) using classical molecular dynamics simulations with an embedded Anderson-Newns Hamiltonian for the redox process and constant potential electrodes. We investigate how negative electrode electrostatic potential affects Volmer step kinetics. We find that the redox solvent reorganization energy is insensitive to changes in interfacial field strength. The negatively charged surface attracts adsorbed H as well as H + , increasing hydrogen binding energy, but also trapping H + in the double layer. While more negative electrostatic potential in the double layer accelerates the oxidation charge transfer, it becomes difficult for the proton to move to the bulk. Conversely, reduction becomes more difficult because the transition state occurs farther from equilibrium solvation polarization. Our results help to clarify how the charged surface plays a role in hydrogen electrocatalysis kinetics.

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

Understanding the Dissolution and Passivation of an Aluminum Electrode during Electrocoagulation of Groundwater Using Neutron and X-ray Reflectometry

An aluminum (Al)-based electrocoagulation (EC) system can effectively remove dissolved silica and hardness in groundwater. The effectiveness of Al-EC in terms of pollutant removal, Faradaic efficiency, and energy consumption depends on the interfacial electrolysis or passivation of the electrode in water. Thus, understanding the electrolysis reaction at the liquid/electrode interface during operation is important for sustainable EC deployment. Here, a continuous flow-through Al-EC system was tested with various groundwater simulants, i.e., chloride (Cl – )-based, sulfate (SO 4 2– )-based, and mixed solutions. High pollutant removal with low energy consumption was observed in Cl – -based groundwater treatment, while low pollutant removal with high energy consumption was observed in SO 4 2– -based groundwater. For example, the required energy per unit mass of Al dosing in SO 4 2– -based groundwater is three times higher than that in Cl – -based groundwater at 10 mA/cm 2 . However, increasing the Cl – concentration significantly reduces this energy demand. In SO 4 2– -based groundwater, the silicate removal efficiency drops from 85.1% to 24.0% compared to that for Cl – -based groundwater, while Mg 2+ and Ca 2+ removal efficiencies decrease to 0.6% from 15.8% and 5.7% from 44.8%, respectively. To better understand this EC performance, we used in situ neutron reflectometry (NR) to examine the interfacial dynamics of Al dissolution and passivation at a 100 nm scale occurring on the surface of the sacrificial Al electrodes during EC. Ex situ X-ray reflectometry (XRR) was also used to support the in situ NR results. Both NR and XRR results revealed that Al dissolution is influenced by the presence of Cl – in the simulants, while a passivating layer forms on the electrode in a SO 4 2– -based solution. In the Cl – -based solution, anodic Al dissolution occurred locally and inhomogeneously across the surface of the Al anode film, resulting in a localized thickness reduction over time. In the SO 4 2– -based solution, no apparent dissolution of the Al anode was identified. Instead, Al underwent oxidation, forming an amorphous Al 2 O 3 surface layer within the Al electrode film that increased in thickness over time. In the mixed solution, both anodic Al dissolution and surface Al 2 O 3 layer formation occurred, indicating that Al dissolution and surface Al 2 O 3 layer formation are attributable to the Cl – and SO 4 2– ions, respectively.

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

Phase-Transition Interlayer Enables High-Performance Solid-State Sodium Batteries with Sulfide Solid Electrolyte

All-solid-state sodium (Na) batteries (ASSSBs) using sulfide-based solid electrolytes (SEs) have attracted intensive attention due to their superior safety, high energy density and low cost. However, interfacial issue is one of the biggest challenges to achieve high-performance sulfide-based ASSSBs due to the serious reactions between active Na metal and sulfide SEs at the interface. To address the interfacial challenges, we propose in this paper a simple and efficient approach by introducing a polymer electrolyte as an interlayer to stabilize the interface. Na 3 SbS 4 as a model sulfide SE is used to demonstrate the interlayer strategy to stabilize the interface by preventing the detrimental reactions and inhibiting Na dendrites. As a result, stable Na plating/stripping was observed in Na symmetric cells under the current density of 0.1 mA cm –2 . Moreover, ASSSBs with Na metal and TiS 2 electrode delivered long-term stability over 300 cycles remaining a specific capacity above 100 mAh g –1 , and FeS 2 ||Na cells exhibited an impressive specific capacity of up to 200 mAh g –1 after the 20th cycles. This work demonstrates an efficient strategy to address interfacial challenges between sulfide SEs and Na metal, which contributes to the development of ASSSBs in next-generation energy storage systems.

25 ENERGY STORAGE↗
NASA NTRS1997

Interactions of anesthetics with the water-hexane interface. A molecular dynamics study

The free energy profiles characterizing the transfer of nine solutes across the liquid-vapor interfaces of water and hexane and across the water-hexane interface were calculated from molecular dynamics simulations. Among the solutes were n-butane and three of its halogenated derivatives, as well as three halogenated cyclobutanes. The two remaining molecules, dichlorodifluoromethane and 1,2-dichloroperfluoroethane, belong to series of halo-substituted methanes and ethanes, described in previous studies (J. Chem. Phys. 1996, 104, 3760; Chem. Phys. 1996, 204, 337). Each series of molecules contains structurally similar compounds that differ greatly in anesthetic potency. The accuracy of the simulations was tested by comparing the calculated and the experimental free energies of solvation of all nine compounds in water and in hexane. In addition. the calculated and the measured surface excess concentrations of n-butane at the water liquid-vapor interface were compared. In all cases, good agreement with experimental results was found. At the water-hexane interface, the free energy profiles for polar molecules exhibited significant interfacial minima, whereas the profiles for nonpolar molecules did not. The existence of these minima was interpreted in terms of a balance between the free energy contribution arising from solute-solvent interactions and the work to form a cavity that accommodates the solute. These two contributions change monotonically, but oppositely, across the interface. The interfacial solubilities of the solutes, obtained from the free energy profiles, correlate very well with their anesthetic potencies. This is the case even when the Meyer-Overton hypothesis, which predicts a correlation between anesthetic potency and solubility in oil, fails.

NASA Center ARC↗
DOE OSTI2023

All-polymer nanocomposites having superior strength, toughness and ultralow energy dissipation

Toughening polymers has attracted significant interest. Traditionally, polymer toughness is enhanced by constructing polymer networks or introducing sacrificial bonds into the chains between crosslink points. These strategies, though, introduce pronounced energy dissipation and associated heat, both of which are undesirable under long-term cyclic loading, for example at the interface of implants in the human body. By incorporating single-chain nanoparticles (SCNPs) into linear polymer chains to generate all-polymer nanocomposites (APNCs), we have been able to achieve high strength, high toughness with low energy dissipation. Using a combination of simulation and experimental results, we are advancing a “SCNPs effect” where tightly cross-linked SCNPs produce a modulus contrast to achieve strengthening and toughening. Benefitting from the soft interface, the penetrable and deformable SCNPs cause the surrounding polymer chains to move in concert, significantly reducing the interfacial friction to achieve low energy dissipation. The intramolecular cross-linking of the SCNPs and adhesion between the SCNPs and polymer matrix are critical for realizing such high-performance systems. Based on a Gaussian regression model and back propagation (BP) neural network, the mechanical strength can be predicted and is supported by simulations. Finally, the APNC concept described can be applied to elastomers and gels, broadening its utilization in high-cycle and low-dissipation applications, like soft robots, flexible sensors and cartilage replacements, and artificial heart valves.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Stable CdTe Photoanodes with Energetics Matching Those of a Coating Intermediate Band

Here, a TiO 2 coating was grown on a CdTe absorber by atomic layer deposition for stabilization against its photocorrosion during photoelectrochemical water splitting. Under simulated sunlight (AM 1.5G, 100 mW cm –2 ), this multilayer CdS/CdTe/TiO 2 /Ni/NiO x photoanode produced a light-limited photocurrent density of 24.5 ± 0.5 mA cm –2 and a photovoltage of 780 ± 20 mV. This record energy-conversion performance was comparable to those of baseline CdS/CdTe solar cells and was achieved only after the development of proper CdTe surface treatments prior to coating the stabilization layer. The TiO 2 coating, with its in-gap charge-transport intermediate band, facilitates hole transport as light exits the CdTe/TiO 2 interface. With proper interfacial chemistry, the electrochemical potential energy of the coating intermediate band matched that of the CdTe valence band. Moreover, the stabilized CdS/CdTe/TiO 2 /Ni/NiO x photoanodes showed 100 h stability for water oxidation under light-on/light-off cycles. This study provides insightful guidance for designing stabilization contacts for efficient and stable light-driven water oxidation.

14 SOLAR ENERGY↗
DOE OSTI2020

The dependence of aluminum lattice orientation on semiconductor lattice parameter in planar InAs/Al hybrid heterostructures

We present a detailed study of 7-nm thick Al layers epitaxially grown on In x Al 1-x As or Al 1-x Ga x Sb y As 1-y (0 0 1) semiconductors using high-resolution transmission electron microscopy (HRTEM) and synchrotron X-ray diffraction (XRD). These techniques provide high spatial and high reciprocal space resolution information about Al lattice orientations and interfacial structure, highlighting the existence of a strong correlation between the surface lattice parameter of the semiconductor and the normal orientation of the aluminum film. The normal orientation of Al layers is found to be [1 1 1] when the in-plane semiconductor surface lattice parameter, a S , is smaller than 5.98 Å, and is [1 1 0] when aS is larger than this value. In the transition between these lattice parameters where one orientation is preferred, both orientations may be observed. Concomitant with the change in normal orientation is an inversion in the strain state of the aluminum film. When the normal orientation is [1 1 1], the Al film is compressively strained; while for [1 1 0] normal orientations, the Al in-plane strain is tensile. An energy balance model, accounting for surface, interfacial, side-face, and strain energy, and the registry of lattice planes across the semiconductor/aluminum interface provide explanations for the observed normal orientation and strain inversion.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Electrolyte Organization Leads to Potential-Dependence in Thermochemical Catalysis of Nonpolar Reactions

Electrochemical polarization is now known to play a key role in thermochemical catalysis at solid–liquid interfaces. However, existing frameworks cannot account for why even nonpolar, nonfaradaic reactions are sensitive to interfacial polarization. In order to uncover the molecular basis of this phenomenon, we herein study the potential-dependent reaction kinetics of ethylene and trans-2-butene hydrogenation at Pt–liquid interfaces. Measurements were performed in aqueous and ortho-difluorobenzene (o-DFB) solutions, spontaneously polarizing the Pt–liquid interfaces by, respectively, varying the pH or dissolving distinct metallocene redox buffers into solution. Here, we find that at comparable mechanistic regimes, the rates of both ethylene and trans-2-butene hydrogenation are maximized near the same electrochemical potential, E. Moreover, the potential-dependence, defined as $\frac{∂ln 𝑟}{∂𝐸}$, of trans-2-butene hydrogenation is approximately 2.2× greater than that of ethylene hydrogenation across the full potential range studied. These observations are all consistent with a model in which polarization of the Pt surface away from the local potential of zero free charge (E PZFC ) induces electrostatic organization of the polar solvent and charged ions near the interface, which impedes olefin adsorption and surface reaction because these surface reactions induce electrolyte displacement. Accordingly, interfacial polarization alters the free energy landscape and thus the rate of nonpolar heterogeneous catalysis by controlling the degree of electrostatic organization of polar and charged spectators at the interface, which do not in general need to be specifically chemisorbed onto the surface but could simply be close enough to the surface to be perturbed by the olefin adsorption. These results point toward electrochemical design handles, namely, the electrolyte, catalyst potential, and local E PZFC of the catalyst, with which to tune interfacial catalysis of thermochemical organic transformations.

adsorption↗
DOE OSTI2020

Inertial dynamics of an interface with interfacial mass flux: Stability and flow fields’ structure, inertial stabilization mechanism, degeneracy of Landau’s solution, effect of energy fluctuations, and chemistry-induced instabilities

This work focuses on the long-standing problem of inertial dynamics of an interface with interfacial mass flux and reports new mechanisms for the interface stabilization and destabilization. The interface is a phase boundary separating fluids of different densities and having interfacial mass flux. To analyze the interface dynamics from a far field, we develop and apply the general matrix method to rigorously solve the boundary value problem involving the governing equations in the fluid bulk and the boundary conditions at the interface and at the outside boundaries of the domain. We find the fundamental solutions for the linearized system of equations and analyze the interplay of interface stability with flow fields’ structure by directly linking rigorous mathematical attributes to physical observables. We find that the interface is stable when the dynamics conserves the fluxes of mass, momentum, and energy; the stabilization is due to an inertial mechanism causing small oscillations of the interface velocity. In the classic Landau’s dynamics, the postulate of perfect constancy of the interface velocity leads to the development of Landau–Darrieus instability. This destabilization is also linked to the imbalance of the perturbed energy at the interface. The classic Landau’s solution is found to have degeneracy; lifting of the degeneracy may lead to singularity and self-similar dynamics. Our results compare well with traditional theories of combustion and propose new experiments to study the dynamics of the interface and the flow fields in combustible systems. We further conduct reactive molecular dynamics simulations to elucidate the complexity of chemical processes, to study the destabilizing effect of energy fluctuations on the interface stability, and to illustrate the chemistry-induced instabilities. In summary, we identify the extreme sensitivity of the interface dynamics to the interfacial boundary conditions, including the formal properties of fundamental solutions and the qualitative and quantitative properties of the flow fields. This provides new opportunities for studies, diagnostics, and control of multiphase flows in a broad range of processes in nature and technology.

42 ENGINEERING↗
DOE OSTI2021

In situ/operando soft x-ray spectroscopy of chemical interfaces in gas and liquid environments

Many energy storage and energy conversion systems are based on the complexity of material architecture, chemistry, and interfacial interactions. To understand and thus ultimately control the energy applications calls for in situ/operando characterization tools. Over the years, in situ/operando soft x-ray spectroscopy has been developed for the studies of gas molecules, molecular liquids, catalytic, and electrochemical reactions. Soft x-ray spectroscopy offers electronic structure characterization of materials in energy conversion, energy storage, and catalysis regarding functionality, complexity of material architecture, and chemical interactions. It has been shown how to use the powerful in situ/operando soft x-ray spectroscopy characterization techniques of interfacial phenomena and how to reveal the mechanism of charge transfer and chemical transformation of solid/gas and solid/liquid interfaces of energy storage and catalytic materials in a realistic environment. It has been demonstrated how to overcome the challenge that soft x-rays cannot easily peek into the high-pressure catalytic or liquid electrochemical reactions. Finally, the unique design of in situ/operando soft x-ray spectroscopy instrumentation and fabrication principle and examples of experiments are presented.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Review—Polymer/Ceramic Interface Barriers: The Fundamental Challenge for Advancing Composite Solid Electrolytes for Li-Ion Batteries

Composite-solid electrolytes, in which ion-conducting polymers are combined with superionic ceramics, could revolutionize electrochemical-energy-storage devices enabling higher energy density, providing greater stability during operation and enhanced safety. However, the interfacial resistance between the ceramic and polymer phases strongly suppresses the ionic conductivity and presents the main obstacle to the use of these materials. Here, we emphasize the need for a distinct focus on reducing energy barriers to interfacial ion transport and improving the cation transference number. To achieve this goal, it is essential to develop a fundamental understanding of the parameters that influence the interfacial barriers to ion transport in composite electrolytes, and to understand the effect of the type of ceramic ("active" and "inert") and its content on ion-transport phenomena. We suggest that adapting the polymer chemistry, mainly directed on polymerized ionic liquids, (PolyILs), and combined with functionalization of the surface of ceramic nanoparticles is a promising route for overcoming the high-energy-barrier challenge. Owing to high content of ion-conducting ceramics and high t+ of PolyILs, the fractional contribution of the migrating cationic species to the total ionic conductivity of polymer-in-ceramic electrolytes via an interfacial percolation path, will be close to unity, thus eliminating complications that might arise from emerging concentration gradients during the operation of solid-state batteries.

25 ENERGY STORAGE↗
DOE OSTI2021

Interfacial Atomistic Mechanisms of Lithium Metal Stripping and Plating in Solid–State Batteries

All-solid-state batteries based on a Li metal anode represent a promising next-generation energy storage system, but are currently limited by low current density and short cycle life. Further research to improve the Li metal anode is impeded by the lack of understanding in its failure mechanisms at lithium–solid interfaces, in particular, the fundamental atomistic processes responsible for interface failure. Here, using large-scale molecular dynamics simulations, the first atomistic modeling study of lithium stripping and plating on a solid electrolyte is performed by explicitly considering key fundamental atomistic processes and interface atomistic structures. In the simulations, the interface failure initiated with the formation of nano-sized pores, and how interface structures, lithium diffusion, adhesion energy, and applied pressure affect interface failure during Li cycling are observed. By systematically varying the parameters of solid-state lithium cells in the simulations, the parameter space of applied pressures and interfacial adhesion energies that inhibit interface failure during cycling are mapped to guide selection of solid-state cells. Furthermore, this study establishes the atomistic modeling for Li stripping and plating, and predicts optimal solid interfaces and new strategies for the future research and development of solid-state Li-metal batteries.

25 ENERGY STORAGE↗
NASA NTRS1992

Phase-field model for isothermal phase transitions in binary alloys

A new phase field model is described which models isothermal phase transitions between ideal binary alloy solution phases. Equations are developed for the temporal and spatial variation of the phase field, which describes the identity of the phase, and of the composition. An asymptotic analysis, as the gradient energy coefficient of the phase field becomes small, was conducted. From the analysis, it is shown that the model recovers classical sharp interface models of this situation when the interfacial layers are thin, and they show how to relate the parameters appearing in the phase field model to material and growth parameters in real systems. Further, three stages of temporal evolution are identified: the first corresponding to interfacial genesis which occurs very rapidly; the second to interfacial motion controlled by the local energy difference across the interface and diffusion; the last taking place on a long time scale in which curvature effects are important and which correspond to Ostwald ripening. The results of the numerical calculations are presented.

Wheeler, A. A.↗
DOE OSTI2024

Wetting mechanism and alteration of nano-sized shale pores: Insights from contrast variation small angle neutron scattering

Wettability of tight shale is crucial for fluid flow and mass transport process in energy geosciences. However, understanding the interfacial chemistry and wetting mechanisms at sub-nano-pore scales remains a formidable challenge. Here, in this study, the Contrast Variation technique of Small Angle Neutron Scattering (CV-SANS) is employed to investigate shale’s interfacial chemistry using reagents that possess a range of different polarities, including water, n-decane, toluene, and dimethyl methanamide. Through five different experimental strategies, we have demonstrated a successful modification of shale wettability, ranging from enhancement, weakening, to reversal. Delving into the mechanisms, we illustrated the crucial role of pre-existing liquid films in these changes, where the uniquely co-existing polar and non-polar functional groups in dimethyl methanamide acted as a conduit for interfacial chemistry adjustments. Furthermore, a solvent immersion led to matrix dilation as well as liberation of residual oil-occupied pores, resulting in altered pore size distributions, with hydrogen bonding playing a significant role in the polar groups. Interestingly, despite shale exhibiting a stronger affinity for oil over water, hydrophilic solvents induced more substantial dilation than lipophilic ones. Collectively, this work elucidates the dynamic change of interfacial chemistry via the configuration of polarity using chemical reagents, and the CV-SANS technique underscores its invaluable utilities in decoding the interfacial wettability traits in nanopore space of shale.

58 GEOSCIENCES↗