Molecular simulations of kinetic stable calcium isotope fractionation at the calcite-aqueous interface
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Lammers, Laura Nielsen (ORCID:0000000285097571)↗
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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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On the enhanced sulfur and coking tolerance of Ni-Co-rare earth oxide catalysts for the dry reforming of methane
In this study, sulfur and coking tolerance of Ni-based dry reforming catalysts were examined. Catalysts utilizing both Ce/Zr and Ce/La oxide supports, some with additional Co, were tested. Long-term reaction runs were conducted with and without sulfur in the feed. Catalysts were also characterized by STEM, XPS, XAFS and XANES and CO chemisorption. Only catalysts where Co was also present, and supported on the Ce-Zr oxide, were capable of extended sulfur tolerance at >20 ppm sulfur. This tolerance, along with a greatly reduced coking rate, is linked to Co in intimate contact with Ni, the mixture existing as clusters anchored and influenced electronically by the oxide support. The activation of methane takes place on these sites. Larger metal aggregates formed by ripening during reaction appear to be spectators. The measured activation energies for dry reforming suggest that CO 2 activation takes place at the oxide interface, and is a kinetically significant step.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Directed energy deposition of functionally graded V-4Cr-4Ti to Fe-9Cr transition for fusion power systems
This study proposes a graded structure via additive manufacturing for divertor and first wall blanket applications in fusion reactors. Materials were selected based on thermodynamic calculations to operate from 1100 °C at the plasma-facing level to 550 °C at the structural steel level. Conventional joining methods often lead to failures due to discrete reaction layers with significant mechanical property differences. Using laser beam-directed energy deposition (LB-DED), this study demonstrates the fabrication of a VCrTi-Gr91 steel functionally graded component through a novel process parameter optimization framework. A systematic approach included powder characterization, single-track depositions, and construction of printability maps. Near full-density specimens of each interlayer were additively manufactured, and a transition from V-based alloys to reduced activation ferritic martensitic steels was achieved. Computational material selection of interlayer alloys and thermodynamic/diffusion kinetics simulations prevented most interface incompatibilities. A brittle intermetallic formed at one interface, causing cracking, which was not predicted by current thermodynamic models. Transition alloy design approach was updated with a more recent database and a mitigation strategy has been proposed to eliminate the formation of deleterious intermetallic phases. Ultimately, LB-DED has proven effective for producing multi-material graded systems for fusion applications, with the demonstrated process parameter optimization framework applicable to various materials.
Additive manufacturing↗
Interfacial Engineering Enabled Novel Bi-Based Layered Oxide Supercells with Modulated Microstructures and Tunable Physical Properties
Two-dimensional layered materials hold great significance to fundamental scientific research and future nanoscale device applications. Besides the well-studied graphene and dichalcogenides, oxide-based layered materials are another family attracting significant research interests, for example, the Bi-based Bi 3 Fe 2 Mn 2 O 10-δ layered supercell (called BFMO322 SC) structure. BFMO322 SC is an excellent room-temperature multiferroic material, but its growth mechanism is unclear. In this work, Bi 2 Fe 1–x Mn x O 6 thin films with different Fe/Mn molar ratios were deposited on CeO 2 buffer layers by pulsed laser deposition. By varying the Fe/Mn molar ratios, it has been determined that Mn can favor the growth of Bi-based layered structures, while Fe cannot facilitate the growth. A series of novel layered supercell structures can be obtained by manipulating the growth kinetics at the substrate/film interface, as achieved by precisely controlling the growth conditions. More interestingly, the magnetization and optical band gap of the Bi-based layered structures can be tuned by varying the Fe/Mn molar ratios. This original work has demonstrated the power of interfacial engineering in enabling new Bi-based layered structures and thus is of great significance for the design of new layered structures with multifunctionalities.
36 MATERIALS SCIENCE↗
Fundamental electrode kinetics
Report presents the fundamentals of electrode kinetics and the methods used in evaluating the characteristic parameters of rapid-charge transfer processes at electrode-electrolyte interfaces. The concept of electrode kinetics is outlined, followed by the principles underlying the experimental techniques for the investigation of electrode kinetics.
Elder, J. P.↗
Analysis of the thermal performance of heat pipe radiators
A comprehensive mathematical model and computational methodology are presented to obtain numerical solutions for the transient behavior of a heat pipe radiator in a space environment. The modeling is focused on a typical radiator panel having a long heat pipe at the center and two extended surfaces attached to opposing sides of the heat pipe shell in the condenser section. In the set of governing equations developed for the model, each region of the heat pipe - shell, liquid, and vapor - is thermally lumped to the extent possible, while the fin is lumped only in the direction normal to its surface. Convection is considered to be the only significant heat transfer mode in the vapor, and the evaporation and condensation velocity at the liquid-vapor interface is calculated from kinetic theory. A finite-difference numerical technique is used to predict the transient behavior of the entire radiator in response to changing loads.
Boo, J. H.↗
Perception and control of rotorcraft flight
Three topics which can be applied to rotorcraft flight are examined: (1) the nature of visual information; (2) what visual information is informative about; and (3) the control of visual information. The anchorage of visual perception is defined as the distribution of structure in the surrounding optical array or the distribution of optical structure over the retinal surface. A debate was provoked about whether the referent of visual event perception, and in turn control, is optical motion, kinetics, or dynamics. The interface of control theory and visual perception is also considered. The relationships among these problems is the basis of this article.
Owen, Dean H.↗
Kinetic versus Thermodynamic Stability of LLZO in Contact with Lithium Metal
Li 7 La 3 Zr 2 O 12 (LLZO) garnet-based oxides are a promising class of solid electrolytes used as the separator in all-solid-state batteries (ASSBs). While LLZO is considered to have a wide electrochemical stability window, its intrinsic stability in contact with lithium metal is not sufficiently well understood, and there is still a debate on the key question of whether LLZO does or does not form passivation layers before and during cycling. Utilizing both in situ and operando X-ray photoelectron spectroscopy techniques, in this work we reveal the presence of a kinetic barrier to the reduction of LLZO by Li metal, with the extent of oxygen-deficient interphase (ODI) formation depending sensitively on the energetics of Li metal arriving at the Li vertical bar LLZO interface. Despite the clear presence of a kinetic barrier to reduction, the electrochemical response of the Li vertical bar LLZO interface is unchanged by the presence of the ODI, indicating that ODI formation during electrochemical cycling does not hinder charge transfer across the Li vertical bar LLZO interface. Overall, these results reveal that the reactivity of LLZO with Li metal depends not only on the material properties of the adjoining phases (i.e., surface purity and active contact) and their resulting thermodynamic stability but also on the energy input at the interface and the resulting reaction kinetics. Furthermore, the presence of a kinetic barrier to reduction highlights the additional complexities governing the reactivity of solid-state interfaces in ASSBs and underscores the importance of operando characterization of interfacial stability to design more robust, high-performance protection strategies for solid electrolytes in contact with reactive electrodes.
25 ENERGY STORAGE↗
Controlling Interfacial Charge Separation Energetics and Kinetics
The overall goal is to probe electron transfer kinetics of the Marcus inverted region at interfaces. This project specifically uses a dye‐semiconductor interface with a reversible electron transfer reagent in solution where the semiconductor conduction band and electron transfer reagent ideally have a potential energy difference firmly within the Marcus inverted region. The goals of this project are: (Goal 1) Identify dye design elements that give dyes with low energy ground‐state oxidation potentials while retaining desirable electron transfer kinetics at the semiconductor interface. (Goal 2) Identify dye designs with excited‐state oxidation potentials set to fixed energies through molecular design while the dye ground‐state oxidation potentials are varied to allow for the evaluation of varied electron transfer reagents/redox shuttles (RS) with different free energies for electron transfer. (Goal 3) Within the context of the functionality identified in goals 1 and 2, goal 3 seeks to design dyes with features maximizing charge carrier lifetimes by minimizing recombination losses at metal oxide interfaces with high voltage systems. (Goal 4) Probe electron transfer kinetics in a high voltage‐dye sensitized solar cell with both the oxidized dye and RS firmly within the Marcus inverted region with regard to the TiO2 CB. (Goal 5) Identify tailored sensitizer/redox shuttle pairs with desirable electron transfer kinetics in defined spectral regions capable of “banding off” incident solar irradiation to give high voltage multijunction systems capable of exceeding the Shockley‐Queisser limit and powering catalytic processes.
14 SOLAR ENERGY↗
Insights into the Electrochemical Oxygen Evolution Reaction with ab Initio Calculations and Microkinetic Modeling: Beyond the Limiting Potential Volcano
Density functional theory calculations are potentially useful for both understanding the activity of experimentally tested catalysts and screening for new catalyst materials. For electrochemical oxygen evolution reaction (OER) catalysts, these analyses are usually performed considering only the thermodynamics of the reaction path, which typically consists of adsorbed OH*, O*, and OOH*. Scaling relationships between the stability of these intermediates lead to a limiting potential volcano whose optimum is constrained by the roughly constant offset between the binding energies of OH* and OOH*. In this work, we evaluate OER kinetics at rutile IrO 2 , RuO 2 , RhO 2 , and PtO 2 surfaces by computing reaction barriers with an explicit model of the electrochemical interface. We conclude that the kinetics of proton transfer between oxygen atoms at the surface and in the electrolyte is facile and that O–O bond formation is most likely rate-determining in all cases. Combining these results with a microkinetic model and a scaling relationship for the OOH* formation barrier, we construct a new activity volcano whose optimum is similar to that of the limiting potential volcano for typical current densities. This kinetic volcano is also shown to agree reasonably well with experimental observations. Based on this analysis, we propose a more precise requirement for improving OER catalysts beyond the state of the art: the transition state for OOH* formation must be stabilized as opposed to the fully formed OOH* final state as has been previously presumed.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Controlling Metal–Organic Framework/ZnO Heterostructure Kinetics through Selective Ligand Binding to ZnO Surface Steps
Metal–organic framework (MOF) heterostructures exhibit unique properties beyond those of individual components, but their design requires an understanding of energetic and kinetic controls at MOF–substrate interfaces. Although the structural relationship has been widely used in heterostructure design, it overlooks the interplay between the organic ligand and the substrate which controls the kinetics and energetics of growth of the final structure. In this study, we used zeolitic imidazolate frameworks (ZIF-8) on ZnO as a model system to evaluate this interplay via in situ monitoring and simulations. Our results demonstrate multiple roles of the 2-methyl-imidazole (2-MIM) ligand as “dissolution-promoter”, “step-pinner”, and “terrace-binder” on the ZnO (001) face and “dissolution-promoter” and “terrace-binder” on the ZnO (100) face. Through these multiple face-specific roles, 2-MIM modulates ZnO dissolution kinetics and, hence, the Zn 2+ release rate, tuning local supersaturations that dictating the characteristic ZIF-8 crystallization kinetics on different substrate faces. The critical thickness for transition from 2D to 3D growth is dictated by competition between interfacial and strain energies. The atomic-scale mechanism of the coupled substrate dissolution and MOF growth, mediated by selective linker–substrate binding, furnishes a new synthesis pathway for other complex heterostructures.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Heterogeneous Solid Electrolyte Interphase Interactions Dictate Interface Instability in Sodium Metal Electrodes
Sodium (Na) metal batteries have attracted recent attention due to their low cost and high abundance of Na. However, the advancement of Na metal batteries is impeded due to key challenges such as dendrite growth, solid electrolyte interphase (SEI) fracture, and low Coulombic efficiency. This study examines the coupled electro‐chemo‐mechanical interactions governing the electrodeposition stability and morphological evolution at the Na/electrolyte interface. The SEI heterogeneities influence transport and reaction kinetics leading to the formation of current and stress hotspots during Na plating. Further, it is demonstrated that the heterogeneity‐induced Na metal evolution and its influence on the stress distribution critically affect the mechanical overpotential, contributing to a faster SEI failure. The analysis reveals three distinct failure mechanisms—mechanical, transport, and kinetic—that govern the onset of instabilities at the interface. Finally, a comprehensive comparative study of SEI failure in Na and lithium (Li) metal anodes illustrates that the electrochemical and mechanical characteristics of the SEI are crucial in tailoring the anode morphology and interface stability. This work delineates mechanistic stability regimes cognizant of the SEI attributes and underlying failure modes and offers important guidelines for the design of artificial SEI layers for stable Na metal electrodes.
25 ENERGY STORAGE↗
Molecular homing and retention of muscle membrane stabilizing copolymers by non-invasive optical imaging in vivo
First-in-class membrane stabilizer Poloxamer 188 (P188) has been shown to confer membrane protection in an extensive range of clinical conditions; however, elements of the systemic distribution and localization of P188 at the organ, tissue, and muscle fiber levels in vivo have not yet been elucidated. Here we used non-invasive fluorescence imaging to directly visualize and track the distribution and localization of P188 in vivo. The results demonstrated that the Alx647 probe did not alter the fundamental properties of P188 to protect biological membranes. Distribution kinetics in mdx mice demonstrated that Alx647 did not interface with muscle membranes and had fast clearance kinetics. In contrast, the distribution kinetics for P188-Alx647 was significantly slower, indicating a dramatic depot and retention effect of P188. Results further demonstrated the significant retention of P188-Alx647 in the skeletal muscle of mdx mice, showing a significant genotype effect with a higher fluorescence signal in the mdx muscles over BL10 mice. High-resolution optical imaging provided direct evidence of P188 surrounding the sarcolemma of skeletal and cardiac muscle cells. Taken together, these findings provide direct evidence of muscle-disease-dependent molecular homing and retention of synthetic copolymers in striated muscles thereby facilitating advanced studies of copolymer-membrane association in health and disease.
60 APPLIED LIFE SCIENCES↗
Electroconvection near an ion-selective surface with Butler–Volmer kinetics
We study the effects of interfacial kinetics on the electro-hydrodynamics of ion transport near an ion-selective surface using a combination of linear stability analysis and numerical simulation. The finite kinetics of the electrolyte–electrode interface affects the ion transfer and electroconvection in many ways. On a surface of fixed topography, such as a metal surface of slow and stable ion deposition or covered by a polymer membrane, the finite kinetics reduces the current in one-dimensional ion diffusion/migration, increases the critical voltage for the onset of the electroconvective instability, changes the dynamics of the electroconvection and the overlimiting current, and enhances the lateral ion diffusion within the interfacial layer. The first three effects are indirectly caused by the reaction kinetics and can be characterized by an effective voltage difference across the liquid electrolyte. In comparison, the last effect is controlled by a direct interplay between kinetics and nonlinear electroconvection. Scaling laws for ion transport and features of electroconvection are proposed. We also analyse the linear stability of a surface which evolves under ion deposition and find that the finite kinetics decreases the growth rate of both electroconvective and morphological instabilities and therefore modifies the wavenumber of the most unstable mode.
Mechanics↗
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↗
An investigation of the effect of surface impurities on the adsorption kinetics of hydrogen chemisorbed onto iron
The goal of this program was to develop an understanding of heterogeneous kinetic processes for those molecular species which produce gaseous hydrogen degradation of the mechanical properties of metallic structural materials. Although hydrogen degradation of metallic materials is believed to result from dissolved protonic hydrogen, the heterogeneous hydrogen interface transport processes often dominate the kinetics of degradation. The initial step in the interface transport process is the dissociative chemisorption of the molecular species at the metal surface followed by hydrogen absorption into and transport through the bulk. The interaction of hydrogen with the surfaces of alpha-2(Ti3Al) titanium aluminide, gamma(TiAl) titanium aluminide, and beryllium were studied.
Shanabarger, Mickey R.↗
Electron escape depth variation in thin SiO2 films measured with variable photon energy
A double crystal monochromator at the Stanford Synchrotron Radiation Laboratory is used to study the Si/SiO2 interface, using photon energies of hv = 1950-3700 eV. This photon energy range allows interfaces to be observed through oxide layers 50 A thick or more. Variations in electron escape depth and/or oxide density as a function of distance from the interface are observed over the entire kinetic energy range (100-3600 eV). These differences are attributed to a strained oxide layer near the interface.
Hecht, M. H.↗
An investigation of the effect of surface impurities on the adsorption kinetics of hydrogen chemisorbed onto iron
The goal was to develop an understanding of heterogeneous kinetic processes for those molecular species which produce gaseous hydrogen degradation of the mechanical properties of metallic structural materials. Although hydrogen degradation of metallic materials is believed to result from dissolved protonic hydrogen, the heterogeneous hydrogen interface transport processes often dominate the kinetics of the degradation process. The initial step in the interface transport process is the dissociative chemisorption of the molecular species at the metal surface followed by hydrogen absorption into and transport through the bulk. Modern advanced aerospace applications often require the use of structural materials in high pressure hydrogen environments at temperatures which range from low cryogenic temperatures to very high temperatures (1300 K and greater). Materials proposed for these applications, such as the titanium aluminides, beta-titanium alloys, nickel- and cobalt-based superalloys, molybdenum-rhenium alloys, beryllium, and various beryllides, need to possess a high degree of immunity from hydrogen induced degradation of mechanical properties. In the present program, the interaction of hydrogen with the surfaces of alpha-2 (Ti3Al) titanium aluminide, gamma (TiAl) titanium aluminide, and beryllium were studied. The interaction of low pressure hydrogen with gamma titanium aluminide and beryllium was found to be relatively weak, in the sense that adsorption leads to a low surface concentration of dissociated hydrogen, i.e., the chemisorption process is reversible at room temperature (300 K) for gamma titanium aluminide and the sticking coefficient for chemisorption is extremely small for beryllium. Hydrogen was found to interact readily with alpha-2 titanium aluminide to form a stable surface hydride at 300 K. These results correlate well with other recent studies which show that the mechanical properties for alpha-2 titanium aluminide are readily degraded in hydrogen while gamma titanium aluminide exhibits less degradation and beryllium essentially no degradation. The interaction of oxygen with the surface of these materials has been studied, also, in the present program.
Shanabarger, Mickey R.↗