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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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Competitive formation of intercalated versus supported metal nanoclusters during deposition on layered materials with surface point defects
Intercalated metal nanoclusters (NCs) can be formed under the surface of graphite after sputtering to generate surface “portal” defects that allow deposited atoms to reach the subsurface gallery. Although, there is a competition between formation of supported NCs on top of the surface and intercalated NCs under the surface, the latter only dominating at sufficiently high temperature. A stochastic model incorporating appropriate system thermodynamics and kinetics is developed to capture this complex and competitive nucleation and growth process. Kinetic Monte Carlo simulation shows that the model captures experimental trends observed for Cu and other metals and reveals that higher temperatures are needed to facilitate detachment of atoms from supported NCs enabling them to reach the gallery.
Non-equilibrium growth of metal clusters on a layered material: Cu on MoS 2
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Theory of mechanical exfoliation of van der Waals bonded layered materials
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Adsorption of Molecules, Clusters, and Layered Materials on Surfaces (Final Report)
This grant supported research assistant professor Hong Tang and graduate student Shah Tanvir ur Rahman Chowdhury, who contributed to most of the research articles [1-10] that acknowledge it (nine published and one in preparation).
Change in Stability and Degradation Pathway of MAPbI3 Arising from Contact with Oxide Transport Layer Materials
F19 MRS meeting presentation on MAPbI3 decomposition
Development of Machine Learned Interatomic Potentials for Modeling the Effect of Mixed Material Layers on Hydrogen Retention
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Mechanisms of adsorbing hydrogen gas on metal decorated graphene
Hydrogen is a key player in global strategies to reduce greenhouse gas emissions. In order to make hydrogen a widely used fuel, we require more efficient methods of storing it than the current standard of pressurized cylinders. An alternative method is to adsorb H 2 in a material and avoid the use of high pressures. Among many potential materials, layered materials such as graphene present a practical advantage as they are lightweight. However, graphene and other 2D materials typically bind H 2 too weakly to store it at the typical operating conditions of a hydrogen fuel cell, meaning that high pressure would still be required. Modifying the material, for example by decorating graphene with adatoms, can strengthen the adsorption energy of H 2 molecules, but the underlying mechanisms are still not well understood. In this work, we systematically screen alkali and alkaline-earth metal decorated graphene sheets for the static thermodynamic adsorption of hydrogen gas from first principles and focus on the mechanisms of binding. We show that there are three mechanisms of adsorption on metal decorated graphene and each leads to distinctly different hydrogen adsorption structures. The three mechanisms can be described as weak van der Waals physisorption, metal adatom facilitated polarization, and Kubas adsorption. Among these mechanisms, we find that Kubas adsorption is easily perturbed by an external electric field, providing a way to tune H 2 adsorption. In conclusion, this work is foundational and builds our understanding of H 2 adsorption under idealized conditions.
LAN: A Materials Notation for Two-Dimensional Layered Assemblies
Two-dimensional (2D) layered materials offer intriguing possibilities for novel physics and applications. Before any attempt at exploring the materials space in a systematic fashion, or combining insights from theory, computation, and experiment, a formal description of information about an assembly of arbitrary composition is required. Here, we introduce a domain-generic notation that is used to describe the space of 2D layered materials from monolayers to twisted assemblies of arbitrary composition, existent or not yet fabricated. The notation corresponds to a theoretical materials concept of stepwise assembly of layered structures using a sequence of rotation, vertical stacking, and other operations on individual 2D layers. Its scope is demonstrated with several example structures using common single-layer materials as building blocks. This work overall aims to contribute to the systematic codification, capture, and transfer of materials knowledge in the area of 2D layered materials.
Tuning Sodium Occupancy Sites in P2-Layered Cathode Material for Enhancing Electrochemical Performan
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Stabilizing Transition Metal Vacancy Induced Oxygen Redox by Co 2+ /Co 3+ Redox and Sodium-Site Doping for Layered Cathode Materials
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Organic photosensitive devices made using semi-orthogonal solvents and methods of making the same
Disclosed herein are organic photosensitive optoelectronic device comprising a first layer comprising one or more of a first layer material, a second layer comprising one or more of a second layer material, and a third layer comprising one or more of a third layer material. The second layer may be dissolved in a semi-orthogonal solvent. The first layer and the third layer may be very slightly soluble or practically insoluble in the semi-orthogonal solvent.
Method of coating high atomic number metals onto oxygen or hydroxyl rich surfaces
Methods for making layered materials and layered materials including high atomic number metals and metal alloys adhered to surfaces are provided. Such surfaces may be oxygen or hydroxyl rich surfaces. Certain methods include depositing a tie down layer of a first metal or metal alloy particles onto a first surface of base material and depositing a high atomic number metal or metal alloy layer onto the first surface after depositing the tie down layer, wherein particles comprising the high atomic number metal or metal alloy layer have a higher atomic number than the first metal or metal alloy particles.
Extended Interfacial Stability through Simple Acid Rinsing in a Li-Rich Oxide Cathode Material
Layered Li-rich Ni, Mn, Co (NMC) oxide cathodes in Li-ion batteries provide high specific capacities (>250 mAh/g) via O-redox at high voltages. However, associated high-voltage interfacial degradation processes require strategies for effective electrode surface passivation. Here, we show that an acidic surface treatment of a Li-rich NMC layered oxide cathode material leads to a substantial suppression of CO 2 and O 2 evolution, ~90% and ~100% respectively, during the first charge up to 4.8 V vs. Li +/0 . CO 2 suppression is related to Li 2 CO 3 removal as well as effective surface passivation against electrolyte degradation. This treatment does not result in any loss of discharge capacity and provides superior long-term cycling and rate performance compared to as-received, untreated materials. We also quantify the extent of lattice oxygen participation in charge compensation (“O-redox”) during Li + removal by a novel ex-situ acid titration. Our results indicate that the peroxo-like species resulting from O-redox originate on the surface at least 300 mV earlier than the activation plateau region around 4.5 V. X-ray photoelectron spectra and Mn -L X-ray absorption spectra of the cathode powders reveal a Li + deficiency and a partial reduction of Mn ions on the surface of the acid-treated material. More interestingly, although the irreversible oxygen evolution is greatly suppressed through the surface treatment, our O K-edge resonant inelastic X-ray scattering shows the lattice O-redox behavior largely sustained. The acidic treatment, therefore, only optimizes the surface of the Li-rich material and almost eliminates the irreversible gas evolution, leading to improved cycling and rate performance. This work therefore presents a simple yet effective approach to passivate cathode surfaces against interfacial instabilities during high-voltage battery operation.