Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “active lattices”

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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Electrolyte-Induced Restructuring of Acid-Stable Oxygen Evolution Catalysts

Crystalline metal oxide catalysts operating under oxygen evolution reaction (OER) conditions invariably restructure, resulting in active sites with hydroxo/oxo species in an amorphous environment. An increase in the population of terminal hydroxo/oxo species (i.e., edge sites) facilitates proton-coupled electron-transfer (PCET) kinetics for oxygen generation and thus improves catalyst competency. While amorphous films benefit from a greater density of active sites, they suffer from diminished charge transport as compared to that of extended crystalline lattices. Managing this amorphous–crystalline dichotomy is essential when designing OER catalysts, which we highlight with the examination of electrodeposited PbO x materials, which historically are very poor OER catalysts. Along these lines, the presence of phosphate during PbO x electrodeposition truncates the growth of an extended lattice owing to its strong bonding to oxide surfaces to afford an amorphous catalyst film (A-PbO x ) with significant charge-transfer resistance (138 ± 42 Ω) and poor OER kinetics (420 ± 105 mV dec –1 Tafel slope). Conversely, electrodeposition of Pb 2+ in the presence of less coordinating electrolytes such as nitrate affords crystalline β-PbO2 with improved charge-transfer resistance (42.6 ± 1.1 Ω), though still poor OER kinetics (134 ± 36 mV dec –1 Tafel slope). By operating amorphous A-PbOx in less coordinating electrolytes, however, a new partially crystalline material can be generated (μc-PbO x ) with further reduced charge-transfer resistance (33.0 ± 1.4 Ω) and improved OER kinetics (70 ± 15 mV dec –1 Tafel slope). The enhanced OER activity of μc-PbO x is the result of coupling the high edge-site population of an amorphous PbOx phase with crystalline-like charge transport properties. Finally, the ability to use an electrolyte to induce OER activity in an inactive amorphous form of PbO x highlights the benefits of optimizing the amorphous–crystalline phase compositions in the design of active OER catalysts.

catalysts↗
DOE OSTI2021

Construction of Lattice Strain in Bimetallic Nanostructures and Its Effectiveness in Electrochemical Applications

Bimetallic nanocrystals (NCs), associated with various surface functions such as ligand effect, ensemble effect, and strain effect, exhibit superior electrocatalytic properties. The stress-induced surface strain effect can alter binding strength between the surface active sites and reactants as well as their intermediates, and the electrochemical performance of bimetallic NCs can be significantly facilitated by the lattice-strain modification via their morphologies, sizes, shell-thickness, surface defectiveness as well as compositions. Here in this review, an overview of fundamental principles, characterization techniques, and quantitative determination of the surface lattice strain is provided. Various strategies and synthesis efforts on creating lattice-strain-engineered bimetallic NCs, including the de-alloying process, atomic layer-by-layer deposition, thermal treatment evolution, one-pot synthesis, and other efforts are also discussed. It is further outlined how the lattice strain effect promotes electrochemical catalysis through the selected case studies. The reactions on oxygen reduction reaction, small molecular oxidation, water splitting reaction, and electrochemical carbon dioxide reduction reactions are focused. In particular, studies of lattice strain arisen from core–shell nanostructure and defectiveness are highlighted. Lastly, the potential challenges are summarized and the prospects of lattice-strain-based engineering on bimetallic nanocatalysts with suggestion and guidance of the future electrocatalyst design are envisioned.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Global quantum phase diagram and non-Abelian chiral spin liquid in a spin- 3 2 square-lattice antiferromagnet

Since strong quantum fluctuations are essential for the emergence of quantum spin liquids, there have been extensive exploration and identification of spin liquid candidates in spin-$\frac{1}{2}$ systems, while such activities are rare in higher spin systems. Here we report an example of non-Abelian chiral spin liquid emerging in a spin-$\frac{3}{2}$ Heisenberg model on a square lattice. By tuning Heisenberg exchange interaction and scalar chirality interaction, we map out a quantum phase diagram enclosing three conventional magnetic orders and a chiral spin liquid based on density-matrix renormalization group studies. The nature of the spin liquid is identified as a long-sought bosonic version of the Read-Rezayi state that supports non-Abelian Fibonacci anyonic statistics, identified by the ground state entanglement spectrum. Significantly, we establish that the non-Abelian chiral spin liquid emerges through the enlarged local degrees of freedom and enhanced quantum fluctuations near the classical phase boundaries of competing magnetic orders. Finally, our numerical discovery of an exotic quantum spin liquid in a spin-$\frac{3}{2}$ system suggests a route for discovering fractionalized quantum phases in frustrated higher spin magnetic compounds.

2-dimensional systems↗
DOE OSTI2021

Ultrafast Carrier and Lattice Dynamics in Plasmonic Nanocrystalline Copper Sulfide Films

Excited carrier dynamics in plasmonic nanostructures determines many important optical properties such as nonlinear optical response and photocatalytic activity. Here it is shown that mesoscopic plasmonic covellite nanocrystals with low free-carrier concentration exhibit a much faster carrier relaxation than in traditional plasmonic materials. A nonequilibrium hot-carrier population thermalizes within first 20 fs after photoexcitation. A decreased thermalization time in nanocrystals compared to a bulk covellite is consistent with the reduced Coulomb screening in ultrathin films. The subsequent relaxation of thermalized, equilibrium electron gas is faster than in traditional plasmonic metals due to the lower carrier concentration and agrees well with that in a bulk covellite showing no evidence of quantum confinement or hot-hole trapping at the surface states. The excitation of coherent optical phonon modes in a covellite is also demonstrated, revealing coherent lattice dynamics in plasmonic materials, which until now was mainly limited to dielectrics, semiconductors, and semimetals. These findings show advantages of this new mesoscopic plasmonic material for active control of optical processes.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Experimental realization of an extended Fermi-Hubbard model using a 2D lattice of dopant-based quantum dots

The Hubbard model is an essential tool for understanding many-body physics in condensed matter systems. Artificial lattices of dopants in silicon are a promising method for the analog quantum simulation of extended Fermi-Hubbard Hamiltonians in the strong interaction regime. However, complex atom-based device fabrication requirements have meant emulating a tunable two-dimensional Fermi-Hubbard Hamiltonian in silicon has not been achieved. Here, we fabricate 3 × 3 arrays of single/few-dopant quantum dots with finite disorder and demonstrate tuning of the electron ensemble using gates and probe the many-body states using quantum transport measurements. By controlling the lattice constants, we tune the hopping amplitude and long-range interactions and observe the finite-size analogue of a transition from metallic to Mott insulating behavior. We simulate thermally activated hopping and Hubbard band formation using increased temperatures. As atomically precise fabrication continues to improve, these results enable a new class of engineered artificial lattices to simulate interactive fermionic models.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Thermodynamics and kinetics of core-shell versus appendage co-precipitation morphologies

What determines precipitate morphologies in co-precipitating alloy systems? We focus on alloys of two precipitating phases, with the fast-precipitating phase acting as heterogeneous nucleation sites for a second phase manifesting slower kinetics. Kinetic lattice Monte Carlo simulations show that the interplay between interfacial and ordering energies, plus active diffusion paths, strongly affect the selection of core-shell verses appendage morphologies. We study a FeCuMnNiSi alloy using the combination of atom probe tomography and simulations, and show that the ordering energy reduction of the MnNiSi phase heterogeneously nucleated on a pre-existing copper-rich precipitate exceeds the energy penalty of a predominantly Fe/Cu interface, leading to initial appendage, rather than core-shell, formation. Diffusion of Mn, Ni and Si around and through the Cu core towards the ordered phase results in subsequent appendage growth. We further show that in cases with higher primary precipitate interface energies and/or suppressed ordering, the coreshell morphology is favored.

Shu, Shipeng↗
DOE OSTI2026

Origin of Electrochemical Activation Leading to Enhanced Cycling Stability of Li‐ and Mn‐Rich Cathodes

Electrochemical activation is a critical step for optimal functioning of Li- and Mn-rich (LMR) cathodes, yet the underlying mechanism for such activation remains elusive. Here, by using scanning/transmission electron microscopy (S/TEM) combined with the associated energy-dispersive x-ray spectroscopy (EDS) and electron energy-loss spectroscopy (EELS), we decipher the origin of the activation enhanced electrochemical properties. We reveal that activation induces the formation of a spinel-like phase within the C2/m domains of the LMR cathode, where the transition-metal ions partially occupy both the tetrahedral (8a) and octahedral (16c) sites of the $Fd\bar{3}m$ spinel lattice, distinguishing the spinel-like phase from the conventional high-voltage spinel. Systematic varying the cycling voltage reveals a critical activation voltage above which this spinel-like phase forms, while lower voltages preserve the layered bulk structure. As the spinel-like phase is a stable structure for electrochemical cycling, the present findings provide direct mechanistic insight into the voltage-dependent activation process and explain how the C2/m to spinel-like transformation upon activation contributes to the electrochemical performance of LMR cathodes, providing guidance for the rational design of Li-rich cathodes with enhanced cycling durability.

Li-rich and Mn-rich cathode↗
DOE OSTI2025

Crossing the Oxo‐Peroxo Wall for Selective Electrochemical Epoxidation

Electrochemical oxidation in water requires the formation of reactive oxygen species to be able to oxidize unsaturated hydrocarbons to epoxides, aldehydes, and ketones. These reactions, broadly classified as alternative oxidation reactions (AOR), directly compete with the prevalent oxygen evolution reaction (OER). In molecular catalysis, the Oxo-Wall dictates a transition from a stable oxo intermediate (OER active) to a meta-stable metal-oxo (OER inactive) generally occurs. In this work on heterogeneous catalysis, the same Oxo-Wall applies, however, a meta-stable oxo preferentially coordinates with lattice oxygen to form a more stable surface peroxo intermediate. A universal free energy onset of this process is identified at 3.39 eV under electrochemical activation in water and show that it is completely decoupled from the OER oxo species. Such decoupling gives rise to a new region of oxygen reactivity relevant for AOR where a selective oxidation of the unsaturated C-C bonds is predicted to occur instead of OER. A distinct AOR overpotential volcano is constructed and identify recently reported electrocatalysts, including palladium-platinum for propylene epoxidation and silver-nickel for ethylene epoxidation, along with others such as TiO 2 and CuO. Broader implications and limitations of electrochemical AOR are discussed, highlighting their potential to enable electrochemically enhanced thermal catalysis.

Electrocatalysis↗
DOE OSTI2025

Atomic dynamics of gas-dependent oxide reducibility

Understanding oxide reduction is critical for advancing metal production, catalysis and energy technologies. Although carbon monoxide (CO) and hydrogen (H 2 ) are widely used reductants, the mechanisms by which they work are often presumed to be similar, both involving lattice oxygen removal. However, because of growing interest in replacing CO with H 2 to lower CO 2 emissions, distinguishing gas-specific reduction pathways is critical. Yet, capturing these atomic-scale processes under reactive gas and high-temperature conditions remains challenging. Here we use environmental transmission electron microscopy, which is capable of real-time, atomic-resolution imaging of gas–solid redox reactions to directly visualize the gas-dependent oxide reduction dynamics in NiO. We show that CO drives surface nucleation and the growth of metallic Ni islands, leading to self-limiting surface metallization. Conversely, H 2 activates a coupled surface-to-bulk transformation, where protons from dissociated H 2 infiltrate the oxide lattice to promote the inward migration of surface-generated oxygen vacancies and enabling bulk metallization. By contrast, oxygen vacancies formed by CO remain confined near the surface, where they rapidly form a metallic Ni layer that inhibits further reduction. Furthermore, these results reveal distinct atomistic pathways for CO and H 2 and provide insights that may guide metallurgical processes and catalyst design.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Elastic Lattice Enabling Reversible Tetrahedral Li Storage Sites in a High-Capacity Manganese Oxide Cathode

The key to breaking through the capacity limitation imposed by intercalation chemistry lies in the ability to harness more active sites that can reversibly accommodate more ions (e.g., Li + ) and electrons within a finite space. However, excessive Li-ion insertion into the Li layer of layered cathodes results in fast performance decay due to the huge lattice change and irreversible phase transformation. Here, in this study, an ultrahigh reversible capacity is demonstrated by a layered oxide cathode purely based on manganese. Through a wealth of characterizations, it is clarified that the presence of low-content Li 2 MnO 3 domains not only reduces the amount of irreversible O loss; but also regulates Mn migration in LiMnO 2 domains, enabling elastic lattice with high reversibility for tetrahedral sites Li-ion storage in Li layers. This work utilizes bulk cation disorder to create stable Li-ion-storage tetrahedral sites and an elastic lattice for layered materials, with a reversible capacity of 600 mA h g –1 , demonstrated in th range 0.6–4.9 V versus Li/Li + at 10 mA g –1 . Admittedly, discharging to 0.6 V might be too low for practical use, but this exploration is still of great importance as it conceptually demonstrates the limit of Li-ions insertion into layered oxide materials.

25 ENERGY STORAGE↗
DOE OSTI2022

Charge density wave activated excitons in TiSe 2 –MoSe 2 heterostructures

Layered materials enable the assembly of a new class of heterostructures where lattice-matching is no longer a requirement. Interfaces in these heterostructures therefore become a fertile ground for unexplored physics as dissimilar phenomena can be coupled via proximity effects. In this article, we identify an unexpected photoluminescence (PL) peak when MoSe 2 interacts with TiSe 2 . A series of temperature-dependent and spatially resolved PL measurements reveal that this peak is unique to the TiSe 2 –MoSe 2 interface, is higher in energy compared to the neutral exciton, and exhibits exciton-like characteristics. The feature disappears at the TiSe 2 charge density wave transition, suggesting that the density wave plays an important role in the formation of this new exciton. We present several plausible scenarios regarding the origin of this peak that individually capture some aspects of our observations but cannot fully explain this feature. These results therefore represent a fresh challenge for the theoretical community and provide a fascinating way to engineer excitons through interactions with charge density waves.

36 MATERIALS SCIENCE↗
DOE OSTI2023

In Situ Reconstructed Mo–doped Amorphous FeOOH Boosts the Oxygen Evolution Reaction

Developing a fast and highly active oxygen evolution reaction (OER) catalyst to change energy kinetics technology is essential for making clean energy. Herein, we prepare three-dimensional (3D) hollow Mo-doped amorphous FeOOH (Mo-FeOOH) based on the precatalyst MoS 2 /FeC 2 O 4 via in situ reconstruction strategy. Mo-FeOOH exhibits promising OER performance. Specifically, it has an overpotential of 285 mV and a durability of 15 h at 10 mA cm –2 . Characterizations indicate that Mo was included inside the FeOOH lattice, and it not only modifies the electronic energy levels of FeOOH but also effectively raises the inherent activity of FeOOH for OER. Additionally, in situ Raman analysis indicates that FeC 2 O 4 gradually transforms into the FeOOH active site throughout the OER process. Finally, this study provides ideas for designing in situ reconstruction strategies to prepare heteroatom doping catalysts for high electrochemical activity.

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

Mapping out the thermodynamic stability of a QCD equation of state with a critical point using active learning

The Beam Energy Scan Theory (BEST) collaboration's equation of state (EoS) incorporates a three-dimensional Ising model critical point into the quantum chromodynamics (QCD) equation of state from lattice simulations. Furthermore, it contains four free parameters related to the size and location of the critical region in the QCD phase diagram. Certain combinations of the free parameters lead to acausal or unstable realizations of the EoS that should not be considered. In this work, we use an active learning framework to rule out pathological EoS efficiently. We find that checking stability and causality for a small portion of the parameters' range is sufficient to construct algorithms that perform with > 96 % accuracy across the entire parameter space. Though in this work we focus on a specific case, our approach can be generalized to any EoS containing a parameter space-class correspondence.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Halting Oxygen Evolution to Achieve Long Cycle Life in Sodium Layered Cathodes

Oxygen redox chemistries at high voltage have materialized as a revolutionary paradigm for cathodes with high-energy density; however, they are plagued by the challenges of labile oxygen loss and rapid degradations upon cycling, even after concerted endeavors from the research community. Here we propose a multi-concentration stratagem propelled by entropy reinforcement to enhance the electronic structure disorder (ESD) at high desodiation states for impeding undesired oxygen mobility and ensuring controlled oxygen activity, elucidated by density functional theory calculations. The increased disorder strengthens the reversible electrochemistry of lattice oxygen redox, leading to effectively suppressed P−O structural evolution and highly stable localized TMO 6 octahedral environments, as demonstrated by soft/hard X-ray absorption spectroscopy. Furthermore, through a comparative analysis of sodium-layered cathodes with different configuration entropy, we reveal that a high-entropy state induced by cationic disordering has the capacity to perturb cationic redox boundaries, significantly restraining the formation of detrimental O′3 phases. As a consequence, the high-voltage cycling stability has been greatly upgraded, up to 4.4 V versus Na + /Na, with an impressive 90.1 % capacity retention at 1 C over 100 cycles and 76.1 % capacity retention at 2 C over 300 cycles. In conclusion, the resilient oxygen redox, enabled through the control of ESD, broadens the horizons for entropy engineering and lays the foundation for advancements in high-energy, long-cycling, and safe batteries.

25 ENERGY STORAGE↗
DOE OSTI2020

Enhancing perovskite electrocatalysis through synergistic functionalization of B-site cation for efficient water splitting

The family of perovskite oxides is a promising class of catalysts for diverse energy conversion processes including water splitting. In this work, a facile two-step manipulation (in-situ exsolution and post-sulfurization) strategy was proposed and applied to LaCo 0.2 Fe 0.8 O 3 (LCF) perovskite parent, through which, the electronic state, spatial immersion and intrinsic activity of B-site cobalt (Co) were stepwise tuned at nanoscale proximity accordingly (i.e., lattice Co ions segregated Co 0 → embedded CoS 2 ). Impressively, the as-prepared catalyst (S-LCF) obtains an emergent oxygen deficient microstructure seamlessly pinned with uniformly distributed CoS 2 nanoparticles (NPs), which demonstrates enhanced performance toward both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), and shows good stability in overall water splitting. The density functional theory (DFT) calculations illustrate the optimized metal-oxygen covalency and hydrogen adsorption Gibbs free energy (Δ G H *) on S-LCF, which further buttresses the prominence of our B-site cation engineering tactics.

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

CH 4 combustion over a commercial Pd/CeO 2 -ZrO 2 three-way catalyst: Impact of thermal aging and sulfur exposure

Thermal aging and sulfur poisoning are major problems influencing the efficiency and lifetime of natural gas three-way catalysts (TWCs) during real-world operation. In the present study, thermal aging and sulfur-induced deactivations on CH 4 combustion were investigated over commercial monolithic honeycombs, i.e., Pd/CexZr 1-x O 2 (CZ)-based TWCs that are thermally aged in the bench (HTA), followed by being operated behind the stoichiometric natural gas engine in high sulfur fuel (HTA + S). In this work, both HTA and HTA + S samples show degraded performance in CH 4 combustion relative to the fresh one, which are caused by the reconstruction of Pd species induced by thermal aging and the decreased reducibility of the support. The 18 O 2 labelling experiments show that in all cases CH 4 combustion proceeds via a MvK mechanism in which lattice O (OL) plays a key role. The sulfation aging (HTA + S sample) promotes the activation of CH 4 and O 2 by forming Pd δ+ -(SO$_4^{2-}$) δ- and Ce 3+ -VO couples at the interface as compared to HTA sample. However, such a promotion effect could be compromised by the blocking effect of sulfate on the exchange of O L from the bulk to the surface and across the surface. The fundamental understanding of thermal and S deactivation mechanisms from this study could help to predict a real-world lifetime use curve of natural gas TWCs.

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

Surface Manipulation on Pt 2.2 Ni(111) Nanocatalysts for Boosting Their ORR Performance in Alkaline Media

We have previously shown that Pt–Ni alloy nano-octahedra with {111} facets exhibit outstanding electrochemical performance in the oxygen reduction reaction (ORR) in acidic media when their surfaces are finely tailored at the atomic level. Here, in this investigation, we further refine the surface structure of Pt 2.2 Ni octahedral nanocatalysts to improve ORR performance in a 0.1 M KOH solution using diverse surface manipulation techniques. Through systematic analysis using electrochemical CO stripping, cyclic voltammetry, and X-ray photoelectron spectroscopy, we examined the surfaces of Pt 2.2 Ni octahedral nanocatalysts pretreated with various methods, including etching in acetic acid or perchloric acid, and subsequent electrochemical activation in an alkaline solution or an acidic solution. Among these treatments, those involving acidic media, particularly electrochemical cycling in acidic electrolytes, demonstrated significantly enhanced ORR activity in 0.1 M KOH. The latter exhibited a mass activity of 2.95 A/mg pt and a specific activity of 8.71 mA/cm 2 at 0.90 V, surpassing state-of-the-art Pt/C by 12-fold and 34-fold, respectively. Furthermore, this identified nanocatalyst displayed robust stability, with negligible activity decay observed after 10,000 cycles. This study suggests that the improved ORR activity can be attributed to the Pt-rich surfaces with well-preserved {111} lattices on the surface-modified Pt–Ni nano-octahedra.

36 MATERIALS SCIENCE↗