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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Elastic NaxMoS2-carbon-BASE triple interface direct robust solid-solid interface for all-solid-state Na-S batteries

The promises of all-solid-state (ASS) sodium batteries for the next generation energy storage are widely recognized but their developments have been severely constrained by the difficulties to design favorable solid-solid interfaces for unhindered Na-ion transport. Using the most promising ß?-Al2O3 solid state electrolyte (BASE) as a platform, we demonstrate here a triple nanojunction strategy that provides simultaneous strong Na adhesion and continuous Na-ions diffusion at solid-solid interface. Such triple junctions (NaxMoS2-carbon-BASE) were constructed by adhering ternary composite Na anodes containing dispersed 3 wt% MoS2 and 3 wt% carbon on BASE, and provide nearly complete adhesion of Na on BASE with a much smaller contact angle (~ 45o vs. 120o of pristine Na). The composite Na anodes exhibited ~ 3 times improved elastic property and the synergy of NaxMoS2 and carbon provides the required ionic and electronic diffusion channels at solid-solid interface, which significantly improve Na utilization and resist premature failure due to loss of solid-solid contact as Na shrink during high capacity stripping. As a result, Na metal at the triple junction exhibited more than five time reduced charge transfer resistance and at least 200 hours stable battery cycling at practical current densities. The novel anode architecture also enabled high capacity cycling of prototype ASS sodium sulfur batteries when coupled with advanced sulfur cathodes containing intrinsic Na-ions diffusion channels and redox catalytic mediators, leading to stable cycling with specific capacity of 1110 mAh g-1.

ß”-Al2O3 solid electrolyte, solid state batteries,↗
DOE OSTI2025

Nonpyrophoric alternative to trimethylaluminum for the atomic layer deposition of Al 2 O 3

We have examined the atomic layer deposition (ALD) of Al 2 O 3 using a nonpyrophoric precursor, which possesses only Al–N bonds and no Al–C bonds: Al(N(CH 3 ) 2 ) 2 (–N(C 2 H 5 )–C 2 H 4 –N(C 2 H 5 ) 2 ), which we refer to as bis-dimethylamino-diamino-aluminum (BDMADA-Al). We employed a quartz crystal microbalance (QCM) to monitor ALD in situ and in real time, and the deposited thin films have been characterized using x-ray photoelectron spectroscopy, spectroscopic ellipsometry, x-ray reflectivity, and atomic force microscopy. Films deposited with BDMADA-Al result in near-stoichiometric Al2O3 at temperatures ranging from T = 120 to 285 °C using H 2 O as the coreactant and at T = 285 °C using t-BuOH as the coreactant. The properties of the films (density, C incorporation, stoichiometry, growth rates) are comparable using either BDMADA-Al or trimethylaluminum (TMA) as the precursor under similar reaction conditions. The N content in the films deposited with BDMADA-Al as the precursor is <1% at both T = 120 and 285 °C. Additionally, both BDMADA-Al|t-BuOH and TMA|t-BuOH processes deposit near-stoichiometric Al 2 O 3 at T = 285 °C, while neither process chemistry produces a constant growth rate per cycle at T = 120 °C. Close examination of single cycle QCM data from BDMADA-Al ALD indicates unique ligand exchange reaction mechanisms during each of the half-reactions. Experimentally, we have evidence supporting the mechanism in which upon the chemisorption of BDMADA-Al, the species on the surface retains the –N(CH 3 ) 2 ligands, while the diamine ligand is mostly lost on dissociative adsorption, except possibly at the higher temperature (285 °C). As a result, our work demonstrates that BDMADA-Al can be used as an effective alternative precursor to TMA for the ALD of Al 2 O 3 .

36 MATERIALS SCIENCE↗
NASA NTRS1986

Oxidation-resistant reflective surfaces for solar dynamic power generation in near Earth orbit

Reflective surfaces for space station power generation systems are required to withstand the atomic oxygen-dominated environment of near Earth orbit. Thin films of platinum and rhodium, which are corrosion resistant reflective metals, have been deposited by ion beam sputter deposition onto various substrate materials. Solar reflectances were then measured as a function of time of exposure to a RF-generated air plasma. Similarly, various protective coating materials, including MgF2, SiO2, Al2O3, and Si3N4, were deposited onto silver-coated substrates and then exposed to the plasma. Analysis of the films both before and after exposure by both ESCA and Auger spectroscopy was also performed. The results indicate that Pt and Rh do not suffer any loss in reflectance over the duration of the tests. Also, each of the coating materials survived the plasma environment. The ESCA and Auger analyses are discussed as well.

Gulino, D. A.↗
DOE OSTI2026

A Dendrite-Resistant Sodium/Porous-Carbon Anode for Solid-State Batteries – Strategies and Challenges for Low-Pressure Operation

Sodium solid-state batteries (Na-SSB) have gained interest recently due to the abundance of Na over Li, but they still tend to fail due to dendrites under practical current densities and cycling capacities. To overcome this, Na-SSBs are frequently tested with impractically high applied pressure. In this work, a porous carbon interfacial layer is utilized in conjunction with Na-ß”-Al2O3 solid electrolytes to enable Na-cycling at milder cell pressures. This sodium/porous carbon layer enables improved solid-state Na cycling in symmetric cells, up to a current density of 10 mA cm-2 at 25 °C. Cycling up to 1 mAh cm-2 is challenging with low pressure, but 1 mAh cm-2 capacity can be reliably cycled at 1 mA cm-2 at an elevated temperature of 60 °C in symmetric cells. Finally, the evolution of the interface and sodium/carbon anode is evaluated with cryogenic ion-milling and cross-sectional imaging revealing that, depending on testing temperature, pressure, current density, and capacity, void formation, Na-extraction from porous carbon, delamination of the porous carbon matrix, or a combination of these occurs at the interface between Na-metal and BASE. Despite this, excellent dendrite resistance is achieved, and a full-cell design utilizing a Na-transition metal oxide cathode is still able to achieve an areal capacity of ~ 2.7 mAh cm-2 at 0.125 mA cm-2. This work demonstrates an alternative pathway toward a Na-metal anode for Na-SSBs without the requirement of excessive stack pressure.

low-cost↗
DOE OSTI2026

UV-Induced Degradation and Associated Metastability in TOPCon Photovoltaic Modules: Understanding Kinetics and Cell Variance

Tunnel oxide passivated contact (TOPCon) silicon photovoltaic (PV) modules are dominating the PV market, but they may be susceptible to degradation under ultraviolet (UV)-containing light. Quantifying the impacts of UV-induced degradation (UVID) is complicated by an associated metastability causing further degradation under dark storage and rapid recovery under sunlight. Here, we study modules that have -2.3% to -3.2% nonrecoverable UVID loss after 60 kWh/m2 dose of 340 nm light and additional recoverable loss under dark storage. We use in situ electroluminescence (EL) imaging to characterize the post-UVID metastability at the module level. The cell-by-cell dark degradation and recovery kinetics span a wide range from +6% to -70% changes in EL intensity after 520 h of dark storage, which returns to +- 4% of the initial post-UVID EL intensity after illumination. The kinetics follow double exponential rates with dark storage degradation time constants of 345 and 45 h, and UV light recovery time constants of 5 min and 36 s. We propose that this is consistent with prior reports of kinetics for light-soaking metastability in Al2O3 passivation. Finally, we further show that cells having high UVID also have injection-dependent effective carrier lifetimes and significant intra-cell variance, suggesting possible origins of processing inconsistency.

14 SOLAR ENERGY↗
DOE OSTI2021

Identification of Recombination Losses in CdSe/CdTe Solar Cells from Spectroscopic and Microscopic Time-Resolved Photoluminescence

Due to the lowest-cost and best reliability, CdTe solar cells are the leading thin-film photovoltaic technology. Increasing open-circuit voltage by reducing recombination represents the most promising path toward further improvements. Analysis is needed to identify limitations that cause efficiency losses. To achieve this goal for Cu-doped CdSe/CdTe solar cells, time-resolved spectroscopy and microscopy are developed and applied. Recombination lifetimes and radiative efficiency identify that defect-mediated recombination is the dominant voltage loss mechanism. When carrier lifetimes are averaged over many crystalline grains, they increase from 180 to 430 ns when Al2O3 is applied to the back contact. The quasi-Fermi-level splitting correspondingly increases from 880–905 to 906–931 mV, indicating a pathway to overcome the long-standing 900 mV voltage limitation. However, the dominant recombination losses are attributed to the absorber bulk. From microscopic carrier lifetime measurements, it is identified that space charge fields due to charged grain boundaries (GBs) lead to recombination in the CdTe absorber bulk. At high injection, GB space charge fields are screened, but that occurs above 1 Sun excitation conditions. Alloying with selenium in the near-interface CdSeTe absorber region reduces GB losses and is identified as one of the factors leading to high radiative and power conversion efficiency.

14 SOLAR ENERGY↗
DOE OSTI2025

Degradation and Accelerated Recovery of Surface Passivation in n+, p+, and Intrinsic Poly-Si/SiOx Passivating Contacts for Silicon Solar Cells

We report on the degradation and recovery of surface passivation of fired poly-Si/SiOx passivating contacts with hydrogen containing Al2O3 during annealing in the dark and under illumination. Upon firing to a peak temperature of 670 degrees C, the iVoc for symmetric test structures with n+, p+, and intrinsic poly-Si/SiOx contacts decreases due to a loss of surface passivation. Upon further annealing over the temperature range of 200-350 degrees C in the dark, depending on the type of doping, the surface passivation either shows further degradation followed by recovery, or direct recovery to the initial iVoc. Annealing at higher temperatures and/or higher illumination intensities accelerates the kinetics for both degradation and recovery processes. We show that the degradation and recovery processes are thermally activated and proceed identically in subsequent firing and annealing steps showing their cyclic nature. We present a series reaction model to explain the kinetics of degradation and recovery processes for n+ and intrinsic poly-Si/SiOx contacts. By fitting the model's rate expressions to the data, the determined effective activation energy barriers for degradation and recovery for n+ poly-Si/SiOx contacts in the dark are 1.24 and 1.51 eV, which are lowered under 7.5 Suns illumination to 0.76 and 1.15 eV, respectively.

14 SOLAR ENERGY↗
DOE OSTI2021

Pre-Oxidation to Improve Liquid Metal Compatibility

Liquid metals represent an aggressive environment where selective degradation can attack structural alloys. Pre-oxidizing structural alloys, particularly those able to form alumina scales, have shown promise for Sn, Pb and Pb–Li concepts for fusion and fission applications. For Pb at 700 °C, a dramatic reduction in mass loss was observed for an alumina-forming austenitic (AFA) steel after pre-oxidation. Likewise, a ferritic FeCrAlMo alloy showed better compatibility in static Sn at 400–500 °C and flowing PbLi when pre-oxidized at 1000 °C to form α-Al2O3. Recent experiments with flowing PbLi at 675–700 °C has shown significant degradation suggesting that alumina-forming alloys are limited to ~ 650 °C in this environment. While the concept is promising, most experiments have been relatively short-term and long-term degradation mechanisms need to be evaluated.

Pint, Bruce↗
DOE OSTI2024

Understanding the Origin of Negative Temperature Dependence and Activity of N-Coordinated Cobalt Sites During Ethylene Dimerization

The on-demand production of short-chain linear alpha olefins (LAOs; C4-C8) via C2H4 dimerization and oligomerization is industrially attractive, prompting extensive research on designing active, selective, and stable catalysts for industrial use. Cobalt supported on ammoniated carbon (Co(NH3)x/C) catalysts have shown remarkable activity and selectivity in this process. However, critical aspects such as the active phase, active site structure, the role of the catalyst support, cobalt loading effects, and the inverse correlation of the reaction rate with temperature remain inadequately understood. This study systematically explores these factors using a combination of steady-state differential catalytic tests, in situ molecular characterization including diffuse reflectance UV-Vis (DR-UV-Vis), Infrared, and Raman spectroscopies, and ex situ X-ray diffraction (XRD) and high annular aberration-corrected dark field transmission electron microscopy (HAADF-STEM). Various supports (SiO2, Al2O3, NH4-ZSM-5, g-C3N4, and C) and cobalt loadings (1.0-3.0 Co nm-2) were studied to determine the optimal catalyst composition and identify the active phase and sites. Carbon-supported catalysts uniquely produce C4-8 LAOs during C2H4 dimerization, with site-time-yield remaining constant (~10-3 s-1) for 1.0-4.0 Co nm-2 at prolonged reaction times (24-48?h time-on-stream). At higher loadings of 6.0 Co nm-2, the formation of crystalline CoO and Co3O4 phases reduces catalytic activity and LAO selectivity. Our findings show that active catalysts lack crystalline cobalt oxides and instead feature dispersed Co2+ sites, tetra-coordinated to a mix of N/NH3 and O/H2O ligands, which catalyze C2H4 dimerization via the Cossee-Arlman mechanism, exhibiting 1st order dependence on C2H4 concentration. The observed inverse rate-temperature correlation is attributed to compensation effects (i.e., presence of Cremer-Constable relationship) linked to changes in adsorption enthalpic and entropic factors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Orientation-dependent structural properties during growth and growth mechanism of CoO films

The orientation-dependent local structural properties of CoO films on sapphire substrates during growth were investigated through linearly-polarized extended X-ray absorption fine structure (EXAFS) measurements. Specifically, CoO(1 1 1) and (100) crystals with a rock-salt structure (Fm3m) were epitaxially grown on alpha-Al2O3(0001) and (1012) substrates, respectively, at 700 degrees C using a radio-frequency sputtering system. The local structural properties of CoO films in the in-plane and out-of-plane orientations were quantitatively determined using linearly-polarized EXAFS at the Co K-edge during growth. The EXAFS analysis revealed that during the initial stages of growth, the local structural properties exhibit significant differences compared to thick films, with short atomic distances and large (small) Debye-Waller factors observed in the out-of-plane (in-plane) orientations. The local structural strain mostly diminished when approximately 20 CoO layers accumulated on the substrate. Density functional theory (DFT) calculations further supported these findings by confirming that cobalt atoms initially form stable bonds with the sapphire surface, leading to the simultaneous growth of oxygen and cobalt layers in a coordinated manner through layer-by-layer growth.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Efficient Synthetic Natural Gas Production from Direct Air Capture Using Titania-Based Dual Function Materials

Converting atmospheric CO2 into methane offers a compelling pathway to store intermittent renewable electricity and enhance energy security using existing natural gas infrastructure. However, current CO2 utilization approaches remain energy- and capital-intensive, largely due to the need for separate capture, purification, and conversion steps. Integrating CO2 capture with catalytic methanation represents a transformative strategy for process intensification on both the unit operation and molecular levels. We report a series of Ru-Na/TiO2 dual function materials (DFMs) for a reactive carbon capture (RCC) process consisting of simulated direct air capture and subsequent CO2 methanation (DACM). Superior methane desorption purity was observed on TiO2-based DFMs (>94 %) relative to state-of-the-art Al2O3-supported DFMs (77 %). Modifying the process to begin CO2 adsorption immediately following the methanation stage, rather than beginning adsorption near ambient temperature, resulted in >97 % methane desorption purity, suitable for injection into the natural gas pipeline without additional CO2 separation steps.

organic↗
DOE OSTI2020

Effect of water vapor on high-temperature oxidation of NiAl alloy

The high-temperature oxidation of NiAl is studied with dry oxygen and water vapor. The oxidation in H 2 O results in a thicker Al 2 O 3 oxide scale than that in O 2 . The oxide scale formed initially is a single layer of γ-Al 2 O 3 that subsequently transforms into a α-Al 2 O 3 /γ-Al 2 O 3 bilayer structure, in which the inner α-Al2O3 layer formed in H2O has a higher porosity than that in O 2 . Finally, further density functional theory calculations show that H protons derived from H 2 O molecules penetrate into the oxide lattice and boost the formation of lattice vacancies in both α-Al 2 O 3 and γ-Al 2 O 3 , thus enhancing the oxide scale growth.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Effects of Water Vapor on the Reactivity of Aluminosilicates in Vapor-Phase Propanal Aldol Condensation

Aluminosilicate materials have been extensively studied as efficient aldol catalysts for C-C coupling reactions due to their acidic nature, high surface area, thermal stability, and porous structure. This work investigated the impact of water vapor pressure on the catalytic reactivity of aluminosilicates for the aldol condensation of propanal to 2-methyl-2-pentenal (MP). The catalytic performance of amorphous SiO2-Al2O3 (A-Si-Al) and aluminated MCM-41 (Al-MCM-41) for the vapor-phase aldol condensation of propanal was evaluated at 200 degrees C as a function of vapor-phase water content at atmospheric pressure. Our findings demonstrate that co-feeding low water vapor pressures (1-18 kPa) with propanal enhances the rates of MP production at 200 degrees C on A-Si-Al. Conversely, water vapor pressures of 25 kPa result in a decrease in aldol dimer formation rates. The rate of MP production evaluated on Al-MCM-41 also increased in the presence of 5 kPa water compared to anhydrous conditions. Propylamine temperature-programmed desorption analyses revealed an increase in Bronsted acid site density when both catalysts were exposed to water, which likely accounts for the observed enhancement in aldol condensation reactivity under hydrous conditions. Reversibility testing of the water vapor effect under reaction conditions, combined with X-ray diffraction analysis of fresh, spent, and regenerated catalysts, revealed no structural changes in either aluminosilicate upon exposure to water or reaction conditions. The rates of aldol condensation and the impact of water vapor were highly consistent across both materials, suggesting that zeolite crystallinity has minimal influence on the catalytic performance.

acid catalysts↗
DOE OSTI2022

Electrical passivation of III-V multijunction solar cells with luminescent coupling effect

Perimeter recombination is one of the causes identified for having a nonuniform luminescent coupling effect in III-V multijunction solar cells. A potential solution could be the electrical passivation of the multijunction solar cell perimeter. To test this hypothesis, electrical passivation of InGaP/GaAs/Ge 3-junction solar cells was done by the atomic layer deposition of thin Al2O3 films. Further, perimeter passivation of a 3-junction solar cell relatively increased current collection measured at luminescent coupling and direct subcell excitation by as much as 11.4% and 29.8%, respectively. Meanwhile, the current homogeneity improved relatively by as much as 7.9% after electrical passivation. At 1-sun global standard illumination (AM 1.5G), 0.2% absolute conversion efficiency increase was achieved. Therefore, electrical passivation of fully working III-V multijunction solar cells is a non-invasive, post-treatment process that can recover losses due to surface defects caused by oxidation.

14 SOLAR ENERGY↗
DOE OSTI2025

Modeling Pb(II) Adsorption on Mineral Surfaces: Bridging Density Functional Theory and Experiment with Thermodynamic Insights

Despite decades of work on aqueous lead (Pb) adsorption on a-Fe2O3 (hematite) and a-Al2O3 (alumina), gaps between measurements and modeling obscure molecular-level understanding. Achieving well-matched geometries between theory and experimental for mineral-water interfaces is a hurdle, as surface functional group type and distribution must be accounted for in determining mechanisms. Additionally, computational methods that can describe the substrate are often not appropriate to capture aqueous effects. Progress requires focusing on well-studied and relevant systems, such as key facets (001),(012), and (110) of hematite and alumina, and ubiquitous contaminants such as aqueous Pb. In the past, bulk-parametrized bond-valence principles were used to rationalize Pb(II) adsorption trends. These approaches can break down at surfaces, where flexible bonding environments and adsorption-induced surface relaxations play a critical role. Here, we adapt and apply a density functional theory (DFT) and thermodynamics framework, integrating DFT-calculated energies with experimental data and electrochemical principles, to predict Pb(II) adsorption. Our model results capture trends across the full set of surfaces and predict that inner-sphere Pb(II) sorption on (001) alumina varies from unfavorable to weakly favorable across a range of pH conditions. This aligns with experiment insights that Pb(II) interacts at that surface through outer-sphere interactions. Extending to Fe(II) adsorption, we demonstrate a coverage-dependent site preference, potentially explaining disorder in overlayers grown by the oxidative adsorption of Fe(II) on hematite (001).

lead contamination↗
DOE OSTI2020

A general mechanism for gel layer formation on borosilicate glass under aqueous corrosion

Mineral and glass dissolution is a scientific topic deeply investigated but incompletely understood and of a great interest for the geochemical and materials science communities. If the interfacial dissolution/reprecipitation mechanism seems to be applicable to most of silicate minerals, the debate remains open concerning glass. Here we studied two model glasses, a ternary borosilicate (CJ1) and the same glass doped with 4.1 mol% of Al2O3 (CJ2). The two glasses were altered at 90°C, pH 9, and in conditions far and close to saturation with respect to amorphous silica, to determine the initial and residual rates. Moreover, a specific experiment was conducted for a short duration with a solution highly enriched with 18O and 29Si isotopes to understand how passivating gels form. SEM, TEM and ToF-SIMS characterization, along with Monte Carlo simulations were used to understand the rate limiting reactions at play and infer the role of Al. We show that Al yields a slower matrix dissolution in dilute conditions. However, it slows down he formation and the maturation of the passivating gel and favors alteration by partial hydrolysis of Si and Al entities followed by in-situ reorganization/relaxation into a porous network. Unexpectedly, CJ1 experienced both interfacial dissolution/reprecipitation and partial hydrolysis followed by in situ reorganization of the silicate network during the course of a single experiment. This study offers a unified concept that can pave the way for the future development of a predictive kinetic model based on a detailed description of bond breaking and bond forming as a function of glass composition and alteration conditions.

Gin, Stephane↗
DOE OSTI2020

Atomic Layer Deposition Overcoating Improves Catalyst Selectivity and Longevity in Propane Dehydrogenation

Propylene, a precursor for commodity chemicals and plastics, is produced by propane dehydrogenation (PDH). An increase in PDH yield via added catalyst activity, lifetime, or selectivity represents significant energy and economic savings. Using Pt dispersed on Al2O3 extrudate supports as a commercially relevant model system, we demonstrate that atomic layer deposition (ALD) metal oxide overcoats, used to tailor metal-active sites, can increase PDH yield and selectivity. We investigate the interplay of Pt loading, ALD overcoat thickness, and Al 2 O 3 support surface area on PDH activity, selectivity, and catalyst stability to show that applying a 6-8 A thick layer of Al 2 O 3 on low-surface area Al 2 O 3 supports of similar to 90 m 2 /g surface area yields the optimal combination of stability and activity, while increasing propylene selectivity from 91 to 96%. Increased stability upon steaming deactivation occurs because the Al 2 O 3 overcoat prevents the Pt nanoparticles from sintering. We speculate that the ALD overcoat selectively binds to the undercoordinated sites on the Pt nanoparticles, while leaving the more selective terrace sites available for dehydrogenation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗