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Results for “interfacial energy”

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DOE OSTI2022

High voltage stable cycling of all-solid-state lithium metal batteries enabled by top-down direct fluorinated poly (ethylene oxide)-based electrolytes

Poly (ethylene oxide) (PEO)-based solid-state polymer electrolytes (SPEs) show prospects in all-solid-state lithium metal batteries. However, they suffer from low ionic conductivity at room temperature and interfacial instability with high voltage cathodes for long-term cycling. In this work, top-down fluorinated PEOs (F-PEOs) for the all-solid-state electrolytes, which are scalable and cost-effective, are developed to improve the battery performance. We demonstrate, that by enhancing the disordering of the F-PEO matrix, the SPE achieves a maximum Li + conductivity of 1.1 x 10 -4 S cm -1 at 40 °C, which is 20 times higher than the baseline. By forming robust cathode/SPE and Li/SPE interfaces, the F-PEO-based SPEs demonstrate stable cycling in the LiFePO 4 /Li and LiNi 0·8 Mn 0·1 Co 0·1 O 2 /Li (3-4.4 V, 500 cycles, capacity retention of 91.6%) based all-solid-state batteries at 40 °C. Therefore, our work highlights the significance of "disordering engineering" for energy storage materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Phonon-Mediated Ultrafast Hole Transfer from Photoexcited CdSe Quantum Dots to Black Dye

We have applied non-adiabatic molecular dynamics (NAMD) and Fewest Switching surface hopping (FSSH) method to simulate the energy dissipation and charge transfer processes in the CdSe quantum dot (QD) functionalized by the Black dye. Our calculations reveal ultrafast hole transfer from the photoexcited QD to the dye, despite a significant energy splitting between QD’s and dye’s occupied states. The mechanism of such ultrafast QD-to-dye hole transfer is rationalized by strong non-adiabatic couplings between the delocalized surface orbitals of the QD and the high-frequency vibrations of isothiocyanate ligands of the Black dye. Here, this mechanism is also confirmed by a very rapid lose of coherency of the excitation due to strong electronic couplings with vibrational modes of the dye.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

NASA NTRS2015

Effects of Atomic-Scale Structure on the Fracture Properties of Amorphous Carbon - Carbon Nanotube Composites

The fracture of carbon materials is a complex process, the understanding of which is critical to the development of next generation high performance materials. While quantum mechanical (QM) calculations are the most accurate way to model fracture, the fracture behavior of many carbon-based composite engineering materials, such as carbon nanotube (CNT) composites, is a multi-scale process that occurs on time and length scales beyond the practical limitations of QM methods. The Reax Force Field (ReaxFF) is capable of predicting mechanical properties involving strong deformation, bond breaking and bond formation in the classical molecular dynamics framework. This has been achieved by adding to the potential energy function a bond-order term that varies continuously with distance. The use of an empirical bond order potential, such as ReaxFF, enables the simulation of failure in molecular systems that are several orders of magnitude larger than would be possible in QM techniques. In this work, the fracture behavior of an amorphous carbon (AC) matrix reinforced with CNTs was modeled using molecular dynamics with the ReaxFF reactive forcefield. Care was taken to select the appropriate simulation parameters, which can be different from those required when using traditional fixed-bond force fields. The effect of CNT arrangement was investigated with three systems: a single-wall nanotube (SWNT) array, a multi-wall nanotube (MWNT) array, and a SWNT bundle system. For each arrangement, covalent bonds are added between the CNTs and AC, with crosslink fractions ranging from 0-25% of the interfacial CNT atoms. The SWNT and MWNT array systems represent ideal cases with evenly spaced CNTs; the SWNT bundle system represents a more realistic case because, in practice, van der Waals interactions lead to the agglomeration of CNTs into bundles. The simulation results will serve as guidance in setting experimental processing conditions to optimize the mechanical properties of CNT composites.

Jensen, Benjamin D.↗

DOE OSTI2026

Two-phase flow numerical analysis of electrode geometry for alkaline water electrolyzers

Hydrogen is a promising component of a future energy-secure and efficient economy, but its competitiveness depends on reducing production costs. One strategy is to operate alkaline water electrolyzers at higher current densities to increase output. However, this intensifies performance losses due to gas bubble accumulation, which blocks transport pathways and deactivates electrochemically active surfaces. Enhancing bubble evacuation through electrode design is therefore essential. Previous studies have explored various approaches — such as modifying surface morphology, applying sonication or pressure modulation, and introducing surfactants — but these efforts have addressed a limited range of conditions due to the complexity of two-phase flow and electrode geometries. Experiments have also largely been focused on either cell level improvements, which lack the information necessary to isolate each contributing factor, or on modified geometries that are not relevant to practical cell operation. From a modeling perspective, conventional Eulerian multiphase models do not track the complex gas–liquid interfacial dynamics and often neglect surface tension and contact angle effects, reducing their predictive accuracy. To provide insights on the effects of different electrode geometries on the performance of alklaine water electrolyzers this work employs an immersed boundary volume-of-fluid method to simulate bubble behavior in 3D porous electrodes. Multiple base electrode geometries, typically used in practice, with varying porosity are evaluated under a constant surface gas generation rate. Simulation data is analyzed to quantify electrode gas coverage, bubble size dynamics and other relevant metrics. Results show that porosity strongly influences bubble accumulation on electrode surfaces, with higher porosity reducing gas coverage, and its not strictly dependent on the electrode geometry. However, the electrode’s base geometry significantly affects gas accumulation at the separator gap, independent of porosity. A foam electrode geometry resulted in the lowest gas coverage of all electrodes with a median volumetric gas coverage of 11%, but at the cost of a 70% reduction in active area compared with the largest surface area electrode, while gyroid electrodes showed the best trade-off between gas coverage, particularly at the separator surface, and electrochemically active area. In conclusion, the results highlight the need for holistic electrode design strategies.

Alkaline↗

DOE OSTI2024

Water–Hydrocarbon Interactions in Anionic Pyrene Monohydrate

Interactions between water and polycyclic aromatic hydrocarbons are essential in many aspects of chemistry, from interstellar and atmospheric processes to interfacial hydrophobicity and wetting phenomena. Despite their growing importance, the intermolecular potentials of the water-hydrocarbon interactions are underdeveloped compared to water-water potentials, and there are similarly few experimental probes that are sensitive to the details of the water-hydrocarbon potential. We present a combined experimental and computational study of anionic pyrene monohydrate, one of the simplest water/hydrocarbon clusters. The action spectrum in the OH region of the mass-selected cluster ion provides a rigorous benchmark for intermolecular potentials and computational methodologies. We identify missing intermolecular interactions and shortcomings in conventional dynamics calculations by comparing experimental data to density functional theory and classical molecular dynamics calculations. Kinetic trapping is prevalent, even for one water molecule and one pyrene molecule, leading to slow equilibration in conventional molecular dynamics calculations, even on nanosecond timescales and at low temperatures (50 K). At constant energy, temperature fluctuations for the pair of molecules are substantial. Immersing the system in a bath of soft spheres and employing parallel tempering alleviates kinetic trapping and dampens temperature fluctuations, bringing the system closer to the thermodynamic limit. With such augmented sampling, a simple, flexible water model reproduces the linewidth and the asymmetric broadening of the symmetric OH stretching mode, which we assign to spectral diffusion. In the OH stretching region, dynamics calculations predict a more intense antisymmetric peak than experiments observe but do not predict the bimodal split symmetric peak that the experiments show. Furthermore, our work suggests that electronic polarization, missing in the empirical force field, is responsible for the first discrepancy and that quantum nuclear effects, captured neither in density functional theory nor in classical dynamics, may be responsible for the second.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Dependence of adhesion on degradation mechanisms of ethylene co-vinyl acetate encapsulants over the lifetime of photovoltaic modules

The long-term reliability of encapsulation has a critical impact on the overall cost and effectiveness of photovoltaic modules. An often overlooked but important element of this reliability concerns adhesive degradation of the encapsulant, which results in delamination. This work critically examines the degradation mechanisms – deacetylation, β-scission, and hydrolytic depolymerization – primarily responsible for adhesion loss in ethylene co-vinyl acetate (EVA) encapsulants to provide evidence and clarity regarding the contribution of these mechanisms to the adhesive degradation over the lifetime of a module. EVA samples obtained from mini-modules exposed in two sets of controlled, accelerated conditions – with and without ultraviolet (UV) radiation – are characterized to find specific evidence for the proposed degradation mechanisms. The mini-modules were exposed up to 10,000 h, which represents up to 15–20 years in the field. Results affirm that initially, deacetylation dominates the degradation before scission takes over, followed by hydrolytic depolymerization. Additional analysis highlights the climacteric interdependency between deacetylation and hydrolytic depolymerization as it relates to eventual delamination, where deacetylation products catalyze interfacial hydrolysis reactions. Furthermore, effects occurring at a given interface are isolated, explicitly providing evidence for how these mechanisms are nonuniform throughout the thickness of the EVA. Results demonstrate that the EVA that interfaces with the glass as opposed to the cell experiences increased levels of degradation, explaining why this initially stronger interface becomes the preferential interface for delamination after longer periods of exposure. Additionally, elevated temperatures alone are shown to induce limited migration of sodium ions across the glass/EVA interface.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Molecular-scale origins of wettability at petroleum–brine–carbonate interfaces

Wettability control of carbonates is a central concept for enhanced petroleum recovery, but a mechanistic understanding of the associated molecular-scale chemical processes remains unclear. We directly probe the interface of calcium carbonate (calcite) with natural petroleum oil, synthetic petroleum analogues, and aqueous brines to understand the molecular scale behavior at this interface. The calcite–petroleum interface structure is similar whether or not calcite was previously exposed to an aqueous brine, and is characterized by an adsorbed interfacial layer, significant structural changes within the calcite surface, and increased surface roughness. No evidence for an often-assumed thin-brine wetting layer at the calcite–petroleum interface is observed. These features differ from those observed at the calcite–brine interface, and for parallel measurements using model synthetic petroleum mixtures (consisting of representative components, including dodecane, toluene, and asphaltene). Changes to the interface after petroleum displacement by aqueous brines are also discussed.

02 PETROLEUM↗

DOE OSTI2024

Enhanced Interfacial Electron Transfer in Photocatalyst-Natural Enzyme Coupled Artificial Photosynthesis System: Tuning Strategies and Molecular Simulations

Laccase is capable of catalyzing a vast array of reactions, but its low redox potential limits its potential applications. The use of photocatalytic materials offers a solution to this problem by converting absorbed visible light into electrons to facilitate enzyme catalysis. Herein, MIL-53(Fe) and NH 2 -MIL-53(Fe) serve as both light absorbers and enzyme immobilization carriers, and laccase is employed for solar-driven chemical conversion. Electron spin resonance spectroscopy results confirm that visible light irradiation causes rapid transfer of photogenerated electrons from MOF excitation to T1 Cu(II) of laccase, significantly increasing the degradation rate constant of tetracycline (TC) from 0.0062 to 0.0127 min -1 . Conversely, there is only minimal or no electron transfer between MOF and laccase in the physical mixture state. Theoretical calculations demonstrate that the immobilization of laccase's active site and its covalent binding to the metal-organic framework surface augment the coupled system's activity, reducing the active site accessible from 27.8 to 18.1 Å. In conclusion, the constructed photo-enzyme coupled system successfully combines enzyme catalysis’ selectivity with photocatalysis's high reactivity, providing a promising solution for solar energy use.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Coupling between interfacial charge and mechanical deformation at high temperatures in ceramics. Final report

Basic research, under this project, has led to new fundamental discoveries in the effect of electric field (and temperature) on diffusion kinetics, electroluminescence and electronic conductivity in ceramic materials. For example, yttria stabilized zirconia sinters in just seconds well below 1000°C, while, at the same time, exhibiting a highly non-linear rise in conductivity, and intense electroluminescence. The phenomenon has been shown to occur in nearly all ceramics whether they are ionic or electronic conductors, or insulators. The rise in conductivity leads to Joule heating but in-situ measurements with a platinum standard at APS and Brookhaven (NSLS-II) have shown that the temperatures are much below what would have been needed to sinter in a few seconds. We have explored the hypothesis that huge concentrations of Frenkel pairs of vacancies and interstitials are produced. While these point defects accelerate sintering (by the interstitials being transported to the pores and the vacancies to the grain boundaries), they may also produce electron-hole pairs which can impart high electrical conductivity or recombine to emit photons. Many measurements, including in-situ measurements of lattice expansion are consistent with this hypothesis. However, the energy barrier for generating Frenkels in zirconia for example is much larger than can be expected at temperature and electrical fields in these experiments. Most recent work suggests that short wavelength phonons play a critical role in the genesis of the “flash” phenomenon. For example, the Debye temperature has been shown to be the lower bound for initiating flash. Molecular dynamics simulations have shown that large concentrations of Frenkel pairs can form under the proliferation of “optical” phonons at the edge of the Brillouin zone, that is with a wavelength at or below the lattice parameter. This project has led to the development of new experimental techniques as well as a software hardware interface for process and control and data analysis in real time, with a time scale of less than one second. This approach spells a new paradigm in materials science research. It potential impact on high rate manufacturing is self evident.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Hard x-ray standing-wave photoemission study of the interfaces in a BiFeO$_3$/La$_{0.7}$Sr$_{0.3}$MnO$_3$ superlattice

Hybrid multiferroics such as BiFeO$_3$ (BFO) and La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO) heterostructures are highly interesting functional systems due to their complex electronic and magnetic properties. One of the key parameters influencing the emergent properties is the quality of interfaces, where varying interdiffusion lengths can give rise to different chemistry and distinctive electronic states. Here we report high-resolution depth resolved chemical and electronic investigation of BFO/LSMO superlattice using standing-wave hard X-ray photoemission spectroscopy in the first-order Bragg as well as near-total-reflection geometry. Our results show that the interfaces of BFO on top of LSMO are atomically abrupt, while the LSMO on top of BFO interfaces show an interdiffusion length of around 1.2 unit cells. The two interfaces also exhibit different chemical gradients, with the BFO/LSMO interface being Sr-terminated by a spectroscopically distinctive high binding energy component in Sr 2p core-level spectra, which is spatially contained within 1 unit cell from the interface. From the electronic point of view, unique valence band features were observed for bulk-BFO, bulk-LSMO and their interfaces. Our X-ray optical analysis revealed a unique electronic signature at the BFO/LSMO interface, which we attribute to the coupling between those respective layers. Valence band decomposition based on the Bragg-reflection standing-wave measurement also revealed the band alignment between BFO and LSMO layers. Our work demonstrates that standing-wave hard x-ray photoemission is a reliable non-destructive technique for probing depth-resolved electronic structure of buried layers and interfaces with sub-unit-cell resolution. Equivalent investigations can be successfully applied to a broad class of material such as perovskite complex oxides with emergent interfacial phenomena.

Martins, HP↗

DOE OSTI2020

Optimization of the compositions of polyanionic sodium-ion battery cathode NaFe 2-x V x (PO 4 )(SO 4 ) 2

Sodium (Na) super ionic conductor (NASICON) polyanionic compounds have recently attracted much attention from the battery community because of their electroactive properties and reasonably high ionic conductivities, leading to their use as a cathode in sodium-ion batteries. This article describes the compositional optimizations, crystallographic evaluations, and electrochemical behavior of a new mixed NASICON polyanionic compound, NaFe 2-x V x (PO 4 )(SO 4 ) 2 . By doping the characteristic Fe 3+ sites of the FeO 6 octahedrons with varying amounts of V 3+ , the electrochemical stability and charge transport in NaFe 2 (PO 4 )(SO 4 ) 2 were enhanced. The resulting best composition, with crystal structure NaFe 1.4 V 0.6 (PO 4 )(SO 4 ) 2 resolved through the Rietveld method, exhibited a stable capacity compared with the other synthesized compositions. In situ powder x-ray diffraction measurements, a single-phase intercalation/deintercalation mechanism of the NASICON structure in the measured sodium concentration window was observed with no impurity phase formation. Further electrochemical assessments revealed the interfacial charge transfer kinetics to be the rate-limiting step in the sodium concentration window. Also, the measured sodium-ion diffusivity values in the range of 6 × 10 -11 to 7 × 10 -11 cm 2 /s in the measured sodium concentration range. The results reported here highlight the potential of compositionally and morphologically optimized NaFe 1.4 V 0.6 (PO 4 )(SO 4 ) 2 with higher particle surface areas as a cathode material for high-performance sodium-ion batteries.

25 ENERGY STORAGE↗

DOE OSTI2024

Elucidating the Transition of 3D Morphological Evolution of Binary Alloys in Molten Salts with Metal Ion Additives

Molten salts serve as effective high-temperature heat transfer fluids and thermal storage media used in a wide range of energy generation and storage facilities, including concentrated solar power plants, molten salt reactors and high-temperature batteries. However, at the salt–metal interfaces, a complex interplay of charge-transfer reactions involving various metal ions, generated either as fission products or through corrosion of structural materials, takes place. Simultaneously, there is a mass transport of ions or atoms within the molten salt and the parent alloys. The precise physical and chemical mechanisms leading to the diverse morphological changes in these materials remain unclear. Here, to address this knowledge gap, this work employed a combination of synchrotron X-ray nanotomography and electron microscopy to study the morphological and chemical evolution of Ni-20Cr in molten KCl-MgCl 2 , while considering the influence of metal ions (Ni 2+ , Ce 3+ , and Eu 3+ ) and variations in salt composition. Our research suggests that the interplay between interfacial diffusivity and reactivity determines the morphological evolution. The summary of the associated mass transport and reaction processes presented in this work is a step forward toward achieving a fundamental comprehension of the interactions between molten salts and alloys. Overall, the findings offer valuable insights for predicting the diverse chemical and structural alterations experienced by alloys in molten salt environments, thus aiding in the development of protective strategies for future applications involving molten salts.

36 - MATERIALS SCIENCE↗

DOE OSTI2025

An Investigation of Thermal Properties of 2D Materials [Dissertation]

Studying the thermal conductivity of 2D materials is important due to the applications of 2D materials in fields such as thermal management, thermoelectricity, renewable energy, and sensors. As such, measurements of the thermal conductivity of these 2D materials become important to measure. Thermal conductivity is often difficult to measure for 2D materials due to their atomically thin nature and many experimental methods for doing so requiring contact with the sample, which can alter the thermal properties. A non-contact method for calculating the thermal conductivity of 2D materials supported on substrates in order to model the thermal conductivity of 2D materials for devices, is proposed and experimentally performed in this dissertation. The optothermal Raman technique is a useful non-contact diagnostic technique useful in determining the thermal conductivity of 2D materials. The optothermal Raman typically does not account for heat losses due to convection or radiation or substrate resistance, which are shown to be important factors to consider when developing an optothermal Raman model. Additionally, the calculation of the interfacial thermal conductance between the bottom surface of the sample and the top surface of the substrate, plays an important role in determining the final value of the thermal conductivity of a supported sample, and will yield differing results based on whether or not the conductance is calculated using an approach such as the Diffuse Mismatch Model (DMM) or calculated directly by varying the laser heating profile (usually done by changing the laser objective). This is shown to be the case for both graphene on Ni, graphene on Cu, and SnSe 2 on Cu. In addition to experimentally calculating the thermal conductivity of a 2D material with the optothermal Raman technique, the thermal conductivity of 2D materials can also be calculated using computational methods. The three-phonon method is a method which can be used to simulate phonon scattering processes and determine the thermal conductivity of semiconductors, wherein phonon scattering is the dominant mechanism which determines the thermal conductivity. The three-phonon method uses relaxation times for phonon scattering with other phonons, electrons, and other material system elements, such as isotopes or material defects, in order to create a single-mode relaxation time approximation (SMRTA), which is used to calculate the final value of the thermal conductivity. An important consideration when determining the thermal conductivity of a 2D material using this method is the device geometry, which is reflected in this work as the phonon-boundary scattering relaxation time. This inclusion is important along with the inclusion of phonon-electron scattering in accurately determining the thermal conductivity of a 2D material. In both the optothermal Raman experiments and the three-phonon method computations, strain is shown to have a demonstrable effect on the thermal conductivity of 2D materials. When a 1.1% strain was applied to the mechanical properties of SnSe, the three-phonon processes yielded a lower thermal conductivity than the no-strain case. For the optothermal Raman experiments, the strain induced in the Cu substrate and transferred to a single-layer graphene (SLG) sample yields a trend where the thermal conductivity of the SLG decreases with respect to strain applied. In the case where the interfacial thermal conductance was calculated directly, the conductance increased with respect to strain applied. This presents strain as a reliable and viable method for tuning the thermal properties of 2D materials for device applications.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Mixed Nanosphere Assemblies at a Liquid–Liquid Interface

The in-plane packing of gold (Au), polystyrene (PS), and silica (SiO 2 ) spherical nanoparticle (NP) mixtures at a water–oil interface is investigated in situ by UV–vis reflection spectroscopy. All NPs are functionalized with carboxylic acid such that they strongly interact with amine-functionalized ligands dissolved in an immiscible oil phase at the fluid interface. This interaction markedly increases the binding energy of these nanoparticle surfactants (NPSs). The separation distance between the Au NPSs and Au surface coverage are measured by the maximum plasmonic wavelength (λ max ) and integrated intensities as the assemblies saturate for different concentrations of non-plasmonic (PS/SiO 2 ) NPs. Further, as the PS/SiO 2 content increases, the time to reach intimate Au NP contact also increases, resulting from their hindered mobility. λ max changes within the first few minutes of adsorption due to weak attractive inter-NP forces. Additionally, a sharper peak in the reflection spectrum at NP saturation reveals tighter Au NP packing for assemblies with intermediate non-plasmonic NP content. Grazing incidence small angle X-ray scattering (GISAXS) and scanning electron microscopy (SEM) measurements confirm a decrease in Au NP domain size for mixtures with larger non-plasmonic NP content. The results demonstrate a simple means to probe interfacial phase separation behavior using in situ spectroscopy as interfacial structures densify into jammed, phase-separated NP films.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Epitaxial Growth of 2D Core‐Crown SnS 2 /SnSe 2 Heterostructure Through Interfacial Modification with Polyvinylpyrrolidone

Abstract Developing generalized strategies for controlled synthesis of 2D heterostructures remains a significant challenge because the existing approaches often suffer from poor reproducibility and scalability. In this study, a solution synthesis approach for epitaxial core‐crown heterostructures with controlled band alignment, that overcomes these challenges is reported. Polyvinylpyrrolidone (PVP) is used as a structure‐directing agent to reduce lattice mismatch between SnS 2 and SnSe 2 (10‐10) surfaces and direct epitaxial growth of SnSe 2 crown on SnS 2 seed. Additionally, PVP adsorption to the basal plane prevents van der Waals stacking and stabilizes 2D heterostructures during synthesis. Driven by interfacial thermodynamics, the formation of the core‐crown heterostructure is highly reproducible and the size of the 2D heterostructure and relative areas of the core and the crown can be precisely controlled in a two‐step process by varying synthesis times for the seed and the crown. The identified growth pathway for 2D heterostructures can be generalized to other combinations of van der Waals materials to provide a platform for synthesizing micron‐size epitaxial heterostructures with a desired electronic structure for catalysis and microelectronics.

Liu, Lili [Physical and Computational Sciences Dir↗

DOE OSTI2020

Effects of Zr substitution on soot combustion over cubic fluorite-structured nanoceria: Soot-ceria contact and interfacial oxygen evolution

Ceria is widely used as a catalyst for soot combustion, but effects of Zr substitution on the reaction mechanism is ambiguous. The present work elucidates effects of Zr substitution on soot combustion over cubic fluorite-structured nanoceria. The nanostructured CeO 2 , Ce 0.92 Zr 0.08 O 2 , and Ce0.84Zr0.16O2 composed of 5–6 nm crystallites display Tm-CO 2 (the temperature at maximum CO 2 yield) at 383, 355, and 375°C under 10 vol.% O 2 /N 2 , respectively. Additionally, the size of agglomerate decreases from 165.5 to 51.9–57.3 nm, which is beneficial for the soot-ceria contact. Moreover, Zr increases the amount of surface oxygen vacancies, generating more active oxygen (O2- and O-) for soot oxidation. Thus, the activities of Ce 0.92 Zr 0.08 O 2 and Ce 0.84 Zr 0.16 O 2 in soot combustion are better than that of CeO2. Although oxygen vacancies promote the migration of lattice O 2- , the enriched surface Zr also inhibits the mobility of lattice O 2- . Therefore, the Tm-CO 2 of Ce 0.84 Zr 0.16 O 2 is higher than that of Ce 0.92 Zr 0.08 O 2 . Based on reaction kinetic study, soot in direct contact with ceria preferentially decomposes with low activation energy, while the oxidation of isolated soot occurs through diffusion with high activation energy. The obtained findings provide new understanding on the soot combustion over nanoceria.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2021

Robust and Spectrally Selective Aerogels for Solar Receivers

The development of next generation concentrated solar thermal (CST) plants requires solar receivers to reach high temperatures (> 600°C) while minimizing costs. Efficiently generating such high temperatures using a line-focusing collector and an air-stable receiver has the potential to change the current CSP paradigm because it would: (1) result in large improvements in system-level efficiency of line-focusing systems by enabling the use of high-efficiency supercritical CO 2 power cycles; (2) decrease the LCOE of line-focusing systems to meet SETO 2030 goals; (3) maintain performance over the lifetime of the CSP plant by avoiding issues related to breakdown of vacuum. The use of aerogels as transparent insulating materials (TIMs) in solar thermal receivers has the potential to enable such improvements. Specifically, aerogels can be placed in front of a black (or partially selective) high-temperature absorber to allow sunlight to transmit to the absorber but block heat from escaping. These materials can improve the efficiency and simplify the complexity of thermal transport systems by enabling operation at moderate or no vacuum levels. These potential benefits have been explicitly identified by SETO as ‘high impact’. The use of mesoporous silica as a TIM has already led to large improvements in solar collection efficiency. Nevertheless, these materials inherently lose structural integrity and the ability to suppress radiation losses at high temperatures. Here, we address these challenges by leveraging 1-cycle atomic layer deposition of aluminum oxide onto a silica aerogel to form a thermally stable interfacial layer that is transparent to sunlight but broadly absorbs in the mid-infrared. This interfacial absorption results in a two-fold reduction in measured heat losses from an absorber at 700°C and solar thermal efficiency of 81% at 700°C under 60 Suns, based on measurements of heat loss and solar transmittance. Extended-duration heat treatment reveals that the multicomponent aerogel is stable at high temperatures relative to a silica aerogel. Furthermore, we experimentally demonstrate the concept of using infrared plasmon resonances to selectively enhance the thermal absorption coefficient of TIMs in order to strongly suppress thermal radiative losses at high temperatures. We term this mechanism plasmon-enhanced greenhouse selectivity (PEGS). Unlike silica aerogels, where much of the IR absorption is lost at high temperatures, local surface plasmon resonances (LSPRs) in doped oxide nanoparticles overlap a significant portion of the blackbody spectrum and are maintained at high temperatures. Overall, this work paves the way for next-generation solar thermal energy using thermally robust transparent insulating materials.

14 SOLAR ENERGY↗

DOE OSTI2020

Robust and Spectrally Selective Aerogels for Solar Receivers (Final Technical Report)

The development of next generation concentrated solar thermal (CST) plants requires solar receivers to reach high temperatures (> 600°C) while minimizing costs. Efficiently generating such high temperatures using a line-focusing collector and an air-stable receiver has the potential to change the current CSP paradigm because it would: (1) result in large improvements in system-level efficiency of line-focusing systems by enabling the use of high-efficiency supercritical CO2 power cycles; (2) decrease the LCOE of line-focusing systems to meet SETO 2030 goals; (3) maintain performance over the lifetime of the CSP plant by avoiding issues related to breakdown of vacuum. The use of aerogels as transparent insulating materials (TIMs) in solar thermal receivers has the potential to enable such improvements. Specifically, aerogels can be placed in front of a black (or partially selective) high-temperature absorber to allow sunlight to transmit to the absorber but block heat from escaping. These materials can improve the efficiency and simplify the complexity of thermal transport systems by enabling operation at moderate or no vacuum levels. These potential benefits have been explicitly identified by SETO as ‘high impact’. The use of mesoporous silica as a TIM has already led to large improvements in solar collection efficiency. Nevertheless, these materials inherently lose structural integrity and the ability to suppress radiation losses at high temperatures. Here, we address these challenges by leveraging 1-cycle atomic layer deposition of aluminum oxide onto a silica aerogel to form a thermally stable interfacial layer that is transparent to sunlight but broadly absorbs in the mid-infrared. This interfacial absorption results in a two-fold reduction in measured heat losses from an absorber at 700°C and solar thermal efficiency of 81% at 700°C under 60 Suns, based on measurements of heat loss and solar transmittance. Extended-duration heat treatment reveals that the multicomponent aerogel is stable at high temperatures relative to a silica aerogel. Furthermore, we experimentally demonstrate the concept of using infrared plasmon resonances to selectively enhance the thermal absorption coefficient of TIMs in order to strongly suppress thermal radiative losses at high temperatures. We term this mechanism plasmon-enhanced greenhouse selectivity (PEGS). Unlike silica aerogels, where much of the IR absorption is lost at high temperatures, local surface plasmon resonances (LSPRs) in doped oxide nanoparticles overlap a significant portion of the blackbody spectrum and are maintained at high temperatures. Overall, this work paves the way for next-generation solar thermal energy using thermally robust transparent insulating materials.

14 SOLAR ENERGY↗