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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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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Interactions between nonfullerene acceptors lead to unstable ternary organic photovoltaic cells

For organic photovoltaic (OPV) devices to achieve consistent performance and long operational lifetimes, organic semiconductors must be processed with precise control over their purity, composition, and structure. This is particularly important for high volume solar cell manufacturing where control of materials quality has a direct impact on yield and cost. Ternary-blend OPVs containing two acceptor–donor–acceptor (A–D–A)-type nonfullerene acceptors (NFAs) and a donor have proven to be an effective strategy to improve solar spectral coverage and reduce energy losses beyond that of binary-blend OPVs. Here, we show that the purity of such a ternary is compromised during blending to form a homogeneously mixed bulk heterojunction thin film. We find that the impurities originate from end-capping C=C/C=C exchange reactions of A–D–A-type NFAs, and that their presence influences both device reproducibility and long-term reliability. The end-capping exchange results in generation of up to four impurity constituents with strong dipolar character that interfere with the photoinduced charge transfer process, leading to reduced charge generation efficiency, morphological instabilities, and an increased vulnerability to photodegradation. As a consequence, the OPV efficiency falls to less than 65% of its initial value within 265 h when exposed to up to 10 suns intensity illumination. We propose potential molecular design strategies critical to enhancing the reproducibility as well as reliability of ternary OPVs by avoiding end-capping reactions.

14 SOLAR ENERGY↗
DOE OSTI2021

DEVELOPMENT OF A LUMPED-PARAMETER THERMAL MODEL FOR ELECTRO-HYDRAULIC ACTUATORS

This paper describes a thermal-hydraulic modeling method of a closed-circuit electro-hydraulic actuator (EHA). Despite the high energy efficiency of EHAs, it is always important to assess their cooling requirements, to guarantee that the operating temperature remains within an acceptable range. The method proposed in this paper is based on a lumped parameter approach and simplifies some of the complex heat transfer processes by introducing empirical correction factors. The model is validated by means of temperature measurements on an EHA architecture developed by the author. The good match between the simulation results and experiments confirms the capability of the proposed methodology to predict the temperature performance of the reference EHA under different drive cycles. The paper presents a detailed analysis of the power losses and passive heat dissipation for the reference system. Based on this analysis, the cooling requirements of the EHA are studied.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2022

Synthesis and Photophysics of Phenylene Based Triplet Donor–Acceptor Dyads: ortho vs. para Positional Effect on Intramolecular Triplet Energy Transfer

Two phenylene based geometrical/isomeric triplet ortho- and para–dyads (o–3 and p–3, respectively) were synthesized and fully characterized using advanced photophysical tools and computations. In dyad o–3, the through-space donor-acceptor interactions led to simultaneous triplet energy transfer and charge transfer with identical kinetics. On the other hand, in the dyad p–3, it was found that the phenylene spacer favors a fast triplet energy delocalization over the charge transfer process. Furthermore, analysis of the results from the present investigation indicates that the deactivation of the photo-excited species (o–3)* occurs through both the intrinsic channel viz. S0←S1 and charge recombination. In the case of dyad p–3, the results indicate that the primary deactivation pathway is self-quenching or triplet-triplet annihilation involving the acceptor unit(s).

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

Tunable angle-dependent electrochemistry at twisted bilayer graphene with moiré flat bands

Tailoring electron transfer dynamics across solid–liquid interfaces is fundamental to the interconversion of electrical and chemical energy. Stacking atomically thin layers with a small azimuthal misorientation to produce moiré superlattices enables the controlled engineering of electronic band structures and the formation of extremely flat electronic bands. Here, we report a strong twist-angle dependence of heterogeneous charge transfer kinetics at twisted bilayer graphene electrodes with the greatest enhancement observed near the ‘magic angle’ (~1.1°). Furthermore, this effect is driven by the angle-dependent tuning of moiré-derived flat bands that modulate electron transfer processes with the solution-phase redox couple. Combined experimental and computational analysis reveals that the variation in electrochemical activity with moiré angle is controlled by a structural relaxation of the moiré superlattice at twist angles of <2°, and ‘topological defect’ AA stacking regions, where flat bands are localized, produce a large anomalous local electrochemical enhancement that cannot be accounted for by the elevated local density of states alone.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Microwave-assisted catalytic gasification of mixed plastics and corn stover for low tar, hydrogen-rich syngas production

The challenge for efficient management of post-consumer plastic and biomass waste has grown over the past few decades due to their dramatic increases. In comparison to conventional gasification, microwave-assisted co-gasification of plastics and corn stover offers many benefits, including increased H 2 yield and gas components compared to unfavorable char/tar. Nonetheless, for future commercialization of the process and ease of product separation, further reduction of the undesirable tar is necessary, which can be achieved over the catalytic route. Here, in this work, we studied the catalytic effect of magnetite for microwave-assisted co-gasification of corn stover and plastic to make syngas with higher H 2 and lower tar selectivity over non-catalytic conditions. A 1:1:1 ratio of plastic-corn stover-magnetite was used to evaluate the reaction parameters such as temperature, space velocity, heating media, and catalytic cycles under gasification conditions. In comparison with the microwave non-catalytic route, a 100% increase in the total H 2 yield with 76% higher H 2 production efficiency (mmol/kWh) was achieved in the presence of the magnetite catalyst, while reducing the overall tar formation from 9% to 2%. When magnetite was reduced in situ during the reaction, it coupled with microwave and delivered oxygen radicals that cracked down plastic and corn stover intermediates generated from the synergistic effect under microwave heating. Soon after the oxygen transfer process initiated, magnetite reached its final oxidation state consisting of microwave-active Fe and Fe 3 C phases that continued coupling with microwaves along with the generated graphitic carbon to maintain the heat necessary to further reduce the generated tar and make additional gaseous products, as confirmed by XRD, Raman, and TGA analyses.

08 HYDROGEN↗
DOE OSTI2023

Theory and Simulation of Ultrafast Multidimensional Nonlinear X-ray Spectroscopy of Molecules (Final Report)

Emerging X-ray free electron laser (XFEL) beam sources offer new types of probes of matter with unprecedented spatial and temporal resolutions. These experimental advances must be met by robust theoretical and computational tools that provide predictive modeling capacity of the underlining electronic and structural dynamics. The latter will be essential for the design of sophisticated multi-pulse experiments and for their interpretation. The proposed research effort will focus on developing cutting- edge simulation tools for nonlinear multidimensional X-ray/optical spectroscopies and aims to address key questions in Priority Research Opportunities 1 (Probing and controlling electron motion within a molecule) and 3 (Capturing rare events and intermediate states in the transformation of matter) as mentioned in the BES Roundtable Report “Opportunities for Basic Research at the Frontiers of XFEL Ultrafast Science”. XFEL multidimensional nonlinear techniques, which combine sequences of X-ray and possibly optical pulses, provide a unique experimental toolbox for probing the dynamics of core and valence electronic excitations, as well as material structure. Predictive modeling of these dynamical processes requires the combination of analytical theory for nonlinear interactions of light and matter, robust quantum-chemical methodologies for the accurate description of electronic structure of various materials, and multiscale ab initio electron and nuclear dynamics techniques operating beyond Born-Oppenheimer approximation. These challenges will be addressed with three research thrusts (i) Develop and implement theoretical apparatus for modeling a broad range of multidimensional spectroscopic techniques enabled by present and upcoming XFEL facilities. This thrust also includes the incorporation of a computational module in the DOE supported open-source NWChem computational chemistry package as well as the development of other open-source codes ready for dissemination across a broad user base; (ii) Propose and design new multi-pulse experiments that make use of the capabilities of the incoming LCLS-II facility; (iii) Perform selected applications to specific molecular systems that can be carried out at LCLS-II and demonstrate how these X-ray sources may be used to study nonadiabatic dynamics through conical interactions, electronic correlations in multi-core excitons, and charge transfer/energy transfer processes. The proposed research will be carried out by a multi-disciplinary four-institution research team which combines academia and national laboratories and spans the broad and necessary expertise in theoretical spectroscopy, nonlinear optics, quantum chemistry, molecular non-adiabatic dynamics and code development. The work will be performed in a highly interactive team environment with junior researchers shared between institutions thus cementing cross- disciplinary interactions. The developed simulation tools will be immediately deployed for XFEL facility users, both experimentalists and theorists, via freely distributed codes and databases. Altogether, this project will facilitate establishing XFEL-based multidimensional spectroscopies as a novel diagnostic tool for monitoring electronic and structural dynamics in molecular materials.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS2008

Polymer Coats Leads on Implantable Medical Device

Langley Research Center s Soluble Imide (LaRC-SI) was discovered by accident. While researching resins and adhesives for advanced composites for high-speed aircraft, Robert Bryant, a Langley engineer, noticed that one of the polymers he was working with did not behave as predicted. After putting the compound through a two-stage controlled chemical reaction, expecting it to precipitate as a powder after the second stage, he was surprised to see that the compound remained soluble. This novel characteristic ended up making this polymer a very significant finding, eventually leading Bryant and his team to win several NASA technology awards, and an "R&D 100" award. The unique feature of this compound is the way that it lends itself to easy processing. Most polyimides (members of a group of remarkably strong and incredibly heat- and chemical-resistant polymers) require complex curing cycles before they are usable. LaRC-SI remains soluble in its final form, so no further chemical processing is required to produce final materials, like thin films and varnishes. Since producing LaRC-SI does not require complex manufacturing techniques, it has been processed into useful forms for a variety of applications, including mechanical parts, magnetic components, ceramics, adhesives, composites, flexible circuits, multilayer printed circuits, and coatings on fiber optics, wires, and metals. Bryant s team was, at the time, heavily involved with the aircraft polymer project and could not afford to further develop the polymer resin. Believing it was worth further exploration, though, he developed a plan for funding development and submitted it to Langley s chief scientist, who endorsed the experimentation. Bryant then left the high-speed civil transport project to develop LaRC-SI. The result is an extremely tough, lightweight thermoplastic that is not only solvent-resistant, but also has the ability to withstand temperature ranges from cryogenic levels to above 200 C. The thermoplastic s unique characteristics lend it to many commercial applications; uses that Bryant believed would ultimately benefit industry and the Nation. "LaRC-SI," he explains, "is a product created in a government laboratory, funded with money from the tax-paying public. What we discovered helps further the economic competitiveness of the United States, and it was our goal to initiate the technology transfer process to ensure that our work benefited the widest range of people." Several NASA centers, including Langley, have explored methods for using LaRC-SI in a number of applications from radiation shielding and as an adhesive to uses involving replacement of conventional rigid circuit boards. In the commercial realm, LaRC-SI can now be found in several commercial products, including the thin-layer composite unimorph ferroelectric driver and sensor (THUNDER) piezoelectric actuator, another "R&D 100" award winner (Spinoff 2005).

Source record↗
DOE OSTI2023

Direct Evidence for Excited Ligand Field State-based Oxidative Photoredox Chemistry of a Cobalt(III) Polypyridyl Photosensitizer

Increasing interest in sustainable chemistry coupled with the quest to explore new reactivity has spurred research on first-row transition metal complexes for potential applications in a variety of settings. One of the more active areas of research is photoredox catalysis, where the synthetically tunable nature of their electronic structures provides a rich palette of options for tailoring their reactivity to a desired chemical transformation. Understanding the mechanism of excited-state reactivity is critical for the informed development of next-generation catalysts, which in turn requires information concerning the propensity of their electronic excited states to engage in the desired electron or energy transfer processes. Herein we provide direct evidence of the highly oxidizing nature of the lowest-energy ligand-field (LF) excited state of a first-row d 6 -low-spin Co(III) photosensitizer [Co(4,4'-Br 2 bpy) 3 ] 3+ (where 4,4'-Br 2 bpy is 4,4'-dibromo-2,2'-bipyridine). The redox potential associated with the LF excited state of the Co(III) complex was bracketed by performing bimolecular quenching studies by using a series of simple organic electron donors. Time-resolved absorption spectroscopy confirmed a dynamic quenching process attributed to reductive quenching of the lowest-energy ligand-field excited state of the Co(III) chromophore. Analysis of the Stern–Volmer plots for each chromophore-quencher pair revealed a limiting value of E red * ~ 1.25 V vs Fc/Fc + for the metal-centered excited state, which is significantly stronger than that of more commonly employed transition metal-based photoredox agents such as [Ru(bpy) 3 ] 2+ (E red * = 0.32 V vs Fc/Fc + ) and [Ir(ppy) 2 (bpy)] + (E red * = 0.27 V vs Fc/Fc + ). Finally, these results suggest that this class of chromophores could find utility in applications requiring the activation of oxidatively resistant organic substrates for photoredox catalysis.

14 SOLAR ENERGY↗
DOE OSTI2026

Facile synthesis of Co(OH)2 nanoneedle arrays grown on stainless steel for industrial electrochemical oxygen evolution reaction

The electrochemical oxygen evolution reaction (OER) is a critical half-reaction in a variety of energy conversion and storage applications, however, OER suffers from sluggish kinetics due to the four proton-electron transfer processes. To remedy this, interfacial engineering proves an effective strategy to design high active OER catalysts. Herein, we report a facile synthesis of Co(OH)2 nanoneedle (Co-NN) arrays grown on stainless steel (SS) via a one-step hydrothermal reaction, and the resultant impressive OER performance. Particularly, the Co-NN/SS needs 267, 307, and 576 mV overpotentials to reach 10, 100, and 1000 mA cm−2 in 1 M KOH & room temperature, and the overpotentials drop to 199, 257, and 283 mV to achieve the same current densities in 30 wt% KOH & 80 °C. Additionally, an alkaline water electrolysis (AWE) cell coupled with Co-NN/SS anode and PtRu/NiMo cathode only requires 1.65 and 1.73 V iR-free cell voltage to reach 1.0 and 2.0 A cm−2, respectively. The sterling OER performance could be attributed to four possible reasons, the Fe in SS surface tailoring the electronic properties of Co(OH)2, the mixed metal oxides on SS surface accelerating surface reconstruction of Co(OH)2 nanoneedles into CoOOH active species, a Ni-rich surface layer formation cooperatively boosting the OER activity, and a local electric field effect concentrating reactants on the tip surface and accelerating the mass transfer. This work provides a facile approach for synthesizing highly efficient OER catalysts for industrial applications by interfacial engineering.

Lyu, Xiang [ORNL] (ORCID:0000000208673248)↗
NASA NTRS2011

An Efficient Monte Carlo Method for Modeling Radiative Transfer in Protoplanetary Disks

Monte Carlo methods have been shown to be effective and versatile in modeling radiative transfer processes to calculate model temperature profiles for protoplanetary disks. Temperatures profiles are important for connecting physical structure to observation and for understanding the conditions for planet formation and migration. However, certain areas of the disk such as the optically thick disk interior are under-sampled, or are of particular interest such as the snow line (where water vapor condenses into ice) and the area surrounding a protoplanet. To improve the sampling, photon packets can be preferentially scattered and reemitted toward the preferred locations at the cost of weighting packet energies to conserve the average energy flux. Here I report on the weighting schemes developed, how they can be applied to various models, and how they affect simulation mechanics and results. We find that improvements in sampling do not always imply similar improvements in temperature accuracies and calculation speeds.

radiative transfer↗
DOE OSTI2021

Simultaneous velocity and density measurements of fully developed Rayleigh-Taylor mixing

Here, the dynamics of molecular mixing and the energy transfer process in the Rayleigh-Taylor instability (RTI) are studied through the collection of simultaneous density-velocity measurements. These experiments provide simultaneous density-velocity field measurements, in contrast to previous point measurements. Statistically stationary experiments are performed in a “convective-type” gas tunnel facility, with density contrast achieved through the injection of helium into the bottom stream. Three experiments at Atwood number ≈ 0.1 are captured at three outer scale Reynolds numbers Re = 520, 2260, and 4050. Particle image velocimetry and laser induced fluorescence are employed simultaneously. Statistics of the density and velocity show self-similar collapse of RTI profiles at large Reynolds number Re >2000. Flat velocity profiles indicate homogeneous turbulence characteristics in the core of the mixing region. Significant anisotropy develops in the flow, with horizontal velocity fluctuations being only 60% of the vertical velocity fluctuations. The turbulent mass flux is found to be asymmetric about the centerline, with increased peak towards the spike. Measurements of the molecular mixing show that mixing is maximized at the core of the flow and increases with increased Reynolds number. The transport equation of density-specific-volume correlation b shows that it is mostly produced in the core of the mixing region, and that the spatial evolution of its profile is the result of transport by bulk motion of the bubble and spike. Energy transfer from gravitational potential energy to turbulent kinetic energy and viscous dissipation is observed to occur in the experiment with a ratio of dissipated energy to potential energy released of 38%. The analysis of the turbulent kinetic energy transport equation budget reveals that production is the primary mechanism towards the growth of turbulent kinetic energy in the core of the flow, and is asymmetrically slightly skewed towards the spike. However, it is through the transport that the strong advection at the edges of the mixing region is maintained.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2023

Validation of Universal Cryogenic Flow Boiling Correlations in Thermal Desktop for Liquid Helium

Understanding two-phase cryogenic propellant behavior is key to enabling technologies for future spaceflight missions. Developing accurate models of two-phase flow phenomena, particularly flow boiling in the heating configuration is relevant to the propellant transfer process both in microgravity and on other planetary surfaces. Currently there is a need for more accurate, direct cryogenic data anchored models for various boiling phenomena. Recently, universal correlations for cryogens flowing in heated tubes have been developed for a wide variety of fluids, thermodynamic conditions, and various regimes across the boiling curve, and have been patched to provide a smooth, continuous predictive curve. This paper demonstrates how these correlations have been ported into Thermal Desktop to improve predictive performance. To test the validity of the new correlations, Thermal Desktop is validated against a historical dataset of flow boiling experiments in the heating configuration using liquid helium. Based on results, the new correlations show a substantial improvement over the original built-in flow boiling correlations in Thermal Desktop in predicting the wall temperature as a function of preponderant parameters for this quantum fluid.

cryogenic propellant transfer↗
NASA NTRSDate not supplied

Validation of Universal Cryogenic Flow Boiling Correlations in Thermal Desktop for Liquid Helium

Understanding two-phase cryogenic propellant behavior is key to enabling technologies for future spaceflight missions. Developing accurate models of two-phase flow phenomena, particularly in the current work, flow boiling in the heating configuration, is relevant to the propellant transfer process both in 1-g and microgravity. Currently there is a need for more accurate, direct cryogenic data anchored models for various boiling phenomena. Recently, universal correlations for cryogens flowing in heated tubes have been developed for a wide variety of fluids, thermodynamic conditions, and various regimes across the boiling curve, and have been patched to provide a smooth, continuous predictive curve. This paper describes implementation and validation of these correlations into Thermal Desktop to improve predictive performance, with a focus on liquid helium. Results from Thermal Desktop using both the built-in and new correlations are validated against a historical dataset of flow boiling experiments in the heating configuration using liquid helium. Based on results, the new correlations show a substantial improvement over the original built-in flow boiling correlations in Thermal Desktop in predicting the wall temperature as a function of preponderant parameters for this quantum fluid at temperatures greater than the lambda temperature, T λ = 2.17K.

cryogenic propellant transfer↗
DOE OSTI2026

Balancing moisture and oxygen can match the crystallization dynamics of inert halide perovskite processing

Understanding crystallization in ambient environments is essential for scaling the fabrication of halide perovskite solar cells. Antisolvent-free perovskite deposition offers improved compatibility with high-throughput processing but introduces distinct crystallization dynamics relative to the more ubiquitous use of antisolvents in lab-scale perovskite fabrication. These dynamics are driven by interactions between solutes, solvent and the deposition environment. Using in situ wide-angle X-ray scattering during spin-coating and annealing, we demonstrate how relative humidity (RH) and oxygen, can be tuned to drive polytype evolution during ambient crystallization of formamidinium lead iodide to match that of inert synthesis and achieve comparable film and device quality. In an inert (N 2 ) environment, we find that perovskite films follow a well-established 2H → 3C phase transformation with a short period of coexistence of the 4H and 6H phase during heating. During crystallization in dry air (RH 0%), the added presence of oxygen leads to the dominance of 4H intermediate for an extended duration, establishing a 2H → 4H → 3C pathway. Introducing low humidity (RH 10%) suppresses the 4H phase to a short-lived intermediate above 100 °C, facilitating a more direct transition to the desired 3C phase and almost replicating the crystallization behavior observed under inert conditions. Interestingly, films crystallized under RH 10% show a lower onset temperature for the perovskite 3C phase than under N 2 . At higher humidity (RH 40%), the strong interaction of oxygen and moisture with iodoplumbates appears to stabilize higher order polytypes (4H and 6H). Devices fabricated under RH 10% achieve higher efficiency and enhanced stability compared to those produced under inert atmosphere. These findings provide mechanistic insight into crystallization pathways in different environments and provide a framework to transfer processes from inert to ambient conditions. The results highlight the critical role of controlled humidity in tuning antisolvent-free perovskite crystallization for scalable processing.

Hossain, Maimur [Univ. of California, San Diego, C↗
NASA NTRS2009

Studying Precipitation Processes in WRF with Goddard Bulk Microphysics in Comparison with Other Microphysical Schemes

A Goddard bulk microphysical parameterization is implemented into the Weather Research and Forecasting (WRF) model. This bulk microphysical scheme has three different options, 2ICE (cloud ice & snow), 3ICE-graupel (cloud ice, snow & graupel) and 3ICE-hail (cloud ice, snow & hail). High-resolution model simulations are conducted to examine the impact of microphysical schemes on different weather events: a midlatitude linear convective system and an Atlantic hurricane. The results suggest that microphysics has a major impact on the organization and precipitation processes associated with a summer midlatitude convective line system. The Goddard 3ICE scheme with the cloud ice-snow-hail configuration agreed better with observations ill of rainfall intensity and having a narrow convective line than did simulations with the cloud ice-snow-graupel and cloud ice-snow (i.e., 2ICE) configurations. This is because the Goddard 3ICE-hail configuration has denser precipitating ice particles (hail) with very fast fall speeds (over 10 m/s) For an Atlantic hurricane case, the Goddard microphysical scheme (with 3ICE-hail, 3ICE-graupel and 2ICE configurations) had no significant impact on the track forecast but did affect the intensity slightly. The Goddard scheme is also compared with WRF's three other 3ICE bulk microphysical schemes: WSM6, Purdue-Lin and Thompson. For the summer midlatitude convective line system, all of the schemes resulted in simulated precipitation events that were elongated in southwest-northeast direction in qualitative agreement with the observed feature. However, the Goddard 3ICE-hail and Thompson schemes were closest to the observed rainfall intensities although the Goddard scheme simulated more heavy rainfall (over 48 mm/h). For the Atlantic hurricane case, none of the schemes had a significant impact on the track forecast; however, the simulated intensity using the Purdue-Lin scheme was much stronger than the other schemes. The vertical distributions of model-simulated cloud species (e.g., snow) are quite sensitive to the microphysical schemes, which is an issue for future verification against satellite retrievals. Both the Purdue-Lin and WSM6 schemes simulated very little snow compared to the other schemes for both the midlatitude convective line and hurricane case. Sensitivity tests with these two schemes showed that increasing the snow intercept, turning off the auto-conversion from snow to graupel, eliminating dry growth, and reducing the transfer processes from cloud-sized particles to precipitation-sized ice collectively resulted in a net increase in those schemes' snow amounts.

Tao, W.K.↗
NASA NTRS2007

New, Improved Goddard Bulk-Microphysical Schemes for Studying Precipitation Processes in WRF

An improved bulk microphysical parameterization is implemented into the Weather Research and Forecasting ()VRF) model. This bulk microphysical scheme has three different options, 2ICE (cloud ice & snow), 3ICE-graupel (cloud ice, snow & graupel) and 3ICE-hail (cloud ice, snow & hail). High-resolution model simulations are conducted to examine the impact of microphysical schemes on two different weather events (a midlatitude linear convective system and an Atlantic hurricane). The results suggest that microphysics has a major impact on the organization and precipitation processes associated with a summer midlatitude convective line system. The Goddard 3ICE scheme with a cloud ice-snow-hail configuration agreed better with observations in terms of rainfall intensity and a narrow convective line than did simulations with a cloud ice-snow-graupel or cloud ice-snow (i.e., 2ICE) configuration. This is because the 3ICE-hail scheme includes dense ice precipitating (hail) particle with very fast fall speed (over 10 in For an Atlantic hurricane case, the Goddard microphysical schemes had no significant impact on the track forecast but did affect the intensity slightly. The improved Goddard schemes are also compared with WRF's three other 3ICE bulk microphysical schemes: WSM6, Purdue-Lin and Thompson. For the summer midlatitude convective line system, all of the schemes resulted in simulated precipitation events that were elongated in the southwest-northeast direction in qualitative agreement with the observed feature. However, the Goddard 3ICE scheme with the hail option and the Thompson scheme agree better with observations in terms of rainfall intensity, expect that the Goddard scheme simulated more heavy rainfall (over 48 mm/h). For the Atlantic hurricane case, none of the schemes had a significant impact on the track forecast; however, the simulated intensity using the Purdue-Lin scheme was much stronger than the other schemes. The vertical distributions of model simulated cloud species (i.e., snow) are quite sensitive to microphysical schemes, which is an important issue for future verification against satellite retrievals. Both the Purdue-Lin and WSM6 schemes simulated very little snow compared to the other schemes for both the midlatitude convective line and hurricane cases. Sensitivity tests are performed for these two WRF schemes to identify that snow productions could be increased by increasing the snow intercept, turning off the auto-conversion from snow to graupel and reducing the transfer processes from cloud-sized particles to precipitation-sized ice.

Tao, Wei-Kuo↗
DOE OSTI2025

Approach to Evaluating Reorganization Energies of Interfacial Electrochemical Reactions

Reaction rate coefficients for electron-transfer processes at the electrode–electrolyte interface are commonly estimated by using the Butler–Volmer equation, but their values are inaccurate beyond a few tenths of volts of overpotential. The Marcus–Hush–Chidsey (MHC) formalism yields correct asymptotic behavior of the rate coefficients vs applied overpotential but has complex dependencies on the redox system’s intrinsic parameters, which can be difficult to model or measure. In this work, we bridge the two kinetics formalisms to estimate the reorganization energy, one of the important parameters for the MHC formalism, and investigate its dependence on other intrinsic parameters such as activation barriers, electronic coupling strength, and the density of states of the electrode surface. We examine the sensitivity of the reorganization energy to these parameters, establish some general relationships for accurately predicting rate coefficients using the MHC formalism over a wide range of applied overpotentials, and compare this approach to calculating MHC rate constants with other empirical approaches for the mechanisms of CO 2 reduction on different metal electrode surfaces.

Butler−Volmer↗