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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 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Theory-driven design of high-valence metal sites for water oxidation confirmed using in situ soft X-ray absorption

The efficiency with which renewable fuels and feedstocks are synthesized from electrical sources is limited at present by the sluggish oxygen evolution reaction (OER) in pH-neutral media. Here, we took the view that generating transition metal sites with high valence at low applied bias should improve the activity of neutral OER catalysts. Using density functional theory, we find that the formation energy of desired Ni 4+ sites is systematically modulated by incorporating judicious combinations of Co, Fe and non-metal phosphorus. Here we synthesized NiCoFeP oxyhydroxides and probed their oxidation kinetics by employing in situ soft X-ray absorption (sXAS). In situ sXAS studies of neutral-pH OER catalysts indicate ready promotion of Ni 4+ under low overpotential conditions. NiCoFeP catalyst outperforms IrO 2 and retains its performance following 100 hours of operation. We showcase NiCoFeP in a membrane-free CO 2 electroreduction system that achieves a 1.99 V cell voltage at 10 mA cm -2 , reducing CO 2 into CO and oxidizing H 2 O to O 2 with a 64% electricity-to-chemical-fuel efficiency.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2025

Operando Contactless EFISH Study of the Rate-Determining Step of Light-Driven Water Oxidation on TiO 2 Photoanodes

For many slow solar-fuel-forming reactions, the accumulation of photogenerated minority carriers on the photoelectrode surface leads to light-induced band edge unpinning, affecting the junction properties by decreasing band bending in the semiconductor space charge layer and increasing the driving force of surface reactions in the electric double layer. In this study, we demonstrate a contactless operando electric field-induced second harmonic generation (EFISH) method for measuring the band bending change (δΔΦ SCR L ) on photoelectrodes upon photoexcitation. For ndoped rutile TiO 2 water oxidation photoanodes at pH 7, δΔΦ SCR L increases at more positive potentials or higher illumination power density until it reaches saturation values. We show that under fast mass transport conditions, δΔΦ SCR L is exclusively attributed to the accumulated charged rate-determining species that can be regarded as temporary surface states, and the relationship between the photocurrent and δΔΦ SCR L can be well modeled by assuming that hole trap states function as the reaction center. Kinetic isotope experiments identify proton-coupled electron transfer as the rate-determining step and suggest a possible chemical nature of the key intermediate. We demonstrate that light-induced band edge unpinning is a beneficial feature under high illumination conditions for oxygen evolution reaction on TiO 2 because it maintains the photon-to-current conversion efficiency by enhancing the surface reaction driving force, shedding light on the actual device application.

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

Establishing Co‐Continuous Network of Conjugated Polymers and Elastomers for High‐Performance Polymer Solar Cells with Extreme Stretchability

High power conversion efficiency (PCE) and mechanical robustness are prerequisites for wearable applications of organic solar cells (OSCs). However, stretchability of present active systems (i.e., crack-onset strain (COS) < 30%) should be improved. While introducing elastomers into active systems is considered a simple method for improving stretchability, the inclusion of elastomers typically results in a decrease in PCE of the OSC with a limited enhancement in the stretchability due to lack of interconnected electrical and mechanical pathways. In this study, it is developed efficient and intrinsically stretchable (IS)-OSCs with exceptional mechanical robustness, by constructing co-continuous networks of conjugated polymers (D18) and elastomers (SEBS) within active layers. It is demonstrated that the blend film with a specific ratio (40:60 w/w) of D18:SEBS is crucial for forming co-continuous structures, establishing well-connected mechanical and electrical channels. Consequently, D18 0.4 :SEBS 0.6 /L8-BO OSCs achieve 16-times higher stretchability (COS = 126%) than the OSCs based on D18/L8-BO (COS = 8%), while achieving 4-times higher PCE (12.13%) compared to the OSCs based on SEBS-rich active layers (D18 0.2 :SEBS 0.8 /L8-BO, PCE = 3.15%). Furthermore, D18 0.4 :SEBS 0.6 -based IS-OSCs preserve 86 and 90% of original PCEs at 50% strain and after 200 stretching/releasing cycles with 15% strain, respectively, demonstrating the highest mechanical robustness among reported IS-OSCs.

14 SOLAR ENERGY↗
DOE OSTI2023

Self-powered ocean buoy using a disk-type triboelectric nanogenerator with a mechanical frequency regulator

Triboelectric nanogenerator (TENG) systems have been demonstrated to generate power with high density. However, the electrical output power obtained from wave energy harvesting using TENG systems is typically limited to several milliwatts. To address this limitation and support various ocean buoy systems, an efficient method to scale-up TENG systems is required. In this paper, we present a self-powered ocean buoy (SPOB) incorporating a disk-type, soft-contact, mechanical frequency regulator TENG (DSMFR-TENG). The mechanical frequency regulator (MFR) enables the conversion of low-frequency wave energy to high-speed mechanical rotation, facilitating high power generation with the disk-type TENG. Here, the SPOB was tested in a wave tank, reaching a peak power output of 470 mW and an average power output of 130 mW after the MFR released the rotational energy. To further enhance the functionality of the buoy, the DSMFR-TENG and a microcontroller, temperature sensor, and acoustic transmitter were integrated with the SPOB. The acoustic transmitter successfully transmitted signals 7, 23, and 30 times over a one-minute period at wave frequencies of 0.33 Hz, 0.5 Hz, and 1 Hz, respectively, thereby demonstrating the power supply capability of the TENG system for ocean buoys.

42 ENGINEERING↗
DOE OSTI2018

Theory of electromagnetic wave frequency upconversion in dynamic media

Frequency upconversion of an electromagnetic wave can occur in ionized plasma with decreasing electric permittivity and in split-ring resonator-structure metamaterials with decreasing magnetic permeability. We develop a general theory to describe the evolution of the wave frequency, amplitude, and energy density in homogeneous media with a temporally decreasing refractive index. We find that upconversion of the wave frequency is necessarily accompanied by partitioning of the wave energy into low-frequency modes, which sets an upper limit on the energy conversion efficiency. In conclusion, the efficiency limits are obtained for both varying permittivity and varying permeability.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2007

Recent Progress Made in the Development of High-Energy UV Transmitter

In this paper, the status of an all-solid-state UV converter development for ozone sensing applications is discussed. A high energy Nd:YAG laser for pumping the UV converter arrangement was recently reported. The pump is an all-solid-state, single longitudinal mode, and conductively cooled Nd:YAG laser operating at 1064 nm wavelength. Currently, this pump laser provides an output pulse energy of greater than 1J/pulse at 50 Hz PRF and a pulsewidth of 22 ns with an electrical-to-optical system efficiency of greater than 7% and a M(sup 2) value of approx. 2. The spatial profile of the output beam is a rectangular super Gaussian. This Nd:YAG pump laser has been developed to pump the nonlinear optics based UV converter arrangement to generate 320 nm and 308 nm wavelengths by means of 532 nm wavelength. Previously, this UV converter arrangement has demonstrated IR-to-UV conversion efficiency of 24% using a flash lamp pumped laser providing a round, flat top spatial profile. Recently, the UV converter was assembled and tested at NASA LaRC for pumping with the diode pumped Nd:YAG laser. With current spatial profile, the UV converter was made operational. Current efforts to maximize the nonlinear conversion efficiency by refining its spatial profile to match RISTRA OPO requirements are progressing.

Prasad, Narasimha S.↗
NASA NTRS2019

Small Stirling Technology Exploration Power for Future Space Science Missions

High efficiency dynamic Radioisotope Power Systems (RPS) could be mission enabling for low power space applications such as small probes, landers rovers, and communication repeaters. These applications would contain science instruments and be distributed across planetary surfaces or near objects of interest where solar flux is insufficient for using solar cells. Small RPS could be used to provide power for sensing radiation, temperature, pressure, seismic activity, and other measurements of interest to planetary scientists. Small RPS would use fractional versions of the General Purpose Heat Source (GPHS) or Light Weight Radioisotope Heater Units (LWRHU), to heat power conversion technologies. Dynamic power systems are capable of three to four times higher conversion efficiency compared to static power conversion technologies, and would provide an equal amount of power using less fuel or more power using an equal amount of fuel. Providing spacecraft with more power could decrease duty cycling of basic functions and, therefore, increase the quality and abundance of science data. NASA GRC is developing a low power dynamic RPS that would convert heat from multiple LWRHU to one watt of usable direct current electric power for spacecraft instrumentation and communication. The power system could be used to charge batteries or capacitors for higher power burst usage. The initial design, called Small Stirling Technology Exploration Power (smallSTEP), is around 3 kg, 11 cm diameter X 32 cm long, and converts 8 watts of heat to one watt of electricity using a Stirling convertor. This low power conversion system represents a new class of RPS with power levels two orders of magnitude lower than prototypes currently being developed for space applications under NASA contracts. Development of the 1-watt RPS includes maturation of convertor and controller designs, performance evaluation of an evacuated metal foil insulation, and development of system interfaces. Initial demonstration of the subsystems has been completed in a laboratory environment and a higher fidelity system is being pursued for demonstration in relevant environments for use on small spacecraft needed to carry out future space science missions.

Wilson, Scott D.↗
DOE OSTI2015

Spin pumping and inverse Rashba-Edelstein effect in NiFe/Ag/Bi and NiFe/Ag/Sb

The Rashba effect is an interaction between the spin and the momentum of electrons induced by the spin-orbit coupling in surface or interface states. We measured the inverse Rashba-Edelstein effect via spin pumping in Ag/Bi and Ag/Sb interfaces. The spin current is injected from the ferromagnetic resonance of a NiFe layer towards the Rashba interfaces, where it is further converted into a charge current. Using spin pumping theory, we quantify the conversion parameter of spin to charge current to be 0.11 ± 0.02 nm for Ag/Bi and a factor of ten smaller for Ag/Sb. The relative strength of the effect is in agreement with spectroscopic measurements and first principles calculations. We also vary the interlayer materials to study the voltage output in relation to the change of the effective spin mixing conductance. The spin pumping experiment offers a straight-forward approach of using spin current as an efficient probe for detecting interface Rashba splitting.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Controlling the dopant profile for SRH suppression at low current densities in λ ≈ 1330 nm GaInAsP light-emitting diodes

The quantum efficiency of double hetero-junction light-emitting diodes (LEDs) can be significantly enhanced at low current density by tailoring the spatial profile of dopants to suppress Shockley–Read–Hall recombination. To demonstrate this effect, we model, design, grow, fabricate, and test a GaInAsP LED (λ≈ 1330 nm) with an unconventional dopant profile. Compared against that of our control design, which is a conventional n + -n - p + double hetero-junction LED, the dopant profile near the n - p + hetero-structure of the design displaces the built-in electric field in such a way that the J 02 space charge recombination current is suppressed. The design principle generalizes to other material systems and could be applicable to efforts to observe and exploit electro-luminescent refrigeration at practical power densities.

42 ENGINEERING↗
DOE OSTI2020

Analysis of a Fluidized-Bed Particle/Supercritical-CO2 Heat Exchanger in a Concentrating Solar Power System

Concentrating solar power (CSP) development has focused on increasing the energy conversion efficiency and lowering the capital cost. To improve performance, CSP research is moving to high-temperature and high-efficiency designs. One technology approach is to use inexpensive, high-temperature heat transfer fluids and storage, integrated with a high-efficiency power cycle such as the supercritical carbon dioxide (sCO 2 ) Brayton power cycle. The sCO 2 Brayton power cycle has strong potential to achieve performance targets of 50% thermal-to-electric efficiency and dry cooling at an ambient temperature of up to 40 °C and to reduce the cost of power generation. Solid particles have been proposed as a possible high-temperature heat transfer or storage medium that is inexpensive and stable at high temperatures above 1000 °C. The particle/sCO 2 heat exchanger (HX) provides a connection between the particles and sCO 2 fluid in emerging sCO 2 power cycles. This article presents heat transfer modeling to analyze the particle/sCO 2 HX design and assess design tradeoffs including the HX cost. The heat transfer process was modeled based on a particle/sCO 2 counterflow configuration, and empirical heat transfer correlations for the fluidized bed and sCO 2 were used to calculate heat transfer area and estimate the HX cost. A computational fluid dynamics simulation was applied to characterize particle distribution and fluidization. This article shows a path to achieve the cost and performance objectives for a particle/sCO 2 HX design by using fluidized-bed technology.

14 SOLAR ENERGY↗
NASA NTRS1985

Bearing development program for a 25 kWe solar-powered organic Rankine-cycle engine

The bearing development program is summarized for a 25-kWe power conversion subsystem (PCS) consisting of an organic Rankine-cycle engine, and permanent magnetic alternator (PMA) and rectifier to be used in a 100-kWe point-focusing distributed receiver solar power plant. The engine and alternator were hermetically sealed and used toluene as the working fluid. The turbine, alternator, and feed pump (TAP) were mounted on a single shaft operating at speeds up to 60,000 rev/min. Net thermal-to-electric efficiencies in the range of 21 to 23% were demonstrated at the maximum working fluid temperature of 400 C (750 F). A chronological summary of the bearing development program is presented. The primary causes of bearing wear problems were traced to a combination of rotordynamic instability and electrodynamic discharge across the bearing surfaces caused by recirculating currents from the PMA. These problems were resolved by implementing an externally supplied, flooded-bearing lubrication system and by electrically insulating all bearings from the TAP housing. This program resulted in the successful development of a stable, high-speed, toluene-lubricated five-pad tilting-pad journal bearing and Rayleigh step thrust bearing system capable of operating at all inclinations between horizontal and vertical.

Nesmith, B.↗
NASA NTRS1991

Infrared power cells for satellite power conversion

An analytical investigation is performed to assess the feasibility of long-wavelength power converters for the direct conversion of IR radiation onto electrical power. Because theses devices need to operate between 5 and 30 um the only material system possible for this application is the HgCdTe system which is currently being developed for IR detectors. Thus solar cell and IR detector theories and technologies are combined. The following subject areas are covered: electronic and optical properties of HgCdTe alloys; optimum device geometry; junction theory; model calculation for homojunction power cell efficiency; and calculation for HgCdTe power cell and power beaming.

Summers, Christopher J.↗
DOE OSTI2024

EchemAMR (electro-chemical microsctructure scale models with adaptive meshing) [SWR-23-111]

A 3D microstructure resolving electrochemical transport and interfacial chemistry solver. Electrode microstructure plays an important role in determining the performance of an electrochemical system, e.g. lithium ion battery. EchemAMR is a microstructure scale model that solves the governing equations for ion transport, electrical current continuity, interfacial chemistry and structural mechanics. Complex microstructure geometries from imaging can be directly imported into EchemAMR. A volume fraction based description of the geometry on Cartesian grid with an immersed interface formulation enables simplified meshing and large-scale simulations with millions of degrees of freedom. EchemAMR has been tested against systems with analytic solutions for numerical convergence and highly resolved lithium ion battery microstructures. EchemAMR demonstrates excellent mass conversation and efficient scaling on heterogenous High-Performance Computing (HPC) with central and graphics processing units.

Sitaraman, Hariswaran↗
DOE OSTI2024

Advancements in Manufacturing of High-Performance Perovskite Solar Cells and Modules Using Printing Technologies

Perovskite photovoltaic technology carries immense opportunity for the solar industries because of its remarkable efficiency and prospect for cost-effective production. However, the successful deployment of perovskite solar modules (PSMs) in the solar market necessitates tackling stability-based obstacles, scalability, and environmental considerations. This paper unveils a comprehensive examination of the cutting-edge advancements in the manufacturing of perovskite solar cells (PSCs) and modules, with an emphasis on high-speed, large-area printing. The paper underscores the substantial progress achieved in printed PSCs and PSMs, demonstrating promising electrical performance and long-term device durability. This review paper categorizes printing techniques compatible with large-area high-speed manufacturing into three distinct families: blade coating, slot die coating, and screen printing, as these common printing practices offer precise control, scalability, cost-effectiveness, high resolution, and efficient material usage. Additionally, this paper presents an in-depth investigation and comparison of superior PSCs and PSMs fabricated by printing on power conversion efficiency (PCE), stability, and scalability.

14 SOLAR ENERGY↗
DOE OSTI2018

Survey of existing and emerging power conversion technologies relevant to a self-powered furnace

Furnaces for residential space heating consume about 2.5% of all annual primary energy consumed in the US. Conventional furnaces utilize electricity from the electric grid to power blowers and other components. A self-powered furnace would utilize fuel energy to generate its own power, while rejecting the waste heat from the power cycle to provide additional useful building heating. Assuming the total energy use remains the same as for a conventional furnace, there are advantages in primary energy efficiency and operating cost. With no electrical connection to the grid, the self-powered furnace also improves resiliency to electric grid outages and reduces demand on the grid, which can be important during periods of peak heating. In addition, when unit size and venting type are maintained, a drop-in replacement with no incremental installation cost and increased potential for market adoption is achieved. In this work, the power generation requirements for such a drop-in-ready, self-powered furnace are analyzed, and available power generation technologies are surveyed.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2017

Electric Motor Thermal Management

Thermal management enables more efficient and cost-effective motors. This Annual Merit Review presentation describes the technical accomplishments and progress in electric motor thermal management R&D over the last year. This project supports a broad industry demand for data, analysis methods, and experimental techniques to improve and better understand motor thermal management.

30 DIRECT ENERGY CONVERSION↗
NASA NTRS2018

Conductivity of a Copper-Carbon Covetic Composite

NASA is currently engaged in the development of highly electrically conductive wire for space and aviation power and propulsion applications. Higher levels of electrical conductivity and lower densities compared to copper and aluminum are needed to improve the efficiency of commercial aviation and space flight. Carbon, in various forms, is being considered as a component in composites to increase conductivity and decrease density in Cu and Al. One form of carbon that is currently receiving much interest is known as covectic. The technology currently known as covetics was first introduced by Shugart and Scherer whose patents claimed "Carbon can be incorporated into any of these metals by melting the metal, mixing the carbon into the molten metal and, while mixing, applying a current of sufficient amperage to the molten mixture such that the carbon becomes incorporated into the metal, thereby forming a single phase metal-carbon material." It is reported that in this process a conversion reaction occurs with the carbon forming covalent bonds with the host metal, and that covetic processing enables higher carbon solubility and improvements in properties. Although there is a growing body of work supporting covetic materials, it is still a very new and somewhat controversial field. Composition, density, and electrical conductivity measurements of a covetically processed alloy ingot of Cu and C, with a nominal composition of Cu-0.4wt.% C, were made. A pure Cu ingot was similarly processed for comparison. Sections of these ingots were worked into wire and tested. Only small amounts of C could be detected in the Cu-0.4wt.% C ingot, and trace amounts (0.006 wt.%) in the wire. All wires had densities very close to the full density of pure Cu, indicating a high level of Cu purity and low void fraction. Finally, the electrical conductivity of the Cu-0.4wt.% C wires were 9% lower than the samples similarly processed but without C additions. The wires made without C additions had conductivities approximately equal to pure Cu. The low conductivity of the Cu-0.4wt.% C material is believed to be due to: (1) a structure of interfaces in the wire created by collapsed voids lined with elemental C, (2) impurities, such as Fe in the Cu, which came from the added C, and (3) a small volume fraction of voids.

Degroh, Henry C.↗