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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 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Sparsely Dispersed CeO x ‑Stabilized Pt Nanoparticles Overcome Pt Loading–Durability Trade-Off for Highly Durable Heavy-Duty Fuel Cells

Proton-exchange-membrane fuel cells (PEMFCs) are clean and sustainable mobile power sources for transportation. Recently, their deployment in heavy-duty vehicles (HDVs) has attracted growing interest owing to their high energy scalability and lower infrastructure requirements. However, to meet the stringent requirements for efficiency and long-term durability for HDV applications, PEMFCs typically employ a relatively high platinum group metal (PGM) loading (>0.2 mg PGM /cm 2 ). This elevated PGM loading significantly increases the stack and system costs, surpassing the U.S. Department of Energy (DOE) target of $\$ 60$/kW for commercial viability. Reducing PGM loading while maintaining performance and durability remains a central challenge for HDV fuel cells. Here we exploit metal oxide–Pt interactions and utilize the strong CeO x –Pt interaction to design a CeO x @Pt catalyst structure with exceptional durability. At a low total PGM loading (0.1 mg PGM /cm 2 ), the CeO x @Pt/C catalyst demonstrates high fuel cell performance (8.8 kW/g PGM ) and stability (power retention >90%) after the challenging HDV durability testing (90,000 accelerated-stress-test cycles). With the CeO x @Pt/C catalyst, we showcase over 70% reduction in Pt cost from the M2FCT target (to $\$ 9$/kW), highlighting its promising potential for enabling stable and cost-effective fuel cell systems for heavy-duty applications.

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

Stress Testing California's Hydroclimatic Whiplash: Potential Challenges, Trade‐Offs and Adaptations in Water Management and Hydropower Generation

Abstract Inter‐annual precipitation in California is highly variable, and future projections indicate an increase in the intensity and frequency of hydroclimatic “whiplash.” Understanding the implications of these shocks on California's water system and its degree of resiliency is critical from a planning perspective. Therefore, we quantify the resilience of reservoir services provided by water and hydropower systems in four basins in the western Sierra Nevada. Using downscaled runoff from 10 climate model outputs, we generated 200 synthetic hydrologic whiplash sequences of alternating dry and wet years to represent a wide range of extremes and transitional conditions used as inputs to a water system simulation model. Sequences were derived from upper (wet) and lower (dry) quintiles of future streamflow projections (2030–2060). Results show that carryover storage was negatively affected in all basins, particularly in those with lower storage capacity. All basins experienced negative impacts on hydropower generation, with losses ranging from 5% to nearly 90%. Reservoir sizes and inflexible operating rules are a particular challenge for flood control, as in extremely wet years spillage averaged nearly the annual basins' total discharge. The reliability of environmental flows and agricultural deliveries varied depending on the basin, intensity, and duration of whiplash sequences. Overall, wet years temporarily rebound negative drought effects, and greater storage capacity results in higher reliability and resiliency, and lesser volatility in services. We highlight potential policy changes to improve flexibility, increase resilience, and better equip managers to face challenges posed by whiplash while meeting human and environmental needs.

Environmental Sciences & Ecology↗
DOE OSTI2016

Trade-offs between microbiome diversity and productivity in a stratified microbial mat

Productivity is a major determinant of ecosystem diversity. Microbial ecosystems are the most diverse on the planet yet very few relationships between diversity and productivity have been reported as compared to macro-ecological studies. Here we evaluated the spatial relationships of productivity and microbiome diversity in a laboratory-cultivated photosynthetic mat. The goal was to determine how spatial diversification of microorganisms drives localized carbon and energy acquisition rates. We measured sub-millimeter depth profiles of net primary-productivity and gross oxygenic photosynthesis in the context of the localized microenvironment and community structure and observed negative correlations between species richness and productivity within the energy-replete, photic zone. Variations between localized community structures were associated with distinct taxa as well as environmental profiles describing a continuum of biological niches. Spatial regions corresponding to high primary productivity and photosynthesis rates had relatively low species richness and high evenness. Hence, this system exhibited negative species-productivity and species–energy relationships. These negative relationships may be indicative of photosynthetically-driven, light-controlled mat ecosystems that are able to be the most productive with a relatively smaller, even distributions of species that specialize within the highly-oxic, photic zones.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Environmental trade-offs of direct air capture technologies in climate change mitigation toward 2100

Abstract Direct air capture (DAC) is critical for achieving stringent climate targets, yet the environmental implications of its large-scale deployment have not been evaluated in this context. Performing a prospective life cycle assessment for two promising technologies in a series of climate change mitigation scenarios, we find that electricity sector decarbonization and DAC technology improvements are both indispensable to avoid environmental problem-shifting. Decarbonizing the electricity sector improves the sequestration efficiency, but also increases the terrestrial ecotoxicity and metal depletion levels per tonne of CO 2 sequestered via DAC. These increases can be reduced by improvements in DAC material and energy use efficiencies. DAC exhibits regional environmental impact variations, highlighting the importance of smart siting related to energy system planning and integration. DAC deployment aids the achievement of long-term climate targets, its environmental and climate performance however depend on sectoral mitigation actions, and thus should not suggest a relaxation of sectoral decarbonization targets.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2025

Synergies and trade-offs of multi-use solar landscapes

Research on multi-use solar-combining solar energy with agriculture (agrivoltaics) or natural vegetation (ecovoltaics)-is developing rapidly, but interdisciplinary integration is needed to better address management issues and to guide future research. Agrivoltaics allows farmers to develop and manage microclimates, which can help to retain or expand agricultural production in the context of changing climate and land-water limitations. However, improvements in food-energy production and other co-benefits are often site-specific, depending on background climate, soil conditions and system design. In conclusion, to optimize multi-use systems, it is essential to consider local economic impacts, ecosystem services and stakeholder perspectives in design and implementation.

14 SOLAR ENERGY↗
DOE OSTI2021

Solving the activity–stability trade-off riddle

Atomically dispersed and nitrogen-coordinated single iron site catalysts hold great promise to replace platinum for proton-exchange membrane fuel cells, but they suffer from significant performance loss. As shown here, solving the conundrum to distinguish durable and non-durable FeN 4 active sites can guide high-performance catalyst design.

08 HYDROGEN↗
DOE OSTI2024

Trade-off between processability and device performance in donor–acceptor semiconductors revealed using discrete siloxane side chains

Donor–acceptor polymeric semiconductors are crucial for state-of-the-art applications, such as electronic skin mimics. The processability, and thus solubility, of these polymers in benign solvents is critical and can be improved through side chain engineering. Nevertheless, the impact of novel side chains on backbone orientation and emerging device properties often remains to be elucidated. Here, we investigate the influence of elongated linear and branched discrete oligodimethylsiloxane (oDMS) side chains on solubility and device performance. Thereto, diketopyrrolopyrrole–thienothiophene polymers are equipped with various oDMS pendants (PDPPTT-Si n ) and subsequently phase separated into lamellar domains. The introduction of a branching point in the siloxane significantly enhanced the solubility of the polymer, as a result of increased backbone distortion. Simultaneously, the charge carrier mobility of the polymers decreased by an order of magnitude upon functionalization with long and/or branched siloxanes. This work unveils the intricate balance between processability and device performance in organic semiconductors, which is key for the development of next-generation electronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Growth of GaAs{sub 1−x}Bi{sub x} by molecular beam epitaxy: Trade-offs in optical and structural characteristics

Recent work has shown that Bi incorporation increases during molecular beam epitaxy (MBE) when surface processes are kinetically limited through increased growth rate. Herein we explore how the structural and optical properties of GaAs{sub 1−x}Bi{sub x} films are modified when grown under conditions with varying degrees of kinetic limitations realized through growth temperature and growth rate changes. Within the typical window of MBE growth conditions for GaAs{sub 1−x}Bi{sub x}, we compare films with similar (∼3%) compositions grown under conditions of reduced kinetic limitations, i.e., relatively low gallium supersaturation achieved at higher temperatures (∼350 °C) and lower growth rates (∼0.5 μm/h), to those grown farther from equilibrium, specifically, higher supersaturation achieved at lower growth temperatures (∼290 °C) and higher growth rates (∼1.4 μm/h). Both the x-ray diffraction full width at half maximum of the omega-2theta scan and the 300 K photoluminescence intensity increase when samples are grown under less kinetically limited conditions. We interpret these findings in relation to the incorporation of Bi-related microstructural defects that are more readily formed during less kinetically limited growth. These defects lead to enhanced luminescence efficiency due to the spatial localization of carriers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Modulation-slippage trade-off in resonant four-wave upconversion

Following up on a proposal to use four-wave mixing in an underdense plasma at mildly relativistic laser intensities to produce vastly more energetic x-ray pulses [V. M. Malkin and N. J. Fisch, Phys. Rev. E, 101, 023211 (2020)], we perform the first numerical simulations in one dimension to illustrate amplification of a short high frequency seed through four-wave mixing. Here, we illustrate how parasitic processes including phase modulation and spatial pulse slippage limit the amplification efficiency. Although the regimes studied were not where the optimal efficiencies were expected, these regimes do expose the basic physical processes at play, while still yielding not insignificant spectral power upshift.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Techno-Economic Analysis of CSP Incorporating sCO2 Brayton Power Cycles: Trade-Off Between Cost and Performance

Concentrating solar power (CSP) plants, thanks to the implementation of cost-competitive thermal energy storage, represent a dispatchable zero-emission alternative to traditional fossil fuel power plants. Next generation solar towers are expected to adopt high temperature receivers (>700 degrees C) coupled to sCO2-based power blocks, which optimal design is generally pushed towards the maximum cycle efficiency, often neglecting the economic impact with the justification that the main share of the capital cost is represented by the heliostat field. As result, the scientific literature lacks in comprehensive studies on techno-economic evaluation of CSP+sCO2 power plants addressing the important correlation that exists between system cost and performances. This work provides a preliminary techno-economic analysis of a solar power tower comparing four different cycle configurations for the sCO2 power block. Results have been reported on a Pareto front, highlighting the tradeoff between the plant investment cost and the solar-to-electricity plant efficiency. The trends of the optimization variables and cycle results have been reported to give useful insights about proper assumptions for the sCO2 power block design. The recompressed cycle with intercooling resulted as the most promising configuration and it has been further analyzed through a comparison of different solutions on the Pareto front. The cost breakdown of the sCO2 power block has been reported to highlight which components have the greatest impact on the overall plant cost and how they vary along the optimal solutions front. Eventually, the optimization has been repeated introducing a correlation to compute the turbomachinery isentropic efficiencies, to investigate their effect on the techno- economic analysis.

concentrated solar power↗
DOE OSTI2018

Life history variation is maintained by fitness trade-offs and negative frequency-dependent selection

Significance Many populations and species have different strategies for maximizing reproductive success in changing environments. For example, some species of plants reproduce only once in their lifetime (annuals), whereas others can reproduce over multiple years (perennials). Such variation can also occur in fishes, and we examine how this variation in life history strategies is maintained in a Pacific salmonid species ( Oncorhynchus mykiss ). We find that fish that successfully migrate between the ocean and their freshwater spawning grounds multiple times (repeat spawners) have more than twice the lifetime reproductive success of fish that only spawn once (single spawners). We also find a striking pattern of negative frequency-dependent selection in which older, larger females have higher lifetime fitness when they are less abundant.

Christie, Mark R.↗
DOE OSTI2021

Finny Merchandise: The Atlantic Cod (Gadus morhua) Trade in Gold Rush–Era San Francisco, California

During California’s Gold Rush of 1849–1855, thousands of miners rushed to San Francisco, Sacramento, and elsewhere throughout northern California, creating a significant demand for food. In this work, we investigate the role of Atlantic cod (Gadus morhua) and Pacific cod (G. macrocephalus) during the Gold Rush era using historical records, ancient DNA, and vertebral morphology in the cod assemblage recovered from Thompson’s Cove (CA-SFR-186H), a Gold Rush–era site in San Francisco. From the 18 cod bones recovered from Thompson’s Cove, our analysis of five specimens for ancient DNA indicates that Atlantic cod were imported during the 1850s, likely as a (largely) deboned, dried and salted product from the East Coast of the United States. Curiously, while locally available in very deep waters off the California coast, Pacific cod were minimally fished during the 1850s and became abundantly available in the 1860s after an Alaska-based fishery developed.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2026

Reassessing Hybrid Vigor or Hybrid Dysfunction Using Physiological Trade-Offs in an Endangered Salamander System

Fitness of interspecific hybrids can be higher or lower than that of their parental genotypes, with major ramifications for evolution and conservation. A recent study found that hybrid tiger salamanders had higher metabolic rates than their parental forms. Specifically, the ratio of resting metabolic rate to water loss, which was used as a measure of performance, was greater in hybrids. Recent genetic research showed that over half of the experimental subjects in that study were genetically pure California tiger salamanders (Ambystoma californiense) misclassified as hybrids. We reanalyzed the data using the corrected identification of hybrids and parentals. As expected, updating the classification revealed even stronger evidence for differences between hybrids and parentals. Hybrids had higher resting metabolic rates and greater water loss than parentals. The ratio of resting metabolic rate to water loss was also higher in hybrids. However, we suggest that this ratio might not be a positive measure of salamander performance. Higher metabolic rate means higher energy expenditure, and higher water loss suggests increased risk of desiccation. Both are major challenges for terrestrial amphibians, especially salamanders, which are hypothesized to be low-energy, low-water-loss specialists. Under this hypothesis, the ratio of energy expenditure to water loss is a ratio of two costs rather than a ratio of benefit to cost. While our analyses corroborate and strengthen the previous statistical results, we suggest that high resting metabolic rate is better interpreted as hybrid dysfunction, not vigor. Here, both hypotheses are speculative, and specific research on the fitness effects of these physiological differences is needed to resolve this important ecological question.

Ambystoma californiense↗