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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Performance degradation in proton-conducting ceramic fuel cell and electrolyzer stacks

Proton-conducting ceramics are emerging as enabling materials for efficient electrochemical electricity generation, energy storage, and fuels synthesis. In this work, we present longer-term degradation results for protonic-ceramic fuel cells and electrolyzers based on a BaCe 0.4 Zr 0.4 Y 0.1 Yb 0.1 O 3-δ (BCZYYb) electrolyte. The cells are packaged within unit-cell stacks, including metallic interconnects, current collectors, sealing glasses and gaskets. Durability is found to be superior in protonic-ceramic electrolyzers in comparison to fuel cells. Operating conditions have a large impact on degradation rates; better stability is found at fuel-cell operating temperatures above 600 °C, and electrolyzer steam feeds below 20%. Here, we find that both fuel-cell and electrolyzer degradation is greatly reduced via the introduction of a gadolinium-doped ceria interlayer between the electrolyte and the air–steam electrode. Fuel-cell degradation falls to 1.2% khr –1 under methane fuel at 600 °C; electrolyzer degradation is reduced to 1% khr –1 at 550 °C and 50% steam. Further analyses of electrochemical impedance spectroscopy and distribution of relaxation times provide insight to root processes and degradation phenomena in protonic electroceramics.

25 ENERGY STORAGE↗
DOE OSTI2023

Performance characterization of metal-supported solid-oxide fuel cell stacks at elevated pressure

Here, in this paper, we present results on performance characterization of solid oxide fuel cell stacks at elevated pressures up to 6 bar a . Stacks are designed and built by Ceres Power, Ltd., and are rated at 1- and 5- kW e . Fuel streams include H 2 / N 2 mixtures, synthetic natural-gas reformate, and simulated anode tail-gas recycle. Elevated operating pressure serves to increase stack electrochemical performance, with the most-pronounced gains found up to 4 bar a . Pressurized operation reduces the extent of methane conversion, promoting more-uniform internal reforming and cooling within the stack. Such cooling is critical at higher-current conditions. A previously developed one dimensional computational stack model is used to provide insight into stack operation. Pressurization is found to slightly increase internal thermal gradients, while promoting more-uniform reactant-concentration profiles across the cell, reducing the likelihood of local fuel starvation. The high fuel dilution brought by anode recycle can modestly decrease stack performance; however, this decrease is recovered through elevated-pressure operation at 3 bar a . Anode recycle further promotes compositional uniformity across the cell. These results reflect that pressurized operation can promote stack performance, while potentially promoting long-term stack durability through uniformity in stack environmental conditions.

25 ENERGY STORAGE↗
DOE OSTI2023

Experimental validation of model predictive control for solid oxide fuel cells

Here, this paper presents implementation of a model predictive controller (MPC) for an experimental solid oxide fuel cell (SOFC) system. The MPC controller is based on a gain-scheduled predictor with block-oriented structure that can capture important non-linear effects while still keeping the computational complexity low enough to meet real time control requirements. Experimental results show the MPC is able to regulate the SOFC cathode outlet temperature in the face of startup transients and input perturbations.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2019

Addition-type alkoxysilyl-substituted polynorbornenes for post-combustion carbon dioxide separations

The separation of CO 2 from N 2 using polymeric membranes has proven a particularly challenging task. One promising class of polymers for this application is alkoxysilyl-substituted vinyl-added polynorbornenes (VAPNBs), which are high T g materials that often exhibit notable CO 2 /N 2 separation performance. This performance is believed to arise from their anomalous behavior in which they display high levels of solubility selectivity, a trait more commonly encountered in rubbery polymers than high T g glassy materials. While this trait has been documented in literature, no systematic investigations have been reported that probe the relationship between alkoxysilyl-substituted VAPNB structure and their resultant gas separation behavior. Here, we describe the synthesis and evaluation of three sets of alkoxysilyl-substituted VAPNBs that are designed to probe distinct facets of their structure-transport relationship. This includes investigations into the effect that alkoxysilyl branching, chain length, and carbon linker length have on CO 2 /N 2 permeability, solubility, and diffusivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Multi-phase characterization of pitch-carbon coated nano-silicon anodes for lithium-ion batteries

Silicon (Si) is a leading next-generation Li-ion battery anode candidate that meets rigorous performance demands for portable power including enhanced power and energy density with robust cycling performance. However, a series of complex and interrelated reactions lead to reduced calendar life in Si-containing systems and therefore challenge practical adoption. In the present work, we probe the mechanisms underlying observed performance improvements by adding a pitch-carbon coating onto nano-Si material. We pair solid-phase (X-ray photoemission spectroscopy, Fourier-transform infrared), semi-volatile phase (solid-phase microextraction-gas chromatography-mass spectrometry), and gas-phase (gas chromatography-flame-ionization detector) characterization signals to comprehensively evaluate the impact of pitch-carbon coating on the evolution of the Si solid-electrolyte interphase (SEI) and the associated impacts on electrode/electrolyte reactivity. The pitch-carbon is found to serve as a physicochemical barrier, reducing the electro-active surface area for Si/electrolyte reactivity and preventing Si oxidation. Further, the pitch-carbon coating promotes the evolution of a more-favorable SEI by subsuming substantial functionality typically associated with the fluoroethylene carbonate (FEC) electrolyte additive - such as alkoxide scavenging and suppression of transesterification pathways - and by shifting the competitive electrolyte degradation pathways' favorability. The multi-phase characterization approach enables holistic end-products evaluation from complex (electro)chemical interfacial reactions, which informs a robust interpretation of the carbon coating's role in electrochemical performance improvements. The present mechanistic evaluation aids the rational design for improved nano-Si materials.

25 ENERGY STORAGE↗
DOE OSTI2015

Divalent europium doped and un-doped calcium iodide scintillators: Scintillator characterization and single crystal growth

Initially, the alkaline-earth scintillator, CaI 2 :Eu 2+ , was discovered around 1964 by Hofstadter, Odell, and Schmidt. Serious practical problems quickly arose, however, that were associated with the growth of large monolithic single crystals of this material due to its lamellar, mica-like structure. As a result of its theoretically higher light yield, CaI 2 :Eu 2+ has the potential to exceed the excellent scintillation performance of SrI 2 :Eu 2+ . In fact, theoretical predictions for the light yield of CaI2:Eu 2+ scintillators suggested that an energy resolution approaching 2% at 662 keV could be achievable. Like the early SrI 2 :Eu 2+ scintillator, the performance of CaI 2 :Eu 2+ scintillators has traditionally suffered due, at least in part, to outdated materials synthesis, component stoichiometry/purity, and single-crystal-growth techniques. Based on our recent work on SrI 2 :Eu 2+ scintillators in single-crystal form, we have developed new techniques that are applied here to CaI 2 :Eu 2+ and pure CaI 2 with the goal of growing large un-cracked crystals and, potentially, realizing the theoretically predicted performance of the CaI 2 :Eu 2+ form of this material. Calcium iodide does not adhere to modern glassy carbon Bridgman crucibles - so there should be no differential thermal-contraction-induced crystal/crucible stresses on cooling that would result in crystal cracking of the lamellar structure of CaI 2 . Here we apply glassy carbon crucible Bridgman growth, high-purity growth-charge compounds, our molten salt processing/filtration technique, and extended vacuum-melt-pumping methods to the growth of both CaI 2 :Eu 2+ and un-doped CaI 2 . Moreover, large scintillating single crystals were obtained, and detailed characterization studies of the scintillation properties of CaI 2 :Eu 2+ and pure CaI 2 single crystals are presented that include studies of the effects of plastic deformation of the crystals on the scintillator performance.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Pair creation energy and Fano factor of silicon measured at 185 K using 55 F e X-rays

Here, the pair creation energy, ωω and the Fano factor of silicon were measured using a CCD sensor and X-rays from an 55 Fe source. The measurements were performed at a sensor temperature of 185K. The pair creation energy was measured for X-rays in the 1.7–6.5 keV range. The measured pair creation energy is ω=(3.650 ± 0.009) eV at the MnK α line energy. The Fano factor at this energy is F = 0.128±0.001. The agreement with theory and previous measurements is satisfactory. The system gain was obtained from flat field exposures using the Poisson distribution properties. These results and the details of our measurement procedure are presented below.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Analytic saddlepoint approximation for ionization energy loss distributions

Here, we present a saddlepoint approximation for ionization energy loss distributions, valid for arbitrary relativistic velocities of the incident particle 0 < v/c < 1, provided that ionizing collisions are still the dominant energy loss mechanism. We derive a closed form solution closely related to Moyal’s distribution. This distribution is intended for use in simulations with relatively low computational overhead. The approximation generally reproduces the Vavilov most probable energy loss and full width at half maximum to better than 1% and 10%, respectively, with significantly better agreement as Vavilov’s κ approaches 1.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Holocene paleoclimate history of Fallen Leaf Lake, CA., from geochemistry and sedimentology of well-dated sediment cores

Millennial-scale shifts in aridity patterns have been documented during the Holocene in the western United States, yet the precise timing, severity, and regional extent of these shifts prompts further study. Here we present lake sediment core data from Fallen Leaf Lake, a subalpine system at the southern end of the Lake Tahoe basin for which 80% of the contemporary inflow is derived from snowpack delivered by Pacific frontal storm systems. A high quality age model has been constructed using 14 C ages on plant macrofossils, 210 Pb, and the Tsoyowata tephra datum (7.74–7.95 cal kyr BP). One core captures the transition from the Late Tioga-younger Dryas glaciolacustrine package to laminated opaline clay at 11.48 cal kyr BP. Early Holocene sedimentation rates are relatively high (~1.9 mm/year) and cooler winter temperatures are inferred by the presence of pebbles interpreted to be transported out into the lake via shore ice. There is a geochemically distinct interval from ~4.71 to 3.65 cal kyr BP that is interpreted as a late Holocene neopluvial, characterized by depleted δ 13 C and lower C:N that point to reduced runoff of terrigenous organic matter, increased winter precipitation, and increased algal productivity. The largest Holocene signal in the cores occurs at the end of the neopluvial, at 3.65 cal kyr BP, and marks a shift into a climate state with variable precipitation, yet is overall more arid than the neopluvial. This new climate state persists for ~3 ka, until the Little Ice Age. Low sedimentation rates (0.5 mm/year), the homogeneous opaline sediment, and steadily increasing contributions of terrestrial vs. algal organic matter in these cores suggest that the lowstand state of Fallen Leaf Lake may have been the norm from 3.65 to 0.55 cal kyr BP, punctuated by short term high precipitation years or multi-year intervals capable of rapid short duration lake level rise. Fallen Leaf Lake is strongly influenced by changes in winter precipitation and temperature, manifested largely by the geochemical proxies, and highlights unique advantages of subalpine lakes in regional paleoclimate reconstructions.

58 GEOSCIENCES↗
DOE OSTI2019

Commercial lunar propellant architecture: A collaborative study of lunar propellant production

Aside from Earth, the inner solar system is like a vast desert where water and other volatiles are scarce. An old saying is, 'In the desert, gold is useless and water is priceless.' While water is common on Earth, it is of very high value in space. Science missions to the Moon have provided direct evidence that regions near the lunar poles, which are permanently in shadow, contain substantial concentrations of water ice. On the lunar surface, water itself is critical for human consumption and radiation shielding, but water can also be decomposed into hydrogen and oxygen via electrolysis. The oxygen thus produced can be used for life support, and hydrogen and oxygen can be combusted for rocket propulsion. Due to the Moon's shallow gravity well, its water-derived products can be exported to fuel entirely new economic opportunities in space. This paper is the result of an examination by industry, government, and academic experts of the approach, challenges, and payoffs of a private business that harvests and processes lunar ice as the foundation of a lunar, cislunar (between the Earth and the Moon), and Earth-orbiting economy. A key assumption of this analysis is that all work - construction, operation, transport, maintenance and repair - is done by robotic systems. No human presence is required.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗