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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Two‐Dimensional Polycyclic Photovoltaic Molecule with Low Trap Density for High‐Performance Photocatalytic Hydrogen Evolution

Abstract Typical organic semiconductors show a high trap density of states (10 16 –10 18 cm −3 ), providing a large number of centers for charge‐carrier recombination, thus hindering the development of photocatalytic hydrogen evolution. Here, we design and synthesize a two‐dimensional polycyclic photovoltaic material, named as TPP, to reduce the trap density to as low as 2.3×10 15 cm −3 , which is 1–3 orders of magnitude lower than those of typical organic semiconductors. Moreover, TPP exhibits a broad and strong absorption, ordered molecular packing with a large crystalline coherence length and enhanced electron mobility. Then, the bulk heterojunction nanoparticles (BHJ‐NPs) based on a blend of polymer donor (PM6) and TPP exhibit an average hydrogen evolution rate (HER) of 64.31 mmol h −1 g −1 under AM1.5G sunlight (100 mW cm −2 ), and 72.75 mmol h −1 g −1 under 330–1100 nm illumination (198 mW cm −2 ) higher than that of the control NPs based on typical PM6 : Y6 (62.67 mmol h −1 g −1 ).

Zhang, Zhenzhen↗
DOE OSTI2021

Two-Dimensional Polycyclic Photovoltaic Molecule with Low Trap Density for High-Performance Photocatalytic Hydrogen Evolution

Typical organic semiconductors show a high trap density of states (10 16 –10 18 cm -3 ), providing a large number of centers for charge-carrier recombination, thus hindering the development of photocatalytic hydrogen evolution. In this report we design and synthesize a two-dimensional polycyclic photovoltaic material, named as TPP, to reduce the trap density to as low as 2.3×10 15 cm -3 , which is 1–3 orders of magnitude lower than those of typical organic semiconductors. Moreover, TPP exhibits a broad and strong absorption, ordered molecular packing with a large crystalline coherence length and enhanced electron mobility. Then, the bulk heterojunction nanoparticles (BHJ-NPs) based on a blend of polymer donor (PM6) and TPP exhibit an average hydrogen evolution rate (HER) of 64.31 mmol h -1 g -1 under AM1.5G sunlight (100,mW cm -2 ), and 72.75 mmol h -1 g -1 under 330–1100 nm illumination (198 mW cm -2 ) higher than that of the control NPs based on typical PM6 : Y6 (62.67 mmol h -1 g -1 ).

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

Wavelength dependent photochemistry of an iron dinitrogen hydride complex via multiple spectroscopies – competing ejection of axial ligands

Nitrogenase (N 2 ase) is a critical enzyme which catalyzes the reaction of N 2 → NH 3 in nature. Studies on the spectroscopy and photochemistry of trans-[Fe II (DMeOPrPE) 2 (N 2 )H][BPh 4 ] (1) and its isotopologues (2–6) provide a possible first step to evaluate the geometries and properties of the real N 2 ase–N 2 structure(s). In this article, we have used FT-IR, FT-Raman, synchrotron-based nuclear resonant vibrational spectroscopy (NRVS) and DFT calculations to examine and assign the normal modes of these complexes. In addition, we have monitored their wavelength dependent photochemistry using mid-IR, near-IR, NRVS, and Mössbauer spectroscopies. Two distinct photolysis pathways are observed with mid-IR at (nominal) 4 K – (1) the cleavage of Fe–N 2 bond in UV or visible light photolyses, which presents a unipolar disappearance of the N 2 peak at 2094 cm −1 and is recombinable; (2) the ejection of trans hydrogen atom with UV irradiation, which has a pair of bipolar peaks with the disappearance of N 2 at 2094 cm −1 and the appearance of a new species at 2056 cm −1 and is non-recombinable. The latter peak is well aligned with the N 2 peak in an Fe I reference complex (7). The combination of mid IR monitored photolysis/recombination and NRVS monitored photolysis form the central evidence for the conclusions in this article. In particular, the Fe II –N 2 and Fe I –H·dissociations are in competition with each other in UV or UV-inclusive photolyses of this dinitrogen hydride complex. In addition, near-IR and Mössbauer also provide consistent evidence about Fe I . This wavelength dependent photochemical work is the first one on a reaction active N 2 ase–N 2 model complex and it also demonstrates the competition ejection between two axial ligands (H· and N 2 ). It offers valuable information for future studies on real N 2 ase–N 2 and its photolysis products.

Dong, Weibing [Liaoning Normal University (China)]↗
NASA NTRS1976

Generation of atomic H in a hydrogen matrix by tritium decay

Webeler's (1976) experimental results for the generation of atomic hydrogen in a hydrogen matrix by tritium decay are reexamined with a variant of Rosen's (1976) mathematical treatment. The analysis retains Rosen's equations for the number densities of trapped and mobile hydrogen atoms, but replaces his enthalpy equation with an equation for the directly measured temperature. Theoretical expressions are derived for the dependence of storage time, recombination time, and maximum density of trapped hydrogen atoms as a function of temperature for a given tritium concentration. A comparison of predictions for the maximum trapped atomic hydrogen number density as a function of storage time reveals that Rosen's estimate for the maximum number density of hydrogen atoms for the zero magnetic field case is a little more optimistic than the estimate obtained in the paper.

Zeleznik, F. J.↗
DOE OSTI2021

Radially resolved active charge exchange measurements of the hydrogenic isotope fraction on DIII-D

Radially resolved hydrogenic isotope fraction measurement capabilities have been developed for DIII-D using the main-ion charge exchange recombination (MICER) spectroscopy system in preparation for mixed hydrogen and deuterium experiments. Constraints on the hydrogenic ion temperatures and velocities based on measurements of the impurity ion properties are required to accurately fit the spectrum. Corrections for cross sectional distortions, spatial smearing due to the halo, and a neoclassical offset between the impurity and hydrogenic toroidal rotation are applied to the constraints prior to fitting the MICER spectrum. Extensive atomic physics calculations have been performed using the FIDASIM code, which has recently been improved to allow simulations using mixtures of hydrogenic species. Overall, these results demonstrate that for the same plasma parameters, the Dα emission is 20%–30% brighter than Hα due to differences in rate coefficients associated with the different ion thermal velocities for the same temperature and therefore must be taken into consideration when calculating absolute densities. However, despite these differences, the absolute error when estimating the hydrogen isotope fraction [n H /(n H + n D )] by using the Hα radiance fraction [L Hα /(L Hα + L Dα )] is typically less than 5% due to the way the fraction is formed, making the radiance fraction a reasonably accurate estimate of the isotope fraction for most cases.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1975

A theory of the Jovian hydrogen torus

The Jovian hydrogen torus associated with Io, that was observed by Judge and Carlson, has been found by them to be a third of a torus rather than a complete torus. It is shown that the energetic particles observed by Pioneer 10 do not ionize atomic hydrogen sufficiently fast to erode the torus as observed. It is proposed that the reason an incomplete torus exists is the presence of a corotating cold magnetospheric plasma. If this explanation is correct, the angular extent of the fractional torus is a measure of the density of the magnetospheric plasma near Io's orbit, which is found to be about 100 per cu cm. It is shown that such a plasma may provide an adequate input to Io, where it can recombine and escape, to form enough hydrogen atoms to explain the number of observed torus atoms. Thus the magnetospheric plasma may serve as both the source and the sink of the torus.

Mcdonough, T. R.↗
NASA NTRS1992

Aeronomy of the current Martian atmosphere

The thermal structure of the Martian atmosphere, which varies diurnally, seasonally and episodically, is discussed. The atomic oxygen airglow at 1304 A is used to determine the density of atomic oxygen, and the 1216-A Lyman-alpha line is used to calculate the density of atomic hydrogen and, when coupled with the temperature measurement, the escape flux of atomic hydrogen. The most intense airglow is the IR atmospheric band of O2 at 1.27 micron that results from the photodissociation of ozone. The escape mechanism for atomic hydrogen is thermal, or Jeans, escape, while the atomic oxygen escape is caused by a nonthermal process, namely, the dissociative recombination of O2(+). The ratio of deuterium to hydrogen is enriched by a factor of 6. Three-dimensional models of the Mars thermospheric circulation show that planetary rotation has a significant effect on the wind, composition, and temperature structure.

Barth, C. A.↗
NASA NTRS1971

Radiofrequency recombination lines from the interstellar medium

Observations of recombination lines form normal H II regions, extended H II regions, nonthermal sources, and the H I medium are discussed. Detection of recombination lines from elements other than hydrogen may provide a means of identifying fossil Stromgren spheres at high temperature.

Dupree, A. K.↗
NASA NTRS1982

Photoionization research on atomic beams. 2: The photoionization cross section of atomic oxygen

An experiment to determine the absolute value of the photo-ionization cross section of atomic oxygen is described. The atoms are produced in an electrical discharge in oxygen gas with 1% hydrogen added. In order to prevent recombination a crossed beam technique is employed. The ions formed are detected by a time-of-flight mass spectrometer. The concentration of oxygen atoms in the beam is 57%. The measured photoionization cross section of atomic oxygen is compared with theoretical data. The results show the participation of autoionization processes in ionization. The cross section at the autoionizing levels detected is considerably higher than the absorption due to the unperturbed continuum. Except for wavelengths where autoionization occurs, the measured ionization cross section is in fair agreement with theory. This holds up to 550 A whereas for shorter wavelengths the theoretical values are much higher.

Comes, F. J.↗
NASA NTRS1991

Large scale cosmic instability

Spectral distortions in cosmic background radiation can create instabilities in matter, whose possible role in generating large scale structure is outlined here. A promising physical mechanism is sketched, based on Ly-alpha resonance scattering, with exponentially amplifies perturbations in neutral hydrogen density on large scales after recombination.

Hogan, Craig J.↗
NASA NTRS2000

HST Studies of the Chromospheres, Wind, and Mass-Loss Rates of Cool Giant and Supergiant Stars

UV spectra of K-M giant and supergiant stars and of carbon stars have been acquired with the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope (HST). These spectra have been used to measure chromospheric flow and turbulent velocities, study the acceleration of their stellar winds, acquire constraints on their outer atmospheric structure, and enable estimates of their mass-loss rates. Results from our observations of the giant stars Gamma Dra (K5 III hybrid), Alpha Tau (K5 III), Gamma Cru (M3.4 III), Mu Gem (M3 IIIab), and 30 Her (MG III), the supergiants Alpha Ori (M2 Iab) and Lambda Vel (K5 Ib), and the carbon stars TX Psc (NO; C6,2) and TW Hor (NO; C7,2) will be summarized and compared. The high resolution and wavelength accuracy of these data have allowed the direct measurement of the acceleration of the stellar winds in the chromospheres of several of these stars (from initial velocities of 3-9 km/s to upper velocities of 15-25 km/s) and of the chromospheric macroturbulence (-25-35 km/s). The high signal-to-noise and large dynamic range of these spectra have allowed the detection and identification of numerous new emission features, including weak C IV emission indicative of hot transition-region plasma in the non-coronal giant Alpha Tau, many new fluorescent lines of Fe II, and the first detection of fluorescent molecular hydrogen emission and of Ca II recombination lines in the UV spectrum of a giant star. The UV spectrum of two carbon stars have been studied with unprecedented resolution and reveal extraordinarily complicated Mg II lines nearly smothered by circumstellar absorptions. Finally, comparison of synthetic UV emission line profiles computed with the Lamers et al. (1987) Sobolev with Exact Integration (SEI) code with observations of chromospheric emission lines overlain with wind absorption features provides estimates of the mass-loss rates for four of these stars.

Carpenter, Kenneth G.↗
NASA NTRS1981

Hot oxygen atoms in the upper atmosphere of Venus

Using data obtained by an ultraviolet spectrometer on the Pioneer-Venus Orbiter, energy and altitude distribution of nonthermal oxygen atoms in the Venus atmosphere for typical daytime and nighttime conditions are calculated using two different numerical methods. Agreement is found between results obtained by the two-stream transport method and the diffusion equation technique. Dissociative recombination of molecular oxygen ions and charge exchange of atomic oxygen ions with the neutral hydrogen and oxygen gas are the source terms, and calculations show that the dissociative recombination term is the dominant one. It is shown that measured hot atom concentrations exceed estimates of the thermal hydrogen atom concentrations derived from Brinton et al. (1980) over most of the daytime exosphere, and the calculated concentrations do so to an even greater extent. It is concluded that hot oxygen atoms are an important component of the dayside exosphere of Venus, their most important effect being the absorption of solar wind.

Nagy, A. F.↗
NASA NTRS1995

Semianalytic continuum spectra of Type 2 supernovae

We extend the approximate radiative transfer analysis of Hershkowitz, Linder, & Wagoner (1986) to a more general class of supernova model atmospheres, using a simple fit to the effective continuum opacity produced by lines (Wagoner, Perez, & Vasu 1991). At the low densities considered, the populations of the excited states of hydrogen are governed mainly by photoionization and recombination, and scattering dominates absorptive opacity. We match the asymptotic expressions for the spectral energy density J(sub nu) at the photosphere, whose location at each frequency is determined by a first-order calculation of the deviation of J(sub nu) from the Planck function B(sub nu). The emergent spectral luminosity then assumes the form L(sub nu) = 4 pi(squared)r(squared)(sub *) zeta(squared)B(sub nu)(T(sub p)), where T(sub p)(nu) is the photospheric temperature zeta is the dilution factor, and r(sub *) is a fiducial radius (ultimately taken to be the photospheric radius r(sub p)(nu)). The atmosphere is characterized by an effective temperature T(sub e) (varies as L(sup 1/4)r(sup -1/2)(sub *)) and hydrogen density n(sub H) = dependence of zeta on frequency nu and the parameters T(sub p), r(sub p), and alpha. The resulting understanding of the dependence of the spectral luminosity on observable parameters which characterize the relevant physical conditions will be of particular use in assessing the reliability of the expanding photosphere method of distance determination. This is particularly important at cosmological distances, where no information about the progenitor star will be available. This technique can also be applied to other low-density photosphere.

Montes, Marcos J.↗
DOE OSTI2022

UV‐induced degradation of high‐efficiency silicon PV modules with different cell architectures

Abstract Degradation from ultraviolet (UV) radiation has become prevalent in the front of solar cells due to the introduction of UV‐transmitting encapsulants in photovoltaic (PV) module construction. Here, we examine UV‐induced degradation (UVID) in various commercial, unencapsulated crystalline silicon cell technologies, including bifacial silicon heterojunction (HJ), interdigitated back contact (IBC), passivated emitter and rear contact (PERC), and passivated emitter rear totally diffused (PERT) solar cells. We performed UV exposure tests using UVA‐340 fluorescent lamps at 1.24 W·m −2 (at 340 nm) and 45°C through 4.02 MJ·m −2 (2000 h). Our results showed that modern cell architectures are more vulnerable to UVID, leading to a significant power decrease (−3.6% on average; −11.8% maximum) compared with the conventional aluminum back surface field (Al‐BSF) cells (<−1% on average). The power degradation is largely caused by the decrease in short‐circuit current and open‐circuit voltage. A greater power decrease is observed in bifacial cells with rear‐side exposure compared with those with front‐side exposure, indicating that the rear side is more susceptible to UV damage. Secondary ion mass spectroscopy (SIMS) confirmed an increase in hydrogen concentration near the Si/passivation interface in HJ and IBC cells after UV exposure; the excess of hydrogen could result in hydrogen‐induced degradation and subsequently cause higher recombination losses. Additionally, surface oxidation and hot‐carrier damage were identified in PERT cells. Using a spectral‐based analysis, we obtained an acceleration factor of 5× between unpackaged cells (containing a silicon nitride antireflective coating on the front) in the UV test and an encapsulated module (with the front glass and encapsulant blocking 90% of the UV at 294 nm and 353 nm, respectively) in outdoor conditions. From the analytical calculations, we show that a UV‐blocking encapsulant can reduce UV transmission in the module by an additional factor of ~50.

14 SOLAR ENERGY↗
DOE OSTI2022

Time-resolved measurements of HO 2 radical in a heated plasma flow reactor

Time-resolved, absolute HO 2 number density in diluted H 2 –O 2 –Ar, CH 4 –O 2 -Ar, and C 2 H 4 –O 2 –Ar mixtures excited by a repetitive ns pulse discharge in a heated plasma flow reactor is measured by Cavity Ringdown Spectroscopy (CRDS). The experimental results are obtained at $\textit{T}$ = 300-600 K and $\textit{P}$ = 130 Torr, both during the discharge pulse burst and in the afterglow. In this work, the HO 2 number density is inferred from the CRDS data using a spectral model exhibiting good agreement with previous measurements of absolute HO 2 absorption cross sections. In the room-temperature H 2 –O 2 mixture, as well as in CH 4 –O 2 and C 2 H 4 –O 2 mixtures over the entire temperature range studied, HO2 is generated only during the discharge burst and decays in the afterglow. However, in the H 2 –O 2 mixture at elevated temperatures, $\textit{T}$ = 400-600 K, HO 2 persists in the afterglow up to 10 ms after the discharge burst, comparable with the flow residence time in the reactor. Comparison with kinetic modeling shows that the sustained reactivity after the source of radicals is turned off is due to a chain propagation / hydrogen oxidation process, which dominates the radical recombination reactions. The kinetic modeling predictions are in good agreement with the relative HO 2 number density measured in all three mixtures, although the model underpredicts the absolute number densities in H 2 –O 2 at $\textit{T}$ = 400-600 K by up to a factor of two. Detection of the sustained low-temperature reactivity in H 2 –O 2 , initiated by the radical generation in the plasma, suggests that the plasma excitation may also affect kinetics of oxidation and reforming of fuels exhibiting low-temperature chemistry below hot ignition point.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1970

Interstellar H3/plus/

Interstellar hydrogen ion production and destruction by electron recombination or photodissociation

Stecher, T. P.↗
NASA NTRS1993

On the escape of oxygen and hydrogen from Mars

Escape rates of oxygen atoms from dissociative recombination of O2(+) above the Martian exobase are computed in light of new information from ab initio calculations of the dissociative recombination process and our recently revised understanding of the Martian dayside ionosphere. Only about 60 percent of the dissociative recombinations occur in channels in which the O atoms are released with energies in excess of the escape velocity. Futhermore, we find that the computed escape fluxes for O depend greatly on the nature of the ion loss process that has been found necessary to reproduce the topside ion density profiles measured by Viking. If it is assumed that the ions are not lost from the gravitational field of the planet, as required by an analysis of nitrogen escape, the computed average O escape rate is 3 x 10 exp 6/sq cm/s, much less than half the H escape rates inferred from measurements of the Lyman-alpha dayglow, which are in the range (1-2) x 10 exp 8/sq cm/s. Suggestions for restoring the relative escape rates of H and O to the stoichiometric ratio of water are explored.

Fox, J. L.↗
NASA NTRS1972

Detection of interstellar recombination lines from emitters of intermediate mass.

The 18-cm microwave spectra of Orion B and W3A show evidence of an emission feature to the high-frequency side of the carbon recombination line. Observations at different frequencies establish that this feature results from electronic recombination. In addition, theoretical considerations, results of 21-cm observations, and computer-simulated spectra suggest that the new feature originates in a predominantly neutral hydrogen region and can be explained by a superposition of recombination lines from any or all of the following elements: Mg-24, Si-28, S-32, and Fe-56.

Chaisson, E. J.↗