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At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Results of Experimental Investigations to Determine External Tank Protuberance Loads Using a 0.03-Scale Model of the Space Shuttle Launch Configuration (Model 47-OTS) in the NASA/ARC Unitary Plan Wind Tunnel, Volume 2

Data were obtained on a 3-percent model of the Space Shuttle launch vehicle in the NASA/Ames Research Center 11x11-foot and 9x7-foot Unitary Plan Wind Tunnels. This test series has been identified as IA19OA/B and was conducted from 7 Feb. 1980 to 19 Feb. 1980 (IA19OA) and from 17 March 1980 to 19 March 1980 and from 8 May 1980 to 30 May 1980 (IA19OB). The primary test objective was to obtain structural loads on the following external tank protuberances: (1) LO2 feedline; (2) GO2 pressure line; (3) LO2 antigeyser line; (4) GH2 pressure line; (5) LH2 tank cable tray; (6) LO2 tank cable tray; (7) Bipod; (8) ET/SRB cable tray; and (9) Crossbeam/Orbiter cable tray. To fulfill these objectives the following steps were taken: Eight 3-component balances were used to measure forces on various sections of 1 thru 6 above; 315 pressure orifices were distributed over all 9 above items. The LO2 feedline was instrumented with 96 pressure taps and was rotated to four positions to yield 384 pressure measurements. The LO2 antigeyser line was instrumented with 64 pressure taps and was rotated to two positions to yield 128 pressure measurements; Three Chrysler miniature flow direction probes were mounted on a traversing mechanism on the tank upper surface centerline to obtain flow field data between the forward and aft attach structures; and Schlieren photographs and ultraviolet flow photographs were taken at all test conditions. Data from each of the four test phases are presented.

Houlihan, S. R.↗
NASA NTRS1994

The Clementine mission: Initial results from lunar mapping

Clementine was a mission designed to test the space worthiness of a variety of advanced sensors for use on military surveillance satellites while, at the same time, gathering useful scientific information on the composition and structure of the Moon and a near Earth asteroid. Clementine was dispatched for an extended stay in the vicinity of Earth's Moon on 25 Jan. 1994 and arrived at the Moon on 20 Feb. 1994. The spacecraft started systematic mapping on 26 Feb., completed mapping on 22 Apr., and left lunar orbit on 3 May. The entire Clementine project, from conception through end of mission, lasted approximately three years. Topographic profiles derived from lidar laser altimetry permitted construction of a global topographic map of the Moon. Clementine also aimed at mapping the color of the Moon in eleven different wavelengths in the visible and near infrared parts of the system. With rock and soil samples of known geological context available from the Apollo and Lunar programs, the Clementine mission offers the data needed to construct a global digital image model of the Moon.

Spudis, P. D.↗
NASA NTRS1996

Polar Vortex Conditions during the 1995-96 Artic Winter: Meteorology and MLS Ozone

The 1995-96 northern hemisphere (NH) 205 winter stratosphere was colder than in any of the previous 17 winters, with lower stratospheric temperatures continuously below the type 1 (primarily HN03) polar stratospheric cloud (PSC) threshold for over 2 1/2 months. Upper tropospheric ridges in late Feb and early Mar 1996 led to the lowest observed NH lower stratospheric temperatures, and the latest observed NH temperatures below the type 2 (water ice) PSC threshold. Consistent with the unusual cold and chemical processing on PSCS, Upper Atmosphere Research Satellite (UARS) MLS observed a greater decrease in lower stratospheric ozone (03) in 1995-96 than in any of the previous 4 NH winters. 03 decreased throughout the vortex over an altitude range nearly as large as that typical of the southern hemisphere (SH). The decrease between late Dec 1995 and early Mar 1996 was about 2/3 of that over the equivalent SH period. As in other NH winters, temperatures in 1996 rose above the PSC threshold before the spring equinox, ending chemical processing in the NH vortex much earlier than is usual in the SH. A downward trend in column 03 above 100 hPa during Jan and Feb 1996 appears to be related to the lower stratospheric 03 depletion.

Manney, G. L.↗
NASA NTRS2001

What is the Relationship Between Heavy Ion Outflow and High-Latitude Energetic Particle Precipitation?

This document is the fourth quarter progress report for year two on contract NAW-99002 'What is the relationship between heavy ion outflow and high latitude energetic particle precipitation'. In this project we are studying the relationship between the fluxes, mean energies, and field-aligned flow speeds of escaping suprathermal H+ and O+ measured by the TEAMS instrument on FAST and the energy flux of precipitating electrons obtained form the LBHL images taken by the Ultraviolet Imagery (UVI) camera on the Polar spacecraft. We have analyzed data from three time intervals, 7-11 Feb, 25-31 Jan, and 1-6 Feb 1997. We find that there indeed is a relationship between the O+ escape fluxes and the intensity of the aurora at the foot point of the field line. The time delay between an auroral intensification and the corresponding increase in escape flux is very short, only a few minutes. At low auroral luminosity the relationship between escape flux and luminosity appears to break down due possibly to the lack of sensitivity of the auroral emissions to large fluxes of low energy electrons.

Wilson, Gordon R.↗
NASA NTRS2001

Day-Scale Variability of 3C 279 and Searches for Correlations in Gamma-Ray, X-Ray and Optical Bands

Light curves of 3C 279 are presented in optical (R-band), X-rays (RXTE/PCA), and gamma rays (CGRO/EGRET) for 1999 Jan-Feb and 2000 Jan-Mar. During both of those epochs the gamma-ray levels were high, and all three observed bands demonstrated substantial variation, on time scales as short as one day. Correlation analyses provided no consistent pattern, although a rather significant optical/gamma-ray correlation was seen in 1999, with a gamma-ray lag of approximately 2.5 days, and there are other suggestions of correlations in the light curves. For comparison, correlation analysis is also presented for the gamma-ray and X-ray light curves during the large gamma-ray flare in 1996 Feb and the two gamma-bright weeks leading up to it; the correlation at that time was strong, with a gamma-ray/X-ray offset of no more than one day.

Hartman, R. C.↗
NASA NTRS2003

Simulated Radar Characteristics of LBA Convective Systems: Easterly and Westerly Regimes

The 3D Goddard Cumulus Ensemble (GCE) model was used to simulate convection that occurred during the TRMM LBA field experiment in Brazil. Convection in this region can be categorized into two different regimes. Low-level easterly flow results in moderate to high CAPE and a drier environment. Convection is more intense like that seen over continents. Low-level westerly flow results in low CAPE and a moist environment. Convection is weaker and more widespread characteristic of oceanic or monsoon-like systems. The GCE model has been used to study both regimes n order to provide cloud datasets that are representative of both environments in support of TRMM rainfall and heating algorithm development. Two different cases are analyzed: Jan 26, 1999, an eastely regime case, and Feb 23, 1999, a westerly regime case. The Jan 26 case is an organized squall line, while the Feb 23 case is less organized with only transient lines. Radar signatures, including CFADs, from the two simulated cases are compared to each other and with observations. The microphysical processes simulated in the model are also compared between the two cases.

Lang, Stephen E.↗
NASA NTRS2002

Cloud-Resolving Model Simulations of LBA Convective Systems: Easterly and Westerly Regimes

The 3D Goddard Cumulus Ensemble (GCE) model was used to simulate convection that occurred during the TRMM LBA field experiment in Brazil. Convection in this region can be categorized into two different regimes. Low-level easterly flow results in moderate to high CAPE and a drier environment. Convection is more intense like that seen over continents. Low-level westerly flow results in low CAPE and a moist environment. Convection is weaker and more widespread characteristic of oceanic or monsoon-like systems. The GCE model has been used to study both regimes in order to provide cloud data sets that are representative of both environments in support of TRMM rainfall and heating algorithm development. Two different case are presented: Jan 26,1999, an easterly regime case, and Feb 23,1999, a westerly regime case. The Jan 26 case is an organized squall line and is initialized with a standard cold pool. The sensitivity to mid-level sounding moisture and wind shear will also be shown. The Feb 23 case is less-organized with only transient lines and is initialized with either warm bubbles or prescribed surface fluxes. Heating profiles, rainfall statistics and storm characteristics are compared and validated for the two cases against observations collected during the experiment.

Lang, Stephen E.↗
NASA NTRS2004

Southern Alaska Glaciers: Spatial and Temporal Variations in Ice Volume

Although temperate mountain glaciers comprise less than 1% of the glacier-covered area on Earth, they are important because they appear to be melting rapidly under present climatic conditions and, therefore, make significant contributions to rising sea level. In this study, we use ICESat observations made in the last 1.5 years of southern Alaska glaciers to estimate ice elevation profiles, ice surface slopes and roughness, and bi-annual and/or annual ice elevation changes. We report initial results from the near coastal region between Yakutat Bay and Cape Suckling that includes the Malaspina and Bering Glaciers. We show and interpret ice elevations changes across the lower reaches of the Bagley Ice Valley for the period between October 2003 and May 2004. In addition, we use off-nadir pointing observations to reference tracks over the Bering and Malaspina Glaciers in order to estimate annual ice elevation change. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Shuttle Radar Topography Mission (SRTM) derived DEMs are used to estimate across track regional slopes between ICESat data acquisitions. Although the distribution and quantity of ICESat elevation profiles with multiple, exact repeat data is currently limited in Alaska, individual ICESat data tracks, provide an accurate reference surface for comparison to other elevation data (e.g. ASTER and SRTM X- and C-band derived DEMs). Specifically we report the elevation change over the Malaspina Glacier's piedmont lobe between a DEM derived from SRTM C-band data acquired in Feb. 2000 and ICESat Laser #2b data from Feb.-March 2004. We also report use of ICESat elevation data to enhance ASTER derived absolute DEMs. Mountain glaciers generally have rougher surfaces and steeper regional slopes than the ice sheets for which the ICESat design was optimized. Therefore, rather than averaging ICESat observations over large regions or relying on crossovers, we are working with well-located ICESat footprint returns to estimate glacier ice elevations and surface characteristics. Additional information is included in the original extended abstract.

Sauber, J.↗
NASA NTRS2005

Elevation change (2000-2004) on the Malaspina Glacier, Alaska

The glaciers of the southeastern Alaska coastal region are the largest temperate glacier meltwater source on Earth and may contribute one third of the total glacier meltwater entering the global ocean. Since melt onset and refreeeze timing in this region show a tendency toward earlier onset and longer ablation seasons, accelerated glacier wastage may be occurring. In this study we focus on one of the largest temperate glacier systems on Earth, the Malaspina Glacier. This glacier, with a length of approximately 110 km and an area of approximately square 5,000 km, has the largest piedmont lobe of any temperate glacier. The entire lobe, which lies at elevations below 600 m, is within the ablation zone. We report and interpret ice elevation change between a digital elevation model (DEM) derived from the Shuttle Radar Topography Mission (SRTM C band) observations in Feb. 2000 and ICESat Laser 1-3 observations between Feb. 2003 and Nov. 2004. We use these elevation change results, along with earlier studies, to address the spatial and temporal variability in wastage of the piedmont lobe. Between 2000 and 2004 ice elevation changes of 10-30 meters occurred across the central Malaspina piedmont lobe. From 1972/73 (USGS DEM) to 1999 (SRTM corrected for estimated winter snow accumulation) Malaspina's (Agassiz, Seward Lobe, and Marvine) mean ice thinning was estimated at -47 m with maximum thinning on parts of the lobes to -160 m. The Malaspina's accumulation area is only slightly larger than its ablation area (2,575 km2 vs. 2,433 km2); unfortunately few glaciological observations are available from this source region. Snow accumulation rates have been largely inferred from low-altitude precipitation and temperature data. Comparing sequential ICESat observations in the Malaspina source region, we estimated short-term elevation increases of up to 5 meters during the winter of 2003/04.

Sauber, J.↗
NASA NTRS2003

Oxygenated Organic Chemicals in the Pacific Troposphere: Distribution, Sources and Chemistry

Airborne measurements of a large number of oxygenated organic chemicals (Oxorgs) were carried out in the Pacific troposphere (0.1-12 km) in the Spring of 2001 (Feb. 24-April 10). Specifically these measuremen ts included acetone, methylethyl ketone (MEK), methanol, ethanol, ace taldehyde, propionaldehyde, PANS, and organic nitrates. Complementary measurements of formaldehyde, organic peroxides, and tracers were al so available. Ox-orgs were abundant in the clean troposphere and were greatly enhanced in the outflow regions from Asia. Their mixing ratios were typically highest in the lower troposphere and declined toward s the upper troposphere and the lowermost stratosphere. Their total a bundance (Ox-orgs) significantly exceeded that of NMHC (C2-C8 NMHC). A comparison of these data with observations collected some seven yea rs earlier (Feb.-March, 1994), did not reveal any significant changes . Throughout the troposphere mixing ratios of Ox-orgs were strongly c orrelated with each other as well as with tracers of fossil and bioma sshiof'uel combustion. Analysis of the relative enhancement of selected Oxorgs with respect to CH3Cl and CO in twelve sampled plumes, origi nating from fires, is used to assess their primary and secondary sour ces from biomass combustion. The composition of these plumes also ind icates a large shift of reactive nitrogen into the PAN reservoir ther eby limiting ozone formation. The Harvard 3-D photochemical model, th at uses state of the art chemistry and source information, is used to compare simulated and observed mixing ratios of selected species. A 1 -D model is used to explore the chemistry of aldehydes. These results will be presented.

Singh, Hanwant B.↗
NASA NTRS1994

Clementine RRELAX SRAM Particle Spectrometer

The Clementine RRELAX radiation monitor chip consists of a p-FET total dose monitor and a 4-kbit SRAM particle spectrometer. Eight of these chips were included in the RRELAX and used to detect the passage of the Clementine (S/C) and the innerstage adapter (ISA) through the earth's radiation belts and the 21-Feb 1994 solar flare. This is the first space flight for this 1.2 micron rad-soft custom CMOS radiation monitor. This paper emphasizes results from the SRAM particle detector which showed that it a) has a detection range of five orders of magnitude relative to the 21-Feb solar flare, b) is not affected by electrons, and c) detected microflares occurring with a 26.5 day period.

Clementine↗
NASA NTRS2006

Using Satellite Data to Characterize the Temporal Thermal Behavior of an Active Volcano: Mount St. Helens, WA

ASTER thermal infrared data over Mt. St Helens were used to characterize its thermal behavior from Jun 2000 to Feb 2006. Prior to the Oct 2004 eruption, the average crater temperature varied seasonally between -12 and 6 C. After the eruption, maximum single-pixel temperature increased from 10 C (Oct 2004) to 96 C (Aug 2005), then showed a decrease to Feb 2006. The initial increase in temperature was correlated with dome morphology and growth rate and the subsequent decrease was interpreted to relate to both seasonal trends and a decreased growth rate/increased cooling rate, possibly suggesting a significant change in the volcanic system. A single-pixel ASTER thermal anomaly first appeared on Oct 1, 2004, eleven hours after the first eruption - 10 days before new lava was exposed at the surface. By contrast, an automated algorithm for detecting thermal anomalies in MODIS data did not trigger an alert until Dec 18. However, a single-pixel thermal anomaly first appeared in MODIS channel 23 (4 um) on Oct 13, 12 days after the first eruption - 2 days after lava was exposed. The earlier thermal anomaly detected with ASTER data is attributed to the higher spatial resolution (90 m) compared with MODIS (1 m) and the earlier visual observation of anomalous pixels compared to the automated detection method suggests that local spatial statistics and background radiance data could improve automated detection methods.

Advanced Spaceborne Thermal Emission and Reflectio↗
NASA NTRS2007

Interplanetary Dust Clouds Near 1AU Detected by STEREO

For a 21 day interval beginning on Jan 28, 2007, the radio and plasma wave instruments (S/WAVES) on the twin STEREO spacecraft detected intense impulse-like emissions in both the time-domain receivers and the low end of the frequency-domain receivers. These emissions were much more intense on the STEREO Ahead instrument, but were detected by both. During that interval, the two STEREO spacecraft were only separated by about 0.1deg in heliocentric longitude. All attempts to understand the emissions in terms of electrical disturbances onboard the spacecraft were unsuccessful and, since the impulsive events essentially ceased on Feb 18,2007, the entire study was put on lower priority. However, beginning abruptly on July 20, 2007, a very similar and more intense episode of impulses was detected exclusively by S/WAVES on the STEREO Ahead spacecraft, now separated from Behind by more than 20deg of heliocentric longitude. This new episode lasted nearly as long as the Jan-Feb episode, some 20 days, ending on Aug. 9. On Aug. 13,2007, the STEREO Behind spacecraft arrived at the same heliocentric longitude as the Ahead spacecraft was at on July 20 and the S/WAVES instrument abruptly started detecting impulsive events, although at lower intensities than those on Ahead. The individual waveform of the detected impulses is very similar to signals recorded by the Voyager plasma wave (PWS) and radio astronomy (PRA) instruments and more recently by the Cassini radio and plasma wave science (RPWS) instrument when those spacecraft plunged through Saturn's rings. Those Saturnian signals are attributed to micron-sized dust particle impacts on the spacecraft which creates a temporary plasma cloud which, in turn, induces an electrical signal on the antennas. We reanalyzed the STEREO episodes along the lines of the Saturnian ring plane analyses and have concluded that the STEREO impulses are very likely due to similar dust impacts with bands or clouds of dust of cometary or, more generally, zodiacal light material near 1 AU. The distribution of these clouds of small dust particles is significantly different than theoretical models of interplanetary dust distribution

Kaiser↗
NASA NTRS2016

Low Ozone over Europe Doesn't Mean the Sky Is Falling, Its Actually Rising

Data Sources: NASA Aura Microwave Limb Sounder (MLS) (O3 profiles and columns), NASA Global Modeling Initiative (GMI) Chemistry and Transport Model (calculated O3depletion), and MERRA Tropopause Heights. Technical Description of Figures: The left graphics show MLS northern hemisphere stratospheric column ozone on Feb. 1, 2016. Very low columns are seen over the UK and Europe (<225 DU, inside dashed circle). The lower graphic shows the GMI-calculated O3 depletion. It's very small, suggesting the low O3 does not indicate significant depletion. The right graphics show how the high tropopause height in this region explains the observed low ozone. The lower panel shows that the high tropopause on Feb. 1 lifts the O3 profile compared to a typical profile found earlier in winter. This motion lifts the profile to lower pressures thus reducing the total column. The GMI Model shows only 4 Dobson Units (DU) of O3 depletion even though the column is more than 100 DU lower than one month earlier. Scientific significant and societal relevance: To quantitatively understand anthropogenic impacts to the stratospheric ozone layer, we must be able to distinguish between low ozone caused by ozone depleting substances and that caused by natural dynamical variability in the atmosphere. Observations and realistic simulations of atmospheric composition are both required in order to separate natural and anthropogenic ozone variability.

Stratospheric↗
DOE OSTI2020

What can the GRACE seasonal cycle tell us about lake-aquifer interactions?

Lake-aquifer interactions have been the subject of investigation and debate for decades. Traditional investigation methods include measurement of water flux across the groundwater-surface water interface, application of heat and environmental tracer methods, conducting numerical simulations of the water flow, and mass balance-based approaches. We first review, evaluate and describe the different approaches that have been applied for examining lake-aquifer interactions and propose an additional complementary approach. While the leakage from lakes and its slow movement through porous media (laminar flow) is well characterized by existing methods, modeling the rapid and turbulent flow through preferred pathways (faults/karst) remains a challenging task. To better understand the nature, and the full scale, of the lake aquifer interactions, and using Lake Nasser and the underlying Dakhla subbasin of the Nubian Sandstone Aquifer System (NSAS) in the Western Desert of Egypt (area: 0.66 x 10 6 km 2 ) as a test site, we examine, model, and correlate temporally and spatially, the variations in Gravity Recovery and Climate Experiment terrestrial water storage (GRACE TWS ) solutions, with precipitation, lake levels, area, and water volume. We review current GRACE applications in hydrology and present our novel approach. Findings include: firstly, large seasonal fluctuations (peak: Nov./Dec.; trough: July/Aug.) in Lake Nasser's surface water levels (average annual fluctuations: from 3.7 m to 7.5 m), area (average area: 3622 km 2 but up to 4530 km 2 ), and volume (annual average: 13.4 km 3 , and up to 34 km 3 ) are observed throughout years 2006 to 2015. These fluctuations are accompanied by an increase in GRACE TWS (average: 50 ± 13 mm/yr, up to 77 ± 18 mm/yr) over Lake Nasser and by a progression of a front of increasing GRACE TWS values (> 50 ± 13 mm) away from the lake reaching distances of up to 700 km some 3 to 5 months following peak lake level periods. The areas witnessing the seasonal increase in GRACE TWS display a progressive increase in phase and decrease in amplitude with distance from the lake. Secondly, the negligible precipitation over the Dakhla subbasin cannot account for the observed seasonal GRACE TWS patterns and neither can the leakage signal from Lake Nasser. Thirdly, overall similarities in the distribution of GRACE TWS seasonal spatial patterns are observed. During high lake level periods (e.g., Dec. 2007; Feb. 2015) additional, and more distant, areas from Lake Nasser saw increases in GRACE TWS and vice versa during low lake level periods (e.g., July 2006; Aug. 2010). These observations are consistent with Lake Nasser being the main source of modern recharge for the Dakhla subbasin and suggest a new conceptual model for the subbasin: a slow groundwater flow through a porous matrix and a rapid groundwater flow along a network of faults, fractures, and karst topography across the matrix. We suggest that the proposed conceptual model for the interaction between Lake Nasser and the Dakhla subbasin could be applicable to aquifers of similar geologic, climatic, and hydrologic settings worldwide and that approaches similar to those advocated here could be used to investigate the validity of this suggestion.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Theory meets experiment: Insights into structure and magnetic properties of Fe 1-x Ni x B alloy

Here, we studied the structural and magnetic properties of the solid solution Fe 1-x Ni x B through theoretical and experimental approaches. Powder X-ray diffraction, X-ray Pair Distribution Function analysis, and energy dispersive X-ray spectroscopy reveal that the Fe 1-x Ni x B solid solution crystallizes in the β-FeB structure type up to x = 0.6–0.7 and exhibits anisotropic unit cell volume contraction with increasing Ni concentration. Magnetic measurements showed a transition from ferromagnetism to paramagnetism around x = 0.7. For x = 0.5, the low (< 0.3 μ B ) magnetic moments suggest itinerant magnetism despite the relatively high Curie temperature (up to 225 K). Theoretical calculations indicated different types of magnetic orderings depending on the Fe/Ni atomic order, with the antiferromagnetic state being stable for ordered FeNiB 2 , whereas the ground state is ferromagnetic for the disordered alloy. Calculations also predicted the coexistence of low- and high-spin states in Fe atoms around the composition with x = 0.5, in line with the experimental evidence from 57 Fe Mössbauer spectroscopy. The two magnetically distinct Fe sites for x = 0.3, 0.4, and 0.5 observed by 57 Fe Mössbauer spectroscopy can also be interpreted as two magnetically different regions or clusters. The formation of these clusters could affect the critical behavior near a quantum magnetic transition based on a potential ferromagnetic quantum critical point identified computationally and experimentally near x = 0.64. This work highlights the complex interplay between structure and magnetism in Fe 1-x Ni x B alloys, suggesting areas for future research on quantum critical behavior.

Bhaskar, Gourab [Iowa State Univ., Ames, IA (Unite↗
DOE OSTI2022

Nuclear Structure and Decay Data for A=31 Isobars

Here, experimental nuclear spectroscopic data are evaluated for 11 known nuclides of mass 31 (F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K). Detailed evaluated information is presented for each reaction and decay experiment. Combining all the available data, recommended values are provided for energies, spins and parities, and half-lives of levels, with energies, branching ratios and multipolarities of γ radiations, and characteristics of β and α radiations in radioactive decays. 31 P is the most extensively studied one among all nuclides via various reactions and decays, followed by 31 S, 31 Si, 31 Mg and 31 Al. Information for excited states in 31 Ne, 31 Na, 31 Cl, 31 Ar and 31 K are limited; no excited states have yet been identified in 31 F, even its ground-state half-life is unknown. Significant new data have become available for the structure of 31 S, with its relevance to astrophysical applications. This work supersedes the earlier evaluation of A=31 by 2013Ou01, with literature cutoff date of Feb 15, 2013.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

MX Anti-MXenes from Non-van der Waals Bulks for Electrochemical Applications: The Merit of Metallicity and Active Basal Plane

Two-dimensional transition-metal compounds (2DTMCs) are promising materials for electrochemical applications, but 2DTMCs with metallicity and active basal planes are rare. In this work, we proposed a simple and effective strategy to extract 2DTMCs from non-van der Waals bulk materials and established a material library of 79 2DTMCs, which we named as anti-MXenes since they are composed of one M atomic layer sandwiched by two X atomic layers. By means of density functional theory computations, 24 anti-MXenes were confirmed to be thermodynamically, dynamically, mechanically, and thermally stable. The metallicity and active basal plane endow these anti-MXenes with potential as excellent electrode materials, for example, as electrocatalysts for hydrogen evolution reactions (HER). Among the noble-metal free anti-MXenes with favorable H-binding, CuS can boost HER at the whole range of H coverages, while CoSi, FeB, CoB, and CoP show promise for HER at some specific H coverages. The active sites are the tetra-coordinating nonmetal atoms at the basal planes, thus rendering a very high density of active sites for these materials. CoB is also a promising anode material for lithium-ion batteries, showing low Li diffusion energy barriers, a very high capacity, and a suitable open circuit voltage. Overall, this work promotes the “computational exfoliation” of 2D materials from non-van der Waals bulks and exemplifies the applications of anti-MXenes in various electrochemical processes.

36 MATERIALS SCIENCE↗