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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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189 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Photoelectrochemically Self Improving Si/GaN Photocathode: Figure 1c Raw Data

Intermittent chronoamperometry (CA) testing was performed on Si/GaN photocathode in hourly manner. The LSV scan at 0 hour, 1 hour CA, 2 hours CA, 3 hours CA, 4 hours CA, 6 hours CA, 8 hours CA and 10 hours CA were recorded to track the changes of the photoelectrochemica (PEC) performance of the photocathode. The scan range was set to be 0V vs open circuit voltage (Eoc) to -0.7V vs RHE. Test was performed under one sun illumination in 0.5M H2SO4 (pH=0.4).

photocathode↗
DOE OSTI2024

Corrosion-Resistant Non-Carbon Electrocatalyst Supports for PEFCS

Insufficient durability of commercial catalysts is a persistent issue for PEFC applications.1 Herein, Pt on Nb-doped-TiO 2 is reported as a highly durable electrocatalyst on which the direct 4-electron reduction of oxygen to water is more facile compared to Pt/C. All performance metrics are reported comparing Pt/Nb-TiO2 with a 15% Pt loading, against a commercial Pt/C catalyst (46.5% Pt loading, Tanaka, K. K.). Nb-doped-TiO 2 with high surface area and high electronic conductivity was synthesized using the supercritical fluid method. Initially, the durability of the catalyst was characterized using accelerated stability tests (ASTs) involving 10,000 high potential cycles (DOE/FCCJ protocol) and the Pt/Nb-TiO 2 was found to retain 78% of its initial electrochemically active surface area (ECSA) compared to the 57.6 % retained by Pt/C. These observations were in excellent agreement with previous reports that the Pt particle size of Pt/C grew from 2nm to 8nm during the AST protocol along with severe corrosion and amorphization of the carbon surface.2, 3 TEM and XPS studies of the Pt-Nb-doped-TiO 2 catalyst showed that the Pt particle size grew from 3nm to 6nm and the Nb(IV) and Ti(III) in the support were oxidized to Nb(V) and Ti(IV) after the durability test. Thus, the improvement in Pt/Nb-TiO 2 ECSA retention was attributed to the lower extent of particle growth and lack of oxidative support loss upon oxidation as compared to Pt/C. The oxygen reduction reaction (ORR) performance was characterized by linear polarization using a rotating disk electrode (RDE). The electrochemical surface areas of Pt/Nb-TiO 2 and Pt/C were found to be 48m2·g -1 and 83m2·g -1 respectively, and the mass activity for the ORR at 0.9V vs. RHE were found to be 150 mA·mg-1Pt and 124 mA·mg-1Pt respectively. The improved mass activity on Pt/Nb-TiO 2 was attributed to strong metal support interaction (SMSI) between the Nb-TiO 2 support and the Pt catalyst based on the 625 meV decrease in the binding energy of the Pt4f x-ray photo-electron spectroscopy (XPS) peaks of Pt/Nb-TiO 2 compared to Pt/C. To quantify the impact of the SMSI, a kinetic model was applied to calculate the elementary reaction rate constants for the various steps of the ORR on both catalysts. The reaction rate constant (k1) for the direct 4-electron transfer pathway to produce H 2 O was significantly larger in Pt/Nb-TiO 2 as compared to Pt/C. Thus, the reduction in the electron binding energy as observed in the XPS was found to aid the facile filling of the higher energy 2p orbitals of O 2 thereby leading to improved 4-electron transfer kinetics and improved overall activity.

08 HYDROGEN↗
DOE OSTI2024

Sulfur-Doped Carbon Support Boosts CO2RR Activity of Ag Electrocatalysts

For presentation at the 70th AVS International Symposium and Exhibition. In this work, we show that the activity of Ag electrocatalysts for electrochemical CO2 to CO conversion is improved when supported on sulfur-doped (S-doped) carbon materials. S-doped carbon support was created by treating the heavily sputtered, highly oriented pyrolytic graphite (HOPG) in H2S at elevated temperatures, as confirmed by the S 2p X-ray photoelectron spectroscopy (XPS) peak. Scanning tunneling microscopy (STM) images indicated that Ag nanoparticles supported on S-doped HOPG had similar size distributions as those supported on sulfur-free (S-free) HOPG. While both catalysts reached > 90% CO Faradaic efficiency (FECO) at E = -1.3 V vs. the reversible hydrogen electrode (RHE) in the CO2 reduction reaction (CO2RR), Ag catalysts supported on S-doped HOPG demonstrated 70% higher CO turnover frequency (TOFCO = 3.4 CO/atomAg/s) than those supported on S-free HOPG (TOFCO = 2.0 CO/atomAg/s). Preliminary calculations based on density functional theory (DFT) indicated a more favorable energetic pathway of CO2-to-CO at the C-S-Ag interface, tentatively consistent with experiments. These results hint at a new approach to design active and selective electrocatalysts for CO2 conversion.

Deng, Xingyi↗
DOE OSTI2022

Few-Atom Copper Catalyst for the Electrochemical Reduction of CO to Acetate: Synergetic Catalysis between Neighboring Cu Atoms

Single-atom catalysts (SACs) are gaining increasing recognition because of their superior catalytic properties for various reactions. However, the performance of SACs is often limited by the lack of neighboring metal centers to cooperate in catalysis. Herein, a synergetic interaction between neighboring Cu atoms of a few-atom catalyst (FAC) on graphdiyne is found to greatly enhance the production of acetate in CO electroreduction reaction relative to Cu SACs. In a 1.0 M KOH electrolyte, this Cu FAC exhibits an acetate Faradaic efficiency of 53.8±1.5 % and an ultrahigh relative purity of up to 97 wt% for liquid products, and excellent stability of over 23 h continuous electrolysis at -0.8 V versus reversible hydrogen electrode (RHE). Theoretical studies suggest that the intersite catalytic communication between two neighboring metal atoms confined in each pore of GDY facilitates the formation of acetic acid through either stepwise hydrogenation of CH 2 CO* or the direct reaction of H 2 O with CH 2 CO*. Our study demonstrates the unprecedented synergetic catalysis of Cu FAC in promoting the selective CO electroreduction toward acetate production.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Oxygen Reduction Reaction Catalyzed by Carbon-Supported Platinum Few-Atom Clusters: Significant Enhancement by Doping of Atomic Cobalt

Oxygen reduction reaction (ORR) plays an important role in dictating the performance of various electrochemical energy technologies. As platinum nanoparticles have served as the catalysts of choice towards ORR, minimizing the cost of the catalysts by diminishing the platinum nanoparticle size has become a critical route to advancing the technological development. Herein, first-principle calculations show that carbon-supported Pt 9 clusters represent the threshold domain size, and the ORR activity can be significantly improved by doping of adjacent cobalt atoms. This is confirmed experimentally, where platinum and cobalt are dispersed in nitrogen-doped carbon nanowires in varied forms, single atoms, few-atom clusters, and nanoparticles, depending on the initial feeds. The sample consisting primarily of Pt 2~7 clusters doped with atomic Co species exhibits the best mass activity among the series, with a current density of 4.16 A mg Pt − 1 at +0.85 V vs. RHE that is almost 50 times higher than that of commercial Pt/C.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2006

Mission Operations Planning with Preferences: An Empirical Study

This paper presents an empirical study of some nonexhaustive approaches to optimizing preferences within the context of constraint-based, mixed-initiative planning for mission operations. This work is motivated by the experience of deploying and operating the MAPGEN (Mixed-initiative Activity Plan GENerator) system for the Mars Exploration Rover Mission. Responsiveness to the user is one of the important requirements for MAPGEN, hence, the additional computation time needed to optimize preferences must be kept within reasonabble bounds. This was the primary motivation for studying non-exhaustive optimization approaches. The specific goals of rhe empirical study are to assess the impact on solution quality of two greedy heuristics used in MAPGEN and to assess the improvement gained by applying a linear programming optimization technique to the final solution.

Bresina, John L.↗
NASA NTRS2006

Dynamics of the DAZd Disks

New observations of DAZ dwarfs suggest that many of these stars---the DAZd subclass---host rings of debris. We will discuss the minerology and dynamics ofthese rings as inferred from models of new mid-infrared spectra and photometry raken with the Spitzer space telescope, I will show that rhe DAZd rings do not need to be recently supplied by a single comet; they can survive for approx. 1 Gyr.

Kuchner, Marc↗
NASA NTRS2011

The Primordial Inflation Explorer (PIXIE): A Nulling Polarimeter for Cosmic Microwave Background Observations

The Primordial Inflation Explorer (PIXIE) is a concept for an Explorer-class mission to measure the gravity-wave signature of primordial inflation through its distinctive imprint on the linear polarization of the cosmic microwave background. The instrument consists of a polarizing Michelson interferometer configured as a nulling polarimeter to measure the difference spectrum between orthogonal linear polarizations from two co-aligned beams. Either input can view the sky or a temperature-controlled absolute reference blackbody calibrator. Rhe proposed instrument can map the absolute intensity and linear polarization (Stokes I, Q, and U parameters) over the full sky in 400 spectral channels spanning 2.5 decades in frequency from 30 GHz to 6 THz (1 cm to 50 micron wavelength). Multi-moded optics provide background-limited sensitivity using only 4 detectors, while the highly symmetric design and multiple signal modulations provide robust rejection of potential systematic errors. The principal science goal is the detection and characterization of linear polarization from an inflationary epoch in the early universe, with tensor-to-scalar ratio r < 10..3 at 5 standard deviations. The rich PIXIE data set can also constrain physical processes ranging from Big Bang cosmology to the nature of the first stars to physical conditions within the interstellar medium of the Galaxy.

Kogut, Alan J.↗
NASA NTRS1973

Detection of S02 and N02 in Stack Plume by Raman Scattering and Fluorescence

We have been studying laser-Raman radar which can be used as the remote detector of sulfur dioxide concentration in the stack plume of boiler exhaust gas, and some results have been published. In this paper, we report the interference of nitrogen dioxide fluorescence against sulfur dioxide Raman scattering and the measuring method of sulfur dioxide and nitrogen dioxide concentration. In a stack plume, high density dust and high concentration carbon dioxide are included, therefore very strong Mie back-scattering and carbon dioxide Raman scattering are observed. The separation of these scattering signals from sulfur dioxide Raman signal was the first problem for the laser-Raman radar. But, this problem was solved by using the filter which have high resolving power. It is well known that nitrogen dioxide can be excited to emit fluorescence of broad spectrum by blue-green light. The light source of the laser-Raman radar is SH of Nd:YAG laser, and boiler exhaust gas includes several tens ppm of nitrogen dioxide, then the interference of nitrogen dioxide fluorescence brings the error to sulfur dioxide measurement. 'rhe rejection of the interference can be achieved by the subtraction of the nitrogen dioxide fluorescence contribution from detected signal at sulfur dioxide Raman scattering wavelength. The nitrogen dioxide fluorescence contribution can be measured by two methods. The first is to convert the nitrogen dioxide fluorescence intensity which is measured at a different wavelength from sulfur dioxide Raman line into the one at sulfur dioxide Raman line. The second is to convert the detected signal intensity, which is obtained when the range gate is set just behind the plume, into the one obtained at the range of the plume using the difference of the time dependence between sulfur dioxide Raman scattering and nitrogen dioxide fluorescence. Nitrogen dioxide fluorescence has lifetime of about 300nS, while Raman scattering has none. By either of the two methods, the contribution of nitrogen dioxide fluorescence is determined. Then, we can measure the nitrogen dioxide and sulfur dioxide concentration.The minimum detectable concentration and the experimental results of the remote sensing of sulfur dioxide and nitrogen dioxide in stack plume will be discussed in detail.

Nakahara, S.↗