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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Standardized protocols for evaluating platinum group metal-free oxygen reduction reaction electrocatalysts in polymer electrolyte fuel cells

Platinum group metal (PGM)-free electrocatalysts for the oxygen reduction reaction at the polymer electrolyte fuel cell cathode have shown substantial improvements in activity—especially those derived from transition metals, nitrogen and carbon. However, their stability and durability remain insufficient. A key to enabling future improvements and performance comparisons lies in the development of test protocols that are relevant to the operating conditions of the fuel cell cathode, can be completed within a reasonable time and are ubiquitously adopted. Here we propose and validate such protocols, designed with special attention to typical catalyst degradation mechanisms of PGM-free catalysts. The results of the cross-laboratory validation study using two different catalysts attest to the strength and feasibility of the proposed approach. We hope that the information provided here can serve as a broad and effective platform for assessing the performance and durability of PGM-free catalysts for polymer electrolyte fuel cells.

25 ENERGY STORAGE↗
DOE OSTI2015

F-state quenching with CH{sub 4} for buffer-gas cooled {sup 171}Y b{sup +} frequency standard

We report that methane, CH{sub 4}, can be used as an efficient F-state quenching gas for trapped ytterbium ions. The quenching rate coefficient is measured to be (2.8 ± 0.3) × 10{sup 6} s{sup −1} Torr{sup −1}. For applications that use microwave hyperfine transitions of the ground-state {sup 171}Y b ions, the CH{sub 4} induced frequency shift coefficient and the decoherence rate coefficient are measured as δν/ν = (−3.6 ± 0.1) × 10{sup −6} Torr{sup −1} and 1/T{sub 2} = (1.5 ± 0.2) × 10{sup 5} s{sup −1} Torr{sup −1}. In our buffer-gas cooled {sup 171}Y b{sup +} microwave clock system, we find that only ≤10{sup −8} Torr of CH{sub 4} is required under normal operating conditions to efficiently clear the F-state and maintain ≥85% of trapped ions in the ground state with insignificant pressure shift and collisional decoherence of the clock resonance.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2021

Standardizing Dainotti-correlated gamma-ray bursts, and using them with standardized Amati-correlated gamma-ray bursts to constrain cosmological model parameters

ABSTRACT We show that each of the three Dainotti-correlated gamma-ray burst (GRB) data sets recently compiled by Wang et al. and Hu et al., that together probe the redshift range 0.35 ≤ z ≤ 5.91, obey cosmological-model-independent Dainotti correlations and so are standardizable. We use these GRB data in conjunction with the best currently available Amati-correlated GRB data, that probe 0.3399 ≤ z ≤ 8.2, to constrain cosmological model parameters. The resulting cosmological constraints are weak, providing lower limits on the non-relativistic matter density parameter, mildly favouring non-zero spatial curvature, and largely consistent with currently accelerated cosmological expansion as well as with constraints determined from better-established data.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Standardizing Platinum Dainotti-correlated gamma-ray bursts, and using them with standardized Amati-correlated gamma-ray bursts to constrain cosmological model parameters

ABSTRACT We show that the Platinum gamma-ray burst (GRB) data compilation, probing the redshift range 0.553 ≤ z ≤ 5.0, obeys a cosmological-model-independent three-parameter Fundamental Plane (Dainotti) correlation and so is standardizable. While they probe the largely unexplored z ∼ 2.3–5 part of cosmological redshift space, the GRB cosmological parameter constraints are consistent with, but less precise than, those from a combination of baryon acoustic oscillation (BAO) and Hubble parameter [H(z)] data. In order to increase the precision of GRB-only cosmological constraints, we exclude common GRBs from the larger Amati-correlated A118 data set composed of 118 GRBs and jointly analyse the remaining 101 Amati-correlated GRBs with the 50 Platinum GRBs. This joint 151 GRB data set probes the largely unexplored z ∼ 2.3–8.2 region; the resulting GRB-only cosmological constraints are more restrictive, and consistent with, but less precise than, those from H(z) + BAO data.

79 ASTRONOMY AND ASTROPHYSICS↗