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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Structural insights into the mechanism of oxidative activation of heme-free H-NOX from Vibrio cholerae

Bacterial heme nitric oxide/oxygen (H-NOX) domains are nitric oxide (NO) or oxygen sensors. This activity is mediated through binding of the ligand to a heme cofactor. However, H-NOX from Vibrio cholerae (Vc H-NOX) can be easily purified in a heme-free state that is capable of reversibly responding to oxidation, suggesting a heme-independent function as a redox sensor. This occurs by oxidation of Cys residues at a zinc-binding site conserved in a subset of H-NOX homologs. Remarkably, zinc is not lost from the protein upon oxidation, although its ligation environment is significantly altered. Using a combination of computational and experimental approaches, we have characterized localized structural changes that accompany the formation of specific disulfide bonds between Cys residues upon oxidation. Furthermore, the larger-scale structural changes accompanying oxidation appear to mimic those changes observed upon NO binding to the heme-bound form. Thus, Vc H-NOX and its homologs may act as both redox and NO sensors by completely separate mechanisms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Increasing Iridium Oxide Activity for the Oxygen Evolution Reaction with Hafnium Modification

Synthesis and implementation of highly active, stable, and affordable electrocatalysts for the oxygen evolution reaction (OER) is a major challenge in developing energy efficient and economically viable energy conversion devices such as electrolyzers, rechargeable metal-air batteries, and regenerative fuel cells. The current benchmark electrocatalyst for OER is based on iridium oxide (IrO x ) due to its superior performance and excellent stability. However, large scale applications using IrO x are impractical due to its low abundance and high cost. In this work, we report a highly active hafnium-modified iridium oxide (IrHf x O y ) electrocatalyst for OER. The IrHf x O y electrocatalyst demonstrated ten times higher activity in alkaline conditions (pH = 11) and four times higher activity in acid conditions (pH = 1) than a IrO x electrocatalyst. The highest intrinsic mass activity of the IrHf x O y catalyst in acid conditions was calculated as 6950 A gIrO x -1 at an overpotential (η) of 0.3 V. Combined studies utilizing operando surface enhanced Raman spectroscopy (SERS) and DFT calculations revealed that the active sites for OER are the Ir-O species for both IrO x and IrHf x O y catalysts. The presence of Hf sites leads to more negative charge states on nearby O sites, and shortening the bond lengths of Ir-O, and lowering free energies for OER intermediates to accelerate the OER process.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Coordination environment tuning of nickel sites by oxyanions to optimize methanol electro-oxidation activity

To achieve zero-carbon economy, advanced anode catalysts are desirable for hydrogen production and biomass upgrading powered by renewable energy. Ni-based non-precious electrocatalysts are considered as potential candidates because of intrinsic redox attributes, but in-depth understanding and rational design of Ni site coordination still remain challenging. Here, we perform anodic electrochemical oxidation of Ni-metalloids (NiP x , NiS x , and NiSe x ) to in-situ construct different oxyanion-coordinated amorphous nickel oxyhydroxides (NiOOH-TO x ), among which NiOOH-PO x shows optimal local coordination environment and boosts electrocatalytic activity of Ni sites towards selective oxidation of methanol to formate. Experiments and theoretical results demonstrate that NiOOH-PO x possesses improved adsorption of OH* and methanol, and favors the formation of CH 3 O* intermediates. The coordinated phosphate oxyanions effectively tailor the d band center of Ni sites and increases Ni-O covalency, promoting the catalytic activity. This study provides additional insights into modulation of active-center coordination environment via oxyanions for organic molecules transformation.

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

Oxophilicity Drives Oxygen Transfer at a Palladium–Silver Interface for Increased CO Oxidation Activity

A single-layer AgO x phase grown on Ag(111) efficiently transfers oxygen to Pd domains at room temperature, rendering the Pd-decorated surface highly reactive toward CO oxidation. Here, oxygen transfer from AgO x to Pd and the surface reactivity toward CO were investigated as a function of the Pd coverage using X-ray photoelectron spectroscopy, surface infrared spectroscopy of adsorbed CO, temperature-programmed reaction spectroscopy, and density functional theory (DFT) calculations. Our results show that all of the oxygen from the AgO x layer (~0.375 monolayer) migrates to the surface of Pd during formation of a nearly complete Pd bilayer at 300 K and that the oxygen coverages generated on Pd increase as the Pd cluster size decreases, reaching values that exceed the oxygen concentration in the AgO x layer by as much as a factor of 2. Experimental measurements and DFT calculations show that preferential binding of oxygen on the edges of the Pd clusters enhances the oxygen coverage on Pd clusters of decreasing size and produces a heterogeneous spatial distribution of oxygen. CO adsorbs in high coverages at 100 K by binding on both the terraces and O-rich edges of the Pd clusters. During subsequent heating, oxidation of the adsorbed CO consumes nearly all of the oxygen that transferred from AgO x to the Pd domains; in contrast, the pure AgO x layer exhibits limited reactivity toward CO adsorbed at 100 K. These results demonstrate that differences in oxophilicity drive facile oxygen transfer from Ag to the edges of Pd nanoclusters and thereby give rise to an efficient pathway for CO oxidation on bimetallic PdAg surfaces. The cooperation between the Pd and Ag domains results in near-interfacial chemistry that may be broadly important in catalysis by bimetallic alloys.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Size‐Dependent Dispersion of Rhodium Clusters into Isolated Single Atoms at Low Temperature and the Consequences for CO Oxidation Activity

Abstract Understanding the dynamic structural evolution of supported metal clusters under reaction conditions is crucial to develop structure reactivity relations. Here, we followed the structure of different size Rh clusters supported on Al 2 O 3 using in situ/operando spectroscopy and ex situ aberration‐corrected electron microscopy. We report a dynamic evolution of rhodium clusters into thermally stable isolated single atoms upon exposure to oxygen and during CO oxidation. Rh clusters partially disperse into single atoms at room temperature and the extent of dispersion increases as the Rh size decreases and as the reaction temperature increases. A strong correlation is found between the extent of dispersion and the CO oxidation kinetics. More importantly, dispersing Rh clusters into single atoms increases the activity at room temperature by more than two orders of magnitude due to the much lower activation energy on single atoms (40 vs. 130 kJ/mol). This work demonstrates that the structure and reactivity of small Rh clusters are very sensitive to the reaction environment.

Albrahim, Malik A.↗
DOE OSTI2023

Size‐Dependent Dispersion of Rhodium Clusters into Isolated Single Atoms at Low Temperature and the Consequences for CO Oxidation Activity

Abstract Understanding the dynamic structural evolution of supported metal clusters under reaction conditions is crucial to develop structure reactivity relations. Here, we followed the structure of different size Rh clusters supported on Al 2 O 3 using in situ/operando spectroscopy and ex situ aberration‐corrected electron microscopy. We report a dynamic evolution of rhodium clusters into thermally stable isolated single atoms upon exposure to oxygen and during CO oxidation. Rh clusters partially disperse into single atoms at room temperature and the extent of dispersion increases as the Rh size decreases and as the reaction temperature increases. A strong correlation is found between the extent of dispersion and the CO oxidation kinetics. More importantly, dispersing Rh clusters into single atoms increases the activity at room temperature by more than two orders of magnitude due to the much lower activation energy on single atoms (40 vs. 130 kJ/mol). This work demonstrates that the structure and reactivity of small Rh clusters are very sensitive to the reaction environment.

Albrahim, Malik A.↗
DOE OSTI2021

Electrodes with silicon oxide active materials for lithium ion cells achieving high capacity, high energy density and long cycle life performance

Improved negative electrodes can comprise a silicon based active material blended with graphite to provide more stable cycling at high energy densities. In some embodiments, the negative electrodes comprise a blend of polyimide binder mixed with a more elastic polymer binder with a nanoscale carbon conductive additive. The silicon-based blended graphite negative electrodes can be matched with positive electrodes comprising nickel rich lithium nickel manganese cobalt oxides to form high energy density cells with good cycling properties.

Venkatachalam, Subramanian↗
DOE OSTI2023

Electrodes with silicon oxide active materials for lithium ion cells achieving high capacity, high energy density and long cycle life performance

Improved negative electrodes can comprise a silicon based active material blended with graphite to provide more stable cycling at high energy densities. In some embodiments, the negative electrodes comprise a blend of polyimide binder mixed with a more elastic polymer binder with a nanoscale carbon conductive additive. The silicon-based blended graphite negative electrodes can be matched with positive electrodes comprising nickel rich lithium nickel manganese cobalt oxides to form high energy density cells with good cycling properties.

Venkatachalam, Subramanian↗
DOE OSTI2021

Synthesis, Characterization, and Water Oxidation Activity of Isomeric Ru Complexes

The synthesis and characterization of the isomeric ruthenium complexes with the general formula cis- and trans-[Ru(trpy)(qc)X] n+ (trpy is 2,2':6',2"-terpyridine, qc is 8-quinolinecarboxylate, cis-1 and trans-1, X = Cl, n = 0; cis-2 and trans-2, X=OH2, n = 1) with respect to the relative disposition of the carboxylate and X ligands are reported. For comparison purposes, another set of ruthenium complexes with general formula cis- and trans-[Ru(trpy)(pic)(OH 2 )]+ (pic is 2-picolinate (cis-3, trans-3)) have been prepared. The complexes with a qc ligand show a more distorted geometry compared to the complexes with a pic ligand. In all of the cases, the trans isomers show lower potential values for all of the redox couples relative to the cis isomers. Furthermore, complexes cis-2 and trans-2 with six-member chelate rings show higher catalytic activity than cis-3 and trans-3. Overall, it was shown that the electronic perturbation to the metal center exerted by different orientation and geometry of the ligands significantly influences both redox properties and catalytic performance.

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

Operando identification of site-dependent water oxidation activity on ruthenium dioxide single-crystal surfaces

Understanding the nature of active sites is central to controlling (electro)catalytic activity. Here we employed surface X-ray scattering coupled with density functional theory and surface-enhanced infrared absorption spectroscopy to examine the oxygen evolution reaction on RuO 2 surfaces as a function of voltage. At 1.5 V RHE , our results suggest that there is an –OO group on the coordinatively unsaturated ruthenium (Ru CUS ) site of the (100) surface (and similarly for (110)), but adsorbed oxygen on the Ru CUS site of (101). Density functional theory results indicate that the removal of –OO from the Ru CUS site, which is stabilized by a hydrogen bond to a neighbouring –OH (–OO–H), could be the rate-determining step for (100) (similarly for (110)), where its reduced binding on (100) increased activity. A further reduction in binding energy on the Ru CUS site of (101) resulted in a different rate-determining step (–O + H 2 O – (H + + e - ) → –OO–H) and decreased activity. Our study provides molecular details on the active sites, and the influence of their local coordination environment on activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Replication Data for: Oxophilicity Drives Oxygen Transfer at a Palladium−Silver Interface for Increased CO Oxidation Activity

The data underlying this published work have been made publicly available in this repository as part of the IMASC Data Management Plan. This work was supported as part of the Integrated Mesoscale Architectures for Sustainable Catalysis (IMASC), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0012573.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1973

Photoemission from cesium-oxide-activated InGaAsP.

Zinc-doped InGaAsP quaternary III-V material of the proper composition range shows superior photoemission properties to either InGaAs or InAsP ternary material. The minority-carrier diffusion length in the quaternary material is at least as long as that in InAsP and much longer than observed in InGaAs. The barrier height at the InGaAsP-Cs2O interface is lowered by cooling, giving increased electron escape probability and new highs in quantum efficiency over a wide wavelength range. For example, a 1.06-micron quantum efficiency of 7.5%/incident photon was observed at -90 C.

James, L. W.↗