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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

The effect of silica oxide support on the catalytic activity of nickel-molybdenum bimetallic catalyst toward ethanol steam reforming for hydrogen production

This work investigates the effects of molybdenum promoter and silica oxide (SiO 2 ) support morphology on the ethanol steam reforming (ESR) performance of Nickel-Molybdenum (NiMo) bimetallic catalysts. Ordered mesoporous SiO 2 (SBA-15) and commercial SiO 2 supports were used as the oxide support materials. The synthesized catalysts were prepared via the wet impregnation method and characterized via XRD, H 2 -TPR, BET, FTIR, and Raman techniques. This study shows that NiMo bimetallic catalyst supported on SBA-15 has superior catalytic activity and better coking resistance at an intermediate temperature of 600 ⁰C than commercial SiO 2 supported catalysts. The presence of a uniform mesoporous structure of SBA-15 with an average pore diameter of ~ 2 nm can obstruct the carbon formation, leading to improved coking resistance. The catalytic enhancement of NiMo bimetallic catalysts toward ESR can also be linked to the ability of Mo promoter in enhancing the interaction between NiMo nanoparticles and SiO 2 support materials and restraining agglomeration of Ni nanoparticles, which results in further improvement of NiMo nanoparticle dispersion and inhibit its sintering. The NiMo bimetallic catalysts supported on SBA-15 illustrated the high H 2 yield of ~ 54% and carbon conversion of ~ 89% with the excellent stability for ESR performed at 600 ⁰C and the steam-to-carbon ratio of 2 over 65 hours.

25 ENERGY STORAGE↗
DOE OSTI2017

Hydrogen Bonding Rescues Overpotential in Seven-Coordinated Ru Water Oxidation Catalysts

In this paper, we describe the synthesis, structural characterization, and redox properties of two new Ru complexes containing the dianionic potentially pentadentate [2,2':6',2"-terpyridine]-6,6"-dicarboxylate (tda 2– ) ligand that coordinates Ru at the equatorial plane and with additional pyridine or dmso acting as monondentate ligand in the axial positions: [Ru II (tda-κ-N 3 O)(py)(dmso)], 1 II and [Ru III (tda-κ-N 3 O 2 )(py)(H 2 O) ax ] + , 2 III (H 2 O) + . Complex 1 II has been characterized by single-crystal XRD in the solid state and in solution by NMR spectroscopy. The redox properties of 1 II and 2 III (H 2 O) + have been thoroughly investigated by means of cyclic voltammetry and differential pulse voltammetry. Complex 2 II (H 2 O) displays poor catalytic activity with regard to the oxidation of water to dioxygen, and its properties have been analyzed on the basis of foot of the wave analysis and catalytic Tafel plots. The activity of 2 II (H 2 O) has been compared with related water oxidation catalysts (WOCs) previously described in the literature. Despite its moderate activity, 2 II (H 2 O) constitutes the cornerstone that has triggered the rationalization of the different factors that govern overpotentials as well as efficiencies in molecular WOCs. The present work uncovers the interplay between different parameters, namely, coordination number, number of anionic groups bonded to the first-coordination sphere of the metal center, water oxidation catalysis overpotential, p K a and hydrogen bonding, and the performance of a given WOC. It thus establishes the basic principles for the design of efficient WOCs operating at low overpotentials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

PGM-Free ORR Catalysts Designed by Templating PANI-Type Polymers Containing Functional Groups with High Affinity to Iron

In this work, a coordination-chemistry approach was used to increase the content of nitrogen-coordinated iron moieties (Fe-N x ) in platinum group metal-free (PGM-free) catalysts for oxygen reduction reaction (ORR). The catalysts were derived from a series of polyaniline (PANI)-type precursors with N-containing functional side chains having high affinity to iron. The PGM-free ORR catalysts synthesized using such polymeric templates were characterized by scanning electron microscopy, X-ray diffractometry, and tested in an electrochemical cell and H 2 -air fuel cell for ORR activity. X-ray photoelectron spectroscopy (XPS) analysis showed that, in spite of similar nitrogen contents, catalysts obtained using PANI-type polymers containing side chains with high affinity to iron had higher Fe content than PANI-derived catalyst. These PGM-free catalysts showed improved ORR activity in an electrochemical cell and in H 2 -air fuel cell testing, compared to the PANI-derived catalyst. A correlation between the content of Fe-N x moieties and the fuel cell performance was observed in these PGM-free ORR catalysts.

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

Simultaneously upgrading CO 2 and light alkanes into value-added products

We will discuss recent results from our group in reacting CO 2 and light alkanes to produce syngas, olefins, aromatics, and oxygenates. We will mainly use the simultaneous upgrading of CO 2 and ethane (SU-CO 2 Et) as examples to demonstrate the feasibility and reaction pathways of these processes. We will briefly discuss synthesis methods and essential structural characterization techniques that can be applied to SU-CO 2 Et catalysts. We will then illustrate how to identify and apply distinct active sites for different upgrading processes, using a combination of kinetic studies, in situ characterization, and density functional theory (DFT) calculations. We will conclude the Perspective by pointing out challenges and potential directions in catalyst design and synthesis, as well as structural characterization and mechanistic investigations, to further advance the simultaneous upgrading of CO 2 and light alkanes.

03 NATURAL GAS↗
DOE OSTI2020

Identifying Dense NiSe 2 /CoSe 2 Heterointerfaces Coupled with Surface High-Valence Bimetallic Sites for Synergistically Enhanced Oxygen Electrocatalysis

Constructing heterostructures with abundant interfaces is essential for integrating the multiple functionalities in single entities. Herein, the synthesis of NiSe 2 /CoSe 2 heterostructures with different interfacial densities via an innovative strategy of successive ion injection is reported. The resulting hybrid electrocatalyst with dense heterointerfaces exhibits superior electrocatalytic properties in an alkaline electrolyte, superior to other benchmarks and precious metal catalysts. Advanced synchrotron techniques, post structural characterizations, and density functional theory (DFT) simulations reveal that the introduction of atomic-level interfaces can lower the oxidation overpotential of bimetallic Ni and Co active sites (whereas Ni$^{2+}$ can be more easily activated than Co$^{2+}$) and induce the electronic interaction between the core selenides and surface in situ generated oxides/hydroxides, which play a critical role in synergistically reducing energetic barriers and accelerating reaction kinetics for catalyzing the oxygen evolution. Hence, the heterointerface structure facilitates the catalytic performance enhancement via increasing the intrinsic reactivity of metallic atoms and enhancing the synergistic effect between the inner selenides and surface oxidation species. This work not only complements the understanding on the origins of the activity of electrocatalysts based on metal selenides, but also sheds light on further surface and interfacial engineering of advanced hybrid materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Partial oxidation of isobutylene using Ni TiO x

In this work, we report an aerobic partical oxidation of isobutylene into isoprene, acetone, and p-xylene using a mesoporous Ni TiO x catalytic material. In this work, two catalysts were found to synthesize two of these three valuable products with high selectivity, with p-xylene being synthesized with a selectivity of 46.0% and isoprene being synthesized with a selectivity of 64.7%, with overall conversions of isobutylene being 34.0% and 11.9% respectively. These reactions were done at relatively low temperatures. (300°C or below) and are conducted at flow rates of 10 sccm oxygen and isobutylene. The nickel titania catalysts were studied extensively using various characterization methodologies such as TEM, Raman, XRD, and XRF.

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

Ordered CoPt oxygen reduction catalyst with high performance and durability

A high-performance and durable polymer electrolyte membrane fuel cell cathode catalyst composed of an ordered L10–CoPt core and a thin Pt shell was designed and prepared. Under practical fuel cell membrane electrode assembly testing conditions, the cathode catalyst showed an outstanding initial mass activity of 0.6 A/mgPt, which satisfies the U.S. Department of Energy performance target while also meeting the durability target of less than 40% loss in mass activity after 30,000 accelerated stress test voltage cycles. The high structural stability of the L10–CoPt@Pt-shell catalyst was confirmed by postmortem materials characterization, and the origin of this robustness was revealed by density functional theory calculations, where the barriers for diffusion of Co atoms were observed to be significantly increased in the ordered intermetallic core.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Photoinduced electron transfer kinetics of linked Ru-Co photocatalyst dyads

Two new supramolecular photocatalyst dyads based on the [Ru(2,2’-bipyridine)3]2+ photosensitizer linked to a macrocyclic Co(II)tetra(pyridyl) catalyst for proton reduction are reported. The dyads differ primarily in the bridging ligand which links the molecular modules; the first being a short and flexible linker, and the second a longer and electronically conjugated linker. Ultrafast transient optical spectroscopy was used to monitor the photoinduced kinetics of the dyads following visible excitation of the photosensitizer module. Direct comparison of transient spectra and kinetics indicates that there are indeed substantial differences between the ultrafast transient optical spectroscopy of the dyads, but there is no indication of oxidative quenching of the photosensitizer module by the catalyst module. These initial design and characterization studies of the linked Ru(II)—Co(II) dyads provide an important foundation for advanced designs of systems for efficient solar energy conversion by molecular architectures.

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

Monitoring Depolymerization in Mesopores Using Dynamic Properties of Polymeric Melt Accessed via Dielectric Spectroscopy

Traditional design principles for heterogeneous catalysis guide the use of catalytic particles with mesosized (∼2–50 nm) pores to increase the number of surface-active sites by way of an increased surface area. However, the entry of long-chain polymers into such pores may be significantly limited by the size and entanglement of polymers in the melt state, thereby decreasing the number of accessible sites. Assessment of catalyst performance from traditional reactor-based studies averages over intrapore reaction events as well as reactions on the surface of a particle, resulting in an inability to distinguish between differences in site accessibility and activity. Techniques that assess the intrapore performance can inform the design of future heterogeneous catalysts for polymer upcycling. In this work, we demonstrate the use of broadband dielectric spectroscopy to monitor depolymerization of a polymer melt within mesopores via changes in the segmental relaxation time scale of amorphous polymer chains. In particular, we highlight the use of an anodic aluminum oxide (AAO) membrane as a readily available model for catalyst pores with a well-characterized pore morphology. The decrease in the segmental relaxation (α-relaxation) time of the melt with increasing chain scission emerges as a measure of the extent of polymer deconstruction inside mesopores. To demonstrate the utility of this technique, we demonstrate the decomposition of two commercial poly(propylene carbonate) polymers with different decomposition rates within mesopores. As the polymers depolymerize, their segmental relaxation time decreases as the molecular weight decreases (as predicted by the Fox–Flory equation). The BDS-measured change in segmental relaxation time mirrors the expected trend based on change in molecular weight measured by size exclusion chromatography.

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

Excited State Covalency, Dynamics, and Photochemistry of Square Planar Ni-Thiolate Complexes Revealed by Ultrafast X-ray Absorption

Highly covalent Ni bis(dithiolene) and related complexes provide an ideal platform for investigating the effects of metal–ligand orbital hybridization on excited state character and dynamics. In particular, we focus on the ligand field excited states that dominate the photophysics of first-row transition metal complexes. Here, we investigate if they can be significantly delocalized off the metal center, possibly yielding photochemical reactivity more similar to charge transfer excited states than metal-centered ligand field excited states. Here [Ni(mpo) 2 ] (mpo = 2-mercaptopyridine- N-oxide) provides a representative example for the larger chemical class and is an active electro- and photo-catalyst for proton reduction. A detailed characterization of the excited state electronic structure, dynamics, and photochemistry of [Ni(mpo) 2 ] is presented based on ultrafast transient X- ray absorption spectroscopy at the Ni and S 1s core absorption K-edges. By comparing the ultrafast Ni K-edge absorption to ab initio calculations, we identify an excited state relaxation mechanism where an initial ligand-to-metal charge transfer excitation results in both excited state electron transfer (generating a catalytically relevant reduced photoproduct [Ni(mpo) 2 ] − ) and relaxation to a pseudo-tetrahedral triplet ligand field excited state. From the ultrafast S K-edge absorption, the ligand field excited state is found to be highly delocalized onto the thiolate ligands and a tetrahedral structural distortion is shown to substantially influence the degree of delocalization. The results identify a significant structural coordinate to target when aiming to control the excited state covalency in square planar complexes.

Lim, Hyeongtaek [SLAC National Accelerator Laborat↗
DOE OSTI2021

Powder diffraction

Powder diffraction is a non-destructive technique, which is experimentally simple in principle. Because the physics behind diffraction is well understood, an exceptionally large amount of information can be obtained from a single measurement. The positions and relative intensities of the peaks yield a fingerprint that can be used for qualitative phase analysis. Quantitative phase analysis can be obtained by detailed analysis of the intensities. Unit cells can be derived from the peak positions. Crystal structures can be solved using powder diffraction data and refined by the Rietveld method. The peak profiles contain information about crystallite size, strain and nanostructure. Non-idealities in the intensities give information on texture. Abandoning the crystallographic model provides information about local structure, by pair distribution function analysis. For powder diffraction, everything is a sample; the technique is commonly applied to characterize minerals, ceramics, metals and alloys, catalysts, polymers, pharmaceuticals, organic compounds, environmental and forensic samples, among others. The major features of contemporary laboratory powder diffractometers are described. Methods for obtaining suitable powder specimens are summarized. Major applications of qualitative and quantitative phase analysis, structure solution, size/strain/nanostructure analysis using peak profiles, texture analysis and pair distribution function analysis are introduced.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Intermetallic alloy structure–activity descriptors derived from inelastic X-ray scattering

Synchrotron spectroscopy and Density Functional Theory (DFT) are combined to develop a new descriptor for the stability of adsorbed chemical intermediates on metal alloy surfaces. This descriptor probes the separation of occupied and unoccupied d electron density in platinum and is related to shifts in Resonant Inelastic X-ray Scattering (RIXS) signals. Simulated and experimental spectroscopy are directly compared to show that the promoter metal identity controls the orbital shifts in platinum electronic structure. The associated RIXS features are correlated with the differences in the band centers of the occupied and unoccupied d bands, providing chemical intuition for the alloy ligand effect and providing a connection to traditional descriptions of chemisorption. The ready accessibility of this descriptor to both DFT calculations and experimental spectroscopy, and its connection to chemisorption, allow for deeper connections between theory and characterization in the discovery of new catalysts.

36 MATERIALS SCIENCE↗
DOE OSTI2025

An unexpectedly shrunken bandgap in V2O5 nanoparticles

Synchrotron x-ray spectroscopy was employed to determine the effects of nanostructuring on electronic band structure in V2O5, a promising cathode material and widely used catalyst. V2O5nanoparticle and bulk powders were characterized via P-XRD, electron microscopy, and diffuse reflectance ultraviolet/visible/near-infrared spectroscopy to confirm the optical bandgap. X-ray emission spectroscopy revealed the nanoparticle valence band O 2pstates to be upshifted relative to the bulk, while x-ray absorption spectroscopy and resonant inelastic x-ray scattering showed the lowest V 3dconduction band states to be static. Together, these changes (in conjunction with an increased density of unoccupied lower conduction band states) produce a shrunken bandgap in the V2O5nanoparticles that defies the Burstein-Moss effect. Changes in nanoparticle band structure are generally attributed to oxygen vacancy defects. While nanostructure bandgap reduction is in line with much previous computational work, it is unexpected from most previous experimental results. To our knowledge, this is the first synchrotron x-ray spectroscopy study of a shrunken bandgap achieved in pure V2O5nanoparticles.

Anquillare, E L↗
DOE OSTI2025

A Full-Cell Model for Direct Toluene Electro-Hydrogenation Electrolysis

Liquid organic hydrogen carriers (LOHCs) are organic molecules that undergo a hydrogenation/dehydrogenation cycle to enable storage and transportation of hydrogen fuel under ambient conditions. One promising LOHC candidate is toluene, which can be converted to methylcyclohexane (MCH) electrochemically, enabling a decarbonized process when green electricity is used. In this study, we developed a full-cell model for the direct electro-hydrogenation of toluene to MCH, utilizing a zero-gap membrane electrode assembly architecture. The model incorporates electrochemical kinetics, ionic transport, water transport across the membrane, and mass transport effects. Electrochemical kinetics are characterized using Tafel analysis on Pt/Ru catalyst. The model is validated against experimental data, including polarization curves, Faradaic efficiencies, and water crossover. A voltage breakdown analysis shows that the performance is dominated by kinetic losses, and the model is used to carry out a comparison of different toluene electro-hydrogenation reaction catalysts. Finally, a sensitivity analysis is conducted on key design parameters illustrating which can be modified to maximize electrolyzer performance. The cathode specific surface area and cathode porous transport layer thickness (PTL) have the largest impact on the current density, while the PTL thickness and Pt loading in the PTL have the largest impact on Faradaic efficiency.

Ehlinger, Victoria M. [Lawrence Livermore National↗
DOE OSTI2019

Tafel Fitter v1.5

This program a new physical insight regarding efforts to evaluate electrochemical catalysts being developed for electrochemical energy conversion and storage. In particular, we ask: The methodology described here offers a solution to the problem of how to conduct Tafel analysis, which is used in determining electrocatalyst performance, in a quantitative manner, rather than through the qualitative guesswork it currently requires. This enables the measurement of electrocatalyst Tafel slopes and their associated parameters in a way that avoids the introduction of researcher bias, a problem to which current methods of Tafel fitting are prone. This procedure should significantly improve the ability of researchers working in the field of electrochemical energy conversion to rate and compare the catalyst materials being developed, advancing the characterization toolkit available to experimental electrochemists. This work is born out of our general hypothesis that it should be possible to determine the proper regions for unambiguously fitting Tafel data by applying some set of physical constraints that link aspects of a Tafel plot to its corresponding J-V polarization curve. This algorithm applies such constraints and achieves the extraction of Tafel slopes in a wholly quantifiable and reliable fashion. Verification of this approach is achieved by pairing the theory with experiment, as the algorithm was tested using experimentally acquired data of three distinct, electrochemical reactions: platinum hydrogen evolution, iridium-catalyzed oxygen evolution, and platinum-catalyzed dioxygen reduction. For each of these cases, the algorithm predicts the same Tafel slope as those reported in long-established bodies of electrochemical literature, results suggesting the general applicability of this method for determining electrocatalyst Tafel slopes.

Agbo, Peter↗
DOE OSTI2023

LTE-P-10 RDE

A standardized procedure for rotating disk electrode (RDE) experiments for the ex-situ characterization of oxygen evolution reaction (OER) catalysts for PEM water electrolyzers. This protocol should allow for the analysis of onset potential, overpotential at a fixed current, catalytic activity, and electrochemical surface area of these catalysts.

08 HYDROGEN↗
DOE OSTI2024

Reduction of Iron (III) Oxide in Microwaves Toward Gasification Studies

The purpose of this study is to reduce hematite (Fe2O3) using hydrogen (H2), carbon monoxide (CO), and methane (CH4) gases using microwave irradiation. Conventional temperature programmed reduction of iron phase transformation under H2, CO, and CH4 agree with the literature. Furthermore, the activation energy for the iron phase transformation in a conventional reactor was in the order of H2>CO>CH4, suggesting that CH4 was the best reductant to initiate the reduction at a much lower temperature than CO, and CO was significantly better than H2 atmosphere. Due to the uneven temperature distribution, the apparent activation energy of microwave reduction under H2 was approximately 1/4th when compared to the conventional reduction in H2. X-ray diffraction (XRD) analysis showed a mixed oxide phase in microwave reduction as opposed to the clear phase transformation in conventional studies. To combat the temperature measurement issues in microwave studies, fiber optic sensors and Forward Looking InfraRed (FLIR) sensors were used to acquire the actual temperature distribution in the catalyst bed. Therefore, a reasonably accurate activation energy estimation was achieved in the catalyst bed. Combining these with the characterization and quantification of the different iron phases in microwave reduction will provide a blueprint for future microwave-assisted gasification studies.

Aireddy, Divakar Reddy↗