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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

Conversion of CO 2 to Methanol and Ethanol on Pt/CeO x /TiO 2 (110): Enabling Role of Water in C–C Bond Formation

The surface chemistry of alcohol synthesis from CO 2 hydrogenation has been investigated using kinetic testing, ambient pressure x-ray photoelectron spectroscopy (AP-XPS) and DFT calculations over a multicomponent system where Pt and ceria nanoparticles coexisted on a titania template, Pt/CeO x /TiO 2 (110). Due to its high ability to bind and activate CO 2 , not seen for typical Cu-ZnO catalysts, the Pt-CeO x -TiO 2 interface is excellent for the hydrogenation of CO 2 to methanol with some ethanol also being produced (21% selectivity). The results of AP-XPS and DFT calculations indicate that the active state involves a mixture of Ti 4+ /Ti 3+ , Ce 3+ and Pt 0 /Pt + . A fast pathway for the formation of CH 3 O species is only plausible when Ce 3+ and Pt are present. The addition of water to the reaction feed facilitates the first hydrogenation of CO 2 and substantially enhances the surface coverage of C-containing species (CH 3 O, HCOO, CO 3 , CH x ), facilitating the formation of C-C bonds and the production of ethanol (38% selectivity).

36 MATERIALS SCIENCE↗
DOE OSTI2024

Single-Atom Alloy Formation via Reaction-Driven Catalyst Restructuring

We demonstrate that single-atom alloy catalysts can be made by exposing physical mixtures of monometallic supported Cu and Pd catalysts to vinyl acetate (VA) synthesis reaction conditions. This reaction induces the formation of mobile clusters of metal diacetate species that drive extensive metal nanoparticle restructuring, leading to atomic dispersion of the precious metal, smaller nanoparticle sizes than the parent catalysts, and high activity and selectivity for both VA synthesis and ethanol dehydrogenation reactions. As a result, this approach is scalable and appears to be generalizable to other alloy catalysts.

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

A General Strategy to Immobilize Single‐Atom Catalysts in Metal–Organic Frameworks for Enhanced Photocatalysis

Abstract Single‐atom catalysts (SACs) are witnessing rapid development due to their high activity and selectivity toward diverse reactions. However, it remains a grand challenge in the general synthesis of SACs, particularly featuring an identical chemical microenvironment and on the same support. Herein, a universal synthetic protocol is developed to immobilize SACs in metal–organic frameworks (MOFs). Significantly, by means of SnO 2 as a mediator or adaptor, not only different single‐atom metal sites, such as Pt, Cu, and Ni, etc., can be installed, but also the MOF supports can be changed (for example, UiO‐66‐NH 2 , PCN‐222, and DUT‐67) to afford M 1 /SnO 2 /MOF architecture. Taking UiO‐66‐NH 2 as a representative, the Pt 1 /SnO 2 /MOF exhibits approximately five times higher activity toward photocatalytic H 2 production than the corresponding Pt nanoparticles (≈2.5 nm) stabilized by SnO 2 /UiO‐66‐NH 2 . Remarkably, despite featuring identical parameters in the chemical microenvironment and support in M 1 /SnO 2 /UiO‐66‐NH 2 , the Pt 1 catalyst possesses a hydrogen evolution rate of 2167 µmol g –1 h –1 , superior to the Cu 1 and Ni 1 counterparts, which is attributed to the differentiated hydrogen binding free energies, as supported by density‐functional theory (DFT) calculations. This is thought to be the first report on a universal approach toward the stabilization of SACs with identical chemical microenvironment on an identical support.

Sui, Jianfei↗
DOE OSTI2026

Effect of Initiator Density, Catalyst Concentration, and Surface Curvature on the Uniformity of Polymers Grafted from Spherical Nanoparticles

Polymer-grafted nanoparticles (PGNPs) are versatile hybrid materials whose properties critically depend on brush dimensions, uniformity, and grafting density. Herein, we systematically investigated how initiator density, catalyst concentration, and nanoparticle curvature govern the growth of poly(methyl methacrylate) (PMMA) brushes grafted from spherical SiO 2 nanoparticles via surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (SI-ARGET ATRP). By tuning the initiator density through a combination of “active” and “dummy” silane initiators anchored on the nanoparticles’ surface and controlling the catalyst concentration, we reveal that increased initiator crowding and smaller surface curvature amplify steric hindrance, leading to decreased initiation efficiency and broader molecular weight distributions. Correlation with the corresponding unattached chains by ARGET ATRP suggests the presence of permanently inaccessible (“buried”) initiation sites, which are a characteristic of surface-grafted systems. At sufficient Cu catalyst concentrations, uniform brush growth is attained across different initiator densities, whereas decreased catalyst concentrations accentuate nonconcurrent initiation and propagation. These findings provide mechanistic insights into the interplay of initiator density, catalyst concentration, and surface curvature, offering design principles for tailoring the PGNP architecture. These results can guide the structural engineering of densely grafted surfaces, including nanoparticles and flat substrates, for applications in nanocomposites, photonics, and functional coatings.

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

Elemental fractionation in aerosol laser-induced breakdown spectroscopy with nanosecond and femtosecond laser ablation

For the purpose of realizing atmospheric radiation plume tracking, laser-induced breakdown spectroscopy (LIBS) was performed to characterize Cs atomic emissions from airborne nanoparticles in a binary particle matrix using nanosecond and femtosecond laser ablation. As a surrogate to multi-element nuclear fallout particulates, both Cs and Na solutions were mixed with Cu at a 1:1.45 M concentration ratio and aerosolized to study elemental fractionation in atomic emissions, revealing Na I resonance emissions are enhanced whereas Cs I resonance emissions are reduced with Cu present despite sharing similar electronic and chemical properties. Femtosecond laser ablation reduced elemental fractionation effects by more than 50% while retaining the same temporal fractionation trends for Cs and Na. The origin of elemental fractionation in aerosol LIBS was further investigated using Al and Ti aerosols which revealed that the particle matrix induces changes to the local plasma temperature, population of atomic states, and subsequent molecular association and emission.

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

Predicting metal–metal interactions. I. The influence of strain on nanoparticle and metal adlayer stabilities

Strain-engineering of bimetallic nanomaterials is an important design strategy for developing new catalysts. In this paper, we introduce an approach for including strain effects into a recently introduced, density functional theory (DFT)-based alloy stability model. The model predicts adsorption site stabilities in nanoparticles and connects these site stabilities with catalytic reactivity and selectivity. Strain-based dependencies will increase the model’s accuracy for nanoparticles affected by finite-size effects. In addition to the stability of small nanoparticles, strain also influences the heat of adsorption of epitaxially grown metal-on-metal adlayers. In this respect, we successfully benchmark the strain-including alloy stability model with previous experimentally determined trends in the heats of adsorption of Au and Cu adlayers on Pt (111). For these systems, our model predicts stronger bimetallic interactions in the first monolayer than monometallic interactions in the second monolayer. We explicitly quantify the interplay between destabilizing strain effects and the energy gained by forming new metal–metal bonds. While tensile strain in the first Cu monolayer significantly destabilizes the adsorption strength, compressive strain in the first Au monolayer has a minimal impact on the heat of adsorption. Hence, this study introduces and, by comparison with previous experiments, validates an efficient DFT-based approach for strain-engineering the stability, and, in turn, the catalytic performance, of active sites in bimetallic alloys with atomic level resolution.

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

Revealing High-Temperature Reduction Dynamics of High-Entropy Alloy Nanoparticles via In Situ Transmission Electron Microscopy

Understanding the behavior of high-entropy alloy (HEA) materials under hydrogen (H 2 ) environment is of utmost importance for their promising applications in structural materials, catalysis, and energy-related reactions. Herein, the reduction behavior of oxidized FeCoNiCuPt HEA nanoparticles (NPs) in atmospheric pressure H-2 environment was investigated by in situ gas-cell transmission electron microscopy (TEM). The reduction reaction front was maintained at the external surface of the oxide. During reduction, the oxide layer expanded and transformed into porous structures where oxidized Cu was fully reduced to Cu NPs while Fe, Co, and Ni remained in the oxidized form. In situ chemical analysis showed that the expansion of the oxide layer resulted from the outward diffusion flux of all transition metals (Fe, Co, Ni, Cu). Revealing the H-2 reduction behavior of HEA NPs facilitates the development of advanced multicomponent alloys for applications targeting H 2 formation and storage, catalytic hydrogenation, and corrosion removal.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

A Metal-on-Metal Growth Approach to Metal–Metal Oxide Core–Shell Nanostructures with Plasmonic Properties

Hybrid core–shell nanoparticles integrate the material properties from individual components; however, the synthesis of core–shell nanoparticles with dissimilar materials remains challenging. Herein, we applied a metal-on-metal thin film growth approach to control the conformal deposition of non-precious metal shells on the Cu-based metal cores to form core–shell structures of metal–metal oxide hybrids (M–M'O x , where M = AuCu 3 or Cu, M' = Fe, Mn, and Ni). The deposition kinetics were controlled by a temperature-regulated thermal decomposition of zerovalent transition metal complexes. It is predicted that the conformal deposition can be promoted by keeping the initial deposition temperature close to the thermal decomposition temperature of the zerovalent precursors. The mechanisms of strain reduction and interdiffusion facilitate conformal deposition over island growth in the synthesis with slow reaction kinetics. This study provides insightful guidance to metal-on-metal growth in solution at the nanoscale and thus the seed-mediated approach to hybrid core–shell structures. The optical properties of these metal–metal oxide hybrids were investigated experimentally and interpreted by theoretical simulations. Despite damping effects, the plasmonic properties of these Cu-based core-metal oxide shell structures may have the potential to enable plasmon-enhanced applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Dynamic Behavior of Pt Multimetallic Alloys for Active and Stable Propane Dehydrogenation Catalysts

Improving the use of platinum in propane dehydrogenation catalysts is a crucial aspect to increasing the efficiency and sustainability of propylene production. A known and practiced strategy involves incorporating more abundant metals in supported platinum catalysts, increasing its activity and stability while decreasing the overall loading. Here, using colloidal techniques to control the size and composition of the active phase, we show that Pt/Cu alloy nanoparticles supported on alumina (Pt/Cu/Al 2 O 3 ) displayed elevated rates for propane dehydrogenation at low temperature compared to a monometallic Pt/Al 2 O 3 catalyst. We demonstrate that the enhanced catalytic activity is correlated with a higher surface Cu content and formation of a Pt-rich core and Cu-rich shell that isolates Pt sites and increases their intrinsic activity. However, rates declined on stream because of dynamic metal diffusion processes that led to a more uniform alloy structure. This transformation was only partially inhibited by adding excess hydrogen to the feed stream. Instead, cobalt was introduced to provide trimetallic Pt/Cu/Co catalysts with stabilized surface structure and stable activity and higher rates than the original Pt/Cu system. In conclusion, the structure–activity relationship insights in this work offer improved knowledge of propane dehydrogenation catalyst development featuring reduced Pt loadings and notable thermal stability for propylene production.

Alloys↗
DOE OSTI2021

First-principles design of a single-atom–alloy propane dehydrogenation catalyst

The complexity of heterogeneous catalysts means that a priori design of new catalytic materials is difficult, but the well-defined nature of single-atom–alloy catalysts has made it feasible to perform unambiguous theoretical modeling and precise surface science experiments. Herein we report the theory-led discovery of a rhodium-copper (RhCu) single-atom–alloy catalyst for propane dehydrogenation to propene. Although Rh is not generally considered for alkane dehydrogenation, first-principles calculations revealed that Rh atoms disperse in Cu and exhibit low carbon-hydrogen bond activation barriers. Surface science experiments confirmed these predictions, and together these results informed the design of a highly active, selective, and coke-resistant RhCu nanoparticle catalyst that enables low-temperature nonoxidative propane dehydrogenation.

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

Iterative redox activation promotes interfacial synergy in an Ag/Cu x O catalyst for oxygen reduction

In this study, an iterative electrochemical activation process is demonstrated to maximize the interface between Ag and Cu x O. Morphological reconstruction and phase transformation of Cu x O occurs through the iterative electrochemical redox reaction, as indicated by energy-dispersive spectroscopy and X-ray photoelectron spectroscopy. The activated Ag/Cu x O/C catalysts exhibits enhanced oxygen reduction reaction performance, with an onset potential of 0.86 V vs. the reversible hydrogen electrode, a Tafel slope of 46mV dec -1 , and a high stability as compared to Ag/C. A mechanistic study using density functional theory shows that the weakened binding energy of the OH intermediate, originating from the charge transfer from Ag to Cu x O, improves the ORR activity at the interface sites of the Ag/Cu x O electrocatalysts. Ag/Cu x O shows a higher limiting potential of 0.14V for interface sites than isolated Ag nanoparticles. The interfacial charge transfer between Ag and CuO is verified experimentally.

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

Surface facet dependence of competing alloying mechanisms

Metal alloys are ubiquitous in many branches of heterogeneous catalysis, and it is now fairly well established that the local atomic structure of an alloy can have a profound influence on its chemical reactivity. While these effects can be difficult to probe in nanoparticle catalysts, model studies using well defined single crystal surfaces alloyed with dopants enable these structure–function correlations to be drawn. The first step in this approach involves understanding the alloying mechanism and the type of ensembles formed. In this study, we examined the atomic structure of RhCu single-atom alloys formed on Cu(111), Cu(100), and Cu(110) surfaces. Our results show a striking difference between Rh atoms alloying in Cu(111) vs the more open Cu(100) and Cu(110) surface facets. Unlike Cu(111) on which Rh atoms preferentially place-exchange with Cu atoms in the local regions above step edges leaving the majority of the Cu surface free of Rh, highly dispersed, homogeneous alloys are formed on the Cu(100) and (110) surfaces. These dramatically different alloying mechanisms are understood by quantifying the energetic barriers for atomic hopping, exchange, swapping, and vacancy filling events for Rh atoms on different Cu surfaces through theoretical calculations. Density functional theory results indicate that the observed differences in the alloying mechanism can be attributed to a faster hopping rate, relatively high atomic exchange barriers, and stronger binding of Rh atoms in the vicinity of step edges on Cu(111) compared to Cu(110) and Cu(100). Furthermore, these model systems will serve as useful platforms for examining structure sensitive chemistry on single-atom alloys.

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

Carbon nanotubes decorated with Pt as a viable electrocatalyst system using electrochemical atomic layer deposition

Surface limited redox replacement (SLRR) is an electrochemical deposition method designed to deposit metal thin films, typically onto other metals, that are mere monolayers in thickness, where such low dimensions allows catalyst-support interactions to affect catalyst efficiency. Here we explore the growth of Pt, using iterative Cu-mediated SLRR cycles, directly onto carbon nanotubes (CNTs) which are potentially good candidates as electrocatalyst supports due to their electrical conductivity and chemical resistance. Here scanning electron microscope images showed that Pt grew as nanoparticles, and hydrogen underpotential deposition from cyclic voltammetry showed that the active surface area approached an asymptotic value around eight iterations. Catalytic activity, measured using the oxygen reduction reaction, reached a maximum at ten iterations. Both are shown to be influenced by the growth mode, but electrochemical modeling indicates that the trend in activity is also due to a change in activation energy, possibly due to changes in Pt electronic structure due to interactions with the CNTs. Durability cycling showed a greater than 85% retention of surface area for the first 10,000 cycles of accelerated stress testing but decayed steadily to about 50% after 30,000 cycles. This performance may be related to the phenomenon that limits surface area growth.

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

PdCu Single Atom Alloys for the Selective Oxidation of Methanol to Methyl Formate at Low Temperatures

The selective catalytic oxidation of methanol to methyl formate (MF) has been considered as an attractive route to produce MF, an important precursor in the chemical industry. Although supported Pd nanoparticles are active for the selective oxidation of methanol to MF, the relatively low MF selectivity and yield remains an unsolved issue. Here in this paper, we show that adding a small amount of Pd into Cu forming PdCu single atom alloy (SAA) catalysts can catalyze the oxidation of methanol to MF selectively at low temperatures, with a high catalyst stability. The atomic dispersion of Pd atoms in the Cu matrix was confirmed by various in-situ characterization techniques. The activity and selectivity of PdCu SAA catalysts were compared to monometallic Cu and Pd catalysts, in a flow reactor at similar conditions. This work may guide the design of new SAA based catalysts for selective oxidation reactions.

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

Chapter 14: Surface plasmon resonance enhanced artificial photosynthesis of chemical fuels for energy storage

Nanostructured noble metals such as Au, Ag, and Cu have interesting optical properties because of the oscillation motions of their surface electrons upon strong coupling with light under resonance conditions. This resonant oscillation motion of conduction electrons refers to surface plasmon resonance (SPR) and localized SPR (LSPR) when localized near the surface of a nanoparticle. The extinction spectrum of a solution of plasmonic nanoparticles has tunable wavelength responses from UV to NIR due to strong light scattering and absorption which are highly sensitive to the permittivity of the nanoparticles, their sizes and shapes, and chemical environment. Strong light scattering due to the LSPR of plasmonic nanoparticles creates a strong localized and far-field intensity capable of enhancing light absorption characteristics of a chromophore near a plasmonic surface. Engineering the chromophores’ radiative decay dynamics can be done by 1) increasing its radiative decay rate to increase its photoluminescence intensity and 2) increasing its nonradiative decay rates associated to direct charge transfer to the metal surface. Such interesting photophysical properties of a chromophore can be extended to other light-absorbing materials such as semiconductor thin films and nanostructures. This plasmonic effect on the photophysics of a light-absorbing material can be theoretically and experimentally validated. The phenomenon has also been applied to advanced optoelectronic devices such as organic light-emitting diodes (OLED)1 and organic photovoltaics (OPV).2-4 The local field created by the SPR can provide an intense EM field to enhance photoluminescence emission of an organic chromophore5-8 and Raman scattering of an organic molecule, and single-molecule Raman9-10 can be detected on specially designed LSPR substrate. (Figure 1 on SPR for energy) Recent studies suggest that LSPR can be incorporated in light-harvesting and conversion systems to increase energy conversion in a solar cell and photoelectrochemical cell and chemical transformations of CO2 to chemical fuels.11-12 Plasmonic active metals naturally exhibit catalytic activities for electrochemical fuel conversion that can be enhanced by engineering their structures to form unique catalytic structures such as symmetry-broken Au-Cu Janus nanocrystals.13 These studies are critical to addressing the global challenges of energy14-15 and CO2 emission from nonrenewable sources such as coal, petroleum, and natural gas.16-17 Electrochemical systems comprised of unique photonic structures and functions that enable efficient and affordable energy harvesting/conversion/storage are highly desired for providing safe and environment-friendly energy sources. This chapter reviews our recent work of LSPR enabled photoelectrochemical water splitting and recent advances in LSPR-enabled CO2 reduction and photochemical reactions reported in the literature. Scientific and technical challenges of applying LSPR to enhance these energy conversion and storage systems are discussed at the conclusion of this chapter.

Pan, Shanlin↗
DOE OSTI2024

Hydrogen activation by rhodium under the cover of a copper oxide thin film

Here, the activation of reactants by catalytically active metal sites at metal-oxide interfaces is important for understanding the effect of metal-support interactions on nanoparticle catalysts and for tuning activity and selectivity. Using a combined experimental and theoretical approach, we studied the activation of H 2 and the effect of CO poisoning on isolated Rh atoms completely or partially covered by a copper oxide (Cu 2 O) thin film. Temperature-programmed desorption (TPD) experiments conducted in ultra-high vacuum (UHV) show that neither a partially nor a fully oxidized Cu 2 O layer grown on a Rh/Cu(111) single-atom alloy can activate hydrogen in UHV. However, in situ ambient pressure X-ray photoelectron spectroscopy (AP-XPS) experiments performed at elevated H 2 pressures reveal that Rh significantly accelerates the reduction of these Cu 2 O thin films by hydrogen. Remarkably, the fastest reduction rate is observed for the fully oxidized sample with all Rh sites covered by Cu 2 O. Both TPD and AP-XPS data demonstrate that these covered Rh sites are inaccessible to CO, indicating that Rh under Cu 2 O is active for H 2 dissociation but cannot be poisoned by CO. In contrast, an incomplete oxide film leaves some of the Rh sites exposed and accessible to CO, and hence prone to CO poisoning. Density functional theory calculations demonstrate that unlike many reactions in which hydrogen activation is rate limiting, the rate-determining step in the dissociation of H 2 on thin-film Cu 2 O with Rh underneath is the adsorption of H 2 on the buried Rh site, and once adsorbed, the dissociation of H 2 is barrierless. These calculations also explain why H 2 can only be activated at higher pressures. Together, these results highlight how different the reactivity of atomically dispersed Rh in Cu can be depending on its accessibility through the oxide layer, providing a way to engineer Rh sites that are active for hydrogen activation but resilient to CO poisoning.

36 MATERIALS SCIENCE↗