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All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Metal Phosphide Nanoparticles Generated via a Molecular Precursor Route for Hydrotreatment of Methyl Laurate

Transition metal phosphide nanoparticles supported on silica were used as catalysts to investigate the hydrodeoxygenation of methyl laurate (used as a model compound for vegetable oils). Ni 2 P, Ni 1 Mo 1 P, and Ni 1.6 Mo 0.4 P were synthesized using a molecular precursor route. The nanoparticles were added to the silica support without any changes in their structure or particle size. As a reference and for comparison, MoP/SiO 2 was also prepared by the phosphite method. The prepared catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and chemical analysis. A higher conversion is reached with the MoP/SiO 2 monometallic catalyst, close to that with Ni 1 Mo 1 P/SiO 2 . However, this observation is misleading because the differences in dispersion obscure the result that the intrinsic activity (turnover frequency) of the bimetallic catalyst, prepared by a molecular precursor route, is significantly higher than that of the monometallic catalyst, prepared by the phosphite route, revealing a synergistic effect on the catalytic activity due to the formation of the bimetallic phosphide.

09 BIOMASS FUELS↗
DOE OSTI2023

Surface‐modified Ag@Ru‐P25 for photocatalytic CO 2 conversion with high selectivity over CH 4 formation at the solid–gas interface

Systematic optimization of the photocatalyst and investigation of the role of each component is important to maximizing catalytic activity and comprehending the photocatalytic conversion of CO 2 reduction to solar fuels. A surface-modified Ag@Ru-P25 photocatalyst with H 2 O 2 treatment was designed in this study to convert CO 2 and H 2 O vapor into highly selective CH 4 . Ru doping followed by Ag nanoparticles (NPs) cocatalyst deposition on P25 (TiO 2 ) enhances visible light absorption and charge separation, whereas H 2 O 2 treatment modifies the surface of the photocatalyst with hydroxyl (–OH) groups and promotes CO 2 adsorption. High-resonance transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray absorption near-edge structure, and extended X-ray absorption fine structure techniques were used to analyze the surface and chemical composition of the photocatalyst, while thermogravimetric analysis, CO 2 adsorption isotherm, and temperature programmed desorption study were performed to examine the significance of H 2 O 2 treatment in increasing CO 2 reduction activity. The optimized Ag 1.0 @Ru 1.0 -P25 photocatalyst performed excellent CO 2 reduction activity into CO, CH 4 , and C 2 H 6 with a ~95% selectivity of CH 4 , where the activity was ~135 times higher than that of pristine TiO 2 (P25). For the first time, this work explored the effect of H 2 O 2 treatment on the photocatalyst that dramatically increases CO 2 reduction activity.

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

New Noncentrosymmetric Tetrel Pnictides Composed of Square‐Planar Gold(I) with Peculiar Bonding

Abstract Three novel isostructural equiatomic gold tetrel pnictides, AuSiAs, AuGeP, and AuGeAs, were synthesized and characterized. These phases crystallize in the noncentrosymmetric (NCS) monoclinic space group Cc (no. 9), featuring square‐planar Au within cis ‐[AuTt 2 Pn 2 ] units (Tt=tetrel, Si, Ge; Pn=pnictogen, P, As). This is in drastic contrast to the structure of previously reported AuSiP, which exhibits typical linear coordination of Au with Si and P. Chemical bonding analysis through the electron localization function suggests covalent two‐center two‐electron Tt−Pn bonds, and three‐center Au−Tt−Au and Au−Pn−Au bonds with 1.6 e − per bond. X‐ray photoelectron spectroscopy studies support the covalent and nonionic nature of Au−Pn and Au−Tt bonds. The title materials were found to be n ‐type narrow‐gap semiconductors or semimetals, with nearly temperature‐independent electrical resistivities and low thermal conductivities. A combination of the semimetallic properties with tunable NCS structure provides opportunities for the development of materials based on gold tetrel pnictides.

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

Single Atom Catalysts: A Review of Characterization Methods

Abstract Single atom catalysts (SACs) harbor a potential to exceed nanoparticle catalysts in terms of activity, stability and selectivity in a growing number of chemical reactions. Although their investigation is attracting significant attention, important fundamental questions focusing on key physicochemical properties of SACs (e. g., structure – property relationships, structural dynamics, reaction‐driven restructuring) remain unanswered. A main challenge for research in the field is how to reliably characterize the environments of single atoms in the presence of complicating factors such as low weight loadings, strong metal‐support interactions, and atomic and multiscale heterogeneity of bonding in the single atom sites. This review addresses this challenge – identifying catalytically relevant features of physicochemical properties of single atoms (charge state, electronic structure, atomic configuration, bonding interactions with a support) and surveying advanced tools/methods for characterizing them. The review places a strong emphasis on multimodal methods exploiting X‐ray absorption, emission and photoelectron spectroscopies, and provides several examples from the authors’ research that demonstrate their use as powerful tools for SAC characterization.

Kottwitz, Matthew↗
DOE OSTI2022

The Effect of Surface Terminations on the Initial Stages of TiO 2 Deposition on Functionalized Silicon

As atomic layer deposition (ALD) emerges as a method to fabricate architectures with atomic precision, emphasis is placed on understanding surface reactions and nucleation mechanisms. ALD of titanium dioxide with TiCl 4 and water has been used to investigate deposition processes in general, but the effect of surface termination on the initial TiO 2 nucleation lacks needed mechanistic insights. Here, this work examines the adsorption of TiCl 4 on Cl–, H–, and HO– terminated Si(100) and Si(111) surfaces to elucidate the general role of different surface structures and defect types in manipulating surface reactivity of growth and non-growth substrates. The surface sites and their role in the initial stages of deposition are examined by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Density functional theory (DFT) computations of the local functionalized silicon surfaces suggest oxygen-containing defects are primary drivers of selectivity loss on these surfaces.

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

Revealing the Chemical State of Palladium in Operating In 2 O 3 Gas Sensors: Metallic Pd Enhances Sensing Response and Intermetallic In x Pd y Compound Blocks It

The sensing response of metal oxides activated with noble metal nanoparticles is significantly influenced by changes to the chemical state of corresponding elements under operating conditions. Here, a PdO/rh-In 2 O3 consisting of PdO nanoparticles loaded onto rhombohedral In 2 O 3 was studied as a gas sensor for H 2 gas (100–40000 ppm in an oxygen-free atmosphere) in the temperature range of 25–450 °C. The phase composition and chemical state of elements were examined by resistance measurements combined with synchrotron-based in situ X-ray diffraction and ex situ X-ray photoelectron spectroscopy. As found, PdO/rh-In 2 O 3 undergoes a series of structural and chemical transformations during operation: from PdO to Pd/PdH x and finally to the intermetallic In x Pd y phase. The maximal sensing response (R N2 /R H2 ) of ~5 · 10 7 towards 40000 ppm (4 vol %) H 2 at 70 °C is correlated with the formation of PdH 0.706 /Pd. The In x Pd y intermetallic compounds formed around 250 °C significantly decrease the sensing response.

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

Photodetachment Dynamics and Structural Flexibility of Undercoordinated Iridium Halides IrCl n − (n = 3−5): An Experimental and Theoretical Investigation

Three undercoordinated iridium chloride anions, IrCl n − (n = 3–5), and their neutral counterparts were investigated by cryogenic anion photoelectron spectroscopy and theoretical calculations. Photodetachment of IrCl n − leads to the formation of the corresponding neutral complex, i.e., a triplet ground state for n = 3, a quartet for n = 4, and close-lying singlet and triplet for n = 5. The vertical detachment energies are determined to be 3.89, 4.98, and 5.14 eV for n = 3, 4, and 5, respectively, revealing superhalogen anion properties with increasing electron detachment energies as chloride ligands added. The IrCl 3 − spectrum features an extremely broad, lowest electron binding energy band, attributed to resonant autodetachment with prominent non-Franck–Condon profiles. In IrCl 5 − , detachment prompts a d-orbital rearrangement that drives a structural transformation from a twisted square-based pyramidal to a trigonal–bipyramidal geometry in the singlet state. In conclusion, these findings provide insights into the electronic and structural adaptability of iridium halides, advancing our understanding of ligand exchange reactions and dissociative stability in transition metal complexes.

Tang, Peng [East China Normal Univ. (ECNU), Shangh↗
DOE OSTI2020

Probing the Li 4 Ti 5 O 12 Interface Upon Lithium Uptake by Operando Small Angle Neutron Scattering

The formation of a solid–electrolyte interphase (SEI) on the surface of Li 4 Ti 5 O 12 (LTO) has become a highly controversial topic, with arguments for it and against it. However, prior studies supporting the formation of an SEI layer have typically suggested that a layer forms upon cycling of a cell, although the layer is probed after disassembling. In this study, cubic mesostructured LTO is synthesized with crystallite domain sizes between 3 and 4 nm and uniform pores with diameters ≤8 nm. The mean pore size is controlled between 4–8 nm through the use of a triblock amphipathic copolymer with a tunable hydrophobic block as template and by thermal treatment. The LTO morphology obtained is spherical and evolves upon heat treatment. We report these materials show excellent electrochemical performance, including high rate capability and capacity retention. The LTO material is subjected to operando small-angle neutron scattering and X-ray photoelectron spectroscopy experiments, which reveal that the highly debated SEI forms at potentials as high as 2.2 V, first as a LiF-rich layer and subsequently by the growth of a carbonaceous layer. These SEI products form first on the smaller pores before forming on the mesopores.

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

Elucidating the Active Site and the Role of Alkali Metals in Selective Hydrodeoxygenation of Phenols over Iron-Carbide-based Catalyst

In this study, iron-carbide-based catalysts have been explored in the selective hydrodeoxygenation (HDO) of phenol, aiming at elucidating the role of active site and alkali metal. Complementary characterization such as X-ray diffraction, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and scanning transmission electron microscopy coupled with electron energy loss spectroscopy, together with catalytic evaluations revealed a rapid structural reconstruction of iron carbide (Fe 3 C) catalysts, leading to a stable defective graphene-covered metallic Fe active phase (G@Fe) under reaction conditions. Further studies using different alkali metals (i.e., Na, K, and Cs) revealed that alkali metals showed negligible effect on the phase transformation of Fe 3 C. However, the reconstructed G@Fe doped with alkali metals inhibited the tautomerization, a facile reaction pathway to saturation of the aromatic ring, leading to enhanced selectivity to arene. The extent of inhibition of tautomerization or selectivity to arene was closely related to the degree of electron donation of alkali metal to Fe.

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

Disordered Au Nanoclusters for Efficient Ammonia Electrosynthesis

The electrochemical nitrogen (N 2 ) reduction reaction (N 2 RR) under mild conditions is a promising and environmentally friendly alternative to the traditional Haber-Bosch process with high energy consumption and greenhouse emission for the synthesis of ammonia (NH 3 ), but high-yielding production is rendered challenging by the strong nonpolar N≡N bond in N 2 molecules, which hinders their dissociation or activation. In this study, disordered Au nanoclusters anchored on two-dimensional ultrathin Ti 3 C 2 T x MXene nanosheets are explored as highly active and selective electrocatalysts for efficient N 2 -to-NH 3 conversion, exhibiting exceptional activity with an NH 3 yield rate of 88.3±1.7 μg h –1 mg cat. –1 and a faradaic efficiency of 9.3±0.4 %. Further, a combination of in situ near-ambient pressure X-ray photoelectron spectroscopy and operando X-ray absorption fine structure spectroscopy is employed to unveil the uniqueness of this catalyst for N 2 RR. The disordered structure is found to serve as the active site for N 2 chemisorption and activation during the N 2 RR process.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Chemical and Electrochemical Characterization of Hot–Pressed Li 6 PS 5 Cl Solid State Electrolyte: Operating Pressure–Invariant High Ionic Conductivity

Sulfide solid state electrolytes (SSE) are among the most promising materials in the effort to replace liquid electrolytes, largely due to their comparable ionic conductivities. Among the sulfide SSEs, Argyrodites (Li 6 PS 5 X, X=Cl, Br, I) further stand out due to their high theoretical ionic conductivity (~1×10 –2 S cm –1 ) and interfacial stability against reactive metal anodes such as lithium. Generally, solid state electrolyte pellets are pressed from powder feedstock at room temperature, however, pellets fabricated by cold pressing consistently result in low bulk density and high porosity, facilitating interfacial degradation reactions and allowing dendrites to propagate through the pores and grain boundaries. Here, we demonstrate the mechanical and electrochemical implications of hot-pressing standalone LPSCl SSE pellets with near-theoretical ionic conductivity, superior cycling performance, and enhanced mechanical stability. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and x-ray diffraction spectroscopy (XRD) analysis reveal no chemical changes to the Argyrodite surface after hot pressing up to 250°C. Furthermore, we use electrochemical impedance spectroscopy (EIS) to understand mechanical stability of Argyrodite SSE pellets as a function of externally applied pressure, demonstrating for the first time pressed standalone Argyrodite pellets with near-theoretical conductivities at external pressures below 14 MPa.

25 ENERGY STORAGE↗
DOE OSTI2025

Active and Stable PtPd Diesel Oxidation Catalysts under Industry‐Defined Test Protocols

Nanoparticle-supported Pt and Pd catalysts are employed industrially to convert CO and hydrocarbon residue from incomplete diesel fuel combustion into more environmentally-benign products. However, these catalysts deactivate over time due to sintering, especially for Pt nanoparticles which readily generate volatile species under high operating temperatures. Here, we turned the detrimental vapor-mediated sintering of Pt into an advantage by using a physical mixture of Pt and Pd catalysts prepared using a raspberry-colloid-templating (RCT) method. The RCT method produced Pt/Al 2 O 3 and Pd/Al 2 O 3 catalysts with partially embedded NPs to inhibit surface-mediated sintering pathways. As validated using an industry-defined emission control test protocol, aging a physical mixture of Pt/Al 2 O 3 and Pd/Al 2 O 3 at high temperature produced an alloyed PtPd/Al 2 O 3 catalyst that outperformed the fresh catalyst mixture and both individual catalysts for hydrocarbon conversion, while exhibiting high catalytic stability and resistance to sintering and to SO 2 poisoning. X-ray photoelectron spectroscopy revealed that in the aged catalyst mixture, half of the Pd content existed in the more active metallic state, compared to the less active oxide forms in the fresh mixture and both individual catalysts, explaining the unusual activity enhancement. Our results represent a practical approach to producing active and stable PtPd/Al 2 O 3 diesel oxidation catalysts for emission control applications.

Lim, Kang Rui Garrick [Harvard University, Cambrid↗
DOE OSTI2020

Surface modification of bamboo fiber with sodium hydroxide and graphene oxide in epoxy composites

Bamboo fibers (BFs) have high mechanical properties and are candidate reinforcement for epoxy matrix composites. However, to improve performance, good fiber-matrix interaction is required. In this work, unidirectional long BF reinforced epoxy composites at fiber volume content of 22%, 40%, and 50% were made by compression molding. The 40 v% untreated BF reinforced composites exhibited 107% and 439% increase for flexural strength and modulus, respectively, compared to neat epoxy. Sodium hydroxide (NaOH) treatment was used to modify the surface of the BFs, and then the NaOH modified BFs were coated with graphene oxide (GO). The 40 v% NaOH modified BF composites showed an improvement from 259.9 to 327.5 MPa for flexural strength and from 16.7 to 21.5 GPa for flexural modulus, compared to 40 v% untreated BF composites. Slight improvement in properties up to 334.6 MPa for flexural strength and up to 23.8 GPa for flexural modulus was achieved for composites made of 40 v% NaOH/GO modified BF. Surface modification of BF after the NaOH and NaOH/GO treatment was confirmed by X-ray photoelectron spectroscopy and by scanning electron microscopy, which showed differences on the fiber surface morphology and on the composite fracture surface. This BF surface modification approach with GO has potential to impart other properties beyond mechanical to produce multifunctional composite and lead to the use of sustainable plant fibers as alternatives to synthetic fibers.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Definition of a new (Doniach-Sunjic-Shirley) peak shape for fitting asymmetric signals applied to reduced graphene oxide/graphene oxide XPS spectra

The existence of asymmetry in X-ray photoelectron spectroscopy (XPS) photoemission lines is widely accepted, but line shapes designed to accommodate asymmetry are generally lacking in theoretical justification. Here in this work, we present a new line shape for describing asymmetry in XPS signals that is based on two facts. First, the most widely known line shape for fitting asymmetric XPS signals that has a theoretical basis, referred to as the Doniach-Sunjic (DS) line shape, suffers from a mathematical inconvenience, which is that for asymmetric shapes the area beneath the curve (above the x-axis) is infinite. Second, it is common practice in XPS to remove the inelastically scattered background response of a peak in question with the Shirley algorithm. The new line shape described herein attempts to retain the theoretical virtues of the DS line shape, while allowing the use of a Shirley background, with the consequence that the resulting line shape has a finite area. To illustrate the use of this Doniach-Sunjic-Shirley (DSS) line shape, a set of spectra obtained from varying amounts of graphene oxide (GO) and reduced GO on a patterned, heterogeneous surface are fit and discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Surface analysis insight note: Synthetic line shapes, integration regions and relative sensitivity factors

Here, methods for estimating photoemission intensity from X-ray photoelectron spectroscopy data are examined. The role played by “synthetic” bell-shaped curves, integration intervals, background curves, and the use of relative sensitivity factors (RSFs) in reporting percentage atomic concentration for a sample is presented. In particular, photoemission lines with differing energy distributions obtained from the NaCl sample surface are used to demonstrate how a comparison of photoemission intensities is dependent on the line shapes, background curves, and appropriate use of RSFs.

42 ENGINEERING↗
DOE OSTI2024

Surface science insight note: A linear algebraic approach to elucidate native films on Fe 3 O 4 surface

Standard materials are often used to obtain spectra that can be compared to those from unknown samples. Spectra measured from these known substances are also used as a means of computing sensitivity factors to allow quantification by X-ray photoelectron spectroscopy (XPS) of less well-defined materials. Spectra from known materials also provide line shapes suitable for inclusion in spectral models which, when fitted to spectra, permit the chemical state for a sample to be assessed. Both types of information depend on isolating photoemission signals from the inelastically scattered signal. In this Insight note, technical issues associated with the use of XPS of as received Fe 3 O 4 powder sample surface are discussed. The Insight note is designed to show how linear algebraic techniques applied to data collected from a sample marketed as pure Fe 3 O 4 powder are used to verify that XPS has been performed on chemistry representative of the sample. The methods described in this Insight note can further be utilized in elucidating complex XPS data obtained from thin films formed or evolved during cyclic/non-steady use of complex (electro)catalyst surfaces, especially in the presence of contaminants.

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

Deriving Stable Peak Models to Fit Complex XPS Data From Cu Contaminated Pt Electrocatalysts

X-ray Photoelectron Spectroscopy spectra peak models, designed to partition photoemission signals emanating from different elements or chemical states within an atom, are fitted to data limited to an energy interval over which inelastically scattered photoemission signal can be estimated. While the choice of background approximation and line shapes of components to the peak model requires careful consideration, the energy interval used to define the data to which the peak model is optimized has a significant impact on the final peak model. The relationship between the background intensity and data intensity at the start and end of the energy interval dictates the line shapes used in the peak model. In this work, we devise a method to peak fit a complex overlapping Cu 3p and Pt 4f XPS peak structure to perform the elemental quantification. We first use an Al 2s peak to illustrate how background curves approach data at the limits of the energy interval over which the background is defined, influencing the analysis of XPS spectra. Next, we demonstrate the nature of interactions between specific line shapes (Voigt and pseudo-Voigt profiles) suitable for photoemission peaks and a specific background curve (Shirley) and a peak model is presented that includes components to the peak model that accommodates background intensity during fitting of the peak model to data. The peak model allowed for quantification of the contributions of Pt 4f peaks emanating from the substrate that exhibits strong asymmetry in the presence of the inhomogeneously distributed Cu species, mostly of Lorentzian character.

XPS↗