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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Photodissociation and Infrared Spectroscopy of U + (CO 2 ) n , UO + (CO 2 ) n , and UO 2+ (CO 2 ) n Cation-Molecular Complexes

Laser vaporization of uranium in a pulsed supersonic expansion of carbon dioxide is used to produce complexes of the form U + (CO 2 ) n , UO + (CO 2 ) n , and UO 2+ (CO 2 ) n . These ions are selected in a reflectron time-offlight mass spectrometer and studied with visible laser photodissociation and tunable infrared laser photodissociation spectroscopy in the region of the CO 2 antisymmetric stretch. The dissociation patterns and spectroscopy of these ions indicate that CO 2 ligands are intact molecules. Although reaction products that form oxide-carbonyl or oxalate species are predicted to be stable, there is no direct evidence in the frequency range studied for the formation of these species. There is no clear indication for the coordination numbers for singly charged uranium and its oxide complexes with CO 2 . However, there is strong support in the vibrational patterns for an eight-coordinate complex of the doubly charged UO 2+ species, i.e., UO 2+ (CO 2 ) 8 .

Cluster chemistry↗
DOE OSTI2025

Photoactivation Transition State and Dynamical Response of the Orange Carotenoid Protein

The orange carotenoid protein (OCP) regulates light harvesting in cyanobacteria by acting as a photoreceptor in its resting form, OCP O , and by effecting the quenching of bilin excitons upon binding to the core of the phycobilisome in its photoactivated red form, OCP R . We show herein using fluorescence anisotropy measurements and the action spectra for the rate constants of the two light-driven steps in the mechanism that the photoactivation of the OCP from Synechocystis sp. PCC 6803 is triggered by excited-state motions of the canthaxanthin chromophore that yield a twisted and bent conformation. Well-tempered metadynamics simulations reveal that a bicycle-pedal configuration, due to twisting of the two adjacent C=C bonds at the C13−C14 and C15−C15′ positions in the center of canthaxanthin’s π-conjugated isoprenoid backbone, can be accommodated by the binding site in the OCP, with the energy of a captured photon required to cross the local activation energy barriers from the dark equilibrium structure. The bicycle-pedal configuration breaks the conserved hydrogen-bonding interactions between the carbonyl substituent of the β-ionone end ring of canthaxanthin and the adjacent W288 and Y201 residues in the C-terminal domain. The action spectra are modulated by the vibronic excitation prepared by absorption transitions to the S 2 state, indicating that the photoactivation reactions are triggered by the canthaxanthin chromophore well prior to vibrational equilibration. These findings show that an ultrafast structural response of the OCP protein to the excited-state motions of the canthaxanthin chromophore controls the photoactivation yield and the sensing of blue light.

Fluorescence↗
DOE OSTI2021

Computational Investigation of the Catalytic Hydrodeoxygenation of Propanoic Acid over a Cu(111) Surface

Cu-based alloy catalysts have recently been investigated experimentally for the hydrodeoxygenation (HDO) of biomass-derived organic acids. Here, the HDO of propanoic acid (PAc) has been studied over Cu(111) by mean-field microkinetic modeling based on parameters obtained from first-principles calculations. Models were developed for the gas- and liquid-phase HDO in condensed water and 1,4-dioxane. In agreement with experimental observations, the gas-phase PAc conversion rate is low at 573 K and increases in liquid water by 1 order of magnitude. In all reaction environments, the decarboxylation mechanism is dominant at low hydrogen partial pressures less than 0.1 bar, and the C–COO bond dissociation is the rate-controlling elementary step. This observation contrasts with the rate-controlling step identified over most group VIII metal surfaces, which is the C–OH bond dissociation in the decarbonylation mechanism. At high hydrogen (H 2 ) partial pressures greater than 10 bar, the HDO of PAc produces propionaldehyde that can readsorb and further react through decarbonylation to produce C 2 alkane products, which is conceptually different from the low H 2 partial pressure scenario. At high H 2 partial pressures, the initial hydrogenation at the carbonyl carbon of PAc becomes the rate-controlling elementary step.

Catalysts↗
DOE OSTI2023

In Situ Attenuated Total Reflectance Infrared Spectroelectrochemistry (ATR-IR-SEC) for the Characterization of Molecular Redox Processes on Surface-Proximal Doped Silicon ATR Crystal Working Electrodes

In situ mid-infrared spectroscopy is a powerful technique for understanding the mechanism of CO 2 reduction (CO 2 R) catalysts because it enables the direct detection of catalytic intermediates and products. Moreover, spectroelectrochemistry (SEC), the coupling of spectroscopy with electrochemistry, allows spectroscopic changes to be correlated with applied potentials to reveal potential-dependent intermediates that are often relevant to photoelectrochemical reactions. Hybrid photoelectrodes, comprised of a narrow bandgap semiconductor, like silicon (Si), with a covalently-linked molecular catalyst, are a promising platform for sunlight-driven catalysis, but characterization of the catalytic mechanism(s) is challenging under photoelectrochemical conditions, particularly when the catalyst is present in monolayer or less concentrations. Here, we have developed a new strategy to use multiple-reflection attenuated total reflectance IR spectroscopy (ATR-IR) coupled with electrochemistry to characterize catalysts directly integrated with a semiconductor surface under applied potential. We show that by surface-proximal n-type or p-type doping of the top ~100-200 nm of the crystal surface, Si ATR crystals can be used simultaneously as the internal reflection element and semiconductor working electrode for ATR-IR-SEC measurements. The surface-proximal doping strategy yields a quasi-equipotential surface with excellent infrared transparency that would have been compromised by free carrier absorption if the crystal was uniformly doped. This approach permits the catalytically-active functionalized surface to be directly probed without modification and overcomes signal-to-noise limitations of other strategies that use separately deposited working electrodes on Si ATR crystals. Proof-of-concept ATR-IR-SEC spectra were collected during the reduction and oxidation of monolayers of Re- and Ru-based transition metal carbonyl complexes, respectively, verifying the viability of the technique to probe redox processes associated with CO 2 R catalysts on Si electrode surfaces with high sensitivity.

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

Quantification of the Electrostatic Effect on Redox Potential by Positive Charges in a Catalyst Microenvironment

Charged functional groups in the secondary coordination sphere (SCS) of a heterogeneous nanoparticle or homogeneous electrocatalyst are of growing interest due to enhancements in reactivity that derive from specific interactions that stabilize substrate binding or charged intermediates. At the same time, accurate benchmarking of electrocatalyst systems most often depends on the development of linear free-energy scaling relationships. Furthermore, the thermodynamic axis in those kinetic–thermodynamic correlations is most often obtained by a direct electrochemical measurement of the catalyst redox potential and might be influenced by electrostatic effects of a charged SCS. In this report, we systematically probe positive charges in a SCS and their electrostatic contributions to the electrocatalyst redox potential. A series of 11 iron carbonyl clusters modified with charged and uncharged ligands was probed, and a linear correlation between the ν CO absorption band energy and electrochemical redox potentials is observed except where the SCS is positively charged.

14 SOLAR ENERGY↗
DOE OSTI2020

Acetic Acid Adsorption and Reactions on Ni(110)

Acetic acid adsorption and reactions at multiple surface coverage values on Ni(110) were studied with temperature-programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS) at 90–500 K. The experimental measurements were interpreted with density functional theory (DFT) calculations that provided information on adsorbate geometries, energies, and vibrational modes. Below the monolayer saturation coverage of 0.36 ML at 90 K, acetic acid adsorbs mostly molecularly. Above this coverage, a physisorbed layer is formed with dimers and catemers, without detectable monomers. Dimers and catemers desorb as molecular acetic acid at 157 and 172 K, respectively. Between 90 and 200 K, the O–H bond in acetic acid breaks to form bridge-bonded bidentate acetate that becomes the dominant surface species. Desorption-limited hydrogen evolution is observed at 265 K. However, even after the acetate formation, acetic acid desorbs molecularly at 200–300 K due to recombination. Minor surface species observed at 200 K, acetyls or acetates with a carbonyl group, decompose below 350 K and generate adsorbed carbon monoxide. At 350 K, the surface likely undergoes restructuring, the extent of which increases with acetic acid coverage. The initial dominant bridge-bonded bidentate acetate species formed below 200 K remain on the surface, but they now mostly adsorb on the restructured sites. Here, the acetates and all other remaining hydrocarbon species decompose simultaneously at 425 K in a narrow temperature range with concurrent evolution of hydrogen, carbon monoxide, and carbon dioxide. Above 425 K, only carbon remains on the surface.

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

Subnanometer Thick Native sp 2 Carbon on Oxidized Diamond Surfaces

Oxygen-terminated diamond has a wide breadth of applications, which include stabilizing near-surface color centers, semiconductor devices, and biological sensors. Despite the vast literature on characterizing functionalization groups on diamond, the chemical composition of the shallowest portion of the surface (<1 nm) is challenging to probe with conventional techniques like XPS and FTIR. In this work, we demonstrate the use of angleresolved XPS to probe the first ten nanometers of both oxygen and hydrogen terminated (100) single-crystalline diamond grown via chemical vapor deposition (CVD). With the use of consistent peakfitting methods, the peak identities and relative peak binding energies were identified for sp 2 carbon, ether, hydroxyl, carbonyl, and C−H groups for both of these diamond surface terminations. For the oxygen-terminated sample, we also quantified the thickness of the sp 2 carbon layer situated on top of the bulk sp 3 diamond bonded carbon to be 0.3 ± 0.1 nm, based on the analysis of the Auger electron spectra and D-parameter calculations. These results indicate that the majority of the oxygen is bonded to the sp 2 carbon layer on the diamond, and not directly to the sp 3 diamond bonded carbon.

Carbon↗
DOE OSTI2022

Synthesis of Poly(Ester-Ether) Polymers via Hydroesterificative Polymerization of α,ω-Enol Ethers

The Pd-catalyzed carbonylative polymerization of α,ω-enol ethers derived from etherification of 10-undecenol with diols is reported, extending the scope of this relatively new polymerization strategy beyond simple 10-undecenol. Here, by varying the length of the aliphatic diol fragment in the α,ω-enol ether monomers the T m and T d of the polymers could be modified, ranging from 53 to 62 °C and 247 to 277 °C. Additionally, polymerization of α,ω-enol ethers containing rigid and bioderived diol moieties has been achieved, expanding the range of structures and polymer properties accessible via hydroesterificative polymerization. These more rigid α,ω-enol ether monomers resulted in further tuning of the polymer physical properties, with T m values ranging from 54 to 68 °C and T g values increasing up to –17 °C.

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

Breaking Scaling Relationships in CO 2 Electroreduction with Isoelectronic Analogs [Fe 4 N(CO) 12 ] – and [Fe 3 MnO(CO) 12 ] –

[Fe 4 N(CO) 12 ] – and [Fe 3 MnO(CO) 12 ] – have the same total electron count and overall charge, as well as similar reduction potentials of –1.21 and –1.17 V vs SCE in MeCN, respectively. Both clusters form the reduced hydride upon single electron transfer (ET) and proton transfer (PT). It is known that [Fe 4 N(CO) 12 ] – is an electrocatalyst for selective CO 2 reduction to formate at –1.2 V vs SCE in either pH 7 buffered water or in MeCN/H 2 O (95:5) and an effective electrocatalyst for H + reduction to H 2 under N 2 under the same conditions. In contrast, [Fe 3 MnO(CO) 12 ] – affords no products upon electrolysis, beyond [H-Fe 3 MnO(CO) 12 ] – . Herein, we determine that [H-Fe 3 MnO(CO) 12 ] – is a weaker hydride donor than [H-Fe 4 N(CO) 12 ] – by about 4 kcal mol –1 , and this is a breaking of the hydricity versus reduction potential scaling relationship previously established for a series of metal carbonyl clusters electrocatalysts.

14 SOLAR ENERGY↗
DOE OSTI2025

Plasma-Induced Tailoring of Graphene Oxide Surfaces for Electrochemical Applications: Functionalization and Etching

This study investigates the use of radio frequency air plasma as an eco-friendly method to rapidly and reversibly tailor the surface properties of graphene oxide (GO) films. We observed a transition from hydrophilic (contact angle ∼55°) to superhydrophilic (<10°) with short plasma exposure, attributed to a synergistic combination of surface modification and etching. Spectroscopic analyses (FTIR, XPS) revealed early stage formation of carbonyl groups and reduction of hydroxyls, while longer treatments induced atomic-level etching (AFM) and structural changes (XRD). This surface engineering enhanced the dielectric properties of GO films but led to reduced aqueous stability. The elucidated interplay between plasma-induced functionalization and etching provides valuable insights for the controlled modification of GO surfaces for various applications, including advanced dielectrics.

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

Understanding Functionalization of Titanium Carbide (MXene) with Quinones and Their Pseudocapacitance

In this work, the interaction mechanism of 1-aminoanthraquinone (AQ) on Ti 3 C 2 T x MXene by noncovalent (AQ@Ti 3 C 2 T x ) and covalent (AQ-Ti 3 C 2 T x ) functionalization is reported. Spectroscopic, X-ray, and scattering techniques confirmed noncovalent functionalization of AQ on Ti 3 C 2 T x MXene without its catalytic decomposition, resulting in intercalation and interaction of AQ with Ti 3 C 2 T x MXene. Diazonium reaction was further used to covalently functionalize AQ molecules on Ti 3 C 2 T x MXene. Optimized AQ-Ti 3 C 2 T x freestanding electrodes of ~44 μm thickness delivered capacitance of ~300 F/g and improved rate performance compared to the pristine counterpart (Ti 3 C 2 T x ) due to carbonyl redox of AQ and improved ionic transport between MXene layers due to pillaring of AQ molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Recent Advances in Probing Electron Delocalization in Conjugated Molecules by Attached Infrared Reporter Groups for Energy Conversion and Storage

This review article reports an overview of the recent developments in the field of electron delocalization study in organic conjugated molecules by utilizing the vibration frequencies exhibited by the attached functional groups such as nitrile (–C≡N), alkyne (–C≡C–), or carbonyl (–C=O). A brief introduction to electron delocalization, methods for study, and their importance is given first, followed by the application of infrared spectroscopy in organic molecules. Details of molecules with various infrared reporter groups have been explained in respective subsections based on the functional groups. All the reported organic molecules have been structured and presented with the electron delocalization properties studied using an infrared reporter group. Finally, an outlook on this recently promising, exciting, and interesting field of probing electron delocalization using infrared reporter groups is provided.

25 ENERGY STORAGE↗
DOE OSTI2021

Effect of Fluoroethylene Carbonate Additives on the Initial Formation of the Solid Electrolyte Interphase on an Oxygen-Functionalized Graphitic Anode in Lithium-Ion Batteries

The formation of a solid electrolyte interphase (SEI) at the electrode/electrolyte interface substantially affects the stability and lifetime of lithium-ion batteries (LIBs). One of the methods to improve the lifetime of LIBs is by the inclusion of additive molecules to stabilize the SEI. To understand the effect of additive molecules on the initial stage of SEI formation, in this work we compare the decomposition and oligomerization reactions of a fluoroethylene carbonate (FEC) additive on a range of oxygen-functionalized graphitic anodes to those of an ethylene carbonate (EC) organic electrolyte. A series of density functional theory (DFT) calculations augmented by ab initio molecular dynamics (AIMD) simulations reveal that EC decomposition on an oxygen-functionalized graphitic ($11\bar{2}0$) edge facet through a nucleophilic attack on an ethylene carbon site (C E ) of an EC molecule (S2 mechanism) is spontaneous during the initial charging process of LIBs. However, decomposition of EC through a nucleophilic attack on a carbonyl carbon (C C ) site (S1 mechanism) results in alkoxide species regeneration that is responsible for continual oligomerization along the graphitic surface. In contrast, FEC prefers to decompose through an S1 pathway, which does not promote alkoxide regeneration. Including FEC as an additive is thus able to suppress alkoxide regeneration and results in a smaller and thinner SEI layer that is more flexible toward lithium intercalation during the charging/discharging process. In addition, we find that the presence of different oxygen functional groups at the surface of graphite dictates the oligomerization products and the LiF formation mechanism in the SEI.

25 ENERGY STORAGE↗
DOE OSTI2022

In Situ Tracking of Nonthermal Plasma Etching of ZIF-8 Films

Surface characterization is critical for understanding the processes used for preparing catalysts, sorbents, and membranes. Nonthermal plasma (NTP) is a process that achieves high reactivity at low temperatures and is used to tailor the surface properties of materials. In this work, we combine the capabilities of infrared reflection absorption spectroscopy (IRRAS) with NTP for the in situ interrogation of zeolitic imidazolate framework-8 (ZIF-8) thin films to probe modifications in the material induced by oxygen and nitrogen plasmas. The IRRAS measurements in oxygen plasma reveal etching of organic ligands with sequential removal of the methyl group and imidazole ring and with the formation of carbonyl moieties (C═O). In contrast, nitrogen plasma induces mild etching and grafting of nitrile groups (−C≡N). Scanning electron microscopy imaging shows that oxygen plasma, at prolonged times, significantly degrades the ZIF-8 film at the grain boundaries. Treatment of ZIF-8 membranes using mild plasma conditions yields a fivefold enhancement for H 2 /N 2 and CO 2 /CH 4 ideal selectivities and an eightfold enhancement for CO 2 /N 2 ideal selectivity. Additionally, the new tools described here can be used for spectroscopic in situ tracking of plasma-induced chemistry on thin films in general.

IRRAS↗
DOE OSTI2026

Unraveling Defect-Dependent Conductivity-Type Switching in CuFe 2 O 4 for Enhanced Photoelectrocatalytic Reduction of Benzaldehyde

Photoelectrocatalytic (PEC) reduction provides a sustainable route for upgrading biomass-derived feedstocks with reduced energy requirements, yet remains largely unexplored beyond hydrogen evolution and CO 2 reduction due to the scarcity of stable photocathodes. Here, we report a defect-engineered CuFe 2 O 4 photocathode that enables directly quantified PEC reduction of benzaldehyde to benzyl alcohol using a singlecomponent, earth-abundant oxide. By controlling annealing temperature and oxygen partial pressure, CuFe 2 O 4 is systematically tuned from n-type to p-type conductivity. Electrochemical measurements, X-ray and ultraviolet photoelectron spectroscopy, and firstprinciples defect calculations collectively show that oxygen-rich annealing conditions suppress deep donor-type oxygen vacancies while stabilizing shallow acceptor-type copper vacancies, resulting in enhanced hole concentration and improved charge transport. In a mixed acetonitrile/water electrolyte employing 1,4-benzoquinone as a redox mediator, the optimized CuFe 2 O 4 photocathode achieves stable photoelectrochemical operation over 18 h under continuous illumination with a benzyl alcohol production rate of 2.57 μmol/h at −0.50 V vs Ag/AgNO 3 , corresponding to a Faradaic efficiency of 51.3%. This PEC approach lowers the required applied potential by ∼1 V compared to traditional electrocatalytic methods, offering a more energy-efficient route for carbonyl reduction. These findings establish CuFe 2 O 4 as a viable photocathode platform for sustainable photoelectrocatalytic organic transformations under mild reaction conditions.

benzaldehyde reduction↗
DOE OSTI2025

Elucidating the Interfacial Effects of Nonmetallic Elements on the Dehydrogenation Behavior of Nanoconfined NaAlH 4 in Zeolite-Templated Carbon

Confining materials within nanoscale volumes alters their physical and chemical properties, with positive consequences for energy storage, conversion, and catalysis. The pore structure and composition of scaffolds are essential variables for optimizing these properties, with carbon-based materials being preferred due to their tunable porous structures and chemical versatility. This study investigates the influence of surface functional groups on the dehydrogenation kinetics of nanoconfined NaAlH4 using zeolite-templated carbons (ZTCs). Here we focus on oxygen functional groups commonly present as intrinsic impurities on carbon scaffolds, analyzing three ZTC scaffolds to determine how their concentrations and configurations affect dehydrogenation behavior. Our findings reveal that carbonyl groups enhance charge transfer and destabilize Al–H bonds more effectively than ether or phenol groups. This indicates that the type of oxygen functional group is more critical than the quantity, highlighting the importance of properly tailoring oxygen defects to improve hydrogen storage performance in nanoconfined systems.

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

Polycaprolactone: A Promising Addition to the Sequential Infiltration Synthesis Polymer Family Identified through In Situ Infrared Spectroscopy

Infiltration of inorganic oxides inside polymers using sequential infiltration synthesis (SIS) is an effective method for creating materials for a broad range of applications. The reactions between various polymer functional groups and organometallic/inorganic precursors are unique, which makes it essential to understand the specific interactions for a range of precursors and polymers to enable predictive process design and to extend the utility of SIS to applications. In this paper, in situ Fourier transform infrared spectroscopy (FTIR) measurements have been performed during Al 2 O 3 and TiO 2 SIS in three different homopolymers: poly(methyl methacrylate) (PMMA), poly(epsilon-caprolactone) (PCL), and poly(2-vinylpyridine) (P2VP). From the FTIR intensity changes after precursor exposure and during the subsequent purge times, it is demonstrated quantitatively that the interaction dynamics and the stability of the intermediate complexes of these polymers with the metal precursors are substantially different. A key finding from this comparative study is that PCL interacts far more strongly with metal precursors, even though its carbonyl (C=O) and ester (C-O-R) functional groups are similar to those of the more weakly interacting PMMA. This behavior suggests that additional factors beyond the identity of the functional groups dictate how polymers interact with metal compounds in SIS. PCL, which has not previously been reported in SIS processes, may be an attractive polymeric template for implementing SIS with improved uniformity and cost-effectiveness.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Water Promotion (or Inhibition) of Condensation Reactions Depends on Exposed Cerium Oxide Catalyst Facets

Nanoparticles with well-defined facets enable quantitative correlations between surface features and catalytic activity. In this work, we explore the role of geometric and acid–base properties in the mechanism of aldol condensation catalyzed by ceria nanoshapes. In the crucial C–C coupling step, the two carbonyl adsorbates are bound to two adjacent cations. On the CeO 2 (110) plane, all atoms lie on the same layer, favoring the interaction between adsorbates and facilitating the bimolecular C–C coupling. Thus, the initial unimolecular deprotonation is rate-limiting. In contrast, the (100) and (111) planes have an open structure with O on the top layer and Ce on the layer below. The former O layer interferes between adsorbates linked to Ce sites, making the C–C coupling rate-limiting. Water helps in overcoming this spatial hindrance by remote bond polarization via H-bonds. Therefore, water promotion is only observed on those planes for which the bimolecular step is rate-limiting.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗