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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Photocatalytic Ammonia Synthesis using Fe-Based MOFs: The Role of Ligand Functionalization

Photocatalytic ammonia (NH 3 ) synthesis offers a carbon-neutral alternative to the Haber−Bosch process, which generates 42 million metric tons of CO 2 equivalent emissions annually. However, solar-to-ammonia conversion with contemporary photocatalysts remains far from practical requirements, and understanding the limiting factors in systems with well-defined active sites is crucial. Here, we show how the μ 3 -oxo-centered trinuclear Fe cluster in MIL-101(Fe) functions as the catalytic motif for N 2 -to-NH 3 conversion through combined experimental and computational investigations. Comparative studies with a molecular analogue demonstrate that the cluster is stabilized within the MOF framework, sustaining redox cycling and maintaining high catalytic activity. We systematically functionalized the dicarboxylate ligands of MIL-101(Fe) with −NH 2 , −Br, −NO 2 , −F, and −CF 3 to probe how ligand chemistry modulates Fe electron density, N 2 adsorption capacity, and proton availability, correlating these properties with catalytic performance using spectroscopic and surface characterization techniques alongside timeresolved infrared to assess excited-state lifetimes. F-functionalization optimally balances N 2 activation, proton availability at Fe active sites, and excited-state lifetimes, boosting NH 3 production by ∼ 60% relative to unmodified MIL-101(Fe). This study of ligandfunctionalized MIL-101(Fe) MOFs uncovers the underlying structure-activity relationships and advances design principles for solardriven NH 3 synthesis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Role of the Character of the Excited State of Singly Reduced Rh 2 (II,II) Intermediates on Photocatalytic Activity

Singly reduced intermediates have recently been implicated as photoactive intermediates in a number of important reactions; however, their photophysical properties remain poorly understood. A series of dirhodium(II,II) complexes, cis-[Rh 2 (p-R-Form) 2 (bncn) 2 ] 2+ (bncn = benzo[c]cinnoline; p-R-Form = N,N′-di-p-R-phenylformamidinate), where R = −OCH 3 (1), −CH 3 (2), −H (3), −F (4), −Cl (5), and −CF 3 (6), and their respective radical anions were prepared and their excited state properties were investigated. Complex 3 acted as a singlemolecule photocatalyst for H 2 production with red light. Substitution on the formamidinate ligands in 1−6 affected the energy of the Rh 2 (δ*)/Form(π,nb) highest occupied molecular orbital (HOMO), consistent with the metal/ligand-to-ligand charge transfer ( 1 ML-LCT) absorption maxima and the 3 ML-LCT excited state lifetime, ranging from 1.6 ns in 1 to 54 ns in 6 in CH 3 CN. The highest turnover number for photocatalytic H 2 evolution was observed for 3, and the lowest values were for 1 and 6. The radical anion, [Rh 2 ] − , formed during photocatalysis, was shown to absorb a photon and undergo a second reduction. The lifetimes of the doublet excited states of [3] − and [6] − were 0.49 and 0.24 ns, respectively. Calculations showed that the lowest energy excited state in [3] − was 2 ML-LCT, whereas that in [6] − was a bncn − → Rh 2 (σ*) ligand-to-metal charge transfer ( 2 LMCT) state. The 2 LMCT state stabilized across the series from [1] − to [6] − , pointing at its role in modulating the photophysical properties. This work highlights the importance of the reductive quenching of [Rh 2 ] − and the generation of the doubly reduced species to effectively catalyze hydrogen evolution.

Absorption↗
DOE OSTI2020

Transient Absorption Spectroscopy Offers Mechanistic Insights for an Iridium/Nickel-Catalyzed C–O Coupling

We report mechanistic insights into an iridium/nickel photocatalytic C–O cross-coupling reaction from time-resolved spectroscopic studies. Using transient absorption spectroscopy, energy transfer from an iridium photocatalyst to a catalytically relevant Ni(II)(aryl) acetate acceptor was observed. Concentration-dependent lifetime measurements suggest the mechanism of the subsequent reductive elimination is a unimolecular process occurring on the long-lived excited state of the Ni(II) complex. Furthermore, we envision that our study of the productive energy-transfer-mediated pathway would encourage the development of new excited-state reactivities in the field of metallaphotocatalysis that are enabled by light harvesting.

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

A Flat Analyzer Polycapillary Spectrometer for X-ray Absorption Spectroscopy of Dilute Transition Metals at X-ray-Free Electron Lasers

X-ray absorption spectroscopy (XAS) coupled with highly intense pulses from an X-ray-free electron laser (XFEL) can be used to track ultrafast chemical dynamics. Nonetheless, measurements for dilute samples (≤1 mM) have been exceptionally challenging, as scattering background signals dominate over the sample’s X-ray fluorescence. We show that femtosecond time-resolved XAS measurements of sub-millimolar transition metal solutions are now possible at the Linac Coherent Light Source (LCLS) using a high-throughput polycapillary XAS spectrometer, designed, developed, and commissioned at LCLS and the Stanford Synchrotron Radiation Lightsource (SSRL). The instrument integrates three polycapillary optics that collect and collimate X-ray fluorescence emitted from the interaction point with a high solid angle. X-ray collimated fluorescence is then selectively diffracted by coupled graphite analyzer crystals. As a result, the contribution of scattered photons is suppressed. Experiments at the Pt L 3 -edge on 0.1 mM aqueous K 2 PtCl 6 (delivered via a 100 μm liquid jet) were successfully performed in the laser pump X-ray probe configuration at the LCLS XCS and XPP instruments. We report the transient spectra of hexachloroplatinate within the first 10 ps after a 266 nm photoexcitation. We observed a short-lived reduced intermediate (≈2 ps). The polycapillary X-ray spectrometer at LCLS now enables the efficient study of the dynamics of ultradilute transition metals in solution. This capability opens the door to investigating plasmonic systems, photocatalysts, enzymes, and other scarce and dilute samples.

LCLS↗
DOE OSTI2024

Correlating activities and defects in (photo)electrocatalysts using in-situ multi-modal microscopic imaging

Photo(electro)catalysts use sunlight to drive chemical reactions such as water splitting. A major factor limiting photocatalyst development is physicochemical heterogeneity which leads to spatially dependent reactivity. To link structure and function in such systems, simultaneous probing of the electrochemical environment at microscopic length scales and a broad range of timescales (ns to s) is required. Here, we address this challenge by developing and applying in- situ (optical) microscopies to map and correlate local electrochemical activity, with hole lifetimes, oxygen vacancy concentrations and photoelectrode crystal structure. Using this multi-modal approach, we study prototypical hematite (α-Fe 2 O 3 ) photoelectrodes. We demonstrate that regions of α-Fe 2 O 3 , adjacent to microstructural cracks have a better photoelectrochemical response and reduced back electron recombination due to an optimal oxygen vacancy concentration, with the film thickness and extended light exposure also influencing local activity. Our work highlights the importance of microscopic mapping to understand activity, in even seemingly homogeneous photoelectrodes.

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

In-situ and wavelength-dependent photocatalytic strain evolution of a single Au nanoparticle on a TiO 2 film

Photocatalysis is a promising technique due to its capacity to efficiently harvest solar energy and its potential to address the global energy crisis. However, the structure–activity relationships of photocatalyst during wavelength-dependent photocatalytic reactions remains largely unexplored because it is difficult to measure under operating conditions. Here we show the photocatalytic strain evolution of a single Au nanoparticle (AuNP) supported on a TiO 2 film by combining three-dimensional (3D) Bragg coherent X-ray diffraction imaging with an external light source. The wavelength-dependent generation of reactive oxygen species (ROS) has significant effects on the structural deformation of the AuNP, leading to its strain evolution. Density functional theory (DFT) calculations are employed to rationalize the induced strain caused by the adsorption of ROS on the AuNP surface. These observations provide insights of how the photocatalytic activity impacts on the structural deformation of AuNP, contributing to the general understanding of the atomic-level catalytic adsorption process.

14 SOLAR ENERGY↗
DOE OSTI2025

Enantioselective Se lattices for stable chiroptoelectronic processing media

Chiroptoelectronic devices are crucial for applications in quantum computing, spin optical communications, and magnetic recording. However, the limited efficiency and low stability of conventional circularly polarized light (CPL)-sensing materials have restricted their broader use. Here, we introduce atomic chiral Se nanorod (NRs) films as broadband CPL detectors, leveraging the intrinsic chirality and stability of Se nanocrystals. We also perform incident circular polarization (ICP)-Raman optical activity (ROA) to explore the chiroptical activity of the large-area films. The Se NRs thin films detected CPL across a broad range from ultraviolet (UV) to short-wavelength infrared (SWIR), with a responsivity dissymmetry factor of up to 0.4, maintaining high stability under ambient conditions for longer than 13 months. CPL-sensitive Se NRs with intrinsic chirality have potential applications in chiral photonic synapses, chiral spin devices, and CPL-sensitive photocatalysts. ICP-ROA mapping also advances the analysis of 2D chiral materials.

Nanophotonics and plasmonics↗
DOE OSTI2026

A guide to transient absorption spectroscopy for porous crystalline materials in photocatalysis

Transient absorption spectroscopy has become an increasingly accessible method for probing the fundamental mechanisms of photocatalytic reaction and has provided important mechanistic insights across a wide range of systems. However, recent studies on metal-organic framework and covalent-organic framework based photocatalysts employ transient absorption primarily as a supplementary characterization technique rather than as a tool for gaining mechanistic insight. This perspective identifies recurring limitations in current practices and outlines strategies for more deliberate application of transient absorption spectroscopy in photocatalysis. By emphasizing clarity in data presentation and interpretation, we aim to elevate transient absorption spectroscopy from a routine characterization tool to a powerful approach for elucidating mechanistic photophysics of framework materials that govern their photocatalytic performance.

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

Visible light enables catalytic formation of weak chemical bonds with molecular hydrogen

The synthesis of weak chemical bonds at or near thermodynamic potential is a fundamental challenge in chemistry, with applications ranging from catalysis to biology to energy science. Proton-coupled electron transfer using molecular hydrogen is an attractive strategy for synthesizing weak element–hydrogen bonds, but the intrinsic thermodynamics presents a challenge for reactivity. Here we describe the direct photocatalytic synthesis of extremely weak element–hydrogen bonds of metal amido and metal imido complexes, as well as organic compounds with bond dissociation free energies as low as 31 kcal mol –1 . Key to this approach is the bifunctional behaviour of the chromophoric iridium hydride photocatalyst. Activation of molecular hydrogen occurs in the ground state and the resulting iridium hydride harvests visible light to enable spontaneous formation of weak chemical bonds near thermodynamic potential with no by-products. In conclusion, photophysical and mechanistic studies corroborate radical-based reaction pathways and highlight the uniqueness of this photodriven approach in promoting new catalytic chemistr

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

Site-selective tyrosine bioconjugation via photoredox catalysis for native-to-bioorthogonal protein transformation

The growing prevalence of synthetically modified proteins in pharmaceuticals and materials has exposed the need for efficient strategies to enable chemical modifications with high site-selectivity. While genetic engineering can incorporate non-natural amino acids into recombinant proteins, regioselective chemical modification of wild-type proteins remains a challenge. In this work, we use photoredox catalysis to develop a site-selective tyrosine bioconjugation pathway that incorporates bioorthogonal formyl groups, which subsequently allows for the synthesis of structurally defined fluorescent conjugates from native proteins. A water-soluble photocatalyst, lumiflavin, has been shown to induce oxidative coupling between a previously unreported phenoxazine dialdehyde tag and a single tyrosine site, even in the presence of multiple tyrosyl side chains, through the formation of a covalent C–N bond. A variety of native proteins, including those with multiple tyrosines, can successfully undergo both tyrosine-specific and single-site-selective labelling. This technology directly introduces aldehyde moieties onto native proteins, enabling rapid product diversification using an array of well-established bioorthogonal functionalization protocols including the alkyne–azide click reaction.

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

Using enzymes to tame nitrogen-centred radicals for enantioselective hydroamination

The formation of C–N bonds—of great importance to the pharmaceutical industry—can be facilitated enzymatically using nucleophilic and nitrene transfer mechanisms. However, neither natural nor engineered enzymes are known to generate and control nitrogen-centred radicals, which serve as valuable species for C–N bond formation. Here we use flavin-dependent ‘ene’-reductases with an exogenous photoredox catalyst to selectively generate amidyl radicals within the protein active site. These enzymes are engineered through directed evolution to catalyse 5-exo, 6-endo, 7-endo, 8-endo, and intermolecular hydroamination reactions with high levels of enantioselectivity. Mechanistic studies suggest that radical initiation occurs via an enzyme-gated mechanism, where the protein thermodynamically activates the substrate for reduction by the photocatalyst. Molecular dynamics studies indicate that the enzymes bind substrates using non-canonical binding interactions, which may serve as a handle to further manipulate reactivity. Furthermore, this approach demonstrates the versatility of these enzymes for controlling the reactivity of high-energy radical intermediates and highlights the opportunity for synergistic catalyst strategies to unlock previously inaccessible enzymatic functions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

A photochargeable semiconductor for highly efficient dehydrogenative coupling of amines

The development of materials with high photocatalytic efficiency is essential for sustainable chemical transformations. Here, in this work, we introduce photochargeable zinc indium sulfide nanocrystals with notable charge storage capacity, enabling highly efficient photocatalytic dehydrogenative coupling of amines. Combined with a nickel cocatalyst, the nanocrystals deliver diamines and hydrogen at rates exceeding 120 mmol per gram of photocatalyst per hour, with > 95% selectivity and an apparent quantum efficiency of up to 39.4% under ambient conditions. The system exhibits excellent scalability, demonstrated by a reaction on a 20-g scale, and broad versatility in promoting amino acid ester coupling and polymerization reactions with concurrent hydrogen evolution. Mechanistic studies attribute the photocharging capability of zinc indium sulfide nanocrystals to in situ-generated trap states such as sulfur vacancies, which extend hydrogen production into the dark catalytic cycle and enhance the overall charge utilization efficiency. These findings position photochargeable semiconductors as promising platforms for a wide range of photocatalytic applications.

nanoscale devices↗
DOE OSTI2023

Automated Construction of a Photocatalysis Dataset for Water-Splitting Applications

We present an automatically generated dataset of 15,755 records that were extracted from 47,357 papers. These records contain water-splitting activity in the presence of certain photocatalysts, along with additional information about the chemical reaction conditions under which this activity was recorded. These conditions include any co-catalysts and additives that were present during water splitting, the length of time for which the photocatalytic experiment was conducted, and the type of light source used, including its wavelength. Despite the text extraction of such a wide range of chemical reaction attributes, the dataset afforded good precision (71.2%) and recall (36.3%). These figures-of-merit were calculated based on a random sample of open-access papers from the corpus. Mining such a complex set of attributes required the development of novel techniques in knowledge extraction and interdependency resolution, leveraging inter- and intra-sentence relations, which are also described in this paper. We present a new version (version 2.2) of the chemistry-aware text-mining toolkit ChemDataExtractor, in which these new techniques are included.

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

Water mediated growth of oriented single crystalline SrCO3 nanorod arrays on strontium compounds

Abstract Morphology-controlled strontianite nanostructures have attracted interest in various fields, such as electrocatalyst and photocatalysts. Basic additives in aqueous strontium solutions is commonly used in controlling strontianite nanostructures. Here, we show that trace water also serves an important role in forming and structuring vertically oriented strontianite nanorod arrays on strontium compounds. Using in situ Raman spectroscopy, we monitored the structural evolution from hydrated strontium to strontianite nanorods, demonstrating the epitaxial growth by vapor–liquid–solid mechanism. Water molecules cause not only the exsolution of Sr liquid droplets on the surface but also the uptake of airborne CO 2 followed by its ionization to CO 3 2− . The existence of intermediate SrHO + –OCO 2 2− phase indicates the interaction of CO 3 2− with SrOH + in Sr(OH) x (H 2 O) y cluster to orient strontianite crystals. X-ray diffraction simulation and transmission electron microscopy identify the preferred-orientation plane of the 1D nanostructures as the (002) plane, i.e., the growth along the c-axis. The anisotropic growth habit is found to be affected by the kinetics of carbonation. This study paves the way for designing and developing 1D architecture of alkaline earth metal carbonates by a simple method without external additives at room temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Structural measurement of electron-phonon coupling and electronic thermal transport across a metal-semiconductor interface

Scattering of energetic charge carriers and their coupling to lattice vibrations (phonons) in dielectric materials and semiconductors are crucial processes that determine the functional limits of optoelectronics, photovoltaics, and photocatalysts. The strength of these energy exchanges is often described by the electron-phonon coupling coefficient, which is difficult to measure due to the microscopic time- and length-scales involved. In the present study, we propose an alternate means to quantify the coupling parameter along with thermal boundary resistance and electron conductivity by performing a high angular-resolution time-resolved X-ray diffraction measurement of propagating lattice deformation following laser excitation of a nanoscale, polycrystalline metal film on a semiconductor substrate. Our data present direct experimental evidence for identifying the ballistic and diffusive transport components occurring at the interface, where only the latter participates in thermal diffusion. This approach provides a robust measurement that can be applied to investigate microscopic energy transport in various solid-state materials.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Ammonia synthesis by photocatalytic hydrogenation of a N 2 -derived molybdenum nitride

Although metal complexes are known to split dinitrogen at ambient temperature and pressure, the synthesis of ammonia from these compounds and using H 2 as the terminal reductant has been rarely achieved. Here, we report photocatalytic ammonia synthesis from a N 2 -derived terminal molybdenum nitride and by using H 2 as the terminal reductant. An iridium hydride photocatalyst mediates the reaction upon irradiation with blue light. A molybdenum pentahydride was identified as the principal metal product arising following ammonia release. Conversion of the molybdenum pentahydride back to the terminal molybdenum nitride was accomplished in three-steps and completes a synthetic cycle for NH3 formation from N 2 and H 2 . Mechanistic investigations support a pathway involving photoexcitation of the iridium hydride and subsequent energy transfer rather than electron transfer. Deuterium labelling confirmed H 2 as the source of the N–H bonds. This photodriven, proton coupled electron transfer allows the use of H 2 as the terminal reductant for catalytic formation of NH 3 from N 2 using metal catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗