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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Degradation Mechanism of Phosphate‐Based Li‐NASICON Conductors in Alkaline Environment

NASICON-type Li conductors (Li-NASICON) have traditionally been regarded as promising candidates for solid-state Li-air battery applications because of their stability in water and ambient air. However, the presence of water in the cathode of a Li-air battery can induce a highly alkaline environment by modifying the discharge product from Li 2 O 2 to LiOH which can potentially degrade cathode and separator materials. This study investigates the alkaline stability of common Li-NASICON chemistries through a systematic experimental study of LiTi x Ge 2-x (PO 4 ) 3 (LTGP) with varying x = 0–2.0. Density functional theory calculations are combined to gain a mechanistic understanding of the alkaline instability. It is demonstrated that the instability of LTGP in an alkaline environment is mainly driven by the dissolution of PO 4 3– groups, which subsequently precipitate as Li 3 PO 4 . The introduction of Ti facilitates the formation of a Ti-rich compound on the surface that eventually passivates the material, but only after significant bulk degradation. Consequently, phosphate-based Li-NASICON materials exhibit limited alkaline stability, raising concerns about their viability in humid Li-air batteries.

25 ENERGY STORAGE↗
DOE OSTI2025

Enhancing Cycle Life in Superoxide‐Based Na–O 2 Batteries by Reducing Interface Reactivity

Abstract Sodium–oxygen (Na–O 2 ) batteries are considered a promising energy storage alternative to current state‐of‐the‐art technologies owing to their high theoretical energy density, along with the natural abundance and low price of Na metal. The chemistry of these batteries depends on sodium superoxide (NaO 2 ) or peroxide (Na 2 O 2 ) being formed/decomposed. Most Na–O 2 batteries form NaO 2 , but reversibility is usually quite limited due to side reactions at interfaces. By using new materials, including a highly active catalyst based on vanadium phosphide (VP) nanoparticles, an ether/ionic liquid‐based electrolyte, and an effective sodium bromide (NaBr) anode protection layer, the sources of interface reactivity can be reduced to achieve a Na–O 2 battery cell that is rechargeable for 1070 cycles with a high energy efficiency of more than 83%. Density functional theory calculations, along with experimental characterization confirm the three factors leading to the long cycle life, including the effectiveness of the NaBr protective layer on the anode, a tetraglyme/EMIM‐BF 4 based electrolyte that prevents oxidation of the VP cathode catalyst surface, and the EMIM‐BF 4 ionic liquid aiding in avoiding electrolyte decomposition on NaO 2 .

Azaribeni, Adel [Department of Chemical and Biolog↗
DOE OSTI2025

Effect of Propagating Dopant Reactivity on Lattice Oxygen Loss in LLZO Solid Electrolyte Contacted with Lithium Metal

Lithium lanthanum zirconium oxide (LLZO) is widely known as the most stable solid electrolyte against lithium metal electrodes. This thermodynamic stability can be lost by the presence of dopants which are required to stabilize the cubic phase of LLZO and can be reduced by lithium metal. However, the role of oxygen in such reactions is taken for granted. In this work, the reduction of Nb-substituted LLZO (Nb-LLZO) is explored by Li metal and shows that interfacial reactions propagate and lead to the decomposition with substantial Nb 5+ reduction deep into the bulk electrolyte. Scanning Transmission Electron Microscopy with Energy Dispersive X-ray Spectroscopy and thermogravimetric analyses show much of the reduction is due to oxygen vacancies formed, leading to increased electronic conductivity mapped with conductive Atomic Force Microscopy. Density functional theory calculations indicate oxygen release is favored by increased excess lithiation of Nb-LLZO. Electrochemical impedance of polycrystalline Nb-LLZO shows the continuous evolution of ionically resistive interphases near the lithium metal interface with Nb-LLZO while single crystals show little reactivity at room temperature and self-limiting reduction at 60°C. This work underlines the role of grain boundaries in propagating destructive solid electrolyte reactions and highlights previously unseen mechanisms involving lattice oxygen in LLZO.

Li metal, solid-state electrolytes↗
DOE OSTI2025

Bio‐Inspired Cascade Photocatalysis on Fe Single‐Atom Carbon Nitride Upcycles Plastic Wastes for Effective Acetic Acid Production

Plastic imposes a critical threat to the environment, ecosystems, and human health because of the low utilization efficiency of plastics. Here, we demonstrate a sustainable, highly efficient cascade photocatalysis for upcycle plastics to value-added acetic acid using Fe single-atom catalysts (Fe@C 3 N 4 SAC) at ambient conditions. Inspired by Phanerochaete chrysosporium microbial, the defective Fe@C 3 N 4 SAC acts as a bifunctional cascade photocatalyst for both Fenton-like and CO 2 reduction reactions. During the reaction, hydroxyl radicals (*OH) form and subsequently oxidize plastics into CO 2 intermediates. These CO 2 intermediates are then photo-reduced to CH 3 COOH on the same catalyst via cascade photocatalysis. The mechanism is confirmed by in situ multimodal microscopy and spectroscopies, with density functional theory calculations. A state-of-art CH 3 COOH yield of 63.8 mg h −1 gcat −1 from PVC, 12.7 mg h −1 gcat −1 from PE, 5.4 mg h −1 gcat −1 from PET, and 5.3 mg h −1 gcat −1 from PP are directly obtained under AM1.5G solar irradiation and further validated under real sunlight (≈0.6 sun), achieving 5.6 mg h −1 gcat −1 from PET, using low-cost Fe@C 3 N 4 SAC in a sealed reactor by enhancing the photon transport and utilization efficiency. The techno-economic analysis shows it is promising to practically mitigate plastic based on broader social welfare assessments.

cascade photocatalysis↗
DOE OSTI2020

High Compression‐Induced Conductivity in a Layered Cu–Br Perovskite

Abstract We show that the onset pressure for appreciable conductivity in layered copper‐halide perovskites can decrease by ca. 50 GPa upon replacement of Cl with Br. Layered Cu–Cl perovskites require pressures >50 GPa to show a conductivity of 10 −4 S cm −1 , whereas here a Cu–Br congener, (EA) 2 CuBr 4 (EA=ethylammonium), exhibits conductivity as high as 2×10 −3 S cm −1 at only 2.6 GPa, and 0.17 S cm −1 at 59 GPa. Substitution of higher‐energy Br 4p for Cl 3p orbitals lowers the charge‐transfer band gap of the perovskite by 0.9 eV. This 1.7 eV band gap decreases to 0.3 eV at 65 GPa. High‐pressure X‐ray diffraction, optical absorption, and transport measurements, and density functional theory calculations allow us to track compression‐induced structural and electronic changes. The notable enhancement of the Br perovskite's electronic response to pressure may be attributed to more diffuse Br valence orbitals relative to Cl orbitals. This work brings the compression‐induced conductivity of Cu‐halide perovskites to more technologically accessible pressures.

Jaffe, Adam↗
DOE OSTI2020

2‐Aminobenzenethiol‐Functionalized Silver‐Decorated Nanoporous Silicon Photoelectrodes for Selective CO 2 Reduction

Abstract A molecularly thin layer of 2‐aminobenzenethiol (2‐ABT) was adsorbed onto nanoporous p‐type silicon (b‐Si) photocathodes decorated with Ag nanoparticles (Ag NPs). The addition of 2‐ABT alters the balance of the CO 2 reduction and hydrogen evolution reactions, resulting in more selective and efficient reduction of CO 2 to CO. The 2‐ABT adsorbate layer was characterized by Fourier transform infrared (FTIR) spectroscopy and modeled by density functional theory calculations. Ex situ X‐ray photoelectron spectroscopy (XPS) of the 2‐ABT modified electrodes suggests that surface Ag atoms are in the +1 oxidation state and coordinated to 2‐ABT via Ag−S bonds. Under visible light illumination, the onset potential for CO 2 reduction was −50 mV vs. RHE, an anodic shift of about 150 mV relative to a sample without 2‐ABT. The adsorption of 2‐ABT lowers the overpotentials for both CO 2 reduction and hydrogen evolution. A comparison of electrodes functionalized with different aromatic thiols and amines suggests that the primary role of the thiol group in 2‐ABT is to anchor the NH 2 group near the Ag surface, where it serves to bind CO 2 and also to assist in proton transfer.

Kan, Miao↗
DOE OSTI2020

Ethylene Dehydroaromatization over Ga‐ZSM‐5 Catalysts: Nature and Role of Gallium Speciation

Abstract Bifunctional catalysis in zeolites possessing both Brønsted and Lewis acid sites offers unique opportunities to tailor shape selectivity and enhance catalyst performance. Here, we examine the impact of framework and extra‐framework gallium species on enriched aromatics production in zeolite ZSM‐5. We compare three distinct methods of preparing Ga‐ZSM‐5 and reveal direct (single step) synthesis leads to optimal catalysts compared to post‐synthesis methods. Using a combination of state‐of‐the‐art characterization, catalyst testing, and density functional theory calculations, we show that Ga Lewis acid sites strongly favor aromatization. Our findings also suggest Ga(framework)–Ga(extra‐framework) pairings, which can only be achieved in materials prepared by direct synthesis, are the most energetically favorable sites for reaction pathways leading to aromatics. Calculated acid site exchange energies between extra‐framework Ga at framework sites comprised of either Al or Ga reveal a site‐specific preference for stabilizing Lewis acids, which is qualitatively consistent with experimental measurements. These findings indicate the possibility of tailoring Lewis acid siting by the placement of Ga heteroatoms at distinct tetrahedral sites in the zeolite framework, which can have a marked impact on catalyst performance relative to conventional H‐ZSM‐5.

Zhou, Yunwen↗
DOE OSTI2021

Thermal Unequilibrium of PdSn Intermetallic Nanocatalysts: From In Situ Tailored Synthesis to Unexpected Hydrogenation Selectivity

Abstract Effective control on chemoselectivity in the catalytic hydrogenation of C=O over C=C bonds is uncommon with Pd‐based catalysts because of the favored adsorption of C=C bonds on Pd surface. Here we report a unique orthorhombic PdSn intermetallic phase with unprecedented chemoselectivity toward C=O hydrogenation. We observed the formation and metastability of this PdSn phase in situ. During a natural cooling process, the PdSn nanoparticles readily revert to the favored Pd 3 Sn 2 phase. Instead, using a thermal quenching method, we prepared a pure‐phase PdSn nanocatalyst. PdSn shows an >96 % selectivity toward hydrogenating C=O bonds of various α,β‐unsaturated aldehydes, highest in reported Pd‐based catalysts. Further study suggests that efficient quenching prevents the reversion from PdSn‐ to Pd 3 Sn 2 ‐structured surface, the key to the desired catalytic performance. Density functional theory calculations and analysis of reaction kinetics provide an explanation for the observed high selectivity.

Chen, Minda↗
DOE OSTI2023

A Porous Crystalline Nitrone‐Linked Covalent Organic Framework**

Abstract Herein, we report the synthesis of a nitrone‐linked covalent organic framework, COF‐115, by combining N , N′ , N′ , N ′′′‐(ethene‐1, 1, 2, 2‐tetrayltetrakis(benzene‐4, 1‐diyl))tetrakis(hydroxylamine) and terephthaladehyde via a polycondensation reaction. The formation of the nitrone functionality was confirmed by solid‐state 13 C multi cross‐polarization magic angle spinning NMR spectroscopy of the 13 C‐isotope‐labeled COF‐115 and Fourier‐transform infrared spectroscopy. The permanent porosity of COF‐115 was evaluated through low‐pressure N 2 , CO 2 , and H 2 sorption experiments. Water vapor and carbon dioxide sorption analysis of COF‐115 and the isoreticular imine‐linked COF indicated a superior potential of N ‐oxide‐based porous materials for atmospheric water harvesting and CO 2 capture applications. Density functional theory calculations provided valuable insights into the difference between the adsorption properties of these COFs. Lastly, photoinduced rearrangement of COF‐115 to the associated amide‐linked material was successfully demonstrated.

Kurandina, Daria↗
DOE OSTI2024

Superoxide Radicals in Uranyl Peroxide Solids: Lasting Signatures Identified by Electron Paramagnetic Resonance Spectroscopy

Abstract U(VI) peroxide phases (studtite and meta‐studtite) are found throughout the nuclear fuel cycle and exist as corrosion products in high radiation fields. Peroxides are part of a family of reactive oxygen species (ROS) that include hydroperoxyl and superoxide species and are produced during alpha radiolysis of water. While U(VI) peroxides have been thoroughly investigated, the incorporation and stability of ROS species within studtite have not been validated. In the current study, electron paramagnetic resonance (EPR) spectroscopy was used to identify the presence of free radicals within a series of U(VI) peroxide samples containing depleted, highly enriched, and natural uranium. Density functional theory calculations indicated that the predicted EPR signals matched well with a superoxide (O 2 − ⋅) species incorporated into the studtite structure, confirming the presence of ROS in the material. Further analysis of samples that were synthesized between 1945 and 2023 indicated that there is a correlation between the radical signal and the product of specific activity multiplied by age of the sample.

Scherrer, Sarah K.↗
DOE OSTI2021

Boosting CO 2 Electrochemical Reduction with Atomically Precise Surface Modification on Gold Nanoclusters

Thiolate-protected gold nanoclusters (NCs) are promising catalytic materials for the electrochemical CO 2 reduction reaction (CO 2 RR). In this work an atomic level modification of a Au 23 NC is made by substituting two surface Au atoms with two Cd atoms, and it enhances the CO 2 RR selectivity to 90–95 % at the applied potential between -0.5 to -0.9 V, which is doubled compared to that of the undoped Au 23 . Additionally, the Cd-doped Au 19 Cd 2 exhibits the highest CO 2 RR activity (2200 mA mg -1 at -1.0 V vs. RHE) among the reported NCs. This synergetic effect between Au and Cd is remarkable. Density-functional theory calculations reveal that the exposure of a sulfur active site upon partial ligand removal provides an energetically feasible CO 2 RR pathway. The thermodynamic energy barrier for CO formation is 0.74 eV lower on Au 19 Cd 2 than on Au 23 . Here these results reveal that Cd doping can boost the CO 2 RR performance of Au NCs by modifying the surface geometry and electronic structure, which further changes the intermediate binding energy. This work offers insights into the surface doping mechanism of the CO 2 RR and bimetallic synergism.

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

Thermal Unequilibrium of PdSn Intermetallic Nanocatalysts: From In Situ Tailored Synthesis to Unexpected Hydrogenation Selectivity

Effective control on chemoselectivity in the catalytic hydrogenation of C=O over C=C bonds is uncommon with Pd-based catalysts because of the favored adsorption of C=C bonds on Pd surface. Here we report a unique orthorhombic PdSn intermetallic phase with unprecedented chemoselectivity toward C=O hydrogenation. We observed the formation and metastability of this PdSn phase in situ. During a natural cooling process, the PdSn nanoparticles readily revert to the favored Pd 3 Sn 2 phase. Instead, using a thermal quenching method, we prepared a pure-phase PdSn nanocatalyst. Furthermore, PdSn shows an >96% selectivity toward hydrogenating C=O bonds of various α,β-unsaturated aldehydes, highest in reported Pd-based catalysts. Further study suggests that efficient quenching prevents the reversion from PdSn- to Pd 3 Sn 2 -structured surface, the key to the desired catalytic performance. Density functional theory calculations and analysis of reaction kinetics provide an explanation for the observed high selectivity.

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

Revisiting the Bonding Model for Gold(I) Species: The Importance of Pauli Repulsion Revealed in a Gold(I)–Cyclobutadiene Complex

Understanding the bonding of gold(I) species has been central to the development of gold(I) catalysis. Herein, we present the synthesis and characterization of the first gold(I)-cyclobutadiene complex, accompanied with bonding analysis by state-of-the-art energy decomposition analysis methods. Analysis of possible coordination modes for the new species not only confirms established characteristics of gold(I) bonding, but also suggests that Pauli repulsion is a key yet hitherto overlooked element. Additionally, we obtain a new perspective on gold(I)-bonding by comparison of the gold(I)-cyclobutadiene to congeners stabilized by p-, d-, and f-block metals. Consequently, we refine the gold(I) bonding model, with a delicate interplay of Pauli repulsion and charge transfer as the key driving force for various coordination motifs. Finally, Pauli repulsion is similarly determined as a significant interaction in Au I -alkyne species, corroborating this revised understanding of Au I bonding.

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

Divergent Stabilities of Tetravalent Cerium, Uranium, and Neptunium Imidophosphorane Complexes

The study of the redox chemistry of mid-actinides (U–Pu) has historically relied on cerium as a model, due to the accessibility of trivalent and tetravalent oxidation states for these ions. Recently, dramatic shifts of lanthanide 4+/3+ non-aqueous redox couples have been established within a homoleptic imidophosphorane ligand framework. Herein we extend the chemistry of the imidophosphorane ligand (NPC=[N=P t Bu(pyrr) 2 ] – ; pyrr=pyrrolidinyl) to tetrahomoleptic NPC complexes of neptunium and cerium (1-M, 2-M, M=Np, Ce) and present comparative structural, electrochemical, and theoretical studies of these complexes. Large cathodic shifts in the M 4+/3+ (M=Ce, U, Np) couples underpin the stabilization of higher metal oxidation states owing to the strongly donating nature of the NPC ligands, providing access to the U 5+/4+ , U 6+/5+ , and to an unprecedented, well-behaved Np 5+/4+ redox couple. Furthermore, the differences in the chemical redox properties of the U vs. Ce and Np complexes are rationalized based on their redox potentials, degree of structural rearrangement upon reduction/oxidation, relative molecular orbital energies, and orbital composition analyses employing density functional theory.

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

A Porous Crystalline Nitrone-Linked Covalent Organic Framework

Herein, we report the synthesis of a nitrone-linked covalent organic framework, COF-115, by combining N, N', N', N'''-(ethene-1, 1, 2, 2-tetrayltetrakis(benzene-4, 1-diyl))tetrakis(hydroxylamine) and terephthaladehyde via a polycondensation reaction. In this study, the formation of the nitrone functionality was confirmed by solid-state 13 C multi cross-polarization magic angle spinning NMR spectroscopy of the 13 C-isotope-labeled COF-115 and Fourier-transform infrared spectroscopy. The permanent porosity of COF-115 was evaluated through low-pressure N 2 , CO 2 , and H 2 sorption experiments. Water vapor and carbon dioxide sorption analysis of COF-115 and the isoreticular imine-linked COF indicated a superior potential of N-oxide-based porous materials for atmospheric water harvesting and CO 2 capture applications. Density functional theory calculations provided valuable insights into the difference between the adsorption properties of these COFs. Lastly, photoinduced rearrangement of COF-115 to the associated amide-linked material was successfully demonstrated.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗