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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Direct observation of electric field-induced magnetism in a molecular magnet

Abstract We report the direct observation of an electrically-induced magnetic susceptibility in the molecular nano- magnet [Fe 3 O(O 2 CPh) 6 (py) 3 ]ClO 4 · py, an Fe 3 trimer. This magnetoelectric effect results from the breaking of spatial inversion symmetry due to the spin configurations of the antiferromagnetic trimer. Both static and very low frequency electric fields were used. Fractional changes of the magnetic susceptibility of 11 ppb $$\pm 2$$ ± 2 per kVm -1 for the temperature range 8 . 5 < T < 13 . 5 K were observed for applied electric fields up to 62 kV m − 1 . The changes in susceptibility were measured using a tunnel diode oscillator operating at liquid helium temperatures while the sample is held at a higher regulated temperature.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2022

Acid anion electrolyte effects on platinum for oxygen and hydrogen electrocatalysis

Platinum is an important material with applications in oxygen and hydrogen electrocatalysis. To better understand how its activity can be modulated through electrolyte effects in the double layer microenvironment, herein we investigate the effects of different acid anions on platinum for the oxygen reduction/evolution reaction (ORR/OER) and hydrogen evolution/oxidation reaction (HER/HOR) in pH 1 electrolytes. Experimentally, we see the ORR activity trend of HClO 4 > HNO 3 > H 2 SO 4 , and the OER activity trend of HClO 4 > HNO 3 ~ H 2 SO 4 . HER/HOR performance is similar across all three electrolytes. Notably, we demonstrate that ORR performance can be improved 4-fold in nitric acid compared to in sulfuric acid. Assessing the potential-dependent role of relative anion competitive adsorption with density functional theory, we calculate unfavorable adsorption on Pt(111) for all the anions at HER/HOR conditions while under ORR/OER conditions ClO$^{-}_{4}$ binds the weakest followed by NO$^{-}_{3}$ and SO$^{2-}_{4}$. Our combined experimental-theoretical work highlights the importance of understanding the role of anions across a large potential range and reveals nitrate-like electrolyte microenvironments as interesting possible sulfonate alternatives to mitigate the catalyst poisoning effects of polymer membranes/ionomers in electrochemical systems. These findings help inform rational design approaches to further enhance catalyst activity via microenvironment engineering.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Mg 2+ ion-catalyzed polymerization of 1,3-dioxolane in battery electrolytes

Electrolyte salts with Mg 2+ and Al 3+ Lewis acidic cations demonstrate polymerization of 1,3-dioxolane. The speed and extent of the reaction depends on coordination of the anion with the Mg 2+ cation catalyst. Weakly coordinating anions such as TFSI - aid faster polymerization while strongly coordinating anions such as ClO 4 - hinder the polymerization.

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

Oxygen-atom transfer photochemistry of a molecular copper bromate complex

Here, we report the synthesis and oxygen-atom transfer (OAT) photochemistry of [Cu(tpa)BrO 3 ]ClO 4 . In situ spectroscopy and in crystallo experiments indicate OAT proceeds from a Cu–O fragment generated by sequential Cu–O bond cleavage and OAT from BrO x to [Cu(tpa)] + . Furthermore, these results highlight synthetic opportunities in M–O photochemistry and demonstrate the utility of in crystallo experiments to evaluating photochemical reaction mechanisms.

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

Recognition competes with hydration in anion-triggered monolayer formation of cyanostar supra-amphiphiles at aqueous interfaces

The triggered self-assembly of surfactants into organized layers at aqueous interfaces is important for creating adaptive nanosystems and understanding selective ion extraction. While these transformations require molecular recognition, the underlying driving forces are modified by the local environment in ways that are not well understood. Herein, we investigate the role of ion binding and ion hydration using cyanosurf, which is composed of the cyanostar macrocycle, and its binding to anions that are either size-matched or mis-matched and either weakly or highly hydrated. We utilize the supra-amphiphile concept where anion binding converts cyanosurf into a charged and amphiphilic complex triggering its self-organization into monolayers at the air–water interface. Initially, cyanosurf forms aggregates at the surface of a pure water solution. When the weakly hydrated and size-matched hexafluorophosphate (PF 6 - ) and perchlorate (ClO 4 - ) anions are added, the macrocycles form distinct monolayer architectures. Surface-pressure isotherms reveal significant reorganization of the surface-active molecules upon anion binding while infrared reflection absorption spectroscopy show the ion-bound complexes are well ordered at the interface. Vibrational sum frequency generation spectroscopy shows the water molecules in the interfacial region are highly ordered in response to the charged monolayer of cyanosurf complexes. Consistent with the importance of recognition, we find the smaller mis-matched chloride does not trigger the transformation. However, the size-matched phosphate (H 2 PO 4 - ) also does not trigger monolayer formation indicating hydration inhibits its interfacial binding. These studies reveal how anion-selective recognition and hydration both control the binding and thus the switching of a responsive molecular interface.

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

A new quinoline-based cobalt( II ) catalyst capable of bifunctional water splitting

We report on a new water-soluble cobalt( II ) complex capable of water splitting bifunctionality, i.e., water reduction and water oxidation. The species [Co II (L Qpy )H 2 O]ClO 4 (1), where L Qpy is the deprotonated form of the new tripodal ligand N 1 ,N 1 -bis(pyridin-2-ylmethyl)-N 2 -(quinolin-8-yl)benzene-1,2-diamine, HL Qpy , was developed aiming to replace an oxidation prone methylene group by a sturdy and redox stable quinoline. The molecular and electronic structures of 1 were evaluated by multiple spectroscopic, spectrometric, electrochemical and computational methods, and detailed pre- and post-catalytic studies were conducted to ascertain the molecular nature of the conversions. Complex 1 performs water reduction at a low onset overpotential (η) of 0.65 V at pH 7, reaching TON 3h 2900 (TOF 970 h −1 ) and TON 18h 12 100 (TOF 672 h −1 ) with up to 98% faradaic efficiency (FE). Species 1 also promotes water oxidation at η = 0.34 V under pH 8, achieving TON 3h 193 (TOF 64 h −1 ) at 84% FE. Experimental and DFT results enabled us to propose reaction intermediates and mechanisms.

Lucecki, Carlos A. [Wayne State University, Detroi↗
DOE OSTI2021

Uranyl oxalate species in high ionic strength environments: stability constants for aqueous and solid uranyl oxalate complexes

Uranyl ion, UO 2 2+ , and its aqueous complexes with organic and inorganic ligands can be the dominant species for uranium transport on the Earth surface or in a nuclear waste disposal system if an oxidizing condition is present. As an important biodegradation product, oxalate, C 2 O 4 2– , is ubiquitous in natural environments and is known for its ability to complex with the uranyl ion. Oxalate can also form solid phases with uranyl ion in certain environments thus limiting uranium migration. Therefore, the determination of stability constants for aqueous and solid uranyl oxalate complexes is important not only to the understanding of uranium mobility in natural environments, but also to the performance assessment of nuclear waste disposal. In this work, we developed a thermodynamic model for the UO 2 2+ –Na + –H + –Cl – –ClO 4 – –C 2 O 4 2– –NO 3 – –H 2 O system to ionic strength up to ~11 mol•kg –1 . We constrained the stability constants for UO 2 C 2 O 4 (aq) and UO 2 (C 2 O 4 ) 2 2– at infinite dilution based on our evaluation of the literature data over a wide range of ionic strengths up to ~11 mol•kg –1 . We also obtained the solubility constants at infinite dilution for solid uranyl oxalates, UO 2 C 2 O 4 •3H 2 O, based on the solubility data over a wide range of ionic strengths. The developed model will enable for the accurate stability assessment of oxalate complexes affecting uranium mobility under a wide range of conditions including those in deep geological repositories.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Materials Data on CaMg2H24(ClO2)6 by Materials Project

(Mg(HCl)2)2Ca(ClO)2(H2)8(H2O2)2(O2)3 crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of one calciumhypochlorite molecule, eight hydrogen molecules, two trioxidane molecules, four water molecules, and one Mg(HCl)2 cluster. In the Mg(HCl)2 cluster, Mg2+ is bonded in a 5-coordinate geometry to two H1+ and three Cl1- atoms. There are one shorter (2.01 Å) and one longer (2.28 Å) Mg–H bond lengths. There are a spread of Mg–Cl bond distances ranging from 2.27–2.41 Å. There are two inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one Mg2+ atom. In the second H1+ site, H1+ is bonded in a single-bond geometry to one Mg2+ atom. There are two inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a single-bond geometry to one Mg2+ atom. In the second Cl1- site, Cl1- is bonded in an L-shaped geometry to two equivalent Mg2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SnCl8O25 by Materials Project

(Sn(O4Cl)6)2(ClO)2Cl2 is zeta silver zinc structured and crystallizes in the trigonal P3 space group. The structure is zero-dimensional and consists of three hydrochloric acid molecules, three hypochlorous acid molecules, and three Sn(O4Cl)6 clusters. In each Sn(O4Cl)6 cluster, Sn is bonded to six O atoms to form SnO6 octahedra that share corners with six ClO4 tetrahedra. There are three shorter (2.10 Å) and three longer (2.12 Å) Sn–O bond lengths. There are eight inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.43 Å. In the second O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.43 Å. In the third O site, O is bonded in a bent 120 degrees geometry to one Sn and one Cl atom. The O–Cl bond length is 1.56 Å. In the fourth O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.44 Å. In the fifth O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.44 Å. In the sixth O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.43 Å. In the seventh O site, O is bonded in a bent 120 degrees geometry to one Sn and one Cl atom. The O–Cl bond length is 1.60 Å. In the eighth O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.43 Å. There are two inequivalent Cl sites. In the first Cl site, Cl is bonded to four O atoms to form ClO4 tetrahedra that share a cornercorner with one SnO6 octahedra. The corner-sharing octahedral tilt angles are 48°. In the second Cl site, Cl is bonded to four O atoms to form ClO4 tetrahedra that share a cornercorner with one SnO6 octahedra. The corner-sharing octahedral tilt angles are 50°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on PtN4(Cl2O)2 by Materials Project

PtCl2(N2)2(ClO)2 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four hypochlorous acid molecules, four nitrogen molecules, and two platinum(ii) chloride molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CrC6N12(ClO3)3 by Materials Project

CrC6(N2O)6(ClO)3 crystallizes in the trigonal R-3 space group. The structure is zero-dimensional and consists of eighteen hypochlorous acid molecules and six CrC6(N2O)6 clusters. In each CrC6(N2O)6 cluster, Cr3+ is bonded in an octahedral geometry to six equivalent O2- atoms. All Cr–O bond lengths are 2.03 Å. C4+ is bonded in a 1-coordinate geometry to two N+0.50- and one O2- atom. There is one shorter (1.34 Å) and one longer (1.35 Å) C–N bond length. The C–O bond length is 1.25 Å. There are two inequivalent N+0.50- sites. In the first N+0.50- site, N+0.50- is bonded in a distorted single-bond geometry to one C4+ atom. In the second N+0.50- site, N+0.50- is bonded in a distorted single-bond geometry to one C4+ atom. O2- is bonded in a bent 120 degrees geometry to one Cr3+ and one C4+ atom.

36 MATERIALS SCIENCE↗
NASA NTRS1975

Estimate of late 1974 stratospheric concentration of gaseous chlorine compounds /ClX/

The total concentration (ClX) versus altitude of Cl-containing molecules (principally HCl, Cl, ClO) is estimated. It is shown that the predicted present stratospheric concentrations are due to photolysis near 30 km of man-made CF2Cl2 and CFCl3, and CCl4 from a ground-level source, either man-made or natural. The contribution of CH3Cl to stratospheric ClX is evaluated from preliminary measurements of the compound at ground level. Although ground-level sources of HCl and Cl2 are large, tropospheric processes preclude significant impact on the stratosphere.

Cicerone, R. J.↗
NASA NTRS1976

Products of the reaction of chlorine atoms and ozone

Preliminary matrix-isolation infrared spectroscopic studies of the gas-phase reaction of chlorine atoms and ozone are reported. It was shown that the major product of the reaction is the symmetric OClO radical, while very little of the asymmetric ClOO radical is produced. It was also shown that the presence of O2 enhances the OClO production and the ClOO is the primary product in the reaction of Cl atoms and pure O2. The radical ClO was observed for the first time in a gas-phase reaction of Cl and O3. A mechanism for these observations is proposed.

Hall, J. H., Jr.↗
NASA NTRS1976

A temperature dependence kinetics study of the reactions of Cl/2-P-3/2/ with O3, CH4, and H2O2

The temperature dependence of two chlorine atom reactions of considerable fundamental importance to stratospheric chemistry was studied using the technique of flash photolysis-resonance fluorescence. The reactions of interest were: (1) Cl + O3 yields ClO + O2 studied at 220-350 K, and (2) Cl + CH4 yields CH3 + HCl studied at 218-401 K. In addition, the reaction Cl + H2O2 yields HCl + HO2 was studied at 300 K. The corresponding rate constants are provided for the three reactions. The new rate data implies the need to revise downward by a factor of 2.4-3 the magnitude of the ozone perturbation due to the presence of ClO/x/ species in the stratosphere, predicted by earlier model calculations.

Watson, R.↗
NASA NTRS1976

A reexamination of the photochemistry of the Cl2-O3 system

An analysis is conducted of experimental data reported by Norrish and Neville (1934) who studied quantum yields for ozone destruction. A reaction scheme is presented for the Cl2-O3 system. It is demonstrated that the reaction scheme provides a quantitative explanation concerning the main features of the experimental data. Attention is given to reactions involving ClO, OClO, ClOO, and ClO3.

Rundel, R. D.↗
NASA NTRS1977

Atomic and molecular fluorescence as a stratospheric species monitor

The results of an investigation are presented evaluating the potential of atomic and molecular fluorescence as a stratospheric monitor of the concentrations of any one of 18 minor species: Cl, Cl2, ClO, ClO2, CO, H2, HCHO, HCl, HNO2, HNO3, H2S, NH3, NO, NO2, N2O, O, OH, and SO2. All spectral regions from the vacuum ultraviolet through the infrared were included. It was found that suitable systems can be constructed for the stratospheric monitoring of CO (5 ppb), NO2 (less than 1 ppb), OH (0.2 ppt), and O (50-200 ppt). The fluorescence sensitivities for Cl (0.5-1.0 ppt), H2 (0.2 ppm at 10 torr) and SO2 (1-10 ppb) are marginally insufficient with current technology.

Schofield, K.↗
NASA NTRS1978

Temporal and latitudinal variations of stratospheric trace gases - A critical comparison between theory and experiment

Global calculations of stratospheric HOx, Clx, and NOx are presented which include the effects of planetary albedo and diurnal and seasonal variations of the insolation. Comparisons are made with a wide range of atmospheric measurements at different latitudes and altitudes. Agreement between theory and observations is generally within a factor of 2. The theory appears to explain adequately the major features of latitude and seasonal distributions of NO2 and HNO3. The results indicate that mesospheric OH makes an appreciable contribution to the total OH column abundance and strongly suggest that nitrogen oxides exist principally in the form of HNO3 at high latitudes in winter. There are difficulties in reconciling OH, ClO, and O3 observations in the upper stratosphere.

Wofsy, S. C.↗