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12 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Light‐driven Transformation of Carbon Monoxide into Hydrocarbons using CdS@ZnS : VFe Protein Biohybrids

Enzymatic Fisher-Tropsch (FT) process catalyzed by vanadium (V)-nitrogenase can convert carbon monoxide (CO) to longer-chain hydrocarbons (>C2) under ambient conditions, although this process requires high-cost reducing agent(s) and/or the ATP-dependent reductase as electron and energy sources. Using visible light-activated CdS@ZnS (CZS) core-shell quantum dots (QDs) as alternative reducing equivalent for the catalytic component (VFe protein) of V-nitrogenase, we first report a CZS : VFe biohybrid system that enables effective photo-enzymatic C−C coupling reactions, hydrogenating CO into hydrocarbon fuels (up to C4) that can be hardly achieved with conventional inorganic photocatalysts. Surface ligand engineering optimizes molecular and opto-electronic coupling between QDs and the VFe protein, realizing high efficiency (internal quantum yield >56 %), ATP-independent, photon-to-fuel production, achieving an electron turnover number of >900, that is 72 % compared to the natural ATP-coupled transformation of CO into hydrocarbons by V-nitrogenase. The selectivity of products can be controlled by irradiation conditions, with higher photon flux favoring (longer-chain) hydrocarbon generation. The CZS : VFe biohybrids not only can find applications in industrial CO removal for high-value-added chemical production by using the cheap, renewable solar energy, but also will inspire related research interests in understanding the molecular and electronic processes in photo-biocatalytic systems.

Chemistry↗
DOE OSTI2020

Thermoelectric transport of semiconductor full-Heusler VFe 2 Al

Seebeck coefficient of VFe 2 Al over a wide range of doping levels can be explained only with a small band-gap ( E g ) range of 0.02–0.04 eV. This E g value is also consistent with high-temperature resistivity data of nominally stoichiometric VFe 2 Al.

Anand, Shashwat↗
DOE OSTI2020

Materials Data on VFe(P2O7)2 by Materials Project

VFe(P2O7)2 crystallizes in the triclinic P1 space group. The structure is three-dimensional. V5+ is bonded to six O2- atoms to form VO6 octahedra that share corners with six PO4 tetrahedra. There are a spread of V–O bond distances ranging from 1.84–1.93 Å. Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six PO4 tetrahedra. There are a spread of Fe–O bond distances ranging from 2.01–2.05 Å. There are four inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one VO6 octahedra, corners with two equivalent FeO6 octahedra, and a cornercorner with one PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 38–49°. There are a spread of P–O bond distances ranging from 1.50–1.62 Å. In the second P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one VO6 octahedra, corners with two equivalent FeO6 octahedra, and a cornercorner with one PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 21–48°. There are a spread of P–O bond distances ranging from 1.51–1.64 Å. In the third P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one FeO6 octahedra, corners with two equivalent VO6 octahedra, and a cornercorner with one PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 31–44°. There are a spread of P–O bond distances ranging from 1.50–1.61 Å. In the fourth P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one FeO6 octahedra, corners with two equivalent VO6 octahedra, and a cornercorner with one PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 39–48°. There are a spread of P–O bond distances ranging from 1.50–1.60 Å. There are fourteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 150 degrees geometry to one V5+ and one P5+ atom. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to one V5+ and one P5+ atom. In the third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Fe3+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a bent 150 degrees geometry to one V5+ and one P5+ atom. In the fifth O2- site, O2- is bonded in a bent 150 degrees geometry to one V5+ and one P5+ atom. In the sixth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one V5+ and one P5+ atom. In the seventh O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms. In the eighth O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms. In the ninth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Fe3+ and one P5+ atom. In the tenth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Fe3+ and one P5+ atom. In the eleventh O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Fe3+ and one P5+ atom. In the twelfth O2- site, O2- is bonded in a bent 150 degrees geometry to one V5+ and one P5+ atom. In the thirteenth O2- site, O2- is bonded in a bent 150 degrees geometry to one Fe3+ and one P5+ atom. In the fourteenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Fe3+ and one P5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on VFe(PO4)2 by Materials Project

VFe(PO4)2 crystallizes in the trigonal R3 space group. The structure is three-dimensional. there are three inequivalent V3+ sites. In the first V3+ site, V3+ is bonded to six O2- atoms to form VO6 octahedra that share corners with six PO4 tetrahedra. There is three shorter (1.90 Å) and three longer (2.02 Å) V–O bond length. In the second V3+ site, V3+ is bonded to six O2- atoms to form VO6 octahedra that share corners with six PO4 tetrahedra and a faceface with one FeO6 octahedra. There is three shorter (1.93 Å) and three longer (2.04 Å) V–O bond length. In the third V3+ site, V3+ is bonded to six O2- atoms to form VO6 octahedra that share corners with six PO4 tetrahedra. There is three shorter (1.92 Å) and three longer (2.04 Å) V–O bond length. There are three inequivalent Fe3+ sites. In the first Fe3+ site, Fe3+ is bonded to six O2- atoms to form distorted FeO6 octahedra that share corners with six PO4 tetrahedra, a faceface with one VO6 octahedra, and a faceface with one FeO6 octahedra. There are three shorter (2.16 Å) and three longer (2.20 Å) Fe–O bond lengths. In the second Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six PO4 tetrahedra and a faceface with one FeO6 octahedra. There are three shorter (1.95 Å) and three longer (2.10 Å) Fe–O bond lengths. In the third Fe3+ site, Fe3+ is bonded in a 6-coordinate geometry to six O2- atoms. All Fe–O bond lengths are 2.21 Å. There are two inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with two FeO6 octahedra and corners with three VO6 octahedra. The corner-sharing octahedra tilt angles range from 27–47°. There are a spread of P–O bond distances ranging from 1.52–1.57 Å. In the second P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with two FeO6 octahedra and corners with three VO6 octahedra. The corner-sharing octahedra tilt angles range from 26–49°. There are a spread of P–O bond distances ranging from 1.53–1.57 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 150 degrees geometry to one V3+ and one P5+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one V3+, one Fe3+, and one P5+ atom. In the third O2- site, O2- is bonded in a bent 150 degrees geometry to one Fe3+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one V3+, one Fe3+, and one P5+ atom. In the fifth O2- site, O2- is bonded in a bent 150 degrees geometry to one V3+ and one P5+ atom. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to two Fe3+ and one P5+ atom. In the seventh O2- site, O2- is bonded in a 3-coordinate geometry to one V3+, one Fe3+, and one P5+ atom. In the eighth O2- site, O2- is bonded in a bent 150 degrees geometry to one V3+ and one P5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on VFe(CuO2)2 by Materials Project

VFe(CuO2)2 crystallizes in the trigonal R-3m space group. The structure is three-dimensional. V3+ is bonded to six O2- atoms to form edge-sharing VO6 octahedra. All V–O bond lengths are 2.05 Å. Fe3+ is bonded to six O2- atoms to form edge-sharing FeO6 octahedra. All Fe–O bond lengths are 2.05 Å. Cu1+ is bonded in a linear geometry to two O2- atoms. Both Cu–O bond lengths are 1.85 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded to three equivalent Fe3+ and one Cu1+ atom to form a mixture of distorted edge and corner-sharing OFe3Cu trigonal pyramids. The O–Cu bond length is 1.85 Å. In the second O2- site, O2- is bonded to three equivalent V3+ and one Cu1+ atom to form distorted OV3Cu trigonal pyramids that share corners with ten OFe3Cu trigonal pyramids and edges with three equivalent OV3Cu trigonal pyramids. The O–Cu bond length is 1.85 Å. In the third O2- site, O2- is bonded to three equivalent Fe3+ and one Cu1+ atom to form a mixture of distorted edge and corner-sharing OFe3Cu trigonal pyramids. In the fourth O2- site, O2- is bonded to three equivalent V3+ and one Cu1+ atom to form distorted OV3Cu trigonal pyramids that share corners with ten OFe3Cu trigonal pyramids and edges with three equivalent OV3Cu trigonal pyramids. In the fifth O2- site, O2- is bonded to three equivalent Fe3+ and one Cu1+ atom to form a mixture of distorted edge and corner-sharing OFe3Cu trigonal pyramids. All O–Fe bond lengths are 2.05 Å. The O–Cu bond length is 1.85 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on VFe by Materials Project

FeV is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. V is bonded in a body-centered cubic geometry to eight equivalent Fe atoms. All V–Fe bond lengths are 2.50 Å. Fe is bonded in a body-centered cubic geometry to eight equivalent V atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on VFe(PO4)2 by Materials Project

Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on VFe by Materials Project

FeV crystallizes in the orthorhombic Cmmm space group. The structure is two-dimensional and consists of two FeV sheets oriented in the (0, 1, 0) direction. V is bonded in a 12-coordinate geometry to four equivalent Fe atoms. All V–Fe bond lengths are 2.50 Å. Fe is bonded in a 12-coordinate geometry to four equivalent V atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2026

A comprehensive first-principles study of the effects of the exchange-correlation functional and magnetism on defect and diffusion properties of the CoCrNi medium-entropy alloy

The present work is a novel, systematic study of the effect of density functional theory input parameters on the vacancy formation energy (VFE), migration barrier for diffusion, and electronic structure for each element in the CoCrNi medium-entropy alloy (MEA). In particular, the novelties include: (1) calculating the aforementioned properties of Co, Cr, or Ni, in the CoCrNi MEA using magnetic and non-magnetic states, and two versions of the generalized gradient approximation: Perdew, Burke, and Ernzerhof (PBE) and the PBE version for solids (PBEsol), and (2) a detailed comparison of 0 K activation energy to experimental creep activation energies. First-principles calculations at 0 K are performed using the Vienna ab-initio simulation package. Special quasirandom structures (SQS) and Widom-type substitution are employed. For each element, Co, Cr, or Ni, non-magnetic calculations result in a higher VFE and larger range of calculated values for the configurations studied. The averaged migration barrier is the highest for Co in the CoCrNi for three of four sets of calculation parameters in the configurations studied. Finally, the results indicate that the average 0 K activation energy for diffusion makes up 70–80% of the experimental creep activation energy, depending on the exchange-correlation functional employed.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Reductant‐ or Light‐Driven ATP‐Independent Reduction of CO 2 by Nitrogenase MoFe Protein

Nitrogenase is a versatile metalloenzyme that activates and reduces small molecules like N 2 , CO, and CO 2 into value-added chemicals at ambient conditions. Previously, it is shown that the Mo-nitrogenase could reduce CO 2 to CO, but not to hydrocarbons, in an ATP-dependent reaction. Here, it is reported that the ability of the catalytic component of Mo-nitrogenase (MoFe protein) enables ATP-independent reduction of CO 2 to up to C 4 hydrocarbons in room-temperature reactions driven by a chemical reductant (Eu II –DTPA) or visible light (via CdS@ZnS (CZS) quantum dots). Moreover, an opposite deuterium isotope effect is observed on the Eu II –DTPA driven reactions of CO 2 reduction by MoFe protein and its V-counterpart (VFe protein), in that the former displays higher activities in H 2 O, and the latter displays higher activities in D 2 O. Furthermore, these results provide an important foundation for further mechanistic exploration of the nitrogenase-enabled, atypical Fischer–Tropsch type reaction that uses CO 2 instead of CO as a substrate; moreover, they serves as a potential template for the future development of nitrogenase-based applications that effectively recycle the greenhouse gas CO 2 into valuable fuel products.

C-C coupling↗
DOE OSTI2020

CO as a substrate and inhibitor of H + reduction for the Mo-, V-, and Fe-nitrogenase isozymes

Three known nitrogenase isozymes, Mo-, V-, and Fe-, catalyze biological reduction of dinitrogen (N 2 ) to ammonia (NH 3 ). All three utilize the same reductive elimination mechanism: an intermediate with two metal-bound hydrides reductively-eliminates hydrogen gas (H 2 ) in a reaction coupled to binding and activation of N 2 . Nonetheless, the three isozymes show dramatically different relative rates of H 2 formation and N 2 reduction, revealing important differences in reactivity with substrates. Carbon monoxide (CO) has been characterized as both an inhibitor and substrate for Mo- and V-nitrogenases, but not for the Fe-nitrogenase. In this work, we present a comparative study of the reactivity of the three isozymes with CO, examining CO both as a substrate and as an inhibitor of proton (H + ) reduction under steady-state conditions. For Mo-nitrogenase, there is neither detectable reduction of CO nor inhibition of H + reduction. Fe- and V-nitrogenase show CO reduction and inhibition of H + reduction that depends on the CO partial pressure. For V-nitrogenase, ethylene (C 2 H 4 ) is the major reduction product with a maximum specific activity of ~7.5 nmol C 2 H 4 /nmol VFe protein/min at 1 atm CO. The major product of CO reduction for Fe-nitrogenase is methane (CH 4 ) with a maximum specific activity of ~4.8 nmol CH 4 /nmol FeFe protein/min at 0.05 atm CO. The rate of CH 4 production by Fe-nitrogenase progressively increases to a maximum at 0.05 atm CO and then declines to ~10% with increasing CO partial pressure up to 1 atm. CO does not inhibit proton reduction in Mo-nitrogenase but shows 16% inhibition for V-nitrogenase and 35% for Fe-nitrogenase.

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

Proton transfer during reduction of the catalytic metallo-cofactors of the three nitrogenase isozymes

Nitrogenase catalyzes biological nitrogen fixation, the conversion of atmospheric N 2 into bioavailable ammonia. The three nitrogenase isozymes—Mo-nitrogenase, V-nitrogenase, and Fe-nitrogenase—utilize catalytic cofactors distinguished by their metal composition (Fe 7 M, M = Mo, V, or Fe; denoted FeM-co). Their catalytic cycles involve stepwise addition of 8[e−/H+] to FeM-co, generating intermediates designated E n , where n is the number of [e − /H + ] delivered. The electron-transfer has been extensively characterized, but the proton delivery has not. Here, we investigate [e − /H + ] delivery during early-stage conversions, primarily E 0 → E 1 (H), for each of the three nitrogenases, using as reductants γ-ray-generated thermolyzed, mobile electrons at 77 K, and radiation-generated solvent radicals during subsequent annealing to higher temperatures. Our results show E 0 → E 1 (H) conversion differs among the three MFe-proteins. The FeMo-co of MoFe-protein accepts an electron (ET) during 77 K γ-irradiation, but proton transfer (PT) to generate E 1 (H) is only enabled by conformational or thermodynamic activation upon cryoannealing to ∼200 K(ET/PT). For VFe-protein, E 1 (H) forms during annealing at-and-above 210 K by electron-transfer to FeV-co from radicals through proton-coupled electron transfer (PCET), which too is enabled by activated proton transfer. FeFe-protein differs in directly exhibiting delivery of protons at 77 K, which together with the mobile electrons react to form E 1 (H). This could well occur by PCET at 77 K, but does not preclude the possibility of sequential 77 K electron/proton transfer (ET/PT). In addition, 450 nm photolysis reveals the E 1 (H) state of FeV-co, like that of FeFe-co, contains a hydride bound to a formally oxidized cofactor. The mechanistic differences observed here provide a contribution towards understanding the sources of catalytic differences among the three nitrogenase isozymes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗