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Oxygen Evolution and Reduction Reaction Activity Investigations on Fe, Co or Ni embedded Tetragonal Graphene by A Thermodynamical Full-Landscape Searching Scheme.

ABSTRACT: Single transition metal (TM) atoms such as Fe, Co and Ni occupying a carbon divacancy in tetragonal graphene (TG) and bonded with four nitrogen atoms (TM@N₄ TG) as electrocatalysts are investigated by means of first-principles calculations. To consider the effect of solvent species on the local configuration of the active single metal, a thermodynamical full-landscape searching (TFLS) scheme is employed. The calculated thermodynamic overpotentials (η_td ) from our TFLS indicate that Co@N₄ TG displays high catalytic activity toward both oxygen evolution reaction (OER) and reduction reaction (ORR), with η_td ^OER and η_td ^ORR as 0.397 and 0.357 V, respectively. Its OER potential cannot be captured if only one four electron reaction loop (FERL) is considered. The actual active pathways do not always turn out to be the reactions starting from the bare site. Our findings demonstrate that TG is a promising support and TM confined TD can be used to design effective and cheap multifunctional electrocatalysts.

SUBMITTER: Gai Y

PROVIDER: S-EPMC8248917 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Synthetic Designs and Structural Investigations of Biomimetic Ni-Fe Thiolates.

Project description:Described are the syntheses of several Ni(?-SR)2Fe complexes, including hydride derivatives, in a search for improved models for the active site of [NiFe]-hydrogenases. The nickel(II) precursors include (i) nickel with tripodal ligands: Ni(PS3)- and Ni(NS3)- (PS33- = tris(phenyl-2-thiolato)phosphine, NS33- = tris(benzyl-2-thiolato)amine), (ii) traditional diphosphine-dithiolates, including chiral diphosphine R,R-DIPAMP, (iii) cationic Ni(phosphine-imine/amine) complexes, and (iv) organonickel precursors Ni( o-tolyl)Cl(tmeda) and Ni(C6F5)2. The following new nickel precursor complexes were characterized: PPh4[Ni(NS3)] and the dimeric imino/amino-phosphine complexes [NiCl2(PCH?NAn)]2 and [NiCl2(PCH2NHAn)]2 (P = Ph2PC6H4-2-). The iron(II) reagents include [CpFe(CO)2(thf)]BF4, [Cp*Fe(CO)(MeCN)2]BF4, FeI2(CO)4, FeCl2(diphos)(CO)2, and Fe(pdt)(CO)2(diphos) (diphos = chelating diphosphines). Reactions of the nickel and iron complexes gave the following new Ni-Fe compounds: Cp*Fe(CO)Ni(NS3), [Cp(CO)Fe(?-pdt)Ni(dppbz)]BF4, [( R,R-DIPAMP)Ni(?-pdt)(H)Fe(CO)3]BArF4, [(PCH?NAn)Ni(?-pdt)(Cl)Fe(dppbz)(CO)]BF4, [(PCH2NHAn)Ni(?-pdt)(Cl)Fe(dppbz)(CO)]BF4, [(PCH?NAn)Ni(?-pdt)(H)Fe(dppbz)(CO)]BF4, [(dppv)(CO)Fe(?-pdt)]2Ni, {H[(dppv)(CO)Fe(?-pdt)]2Ni]}BF4, and (C6F5)2Ni(?-pdt)Fe(CO)2(dppv) (DIPAMP = (CH2P(C6H4-2-OMe)2)2; BArF4- = [B(C6H3-3,5-(CF3)2]4-)) Within the context of Ni-(SR)2-Fe complexes, these new complexes feature new microenvironments for the nickel center: tetrahedral Ni, chirality, imine, and amine coligands, and Ni-C bonds. In the case of {H[(dppv)(CO)Fe(?-pdt)]2Ni}+, four low-energy isomers are separated by ?3 kcal/mol, one of which features a biomimetic HNi(SR)4 site, as supported by density functional theory calculations.

| S-EPMC6379113 | biostudies-literature

Theoretical Investigations of the Electrochemical Reduction of CO on Single Metal Atoms Embedded in Graphene.

Project description:Single transition metal atoms embedded at single vacancies of graphene provide a unique paradigm for catalytic reactions. We present a density functional theory study of such systems for the electrochemical reduction of CO. Theoretical investigations of CO electrochemical reduction are particularly challenging in that electrochemical activation energies are a necessary descriptor of activity. We determined the electrochemical barriers for key proton-electron transfer steps using a state-of-the-art, fully explicit solvent model of the electrochemical interface. The accuracy of GGA-level functionals in describing these systems was also benchmarked against hybrid methods. We find the first proton transfer to form CHO from CO to be a critical step in C1 product formation. On these single atom sites, the corresponding barrier scales more favorably with the CO binding energy than for 211 and 111 transition metal surfaces, in the direction of improved activity. Intermediates and transition states for the hydrogen evolution reaction were found to be less stable than those on transition metals, suggesting a higher selectivity for CO reduction. We present a rate volcano for the production of methane from CO. We identify promising candidates with high activity, stability, and selectivity for the reduction of CO. This work highlights the potential of these systems as improved electrocatalysts over pure transition metals for CO reduction.

| S-EPMC5746853 | biostudies-literature

Carbothermal Synthesis of Ni/Fe Bimetallic Nanoparticles Embedded into Graphitized Carbon for Efficient Removal of Chlorophenol.

Project description:The reactivity of nanoscale zero-valent iron is limited by surface passivation and particle agglomeration. Here, Ni/Fe bimetallic nanoparticles embedded into graphitized carbon (NiFe@GC) were prepared from Ni/Fe bimetallic complex through a carbothermal reduction treatment. The Ni/Fe nanoparticles were uniformly distributed in the GC matrix with controllable particle sizes, and NiFe@GC exhibited a larger specific surface area than unsupported nanoscale zero-valent iron/nickel (FeNi NPs). The XRD results revealed that Ni/Fe bimetallic nanoparticles embedded into graphitized carbon were protected from oxidization. The NiFe@GC performed excellently in 2,4,6-trichlorophenol (TCP) removal from an aqueous solution. The removal efficiency of TCP for NiFe@GC-50 was more than twice that of FeNi nanoparticles, and the removal efficiency of TCP increased from 78.5% to 94.1% when the Ni/Fe molar ratio increased from 0 to 50%. The removal efficiency of TCP by NiFe@GC-50 can maintain 76.8% after 10 days of aging, much higher than that of FeNi NPs (29.6%). The higher performance of NiFe@GC should be ascribed to the significant synergistic effect of the combination of NiFe bimetallic nanoparticles and GC. In the presence of Ni, atomic H* generated by zero-valent iron corrosion can accelerate TCP removal. The GC coated on the surface of Ni/Fe bimetallic nanoparticles can protect them from oxidation and deactivation.

| S-EPMC8226776 | biostudies-literature

Ni-Fe/Reduced Graphene Oxide Nanocomposites for Hexavalent Chromium Reduction in an Aqueous Environment.

Project description:We designed and synthesized a novel high efficiency Cr(VI) removal material using reduced graphene oxide (RGO) as a support with high specific surface area and a mixture of Fe and Ni nanoparticles (NPs) as a catalytic reducing agent. Such a design enables the composite particle to be integrated with three functions of adsorption, catalysis, and reduction, where RGO could enhance Cr(VI) adsorption, while Fe/Ni NPs increase the catalytic reducing efficiency. The application of a microchip mixer guaranteed a better mixing of GO and subsequent decoration of Fe and Ni NPs on RGO. Cr(VI) removal experiments with various materials are performed, and the results demonstrated that the Ni-Fe/RGO achieved an adsorption capacity of 150.45 mg/g at pH = 7 and 197.43 mg/g at pH = 5 for Cr(VI), which is higher than those of other reported materials at a pH of ∼7. To the best of our knowledge, this is the first example of Ni-Fe/RGO for efficient Cr(VI) removal by using the synergistic effects of increased adsorption, catalysis-assisted reduction, and enhanced mixing effect of a microchip mixer. This work also provides us with a simple and low-cost method for the fabrication of an effective Cr(VI) removal material.

| S-EPMC8829916 | biostudies-literature

Fe@N-Graphene Nanoplatelet-Embedded Carbon Nanofibers as Efficient Electrocatalysts for Oxygen Reduction Reaction.

Project description:An activated carbon nanofiber (CNF) is prepared with incorporated Fe-N-doped graphene nanoplatelets (Fe@NGnPs), via a novel and simple synthesis approach. The activated CNF-Fe@NGnP catalysts exhibit substantially improved activity for the oxygen reduction reaction compared to those of commercial carbon blacks and Pt/carbon catalysts.

| S-EPMC5049621 | biostudies-literature

Tetragonal to triclinic--a phase change for [Fe(TPP)(NO)].

Project description:The temperature dependence of the crystalline phase of (nitrosyl)(tetraphenylporphinato)iron(II), [Fe(TPP)(NO)], has been explored over the temperature range of 33-293 K. The crystalline complex is found in the tetragonal crystal system at higher temperatures and in the triclinic crystal system at lower temperatures. In the tetragonal system, the axial ligand is strongly disordered, with the molecule having crystallographically required 4/m symmetry, leading to eight distinct positions of the single nitrosyl oxygen atom. The phase transition to the triclinic crystal system leads to a partial ordering with the molecule now having inversion symmetry and disorder of the axial nitrosyl ligand over only two positions. The increase in ordering allows subtle molecular geometry features to be observed; in particular, an off-axis tilt of the Fe-N(NO) bond from the heme normal is apparent. The transition of the reversible phase change begins at about 250 K. This transition has been confirmed by both X-ray diffraction studies and a differential scanning calorimetry study.

| S-EPMC2680005 | biostudies-literature

Fe-vacancy order and superconductivity in tetragonal ?-Fe1-xSe.

Project description:Several superconducting transition temperatures in the range of 30-46 K were reported in the recently discovered intercalated FeSe system (A1-xFe2-ySe2, A = K, Rb, Cs, Tl). Although the superconducting phases were not yet conclusively decided, more than one magnetic phase with particular orders of iron vacancy and/or potassium vacancy were identified, and some were argued to be the parent phase. Here we show the discovery of the presence and ordering of iron vacancy in nonintercalated FeSe (PbO-type tetragonal ?-Fe1-xSe). Three types of iron-vacancy order were found through analytical electron microscopy, and one was identified to be nonsuperconducting and magnetic at low temperature. This discovery suggests that the rich-phases found in A1-xFe2-ySe2 are not exclusive in Fe-Se and related superconductors. In addition, the magnetic ?-Fe1-xSe phases with particular iron-vacancy orders are more likely to be the parent phase of the FeSe superconducting system instead of the previously assigned ?-Fe1+?Te.

| S-EPMC3890877 | biostudies-other

Evaluation of electrosynthesized reduced graphene oxide-Ni/Fe/Co-based (oxy)hydroxide catalysts towards the oxygen evolution reaction.

Project description:In this work, the specific role of the addition of graphene oxide (GO) to state-of-the-art nickel-iron (NiFe) and cobalt-nickel-iron (CoNiFe) mixed oxides/hydroxides towards the oxygen evolution reaction (OER) is investigated. Morphology, structure, and OER catalytic activity of the catalysts with and without GO were studied. The catalysts were fabricated via a two-step electrodeposition. The first step included the deposition of GO flakes, which, in the second step, were reduced during the simultaneous deposition of NiFe or CoNiFe. As a result, NiFe-GO and CoNiFe-GO were fabricated without any additives directly on the nickel foam substrate. A significant improvement of the OER activity was observed after combining NiFe with GO (OER overpotential η(10 mA·cm-2): 210 mV) compared to NiFe (η: 235 mV) and GO (η: 320 mV) alone. A different OER activity was observed for CoNiFe-GO. Here, the overall catalytic activity (η: 230 mV) increased compared to GO alone. However, it was reduced in comparison to CoNiFe (η: 224 mV). The latter was associated with the change in the morphology and structure of the catalysts. Further OER studies showed that each of the catalysts specifically influenced the process. The improvement in the OER by NiFe-GO results mainly from the structure of NiFe and the electroactive surface area of GO.

| S-EPMC10071521 | biostudies-literature

A trinuclear Fe-Fe-Ni complex formed by ligand reshuffling.

Project description:The title complex, dicarbonyl-3?(2)C-(?(3)-3,6-dimethyl-3,6-diaza-octane-1,8-dithiol-ato-1:2:3?(7)S:S,N,N',S':S,S')(?(2)-3,6-di-methyl-3,6-diaza-octane-1,8-dithiol-ato-1:2?(5)S,N,N',S':S)-1,2-diiron(II)-3-nickel(0) [Fe(2)Ni(C(8)H(18)N(2)S(2))(2)(CO)(2)], is the second example showing M(?-SR)(2)Ni(0)(CO)(2) coordination (M = any metal atom). Both Fe(II) ions are five-coordinated in distorted trigonal-bipyramidal geometries by two N atoms and three S atoms. The Ni atom is four-coordinated in a distorted tetra-hedral geometry by two S atoms and two carbonyl ligands. One of the 3,6-dimethyl-3,6-diaza-octane-1,8-dithiol-ate ligands is disordered, the major component having a refined occupancy of 0.873?(2). The Fe?Fe distance is 3.0945?(3)Å and the Ni?Fe distance is 2.8505?(3)?Å.

| S-EPMC3120414 | biostudies-literature

Secure searching of biomarkers through hybrid homomorphic encryption scheme.

Project description:As genome sequencing technology develops rapidly, there has lately been an increasing need to keep genomic data secure even when stored in the cloud and still used for research. We are interested in designing a protocol for the secure outsourcing matching problem on encrypted data.We propose an efficient method to securely search a matching position with the query data and extract some information at the position. After decryption, only a small amount of comparisons with the query information should be performed in plaintext state. We apply this method to find a set of biomarkers in encrypted genomes. The important feature of our method is to encode a genomic database as a single element of polynomial ring.Since our method requires a single homomorphic multiplication of hybrid scheme for query computation, it has the advantage over the previous methods in parameter size, computation complexity, and communication cost. In particular, the extraction procedure not only prevents leakage of database information that has not been queried by user but also reduces the communication cost by half. We evaluate the performance of our method and verify that the computation on large-scale personal data can be securely and practically outsourced to a cloud environment during data analysis. It takes about 3.9 s to search-and-extract the reference and alternate sequences at the queried position in a database of size 4M.Our solution for finding a set of biomarkers in DNA sequences shows the progress of cryptographic techniques in terms of their capability can support real-world genome data analysis in a cloud environment.

| S-EPMC5547457 | biostudies-other

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