Enhancing the CO2 Electroreduction of Fe/Ni-Pentlandite Catalysts by S/Se Exchange

The electrochemical reduction of CO₂ is an attractive strategy towards the mitigation of environmental pollution and production of bulk chemicals as well as fuels by renewables. The bimetallic sulfide Fe_4.5Ni_4.5S₈ (pentlandite) was recently reported as a cheap and robust catalyst for electrochemical water splitting, as well as for CO₂ reduction with a solvent-dependent product selectivity. Inspired by numerous reports on monometallic sulfoselenides and selenides revealing higher catalytic activity for the CO₂ reduction reaction (CO₂RR) than their sulfide counterparts, the authors investigated the influence of stepwise S/Se exchange in seleno-pentlandites Fe_4.5Ni_4.5S_8-YSe_Y (Y=1–5) and their ability to act as CO₂ reducing catalysts. It is demonstrated that the incorporation of higher equivalents of selenium favors the CO₂RR with Fe_4.5Ni_4.5S₄Se₄ revealing the highest activity for CO formation. Under galvanostatic conditions in acetonitrile, Fe_4.5Ni_4.5S₄Se₄ generates CO with a Faradaic Efficiency close to 100 % at applied current densities of −50 mA cm⁻² and −100 mA cm⁻². This work offers insight into the tunability of the pentlandite based electrocatalysts for the CO₂ reduction reaction.     

Thermal oxidation of concentrates of Co-Ni thiospinels

Co-Ni concentrates whose major phase components are pentlandite (Ni,Fe,Me)₉S₈, linneite Co₃S₄, polydymite Ni₃S₄, and siegenite NiCo₂S₄ were subjected to oxidation with atmospheric oxygen under the conditions of nonisothermal and isothermal heating in the interval 20–900°C. The process was studied by differential thermal, X-ray phase, and chemical analysis. The reaction schemes based on the data obtained were suggested, and the optimal temperature interval of low-temperature sulfatizing roasting of Co-Ni thiosphinels was chosen.     

The section of the Fe–Ni–S phase diagram constructed by directional crystallization and thermal analysis

A nontrivial polythermal cross-section through the Fe–Ni–S phase diagram was plotted using a combination of directional crystallization and DTA methods. The crystallized sample was grown from the liquid (L) of the following composition Fe = 18, Ni = 35, and S = 47 at.%. It consisted of two single-phase sites formed from mss (Fe _z Ni_1?z )S_1±δ and hzss (Ni _z Fe_1?z )_3±δS₂. The phase reaction L + mss = hzss proceeded on the boundary between these sites. The trajectories of melt and solid composition on the Gibbs triangle were calculated from the distribution of components along the sample. The tie-line transformation was determined from these data. Liquidus temperatures along the trajectory were measured by the DTA method and calculated with the help of a mathematical model. The nontrivial cross-section of the diagram constructed from these data shows the phase equilibrium conditions. The cross-section consists of two tie-line linear surfaces L–mss and L–hzss.     

Synthesis and characterization of new heterometallic iron sulfur nitrosyl clusters

The reactivity of the (PPN)₂[Fe₈S₆(NO)₈] and (PPN)₂[Fe₆S₆(NO)₆] clusters is explored and new derivative clusters have been synthesized and structurally characterized. The unique (PPN)₂Fe₄S₄(NO)₆ “open-cubane” cluster with a chair like Fe₄S₄ core is obtained along with the mixed metal pentandite-like clusters (PPN)₂[Mo₂Fe₆S₆(NO)₆(CO)₆], (PPr₃)₂Cu₂Fe₆S₆(NO)₆, (PPr₃)₄Cu₄Fe₄S₆(NO)₄, (PPr₃)₂Ni₂Fe₆S₆(NO)₆, (PPr₃)₃Ni₃Fe₄S₆(NO)₄. The rich electrochemistry of the mixed metal clusters is presented as well.     

Fe0.45S0.55-Ni0.66S0.34 section of the Fe-Ni-S phase diagram

The Fe_0.45S_0.55-Ni_0.66S_0.34 section of the Fe-Ni-S phase diagram was constructed using thermal analysis, microscopy, X-ray powder diffraction, and electron probe microanalysis data obtained for the samples prepared by isothermal annealing and thermal analysis and by directional solidification of Fe_0.2665Ni_0.2665S_0.467 melt under quasi-equilibrium conditions. Four invariant phase reactions are found in this section. The solid-phase mechanism of pentlandite formation is verified. Original Russian Text ? V.I. Kosyakov, E.F. Sinyakova, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 7, pp. 1212–1219.     

The role of pyrrhotite (Fe7S8) and the sample texture in the hydrothermal transformation of pentlandite ((Fe,Ni)9S8) to violarite ((Ni,Fe)3S4)

The catalytic role of pyrrhotite (Fe₇S₈) in the reaction kinetics of the hydrothermal transformation of pentlandite ((Fe,Ni)₉S₈) to violarite ((FeNi₂S₄) was found to depend on the physical form of pyrrhotite. Pyrrhotite in fine scale intergrown with pentlandite boosts the reaction, whereas in a mechanical mixture of pyrrhotite and pentlandite, it plays the opposite role. This phenomenon was interpreted as result of dissolution of pyrrhotite under reaction conditions.     

Sustainable and rapid preparation of nanosized Fe/Ni-pentlandite particles by mechanochemistry

In recent years, metal-rich sulfides of the pentlandite type (M₉S₈) have attracted considerable attention for energy storage applications. However, common synthetic routes towards pentlandites either involve energy intensive high temperature procedures or solvothermal methods with specialized precursors and non-sustainable organic solvents. Herein, we demonstrate that ball milling is a simple and efficient method to synthesize nanosized bimetallic pentlandite particles (Fe_4.5Ni_4.5S₈, Pn) with an average size of ca. 250 nm in a single synthetic step from elemental- or sulfidic mixtures. We herein highlight the effects of the milling ball quantity, precursor types and milling time on the product quality. Along this line, Raman spectroscopy as well as temperature/pressure monitoring during the milling processes provide valuable insights into mechanistic differences between the mechanochemical Pn-formation. By employing the obtained Pn-nanosized particles as cathodic electrocatalysts for water splitting in a zero-gap PEM electrolyzer we provide a comprehensive path for a potential sustainable future process involving non-noble metal catalysts.

A sustainable and rapid mechanochemical method for the preparation of bimetallic nanosized pentlandite particles as cathode material is developed and tested within zero-gap PEM cells.     

Crystal structure and magnetism of the FexNi8-xSi3 materials, 0 ≤ x ≤ 8

The crystal structure and magnetic properties of the materials Fe_xNi_8-xSi₃ with 0 ≤ x ≤ 8 have been investigated to estimate any possible magnetocaloric effect and compare it to that in known magnetocalorics. Two structural ranges could be identified in this system by X-ray and neutron diffraction. The structure of the samples with 0 ≤ x ≤ 4 is related to the trigonal structure of Ni₃₁Si₁₂. Doubled c lattice parameters compared to the one in Ni₃₁Si₁₂ are observed in the samples with x = 2 and x = 3. The average structure of Fe₂Ni₆Si₃ has been determined by X-ray single-crystal diffraction. The compounds with the compositions 5 ≤ x ≤ 8 crystallize in cubic Fe₃Si-type structure. Magnetic measurements have shown that the compound Fe₃Ni₅Si₃ displays a phase transition close to room temperature. However, its magnetocaloric effect is much smaller than the one in the promising magnetocaloric materials.     

Thermodynamic parameters of liquid ternary Fe1−x(Ni5/6Cr1/6)x alloys

Summary Computer-aidedKnudsen cell mass spectrometry is used for thermodynamic investigations on liquid ternary Fe_1–x(Ni_5/6Cr_1/6)_x alloys. The thermodynamic excess properties have been determined by means of the Digital Intensity-Ratio (DIR) method. Liquid ternary Fe_1–x(Ni_5/6Cr_1/6)_x alloys are characterized by exothermic molar heats of mixingH ^E, negative molar excessGibbs energiesG ^E, and negative molar excess entropiesS ^E. At 1850 K, the minimumH ^E value is –3120 J/mol (42.3 at.% Fe), the minimumG ^E value is –2540 J/mol (30 at.% Fe), and the minimumS ^E value is –0.44 J/(mol K) (60 at.% Fe). At 1850 K, the thermodynamic activities of Fe show slight negative deviations from the ideal behaviour for alloys with a Fe-content of less than 75 at.%, and ideal behaviour for the Fe-rich alloys (x _Fe>0.75).

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Thermodynamische Parameter flüssiger ternärer Fe_1–x(Ni_5/6Cr_1/6)_x-Legierungen

Zusammenfassung Die Thermodynamik flüssiger ternärer Fe_1–x(Ni_5/6Cr_1/6)_x-Legierungen wurde mit Hilfe der computerunterstützten Knudsenzellen-Massenspektrometrie studiert. Die thermodynamische Auswertung der experimentellen Untersuchungen erfolgte nach der digitalen Intensitätsverhältnismethode (DIR). Flüssige ternäre Fe_1–x(Ni_5/6Cr_1/6)_x-Legierungen zeigen exotherme molare MischungswärmenH ^E, negative molareGibbssche ZusatzenergienG ^E, und negative molare ZusatzentropienS ^E. Bei 1850 K sind die Minimumswerte fürH ^E –3120 J/mol (42.3 At.% Fe), fürG ^E –2540 J/mol (30 At.% Fe) und fürS ^E –0.44 J/(mol K) (60 At.% Fe). Bei 1850 K zeigen die thermodynamischen Aktivitäten von Fe bei Legierungen mit einem Fe-Gehalt von höchstens 75 At.% leichte negative Abweichungen vom idealen Verhalten, die Fe-reichsten Legierungen (x _Fe>0.75) verhalten sich hingegen nahezu ideal.

     

泡沫镍负载Fe2O3@Ni3S2纳米线网状结构电极的制备及其电催化析氧性能

通过两步水热法制备泡沫镍(NF)负载Fe_2O_3纳米粒子@Ni_3S_2纳米线网状结构电极(Fe_2O_3@Ni_3S_2/NF)。运用X射线衍射(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)、N_2吸附-脱附测试等方法对电极材料的物相和微观结构特征等进行了表征。水热条件下原位表面化学刻蚀生成的Ni_3S_2纳米线与三维多孔NF基体间拥有强结合力和低界面电阻,Fe_2O_3粒子均匀分布在纳米线的表面。在1 mol·L~(-1)的KOH溶液中,运用线性扫描伏安测试(LSV)、计时电位法、电化学交流阻抗测试(EIS)等对电极的电催化析氧(OER)性能进行了测试。结果表明:在100 mA·cm~(-2)的超高电流密度下,Fe_2O_3@Ni_3S_2/NF电极的OER过电势仅为223 mV,比Ni_3S_2/NF材料的过电势降低了285 mV;经过10 h计时电位测试,性能保持率高达80%。     

Electronic structure of paramagnetic clusters of transition metal ions. 3. Magnetic properties and scattered wave description of the electronic structure of the hexanuclear octahedral cluster [Fe6(μ3−S)8(PEt3)6] (BPh4)2

Spin-polarized Xα–SW calculations of [Fe₆(μ₃?S)₈(PH₃)₆]²⁺ as a model of the cluster [Fe₆(μ₃?S)₈(PEt₃)₆] (BPh₄)₂ have been performed. The highest occupied energy levels are well separated from empty levels, and up to a maximum of eight electrons can be unpaired, giving a maximum spin state with S = 4. This electronic state is consistent with the magnetic data of [Fe₆(μ₃?S)₈(PEt₃)₆](BPh ₄)₂, which have been interpreted using the Heisenberg–Dirac–Van Vleck exchange spin Hamiltonian. The S = 4 state arises from the magnetic coupling between five low-spin (S_i = 1/2) and one intermediate-spin (S = 3/2) iron(III) center. © 1994 John Wiley & Sons, Inc.     

介孔调控Co9S8/Ni3S2复合电极材料及电催化析氢性能

利用快速凝固结合化学脱铝模板法制备前驱体纳米多孔Ni-Co合金,再经气相沉积硫和热氢还原制备纳米多孔Co₉S₈/Ni₃S₂复合电极材料。研究表明,通过气相沉积,硫原子与Ni-Co合金原位生成CoS₂/NiS₂复合相,再经过热氢还原后,形成硫原子比例较低的Co₉S₈/Ni₃S₂复合相。该热氢还原过程不仅提高了Co₉S₈/Ni₃S₂各元素周围的电子密度,而且在其表面调制出有介孔结构的异质界面,进而提高其电子传输能力并增大活性比表面积。相比于其他同条件下制备的Ni、Co硫化物,Co₉S₈/Ni₃S₂拥有更佳的析氢反应（HER）活性,在50 mA·cm^-2的电流密度下,Co₉S₈/Ni₃S₂的HER过电位为234 mV,Tafel斜率为106 mV·dec^-1,经稳定性测试后,电压变化仅为14 mV。     

Phase relations of ternary compounds in the BaFeS system

The phase relations of the ternary phases at 900 and 700°C were determined by heating mixtures in the regions BaSFeSFeS₂ and FeFeSBaS and identifying the products by powder X-ray diffraction. The stable ternary phases at 900°C are BaFe₂S₃, Ba₂FeS₃, Ba₆Fe₈S₁₅, a solid solution BaFeS₂Ba₇Fe₆S₁₄, Ba₂FeS₄, the infinitely adaptive series $\text{Ba}{}_3\text{Fe}{}_{\mathrm{1+x}}\text{S}{}_5\text{,}\text{1}\text{3}\text{≤ x ≤}\text{2}\text{5}$, and Ba₉Fe₁₆S₃₂ which belongs to the infinitely adaptive series Ba_1+xFe₂S₄. At 700°C the stable ternary phases are: BaFe₂S₃, Ba₂FeS₃, BaFeS₂Ba₇Fe₆S₁₄ (solid solution), Ba₆Fe₈S₁₅, Ba₂FeS₄, Ba₅Fe₄S₁₁, and two infinitely adaptive series: Ba₃Fe_1+xS₅ and Ba_1+xFe₂S₄. A stable ternary phase at 700 and 900°C with probable composition Ba₂Fe₄S₅ was found in the FeFeSBaS section.     

单分散NixZn1-xFe2O4纳米颗粒的制备及其磁热效应

以乙酰丙酮金属盐为前驱体,三乙二醇为溶剂,采用多元醇法制备了镍锌不同配比的Ni_xZn_(1-x)Fe_2O_4(x=0,0.3,0.5,0.7和1.0)铁氧体,并通过X射线衍射仪(XRD),透射电子显微镜(TEM)和振动样品磁强计(VSM)等对样品的结构、形貌、磁性能和磁热性能进行了表征。结果表明:Ni_xZn_(1-x)Fe_2O_4铁氧体分散性较好,尺寸均一,形状近似球形,平均粒径为4~5 nm。Ni_xZn_(1-x)Fe_2O_4纳米颗粒在室温下表现出亚铁磁性,饱和磁化强度随着镍含量的增加先增大后减小,当x=0.5时达到最大值29.38 emu·g~(-1)。在382k Hz交变磁场作用下,Ni_(0.5)Zn_(0.5)Fe_2O_4铁氧体温度可升温至313 K,表现出较好的磁热性能。     

Weak Antiferromagnetic Exchange and Ferromagnetic Alignment of FeII (S=2) Spins in Differently Charged {HAT ⋅ (FeIICl2)3}n (n=2- and 3-) Assemblies of Hexaazatriphenylenes (HAT)

Hexaazatrianthracene (HATA) and hexaazatriphenylenehexacarbonitrile {HAT(CN)₆} are reduced by metallic iron in the presence of crystal violet (CV⁺)(Cl⁻). Anionic ligands are produced, which simultaneously coordinate three Fe^IICl₂ to form (CV⁺)₂{HATA ⋅ (Fe^IICl₂)₃}²⁻ ⋅ 3 C₆H₄Cl₂ ( 1 ) and (CV⁺)₃{HAT(CN)_6. (Fe^IICl₂)₃}³⁻ ⋅ 0.5CVCl ⋅ 2.5 C₆H₄Cl₂ ( 2 ). High-spin (S=2) Fe^II atoms in both structures are arranged in equilateral triangles at a distance of 7 Å. An antiferromagnetic exchange is observed between Fe^II in {HATA ⋅ (Fe^IICl₂)₃}²⁻ ( 1 ) with a Weiss temperature (Θ) of −80 K, the PHI estimated exchange interaction (J) is −4.7 cm⁻¹. The {HAT(CN)₆ ⋅ (Fe^IICl₂)₃}³⁻ assembly is obtained in 2 . The formation of HAT(CN)₆^.3− is supported by the appearance of an intense EPR signal with g=2.0037. The magnetic behavior of 2 is described by a strong antiferromagnetic coupling between the Fe^II and HAT(CN)₆^.3− spins with J₁=−164 cm⁻¹ (−2 J formalism) and by a weaker antiferromagnetic coupling between the Fe^II spins with J₂=−15.4 cm⁻¹. The stronger coupling results in the spins of the three Fe^IICl₂ units to be aligned parallel to each other in the assembly. As a result, an increase of the χ_MT values is observed with the decrease of temperature from 9.82 at 300 K up to 15.06 emu ⋅ K/mol at 6 K, and the Weiss temperature is also positive being at +23 K. Thus, a change in the charge and spin state of the HAT-type ligand to ⋅3⁻ results in ferromagnetic alignment of the Fe^II spins, yielding a high-spin (S=11/2) system. DFT calculations showed that, due to the high symmetry and nearly degenerated LUMO of both HATA and HAT(CN)₆, their complexes with Fe^IICl₂ have a variety of closely lying excited high-spin states with multiplicity up to S=15/2.     

Preparation and formation process of Ni2+–Fe3+ CO32− LDHs materials with high crystallinity and well-defined hexagonal shapes

A new complexing agent assisted homogeneous precipitation technology was successfully developed to synthesize Ni²⁺–Fe³⁺ CO₃^2? LDHs materials with crystallinity and well-defined hexagonal shape [1]. By using urea as hydrolysis agent and trisodium citrate as complexing agent, Ni²⁺–Fe³⁺ CO₃^2? LDHs with different ratios of Ni²⁺/Fe³⁺ were prepared under optimized reaction conditions, and their formation process was discussed on the basis of the experimental results. Ni²⁺–Fe³⁺ CO₃^2? LDHs thin hexagonal nanoplates with high crystallinity were obtained for from the ratios of Ni²⁺/Fe³⁺ = 3 and 4, while Ni²⁺–Fe³⁺ CO₃^2? LDHs material from Ni²⁺/Fe³⁺ = 2 could not be obtained due to the formation of impurity β-Ni(OH)₂. The as-prepared Ni²⁺–Fe³⁺ CO₃^2? LDHs materials were completely converted to Cl^? LDHs materials by treating with a NaCl–HCl mixed solution, showing a good anion exchange property. Sodium fluoride, tartarate and trisodium citrate with different molecular structures were chosen as a complexing agent to investigate their effect on the crystalline and shape of the as-prepared materials. Not only had the molecular structure of the complexing agents but also the amount had an obvious effect in the formation of the as-prepared materials. Trisodium citrate played a key role for the formation of Ni²⁺–Fe³⁺ CO₃^2? LDHs materials with high crystalline and well-defined hexagonal shapes, which made the pH deposition range of Fe(OH)₃ increase due to the formation of metal ligand [Fe(C₆H₄O₇)₂]^5? when the pH of the reaction system was above 8. The formed metal ligand [Fe(C₆H₄O₇)₂]^5? changed the translation process of Fe(OH)₃ with Ni²⁺ ions, which reacted with free Ni²⁺ ions and formed Ni²⁺–Fe³⁺ CO₃^2? LDHs materials with high crystallinity and well-defined hexagonal shapes.     

Synthesis and properties of the Co7Se8−xSx and Ni7Se8−xSx solid solutions

We report the synthesis and elementary properties of the Co₇Se_8−xS_x (x=0-8) and Ni₇Se_8−xS_x (x=0-7) solid solutions. Both systems form a NiAs-type structure with metal vacancies. In general, the lattice parameters decrease with increasing x, but in the Ni₇Se_8−xS_x system c increases on going from x=5 to 7. Magnetic susceptibility measurements show that all samples exhibit temperature-independent paramagnetism from 25-250 K. Samples within the Co₇Se_8−xS_x system, as well as Ni₇Se₈ and Ni₇SeS₇, were found to be poor metals with resistivities of ∼0.20 and ∼0.06 mΩ cm at 300 K, respectively. The Sommerfeld constant (γ) was determined from specific heat measurements to be ∼13 mJ/mol_CoK² and ∼7 mJ/mol_NiK² for Co₇Se_8−xS_x and Ni₇Se_8−xS_x, respectively.     

Nanoporous Ni3S2 Film on Ni Foam as Highly Efficient Electrocatalyst for Hydrogen Evolution in Acidic Electrolyte

In this work, nanoporous Ni₃S₂ film (Ni₃S₂/Ni) is in situ synthesized by direct sulfurization of Ni foam under a mild hydrothermal process. Surprisingly, it is found out that the obtained Ni₃S₂/Ni exhibits outstanding HER activity and excellent stability in acidic electrolyte. The structure and nature of the Ni₃S₂/Ni are analyzed with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscope (FE-SEM). On Ni₃S₂/Ni, the onset potential is only ?6.23 mV (vs. RHE) while the large exchange current density is 790 µA cm^?2 and the Tafel slope is 62.47 mV dec^?1. The experimental results demonstrate the potential of Ni₃S₂/Ni for its replacement of Pt-based catalysts.

     

Kinetics of the interaction of iron,copper, and nickel sulfides with a sodium nitrate-sodium carbonate mixture

The interaction of FeS₂, Cu₂S, and Ni₃S₂ with sodium nitrate and sodium carbonate between 573 and 973 K has been investigated by chemical analysis, X-ray diffraction, electron probe X-ray microanalysis, and thermal analysis. The kinetic limitations in these reactions are due to the formation of a passivating layer of reaction products on metal sulfide particles. The solid products of the reactions are sodium sulfate, Fe₂O₃, CuO, NiO, and copper metal.