VIB Elements Research Articles

Doping-mediated interface engineered Ni3S2: Economically viable electrochemical methanol-mediated water splitting

Electrochemical water splitting is the front runner to meet the global green hydrogen demand. The development of a noble metal-free earth-abundant electrocatalyst is desired to rationalize an economically viable electrochemical water-splitting system. The sluggish anodic oxygen evolution reaction (OER) is the bottleneck of the electrochemical water-splitting system. Herein, to improve OER kinetics, group VIB elements such as chromium (Cr), molybdenum (Mo), and tungsten (W) doped nickel sulfides (Ni3S2) nanosheets (NSs) are synthesized by two-step hydrothermal method to modulate the intrinsic electrocatalytic activity of the pure Ni3S2. Among all the doped samples, the Cr-doped Ni3S2 catalyst exhibited excellent OER with an ultra-low overpotential of 248 mV and MOR with a potential of 1.36 V @ 10 mA cm−2 vs RHE achieving a lower Tafel slope of 95.5 mV/dec and 46.4 mV/dec and outstanding durability with negligible degradation respectively. Furthermore, the Pt/C||Cr-Ni3S2 (1.48 V) system outperforms commercial Pt/C||RuO2 (1.53 V @ 10 mA cm−2) in a two-electrode configuration. The methanol-mediated hybrid water splitting system only warranted a cell voltage of 1.38 V to attain 10 mA cm−2 for the Pt/C||Cr-Ni3S2 system in the presence of 0.1 M methanol (MeOH). The methanol oxidation reaction (MOR) mediated the hybrid water electrolyzer system demonstrates reduced operation cell voltage while additionally electro-synthesizing formate as a value-added chemical. The overall work is motivated to rationalize the importance of doping-mediated interface-engineered catalyst synthesis to improve the electrocatalytic efficiency of the hybrid water electrolyzer.

Carbon defect induced evolution of structural and mechanical properties in substoichiometric (HfMoNbZr)Cx films

Substoichiometric (HfMoNbZr)Cx films with varied carbon content were synthesized using non-reactive magnetron sputtering. Findings reveal that the (HfMoNbZr)Cx film predominantly exhibits a single-phase FCC structure, which transforms to a dual-phase structure consisting of FCC and Hex. phases at higher carbon content. This behavior arises from the segregation of group VB (Nb) and VIB (Mo) elements from the FCC lattice. The film hardness (H) and elastic modulus (E) increases with rising carbon content accompanied by a decrease of coefficient of friction (COF). However, the wear rate is not decreased despite the increased H and reduced COF of the as-deposited films. This phenomenon is explained by examining the differences in the wear mechanisms between (HfMoNbZr)Cx films with single- and dual- phase structures.

Effect of doping IVB, VB and VIB elements on structure, stability, elastic and electronic properties of the O and B2 of Ti2AlNb intermetallic: A first principles study

The intermetallic stability, structural, and elastic properties of the B2 and the O intermetallic of Ti2AlNb intermetallic doped with IVB, VB, and VIB elements of the periodic table are studied using density functional theory. The energy of formation and calculated elastic constants reveal that all the doped intermetallics are thermodynamically and mechanically stable. The derived elastic moduli and Pugh's ratio confirm that doping with quaternary elements can enhance the mechanical properties and ductility of the Ti2AlNb intermetallic in both the B2 and the O intermetallic. Further, elements that enhance the ductility and hardness in the O intermetallic, decrease the same in the B2 intermetallic. Among all the systems, Mo and W provide the most enhancement in B, G, and E values in both the B2 and O intermetallic. Ductility of the B2 intermetallic is most enhanced by Ti and Nb while of the O intermetallic by Cr and Mo. All the dopants increase the melting point where W provides the most enhancement. Poisson's ratio, hardness, and Cauchy pressures are further investigated. The electronic density of states indicates that dopants induce redistribution of charge due to new bond formations resulting to a significant change in intermetallic stability and mechanical properties.

Structures and optoelectronic properties of two-dimensional MC6 (M = Ti and Hf) predicted by computational approaches

The group ⅥB elements have good compatibility with carbon to form two-dimensional carbides. In this work, two kinds of two-dimensional metal carbides (2D-MC6, M = Ti and Hf) were theoretically proposed. Using first-principles calculations, we optimized their structures and checked their dynamical/thermal stabilities. Furthermore, their electronic, mechanical and optical properties were also computationally investigated. Calculations on electronic properties show that the 2D-TiC6 and 2D-HfC6 exhibit direct band gap of 0.82 eV and indirect band gap of 1.20 eV, respectively. Calculations on mechanical properties indicate that 2D-TiC6 and 2D-HfC6 have good elasticity. By applying biaxial strain or external electric field, the electronic band gap of 2D-TiC6 and 2D-HfC6 can be effectively tuned. Due to the moderate direct band gap, the 2D-TiC6 exhibits smaller exciton binding energy (0.58 eV) and larger absorbed photon flux (0.66 mA cm−2) than those of 2D-HfC6. Particularly, the 2D-TiC6 shows potential for short wave infrared detection or emission applications when certain tensile strain is applied. This study provides new insight into the rational design of functional nanomaterials.

HER activity of MxNi1-x (M = Cr, Mo and W; x ≈ 0.2) alloy in acid and alkaline media

Reported are the synthesis and HER activity of MxNi1-x (M = Cr, Mo and W; x ≈ 0.2) alloy in acid and alkaline media. It was realized that doping group ⅥB element (Cr, Mo, W) in Ni metal matrix can greatly improve corresponding HER activity in both acid and alkaline electrolyte. MoxNi1-x exhibits the highest HER activity among all samples in 1.0 M H2SO4 electrolyte, which it requires only 64 mV to reach current density of 10 mA/cm2. Calculated free-energy of ΔGH∗ for MxNi1-x (M = Cr, Mo and W) well explained their HER activity trend in acid and it follows the order of MoxNi1-x > WxNi1-x > CrxNi1-x. In alkaline condition, their HER activities all deteriorate except CrxNi1-x. HER activity of CrxNi1-x in 1.0 M KOH (η10(base) = 106 mV) surpasses that in 1.0 M H2SO4 (η10(acid) = 160 mV) is quite unexpected. The DFT calculation suggesting the adsorbed OH holds the key and will alter the adsorption energy (ΔGH∗) of neighboring H atom on the surface in alkaline condition. This case study offers a good opportunity to investigate the factor to influence HER behavior of electrocatalyst in acid and alkaline media.

Multifunctional 2H-TaS2 nanoflakes for efficient supercapacitors and electrocatalytic evolution of hydrogen and oxygen.

Layered transition-metal dichalcogenides based on VIB elements have attracted substantial attention for their applications in energy storage and conversion. However, few studies have concentrated on VB element dichalcogenides. Herein, we report that trifunctional 2H-TaS2 nanoflakes exhibit high performance when applied in supercapacitors, hydrogen evolution reactions (HER) and oxygen evolution reactions (OER). Notably, TaS2 nanoflakes delivered a large volumetric capacitance (502 F cm-3 at the scan rate of 10 mV s-1) and remarkable cycling stability (over 91% after 5000 cycles). TaS2 nanoflakes also exhibited remarkable catalytic performances in HER and OER processes, showing very small overpotentials and Tafel slopes, which are far better than those of the previously reported TaS2 electrocatalysts. Furthermore, TaS2 is highly stable in both alkaline and acidic electrolyte solutions. This work offers a new concept to design VB element-based electrodes for future energy storage and conversion applications.

Impact of Alloying on Stacking Fault Energies in γ-TiAl

Microstructure and mechanical properties are key parameters influencing the performance of structural multi-phase alloys such as those based on intermetallic TiAl compounds. There, the main constituent, a γ -TiAl phase, is derived from a face-centered cubic structure. Consequently, the dissociation of dislocations and generation of stacking faults (SFs) are important factors contributing to the overall deformation behavior, as well as mechanical properties, such as tensile/creep strength and, most importantly, fracture elongation below the brittle-to-ductile transition temperature. In this work, SFs on the { 111 ) plane in γ -TiAl are revisited by means of ab initio calculations, finding their energies in agreement with previous reports. Subsequently, stacking fault energies are evaluated for eight ternary additions, namely group IVB–VIB elements, together with Ti off-stoichiometry. It is found that the energies of superlattice intrinsic SFs, anti-phase boundaries (APBs), as well as complex SFs decrease by 20–40% with respect to values in stoichiometric γ -TiAl once an alloying element X is present in the fault plane having thus a composition of Ti-50Al-12.5X. In addition, Mo, Ti and V stabilize the APB on the (111) plane, which is intrinsically unstable at 0 K in stoichiometric γ -TiAl.

Preferential site occupancy of alloying elements in TiAl-based phases

First principles calculations are used to study the preferential occupation of ternary alloying additions into the binary Ti-Al phases, namely, γ-TiAl, α2-Ti3Al, βo-TiAl, and B19-TiAl. While the early transition metals (TMs, group IVB, VB, and VIB elements) prefer to substitute for Ti atoms in the γ-, α2-, and B19-phases, they preferentially occupy Al sites in the βo-TiAl. Si is, in this context, an anomaly, as it prefers to sit on the Al sublattice for all four phases. B and C are shown to prefer octahedral Ti-rich interstitial positions instead of substitutional incorporation. The site preference energy is linked with the alloying-induced changes of energy of formation, hence alloying-related (de)stabilisation of the phases. We further show that the phase-stabilisation effect of early TMs on βo-phase has a different origin depending on their valency. Finally, an extensive comparison of our predictions with available theoretical and experimental data (which is, however, limited mostly to the γ-phase) shows a consistent picture.

Effects of Double Substitution with Ge and Te on Thermoelectric Properties of a Skutterudite Compound

Studies have shown that the thermoelectric properties of CoSb3 could be improved by the substitution of group IVB or VIB elements for Sb. However, the substitution volume is limited. To get a better picture of the substitution volume in view of thermoelectric properties, Ge and Te double-substituted skutterudite materials were prepared with the nominal composition of Co4Sb x Ge5.9−0.5x Te6.1−0.5x (x = 11, 10, 9, 8) by the traditional solid-state reaction method and spark plasma sintering, and Rietveld analysis was employed to refine the crystal structure. The results showed that the lattice parameter decreased linearly and the solubility limitations of group IVB and VIB elements were greatly alleviated by the Ge and Te codoping. Besides, the thermoelectric properties were analyzed through measurements of electrical and thermal conductivities as well as room-temperature electrical transport properties. The results showed that the substitution volume of Ge and Te could play an important role in the thermoelectric properties, and a minimum lattice thermal conductivity value of 1.56 W m−1 K−1 was obtained at around 673 K for Co4Sb8Ge1.9Te2.1. Co4Sb11Ge0.4Te0.6 achieved the best figure of merit of 0.89 at around 773 K, which was remarkably improved over that of untreated CoSb3.

Importance of cluster distortions in the tetrahedral cluster compoundsGaM4X8(M=Mo,V,Nb,Ta;X=S,Se):Ab initioinvestigations

In this paper, we study the structural properties of selected representatives of the so-called molybdenum cluster compounds. Belonging to this family are the $\mathrm{Ga}{M}_{4}{X}_{8}$ compounds with $M=\mathrm{Mo}$ as a group VIB element and V, Nb, or Ta as a group VB element. $X$ denotes either S or Se. These compounds are known to exhibit semiconducting behavior in the electrical resistivity, caused by hopping of electrons between well-separated metal clusters. The large separation of the tetrahedral metal $({M}_{4})$ clusters is believed to be the origin of strong correlations. We show that recent calculations neglected an important type of structural distortion, namely, those happening only within the ${M}_{4}$ unit at a fixed angle $\ensuremath{\alpha}=60\ifmmode^\circ\else\textdegree\fi{}$ of the trigonal (fcc-like) cell. These internal distortions gain a significant amount of energy compared to the cubic cell and they are---to our knowledge---almost undetectable with powder x-ray diffraction experiments. However, they strongly influence the band-structure by opening up a gap at the Fermi-energy. This, however, puts into question whether all compounds of this family are really Mott insulators as stated elsewhere. In particular, ferromagnetic $\mathrm{Ga}{\mathrm{Mo}}_{4}{\mathrm{S}}_{8}$ and $\mathrm{Ga}{\mathrm{V}}_{4}{\mathrm{S}}_{8}$ are well described within density functional theory. Only the Nb- and Ta-based representatives require a large effort due to the lack of magnetic long-range order caused by frustrated antiferromagnetic $M\text{\ensuremath{-}}M$ interactions.

Cr, Mo and W used as VPO promoters in the partial oxidation of n-butane to maleic anhydride

The present work addresses the issue of the promoter effect produced by group VIB elements added to the basic VPO formulation using different methods and loads in order to obtain information linking the catalytic behavior of the solids with their physicochemical properties. The unpromoted VPO precursor (VOHPO 4·1/2H 2O) was prepared from V 2O 5 reduced with an alcoholic mixture and 100% H 3PO 4. Cr, Mo or W were either impregnated on the VPO precursor or co-precipitated during the precursor synthesis. The precursors containing varying loads of the promoter were activated following a standard procedure in the same flow micro-reactor where the catalytic performance was evaluated. The precursors and the catalysts were characterized by X-ray diffraction (XRD) and laser Raman spectroscopy (LRS). Acetonitrile was used as a probe molecule to test the strength of the Lewis acid sites monitored by FTIR. The amount of chemisorbed acetonitrile was measured in a standard high vacuum system. The addition of the promoters invariably increased the catalytic activity but in every case there was an optimum load to achieve the best selectivity. The origin of this maximum could be ascribed to the right balance between the presence of very strong Lewis acid sites and the development of V 5+ isolated sites in the matrix of the vanadyl pyrophosphate, by far the major crystalline phase present in the catalyst. The three group VIB promoters affect the balance between acid and redox properties but increase the overall activity in all cases.

Spiral chain structure of high pressureselenium−II′andsulfur−IIfrom powder x-ray diffraction

The structure of high pressure phases, selenium-II{sup '} (Se-II{sup '}) and sulfur-II (S-II), for {alpha}-Se{sub 8} (monoclinic Se-I) and {alpha}-S{sub 8} (orthorhombic S-I) was studied by powder x-ray diffraction experiments. Se-II{sup '} and S-II were found to be isostructural and to belong to the tetragonal space group I4{sub 1}/acd, which is made up of 16 atoms in the unit cell. The structure consisted of unique spiral chains with both 4{sub 1} and 4{sub 3} screws. The results confirmed that the structure sequence of the pressure-induced phase transitions for the group VIb elements depended on the initial molecular form. The chemical bonds of the phases are also discussed from the interatomic distances that were obtained.

The Crystal Chemistry of Sulfate Minerals

Research Article| January 01, 2000 The Crystal Chemistry of Sulfate Minerals Frank C. Hawthorne; Frank C. Hawthorne Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2 Search for other works by this author on: GSW Google Scholar Sergey V. Krivovichev; Sergey V. Krivovichev Department of Civil Engineering and Geological Sciences, 156 Fitzpatrick Hall, University of Notre Dame, Notre Dame, Indiana 46556 Search for other works by this author on: GSW Google Scholar Peter C. Burns Peter C. Burns Department of Civil Engineering and Geological Sciences, 156 Fitzpatrick Hall, University of Notre Dame, Notre Dame, Indiana 46556 Search for other works by this author on: GSW Google Scholar Reviews in Mineralogy and Geochemistry (2000) 40 (1): 1–112. https://doi.org/10.2138/rmg.2000.40.1 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Frank C. Hawthorne, Sergey V. Krivovichev, Peter C. Burns; The Crystal Chemistry of Sulfate Minerals. Reviews in Mineralogy and Geochemistry 2000;; 40 (1): 1–112. doi: https://doi.org/10.2138/rmg.2000.40.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyReviews in Mineralogy and Geochemistry Search Advanced Search Sulfur is the fifteenth most abundant element in the continental crust of the Earth (260 ppm), and the sixth most abundant element in seawater (885 ppm). Sulfur (atomic number 16) has the ground-state electronic structure [Ne]3s23p4, and is the first of the group VIB elements in the periodic table (S, Se, Te, Po). In minerals, sulfur can occur in the formal valence states S2−, S0, S4+, and S6+, corresponding to the sulfide minerals, native sulfur, the sulfite minerals, and the sulfate minerals. In the sulfide minerals,... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

5624547 Process for pretreatment of hydrocarbon oil prior to hydrocracking and fluid catalytic cracking

Disclosed is a process for pretreatment of hydrocarbon feed containing sulfur and nitrogen compounds and aromatics prior to hydrocracking or fluid catalytic cracking which comprises: contacting said feedstock with a sulfided catalyst comprising a metal of non-noble Group VIII and Group VIB, and, optionally one or more elements selected from Group IIIA and Group VA of the Periodic Table on a carbon support consisting essentially of activated carbon, optionally on a carbon support treated with phosphorus, having a B.E.T. (Braunauer-Emmett Teller) surface area of at least 100 m 2 /g and an average Pore Diameter greater than 12Å and a Total Pore Volume greater than 0.3 cc/g.

Mixing enthalpies of liquid iron with Vb and VIb elements

By means of a comprehensive literature review and own experiments carried out by levitation alloying calorimetry the mixing enthalpies of liquid iron with Vb and VIb elements were presented. The experimental data were interpreted and analytically represented by different mixing models.

Band structure and structural stability of the high-pressure phases of the group VIb elements

The group VIb elements, such as sulfur, selenium and tellurium, exhibit similar successive structural phase transitions under pressure. The electronic band-structure of the high-pressure phases of these elements is investigated on the basis of first principles calculation. In particular, the structural stability of the β-Po type rhombohedral phase of selenium has been studied, and the result suggests that the rhombohedral structure becomes unstable owing to monoclinic distortion.

特集 半導体 ＶＩｂ族Ｓ，Ｓｅ，ＴｅとＣ７０の圧力誘起構造相転移

X-ray diffraction measurement for selenium and sulfur under high pressure was performed through the angle dispersive method. The structural-transition sequence similar to that of Te was found and the unified interpretation was obtained for pressure-induced structural phase transition of VIb element except for oxygen. In the case of solid C70, the transition from fcc to a simple rhombohedral structure was observed and the rhombohedral phase was concluded to be realized by the partial freezing out of molecular rotation.

Palladium as a Matrix Modifier in Graphite-Furnace Atomic Absorption Spectrometry of Group IIIB - VIB Elements

The performances of palladium as a matrix modifier for group IIIB-VIB elements in graphite-furnace atomic absorption spectrometry were compared to those of other modifiers hitherto reported. The application of palladium and mixed modifiers containing palladium to biological, mineral sediment or natural water samples is summarized. The addition of palladium generally makes a higher thermal pretreatment temperature possible without any sensitivity loss, thus reducing the interferences of coexisting materials. Mass spectrometry connected to graphite-furnace atomic absorption spectrometry enabled real-time observations of the vaporized species in the furnace and revealed the vaporization and atomization process of arsenic and selenium in the presence of palladium. Both elements form compounds PdnMmOl (M=As or Se), which are then decomposed to PdM and finally to atomic vapor of M.The performances of palladium as a matrix modifier for group IIIB-VIB elements in graphite-furnace atomic absorption spectrometry were compared to those of other modifiers hitherto reported. The application of palladium and mixed modifiers containing palladium to biological, mineral sediment or natural water samples is summarized. The addition of palladium generally makes a higher thermal pretreatment temperature possible without any sensitivity loss, thus reducing the interferences of coexisting materials. Mass spectrometry connected to graphite-furnace atomic absorption spectrometry enabled real-time observations of the vaporized species in the furnace and revealed the vaporization and atomization process of arsenic and selenium in the presence of palladium. Both elements form compounds PdnMmOl (M=As or Se), which are then decomposed to PdM and finally to atomic vapor of M.

Nonequilibrium synthesis of NbAl3 and Nb-Al-V Alloys by Laser Cladding: Part I. Microstructure

NbAl3, like many ordered intermetallic compounds, appears to have great potential for application as high-temperature structural material because of the high melting point and stability in high- temperature oxidizing environments. However, the D022 (tI8) lattice structure shows limited ductility at room temperature. Addition of group IVB, VB, and VIB elements to A13X (D022 type of compounds) as partial replacement of X is a method being applied by various researchers to promote ductility in these materials by activation of numerous dislocations and ordered twin- ning. In this study, V was added in different amounts to improve the ductility of NbAl3. How- ever, this has an adverse effect on the oxidation response of the system, as is explained in Part II of this article. This article deals with the microstructure evolution, phase identification, and characterization of laser-clad (rapidly solidified) nominal NbAl3 and also studies the effect of V additions on the final microstructure in this system. Laser cladding of nominal NbAl3 produces two metastable unreported phases [body-centered tetragonal (bct) and base-centered orthorhombic phases]. Addition of V suppresses the primary phase (NbAl3) in the Nb-Al-V system.

Enhancement Effect of Palladium and Albumin on the Sensitivities of Group IIIB - VIB Elements in Graphite Furnace Atomic Absorption Spectrometry

Enhancement Effect of Palladium and Albumin on the Sensitivities of Group IIIB - VIB Elements in Graphite Furnace Atomic Absorption Spectrometry