Tungsten pentaboride WB5-x

Tungsten pentaboride (WB_5-x) is a unique material possessing a number of exciting physical and chemical properties

Theoretical study of adsorption properties and CO oxidation reaction on surfaces of higher tungsten boride (Sci. Rep. 2024, 14, 12788) PDF
Most modern catalysts are based on precious metals and rear-earth elements, making some of organic synthesis reactions economically insolvent. Density functional theory calculations are used here to describe several differently oriented surfaces of the higher tungsten boride WB_5-x, together with their catalytic activity for the CO oxidation reaction. Based on our findings, WB_5-x appears to be an efficient alternative catalyst for CO oxidation. Calculated surface energies allow the use of the Wulff construction to determine the equilibrium shape of WB_5-x particles. It is found that the (010) and (101) facets terminated by boron and tungsten, respectively, are the most exposed surfaces for which the adsorption of different gaseous agents (CO, CO₂, H₂, N₂, O₂, NO, NO₂, H₂O, NH₃, SO₂) is evaluated to reveal promising prospects for applications. CO oxidation on B-rich (010) and W-rich (101) surfaces is further investigated by analyzing the charge redistribution during the adsorption of CO and O₂ molecules. It is found that CO oxidation has relatively low energy barriers. The implications of the present results, the effects of WB_5-x on CO oxidation and potential application in the automotive, chemical, and mining industries are discussed.

Application of tungsten pentaboride as cocatalyst for photocatalytic H2 evolution and CO2 reduction (Appl. Surf. Sci. 2024, 661, 160095) PDF
Catalytic reactions play an important role in modern industry as almost 90 % of the chemical industry is based on catalytic reactions. The development of new, more efficient catalysts will allow significant advances in chemical production, but still remains a rather challenging problem for materials scientists. Here, we have proposed and investigated a new composite photocatalyst based on WB_5-x-WB₂ and TiO₂ for H₂ evolution from aqueous ethanol solution and CO₂ reduction under visible light irradiation (410 nm). New composite photocatalysts WB_5-x-WB₂/TiO₂ were synthesized and characterized by X-ray diffraction, UV–vis spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. Photocatalytic measurements show that the maximum activity of the composite photocatalyst 4 and 23 times higher than the activity of unmodified TiO₂ in CO₂ reduction and H₂ evolution, respectively. Density functional calculations of the proposed reaction are in agreement with the provided experiments confirming the higher efficiency of the modified catalyst compared to TiO₂.

Optimization of synthesis in collaboration with Tomsk Polytechnic University (Inorg. Chem. 2022, 61, 18, 6773–6784) PDF
Followed by the previous achievements we proposed an efficient method toward the synthesis of higher tungsten boride WB_5–x in the vacuumless direct current atmospheric arc discharge plasma. The crystal structure of the synthesized samples of boron-rich tungsten boride was determined using computational techniques, showing a two-phase system. We determined the optimal parameters of synthesis to obtain samples with 61.5% WB_5–x by volume. Our study shows the possibility of using the proposed vacuumless method as an efficient and inexpensive way to synthesize superhard WB_5–x without employing resource-consuming vacuum techniques

WB5−x: Synthesis, Properties, and Crystal Structure—New Insights into the Long-Debated Compound (Adv. Sci. 2020, 7, 2000775) PDF
The recent theoretical prediction of a new compound, WB₅, has spurred the interest in tungsten borides and their possible implementation in industry. In this research, the experimental synthesis and structural description of a boron-rich tungsten boride and measurements of its mechanical properties are performed. The ab initio calculations of the structural energies corresponding to different local structures make it possible to formulate the rules determining the likely local motifs in the disordered versions of the WB₅ structure, all of which involve boron deficit. The generated disordered WB_4.18 and WB_4.86 models both perfectly match the experimental data, but the former is the most energetically preferable. The precise crystal structure, elastic constants, hardness, and fracture toughness of this phase are calculated, and these results agree with the experimental findings. Because of the compositional and structural similarity with predicted WB₅, this phase is denoted as WB_5−x. Previously incorrectly referred to as “WB₄,” it is distinct from earlier theoretically suggested WB₄, a phase with a different crystal structure that has not yet been synthesized and is predicted to be thermodynamically stable at pressures above 1 GPa. Mild synthesis conditions (enabling a scalable synthesis) and excellent mechanical properties make WB_5−x a very promising material for drilling technology.

New Tungsten Borides, Their Stability and Outstanding Mechanical Properties  (J. Phys. Chem. Lett. 2018, 9, 12, 3470–3477) PDF
We predict new tungsten borides, some of which are promising hard materials that are expected to be stable in a wide range of conditions, according to the computed composition–temperature phase diagram. New boron-rich compound WB₅ is predicted to be superhard, with a Vickers hardness of 45 GPa, to possess high fracture toughness of ∼4 MPa·m^0.5, and to be thermodynamically stable in a wide range of temperatures at ambient pressure. Temperature dependences of the mechanical properties of the boron-richest WB₃ and WB₅ phases were studied using quasiharmonic and anharmonic approximations. Our results suggest that WB₅ remains a high-performance material even at very high temperatures..