Molybdenum Boride Research Articles

Low loading of Pt on MoB Constructed by microwave Quasi-solid approach with solvent Regulation for hydrogen evolution reaction

The interaction between metal nanoclusters and the carrier can enhance the electron transfer rate to optimize the hydrogen evolution reaction (HER) performance, but the common synthesis approaches often lead to metal particle agglomeration, and then blocking active sites. Herein, highly-dispersed Pt nanoclusters supported onto molybdenum boride (MoB) is developed through microwave approach with various solvent to regulate the catalytic performance. The synthesized electrocatalyst with the addition of methanol (Pt/MoB-M) exhibits excellent electrocatalytic performance towards HER with low overpotential (13 mV at 10 mA cm−2), small Tafel slope (24 mV dec−1), and high mass activity (10.06 A/mgPt at 50 mV). This work presents a novel approach to prepare highly-efficient electrocatalysts for renewable energy-related applications of non-carbon supported low loading of precious metals.

Kinetic study and simulation of molybdenum borides for hydrogen evolution reaction

Kinetic study and simulation of molybdenum borides for hydrogen evolution reaction

Research on the air cathode catalytic mechanism and performance of long life for air-breathing hybrid electrolyte lithium-air battery

Hybrid electrolyte lithium-air batteries offer a high energy density compared to other batteries. However, their internal redox efficiency is low when utilizing traditional catalysts, resulting in a shorter lifespan. Among the two-dimensional transition metal borides (MBenes) is two-dimensional molybdenum boride (2D-MoB), which has superior mechanical, electrochemical, and electrical conductivity qualities. This work discusses the hydrothermal preparation of 2D-MoB and its mixing with CNTs for in hybrid electrolyte lithium-air batteries. Density functional theory (DFT) was used to study the electrochemical characteristics of the compound as well as its redox process. The hydrothermally generated 2D-MoB exhibits more reactive active sites, a more significant specific surface area, and an evident layer structure. Using 2D-MoB as a catalyst for hybrid electrolyte lithium-air batteries can significantly extend their cycle life and lower their overpotential, according to ambient air’s constant-capacity charge/discharge tests. At a current of 0.1 mA (0.05 mA·cm−2), the battery life reached 3160 h, and its initial maximum discharge capacity was 9779 mAh·g−1. According to DFT calculations, the overpotential of 2D-MoB as a catalyst for lithium-air hybrid electrolyte batteries was 0.46 V, which was nearer the value observed in experiments. According to this study, 2D-MoB can be used as a cathode catalyst in lithium-air hybrid electrolyte batteries.

Density Functional Theory Investigation on the Nitrogen Reduction Mechanism in Two-Dimensional Transition-Metal Boride with Ordered Metal Vacancies.

The creation of ordered collective vacancies in experiment proves challenging within a two-dimensional lattice, resulting in a limited understanding of their impact on catalyst performance. Motivated by the successful experimental synthesis of monolayer molybdenum borides with precisely ordered metal vacancies [Zhou et al. Science 2021, 373, 801-805] through dealloying, the nitrogen reduction reaction (NRR) in monolayer borides was systematically investigated to elucidate the influence of such ordered metal vacancies on catalytic reactions and the underlying mechanisms. The results reveal that the N-containing intermediates tend to dissociate, facilitating the NRR process with reduced UL. The emergence of ordered metal vacancies modulates the electronic properties of the catalyst and partially facilitates the decomposition of N-containing intermediates. However, the UL for NRR in Mo4/3B2 and W4/3B2 exhibits a significant increase. The compromised electrochemical performance is explained through the development of a simple electronic descriptor of the d-p band center (ΔdM-pB). Among these materials, Mo4/3Sc2/3B2 exhibits the most superior catalytic activity with a UL of -0.5 V and favorable NRR selectivity over the HER. Our results provide mechanistic insights into the role of ordered metal vacancies in transition-metal boride for the NRR and highlight a novel avenue toward the rational design of superior NRR catalysts.

Recent Developments and Future Perspectives of Molybdenum Borides and MBenes (Adv. Sci. 21/2024)

Recent Developments and Future Perspectives of Molybdenum Borides and MBenes (Adv. Sci. 21/2024)

Laser‐induced self‐propagating synthesis and electromagnetic wave absorption properties of MoAlB powders

AbstractMoAlB powders with a purity of 96 wt.% were successfully fabricated by a laser‐induced self‐propagating method using molybdenum boride (MoB) and aluminum powders as starting materials under the conditions of an n(MoB): n(Al) ratio of 1.0:1.4 and the laser linear energy density (El) of 0.9 J/mm, and the effect of raw material composition and El on the phase composition and microstructure of the resultant MoAlB powders were investigated. The minimum reflection loss (RLmin) value and effective absorption bandwidth (EAB) of the as‐prepared MoAlB absorber with a thickness of 5.0 mm were only determined as −12.5 dB (at 16.9 GHz) and 0.9 GHz (16.4–17.3 GHz) in the frequency of 1–18 GHz, respectively. Nevertheless, the RLmin and EAB of as‐prepared MoAlB powders oxidized after 3 h at 773 K increased to −18.59 dB (at 15.82 GHz) and 2.13 GHz (15.22–17.35 GHz), respectively, demonstrating that the as‐prepared MoAlB powders are potential candidates for high‐temperature microwave absorption applications. This study proposes a new efficient strategy for the preparation of boron‐based ternary compounds for high‐temperature electromagnetic wave absorption application.

Two-dimensional molybdenum boride coordinating with ruthenium nanoparticles to boost hydrogen generation from hydrolytic dehydrogenation of ammonia borane

The coordination between carrier and active metal is critical to the catalytic efficiency of ammonia borane (AB) hydrolysis reaction. In the present study, we report a new type of catalytic support based on molybdenum boride (MBene) MoAl1-xB and demonstrate that the effective combination of MoAl1-xB with Ru nanoparticles can realize the significantly enhanced performance for hydrogen generation. Owing to the efficient activation and dissociation of reactants, the optimal Ru/MoAl1-xB catalyst achieves the large turnover frequency of 494 molH2 molRu-1 min−1, high hydrogen generation rate of 119817 mL min−1 gRu-1 and favorable apparent activation energy of 39.2 kJ mol−1 for the catalytic hydrolysis of AB under alkaline-free condition. The isotopic test suggests the cleavage of OH bond in H2O is the rate-determining step for hydrolysis reaction, while the fracture of B–H bond in AB is also well revealed by attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) spectroscopy. Significantly, the flexible on-demand hydrogen generation is achieved by using chemical switches for on–off AB hydrolysis. This study provides a new support platform based on two-dimensional MBene to exploit efficient catalysts to boost AB dehydrogenation.

Use of molybdenum in Ni 620 filler metal to influence the microstructure of brazed hot work steel

AbstractBrazing of hot work steel with nickel‐based filler metals is a widely used process for manufacturing casting tools. However, the formation of brittle phases in the joint impairs its mechanical properties. Reducing these intermetallic phases is an important aspect. Thermodynamic equilibrium calculations are used to estimate the change in melting range and apearance of intermetallic phases by adding different amounts of molybdenum to Ni 620. The filler metals are then produced and their solidus and liquidus temperatures are investigated using differential scanning calorimetry. Specimens of X37CrMoV5‐1 are then brazed in a vacuum furnace and their microstructure is analysed by scanning electron microscopy/electron dispersive spectroscopy and their hardness properties by nanoindentation. The addition of molybdenum to the Ni 620 filler metal leads to the formation of chromium molybdenum boride rich phases and reduced hardness values in brazed joints. Manipulation of Ni 620 by molybdenum helps to improve relevant properties in brazing hot work steel.

Recent Developments and Future Perspectives of Molybdenum Borides and MBenes.

Metal borides have received a lot of attention recently as a potentially useful material for a wide range of applications. In particular, molybdenum-based borides and MBenes are of great significance, due to their remarkable properties like good electronic conductivity, considerable stability, high surface area, and environmental harmlessness. Therefore, in this article, the progress made in molybdenum-based borides and MBenes in recent years is reviewed. The first step in understanding these materials is to begin with an overview of their structural and electronic properties. Then synthetic technologies for the production of molybdenum borides, such as high-temperature/pressure methods, physical vapor deposition (PVD), chemical vapor deposition (CVD), element reaction route, molten salt-assisted, and selective etching methods are surveyed. Then, the critical performance of these materials in numerous applications like energy storage, catalysis, biosensors, biomedical devices, surface-enhanced Raman spectroscopy (SERS), and tribology and lubrication are summarized. The review concludes with an analysis of the current progress of these materials and provides perspectives for future research. Overall, this review will offer an insightful reference for the understanding molybdenum-based borides and their development in the future.

Two-Dimensional Molybdenum Boride (MBene) Mo4/3B2Tx with Broadband and Termination-Dependent Ultrafast Nonlinear Optical Response.

Two-dimensional molybdenum borides (MBenes) comprise a new class of 2D transition metal borides that exhibit potential photonics applications. Recently, the synthesis of individual single-layer Mo4/3B2Tx (T = O, F, OH) MBene sheets has been realized, which attracted considerable attention in optoelectronics. However, there is still a lack of understanding and regulation of the photophysical processes of Mo4/3B2Tx MBene. Here, we demonstrate that Mo4/3B2Tx MBene exhibits a surface termination-dependent electronic structure, carrier dynamics, and nonlinear optical response over a wide wavelength range (500-1550 nm). As prepared 2D Mo4/3B2F2 MBene possesses a semimetal material property that exhibits a shorter intraband scattering process (<100 ps) and a considerable nonlinear optical response at a broadband cover optical communication C band at 1550 nm. These thrilling results are confirmed theoretically and experimentally. The analysis of these results adds to the regulating and understanding of the basic photophysical processes, which is anticipated to be beneficial for the further design of MBene-based photonics and nanoelectronics devices.

Phase-Tunable Molybdenum Boride Ceramics as an Emerging Sensitive and Reliable SERS Platform in Harsh Environments.

Traditional surface-enhanced Raman scattering (SERS) sensors rely heavily on the use of plasmonic noble metals, which have limitations due to their high cost and lack of physical and chemical stability. Hence, it is imperative to explore new materials as SERS platforms that can withstand high temperatures and harsh conditions. In this study, the SERS effect of molybdenum boride ceramic powders is presented with an enhancement factor of 5 orders, which is comparable to conventional noble metal substrates. The molybdenum boride powders synthesized through liquid-phase precursor and carbothermal reduction have β-MoB, MoB2, and Mo2B5 phases. Among these phases, β-MoB demonstrates the most significant SERS activity, with a detection limit for rhodamine 6G (R6G) molecules of 10-9m. The impressive SERS enhancement can be attributed to strong molecule interactions and prominent charge interactions between R6G and the various phases of molybdenum boride, as supported by theoretical calculations. Additionally, Raman measurements show that the SERS activity remains intact after exposure to high temperature, strong acids, and alkalis. This research introduces a novel molybdenum boride all-ceramic SERS platform capable of functioning in harsh conditions, thereby showing the promising of boride ultrahigh-temperature ceramics for detection applications in extreme environments.

First-Principles Studies on Transition Metal Doped Mo2B2 as Anode Material for Li-Ion Batteries.

New two-dimensional (2D) transition-metal borides have attracted considerable interest in research on electrode materials for Li-ion batteries (LIBs) owing to their promising properties. In this study, 2D molybdenum boride (Mo2B2) with and without transition metal (TM, TM=Mn, Fe, Co, Ni, Ru, and Pt) atom doping was investigated. Our results indicated that all TM-doped Mo2B2 samples exhibited excellent electronic conductivity, similar to the intrinsic 2D Mo2B2 metal behavior, which is highly beneficial for application in LIBs. Moreover, we found that the diffusion energy barriers of Li along paths 1 and 2 for all TM-doped Mo2B2 samples are smaller than 0.30 and 0.24 eV of the pristine Mo2B2. In particular, for 2D Co-doped Mo2B2, the diffusion energy barriers of Li along paths 1 and 2 are reduced to 0.14 and 0.11 eV, respectively, making them the lowest Li diffusion barriers in both paths 1 and 2. This indicates that TM doping can improve the electrochemical performance of 2D Mo2B2 and that Co-doped Mo2B2 is a promising electrode material for LIBs. Our work not only identifies electrode materials with promising electrochemical performance but also provides guidance for the design of high-performance electrode materials for LIBs.

Microwave Quasi‐Solid State to Construct Strong Metal‐Support Interactions with Interfacial Electron‐Enriched Ru for Anion Exchange Membrane Electrolysis

AbstractRegulating the metal‐support interaction of the anchored metal nanoclusters is recognized as valid approach to optimize the electrocatalytic performance through tuning the interfacial electronic structure. However, developing novel support and understanding the interfacial electron accumulation on modulating the reaction kinetics are still elusive. Herein, highly‐dispersed Ruthenium (Ru) nanoclusters anchored onto phosphorous doped molybdenum boride (Ru/P‐MoB) is developed through ultrafast microwave‐plasma (60 s) approach. The synthesized Ru/P‐MoB impressively promote the hydrogen evolution with low overpotentials of 34, 45, and 40 mV to drive 10 mA cm−2 in alkaline freshwater, alkaline seawater and acid media. Specially, it presents superior turnover frequency and mass/specific activity relative to Pt/C, Ru/C, and Ru/MoB. Moreover, the anion exchange membrane (AEM) electrolyzer cell based on Ru/P‐MoB can achieve 500 and 1000 mA cm−2 with small voltages of 1.71 and 1.78 V with good durability. Experimental and density functional theoretical (DFT) analysis reveal that the strong metal‐support interactions (Ru─Mo and Ru─P bonds) with generated interfacial electron‐enriched Ru, and then favoring the water‐molecule adsorption/dissociation and optimal H intermediate adsorption free energy. This work provides novel designing avenue to exploit electrocatalysts with outstanding catalytic performance under high current density at practical high‐temperature.

Electronic, mechanical and contact properties of Mo4/3B2T2 (T=F, O, OH) monolayer: A first principles study

Single-layer 2D molybdenum boride sheets, Mo4/3B2T2 (T = F, O and OH), have been realized in recent experiment. Here, the electronic structure and mechanical flexibility of its most stable configurations are investigated by using first principles calculations. Mo4/3B2F2 and Mo4/3B2(OH)2 perform as 2D metal, while Mo4/3B2O2 is a semiconductor with indirect band gap ∼0.36 eV. These three monolayers can individually sustain the maximum stress and the strain limits at least ∼15 Gpa and 15 %, such mechanic flexibility is comparable to borophene and MoS2. When forming heterojunction with MoS2, p-type and n-type Schottky contact with barrier height ∼0.16 eV and 0.23 eV occur in Mo4/3B2F2 and Mo4/3B2(OH)2, respectively. Fortunately, the contact barrier can be eliminated by external field. In addition, a type-II heterojunction with a large conduction band offset is found in Mo4/3B2O2/MoS2, which may be a potential candidate for optoelectronics.

Investigation on microstructure and mechanical properties of boron-modified 13Cr5Ni2Mo by powder-pack boriding

ABSTRACT The main objective of the present paper is to investigate the effect of pack boriding treatment at 950°C/4 h on surface 13 Cr supermartensitic stainless steel. Scanning electron microscopy and X-ray diffractometry were used to characterise the grown boride layers microstructures. In addition, we performed 3D profilometry, microhardness measurements, nanoindentation tests with a Berkovich diamond tip, Daimler-Benz Rockwell-C adhesion, and ball-on-disk wear tests in order to evaluate the mechanical properties. After boriding, the phases were found to be iron borides (FeB/Fe2B), chromium borides (CrB), nickel borides (Ni2B), and molybdenum borides (Mo2B). The results showed that the use of the powder-pack boriding process on 13Cr SMSS at 950°C/4 h conducted in the presence of dual phases (FeB/Fe2B) improved the mechanical properties compared to untreated material.

Crystal structures of molybdenum borides dictate electrocatalytic ammonia synthesis efficiency

Rather than multivalence molybdenum (Mo), the low valence Mo has rarely been reported as active site for nitrogen reduction. Herein, molybdenum borides with various Mo-B stoichiometry ratios (Mo2B, α-MoB, and Mo2B4) in which Mo shows low valence (<1) are synthesized as electrochemical nitrogen reduction reaction (eNRR) catalysts. Mo2B4 demonstrates the highest NH3 yield of 7.65 µg h− 1/mg at − 0.15 V with Faradaic efficiency (FE) of 12.47 %, while α-MoB exhibits the fastest intrinsic eNRR reaction rate with a higher FE of 17.17 % after considering electrochemically active surface area. DFT calculations reveal that both enzymatic and consecutive mechanisms via side-on configuration can proceed on α-MoB. Additionally, α-MoB exhibits suppressed HER activity due to an optimal surface B occupancy. The eNRR of molybdenum borides were verified qualitatively and quantitatively by 15N2 isotope experiments. This study demonstrated a synergistic design of eNRR and HER activity to achieve efficient electrocatalytic ammonia production with high eNRR selectivity.

Toward MBenes Battery Electrode Materials: Layered Molybdenum Borides for Li-Ion Batteries.

Lithium-ion and sodium-ion batteries (LIBs and SIBs) are crucial in our shift toward sustainable technologies. In this work, the potential of layered boride materials (MoAlB and Mo2 AlB2 ) as novel, high-performance electrode materials for LIBs and SIBs, is explored. It is discovered that Mo2 AlB2 shows a higher specific capacity than MoAlB when used as an electrode material for LIBs, with a specific capacity of 593mAh g-1 achieved after 500 cycles at 200mA g-1 . It is also found that surface redox reactions are responsible for Li storage in Mo2 AlB2 , instead of intercalation or conversion. Moreover, the sodium hydroxide treatment of MoAlB leads to a porous morphology and higher specific capacities exceeding that of pristine MoAlB. When tested in SIBs, Mo2 AlB2 exhibits a specific capacity of 150mAh g-1 at 20mA g-1 . These findings suggest that layered borides have potential as electrode materials for both LIBs and SIBs, and highlight the importance of surface redox reactions in Li storage mechanisms.

Enhancing the Catalytic Activity of Mo(110) Surface via Its Alloying with Submonolayer to Multilayer Boron Films and Oxidation of the Alloy: A Case of (CO + O2) to CO2 Conversion

In-situ formation of boron thin films on the Mo(110) surface, as well as the formation of the molybdenum boride and its oxide and the trends of carbon monoxide catalytic oxidation on the substrates formed, have been studied in an ultra-high vacuum (UHV) by a set of surface-sensitive characterization techniques: Auger and X-ray photoelectron spectroscopy (AES, XPS), low-energy ion scattering (LEIS), reflection-absorption infrared spectroscopy (RAIRS), temperature-programmed desorption (TPD), electron energy loss spectroscopy (EELS) and work function measurements using the Anderson method. The boron deposited at Mo(110) via electron-beam deposition at a substrate temperature of 300 K grows as a 2D layer, at least in submonolayer coverage. Such a film is bound to the Mo(110) via polarized chemisorption bonds, dramatically changing the charge density at the substrate surface manifested by the Mo(110) surface plasmon damping. Upon annealing of the B-Mo(110) system, the boron diffuses into the Mo(110) bulk following a two-mode regime: (1) quite easy dissolution, starting at a temperature of about 450 K with an activation energy of 0.4 eV; and (2) formation of molybdenum boride at a temperature higher than 700 K with M-B interatomic bonding energy of 3.8 eV. The feature of the formed molybdenum boride is that there is quite notable carbon monoxide oxidation activity on its surface. A further dramatic increase of such an activity is achieved when the molybdenum boride is oxidized. The latter is attributed to more activated states of molecular orbitals of coadsorbed carbon monoxide and oxygen due to their enhanced interaction with both boron and oxygen species for MoxByOz ternary compound, compared to only boron for the Mox'By' double alloy.

Introducing Porosity into Refractory Molybdenum Boride through Controlled Decomposition of a Metastable Mo–Al–B Precursor

The high temperatures typically required to synthesize refractory compounds preclude the formation of high-energy morphological features, including nanoscopic pores that are beneficial for applications, such as catalysis, that require higher surface areas. Here, we demonstrate a low-temperature multistep pathway to engineer mesoporosity into a catalytic refractory material. Mesoporous molybdenum boride, α-MoB, forms through the controlled thermal decomposition of nanolaminate-containing sheets of the metastable MAB (metal-aluminum-boron) phase Mo2AlB2 and amorphous alumina. Upon heating, the Mo2AlB2 layers of the Mo2AlB2-AlOx nanolaminate, which is derived from MoAlB, begin to bridge and decompose, forming inclusions of alumina in a framework of α-MoB. The alumina can be dissolved in aqueous sodium hydroxide in an autoclave, forming α-MoB with empty and accessible pores. Statistical analysis of the morphologies and dimensions of the pores reveals a correlation with grain size, which relates to the pathway by which the alumina inclusions form. The transformation of Mo2AlB2 to α-MoB is topotactic due to crystal structure relationships, resulting in a high density of stacking faults that can be modeled to account for the observed experimental diffraction data. Porosity was validated by comparing surface areas and demonstrating catalytic viability for the hydrogen evolution reaction.

Size-controlled preparations of tungsten and molybdenum borides in calcium or aluminum melt

Tungsten and molybdenum borides are widely used in ultra-high temperature ceramics (UHTCs) and electrode material. In this research, ultra-fine and ultra-coarse binary borides (WB, W2B5, MoB, Mo2B5) and MoAlB powders were prepared with W/Mo and B4C as raw materials and Ca/Al as the decarbonization agent. The feasibility of using Ca and Al as decarburizing agents was assessed by thermodynamic calculations. Meanwhile, the effects of reaction temperature, decarbonization agent type and its additional amount on the phase, morphology and size distribution of the powder products were thoroughly investigated. The results revealed that single phase products with carbon content of less than 1 wt% could be prepared. Moreover, the morphology and particle size of products were significantly affected by the reaction temperature and type of decarburization agent. When using Ca as the decarburizing agent, ultra-fine WB and MoB powders were effectively prepared, probably owing to the fact that W/Mo are essentially insoluble in Ca melt. However, the great solubility of W/Mo in Al makes it easily to synthesize ultra-coarse borides at high temperatures via the dissolution-precipitation mechanism. Additionally, ultra-fine borides particle can also be prepared by lowering the temperature and amount of Al to weak the dissolution-precipitation mechanism.