Molybdenum Dioxide Nanoparticles Research Articles

Electrical and dielectric characteristics of molybdenum dioxide nanoparticles for high-performance electrocatalysis

As an attempt to improve the catalytic processes in different electrochemical systems, molybdenum dioxide nanoparticles were prepared using the hydrothermal method, and their electrical and dielectric properties were investigated. The nanoparticles were polycrystalline with an orthorhombic structure. AC electrical transport properties of the pressed disc were conducted over a temperature range of 303–423 K and a frequency range of 42–5 × 106 Hz. The AC conductivity follows Jonscher's universal dynamic law, and it has been determined that correlated barrier hopping (CBH) is the primary conduction mechanism. The maximum barrier height (WM) was found to be 0.92 eV. The low activation energy showed that hopping conduction is the dominant mechanism of transporting current. The dielectric parameters were analyzed using both complex permittivity and complex electric modulus, with a focus on how they vary with temperature and frequency. At relatively high temperatures and low frequencies, the dielectric parameters showed a high-frequency dependence. The dielectric modulus showed that relaxation peaks move towards lower frequency when temperature increases. The dielectric relaxation activation energy, Δ Eω was determined to be 0.31 eV.

MoO2/t-C3N4 Heterogeneous Materials with Bidirectional Catalysis for the Rapid Conversion of S Species in Li-S Batteries.

Li-S batteries have drawn a lot of attention for their high theoretical specific capacity and significant economic benefits. However, the shuttle effect of polysulfides prevents them from being used widely. To tackle this difficulty, a heterogeneous structure based on tubular carbon nitride with evenly dispersed molybdenum dioxide nanoparticles (MoO2/t-C3N4) as the S host is constructed in this work. As a polar material with a large specific surface area, MoO2/t-C3N4 has a strong anchoring effect on polysulfide. Additionally, the heterogeneous material has excellent bidirectional catalytic ability for the redox process of S species based on the action of the built-in electric field formed by electron directional transfer. Not only does it improve the reaction kinetics of the redox process of the polysulfides but it also prevents polysulfides from accumulating on the surface of the modified material and deactivating it, further improving the utilization of the active material. Thus, MoO2/t-C3N4/S shows the high initial-discharge specific capacity of 812.7 mAh g-1 at the current density of 5C, and the Coulombic efficiency is maintained at more than 95% after 400 charge/discharge cycles. Moreover, MoO2/t-C3N4/S achieved a capacity retention of 89% after 100 cycles at the current density of 0.1C under the high S loading. Therefore, the research results of this work provide a trustworthy reference for the future commercial application of Li-S batteries.

Boosting potassium-storage performance via confining highly dispersed molybdenum dioxide nanoparticles within N-doped porous carbon nano-octahedrons

The development of durable and stable metal oxide anodes for potassium ion batteries (PIBs) has been hampered by poor electrochemical performance and ambiguous reaction mechanisms. Herein, we design and fabricate molybdenum dioxide (MoO2)@N-doped porous carbon (NPC) nano-octahedrons through metal–organic frameworks derived strategy for PIBs with MoO2 nanoparticles confined within NPC nano-octahedrons. Benefiting from the synergistic effect of nanoparticle level of MoO2 and N-doped carbon porous nano-octahedrons, the MoO2@NPC electrode exhibits superior electron/ion transport kinetics, excellent structural integrity, and impressive potassium-ion storage performance with enhanced cyclic stability and high-rate capability. The density functional theory calculations and experiment test proved that MoO2@NPC has a higher affinity of potassium and higher conductivity than MoO2 and N-doped carbon electrodes. Kinetics analysis revealed that surface pseudocapacitive contributions are greatly enhanced for MoO2@NPC nano-octahedrons. In-situ and ex-situ analysis confirmed an intercalation reaction mechanism of MoO2@NPC for potassium ion storage. Furthermore, the assembled MoO2@NPC//perylenetetracarboxylic dianhydride (PTCDA) full cell exhibits good cycling stability with 72.6 mAh g−1 retained at 100 mA g−1 over 200 cycles. Therefore, this work present here not only evidences an effective and viable structural engineering strategy for enhancing the electrochemical behavior of MoO2 material in PIBs, but also gives a comprehensive insight of kinetic and mechanism for potassium ion interaction with metal oxide.

Novel one-pot microwave assisted synthesis of MoO2 nanoparticles

Microwave method has not been so well explored for synthesis of MoO2 nanoparticles. The article presents first of its kind microwave assisted synthesis of molybdenum dioxide nano-particles by use of home microwave oven. The commercial molybdenum trioxide upon excessive etching by hydrazine hydrate yielded nearly phase pure nanostructured MoO2 with particle diameter of less than 14 nm.

Molybdenum Dioxide Nanoparticles Anchored on Nitrogen‐Doped Carbon Nanotubes as Oxidative Desulfurization Catalysts: Role of Electron Transfer in Activity and Reusability

AbstractElectron transfer between metal‐oxides and supports considerably affects the oxidative desulfurization (ODS) performance of catalysts, while this is far from being well understood. Herein, molybdenum dioxide with oxygen vacancies (VO‐MoO2) catalysts derived from Mo‐based metal‐organic frameworks are anchored on electron‐rich nitrogen‐doped carbon nanotubes (NC) to obtain excellent ODS activity and reusability. Results show that either dibenzothiophene (DBT) or 4,6‐dimethyldibenzothiophene (4,6‐DMDBT) is removed 100% on the composite catalyst (VO‐MoO2@NC) within 40 min of reaction when cumene hydroperoxide is chosen as an oxidant. After five cycles of reaction, DBT and 4,6‐DMDBT removal still exceeded 99.5 and 95.0%, respectively. Results from density functional theory calculations and characterizations confirm that the strong electron‐donating effect of NC on VO‐MoO2 can promote the dispersion of VO‐MoO2 and reduce the bond energy of the MoO bond, leading to exposure of active sites and enrichment of oxygen vacancies (VO). Furthermore, the strong interfacial electrostatic interaction caused by the electron transfer from NC to VO‐MoO2 can reduce the leaching of active sites of the catalyst. This study provides a versatile strategy of constructing strong electronic interaction between metal‐oxide and support via anchoring on NC for the design of high‐performance ODS catalysts.

Preparation and enhanced supercapacitance performance of carbonized silk by feeding silkworms MoO2 nanoparticles

As a key building block to power flexible electronics, there is need for the development of flexible current collectors. Bombyx mori silk, a traditional textile, attracts increasing attention for its potential application in flexible electronics and is a promising raw material for flexible carbon electrodes in current collector fabrication. In this work, molybdenum dioxide nanoparticles (MoO2 NPs), which possess chemical stability and high mass specific capacitance, was used as a feed additive and combined with mulberry leaves to raise silkworms. It was found that the MoO2 NPs were embedded within the silk fibers, which endowed the resulting silk with favorable features for electrochemical energy storage in flexible electronics. After carbonization, the specific capacitance of electrodes prepared with silk from the MoO2 NPs feeding group, with a mass/volume ratio of 5 g/L, was enhanced from 100 F/g to 245 F/g at a current density of 0.2 A/g. Impressively, the electrodes show high coulombic efficiency with excellent stability. This work demonstrates the possibility of producing carbonized silk with superior properties for developing silk-based flexible electrodes for use in energy storage devices in a large-scale, green, low-cost way.

MXene coupled with molybdenum dioxide nanoparticles as 2D-0D pseudocapacitive electrode for high performance flexible asymmetric micro-supercapacitors

Recently, two-dimensional (2D) transition metal carbides and carbonitrides (MXenes), have shown great potential in micro-supercapacitors (MSCs). However, the maximum voltage output of symmetric MXene MSCs is limited to 0.6 V due to the oxidation effects at high anodic potentials. Herein, we developed asymmetric micro-supercapacitors (AMSCs) based on titanium carbide MXene (Ti3C2Tx) and MXene-MoO2 electrodes with an enlarged voltage window of 1.2 V, which is twice wider than that of symmetric MXene MSCs. The 2D-0D MXene-MoO2 microelectrode is fabricated by homogenous dispersing zero-dimensional (0D) MoO2 nanoparticles into MXene layers to impede layers stacking and MoO2 nanoparticles aggregation. Notably, the AMSCs delivered good electrochemical performances of areal capacitance of ∼19 mF cm−2 and volumetric capacitance of 63 F cm−3 at a scan rate of 2 mV s−1, and high energy density of 9.7 mW h cm−3 at a power density of 0.198 W cm−3. The AMSCs also presented exceptionally mechanical flexibility under different bending states and excellent cyclic stability, with 88% capacitance retention after 10000 cycles at a discharge current density of 0.5 mA cm−2. For practical application, the serially connected AMSCs are fully affordable to power electronics, which is beneficial for soft and wearable power devices.

Co-modified MoO2 nanoparticles highly dispersed on N-doped carbon nanorods as anode electrocatalyst of microbial fuel cells

Cobalt-modified molybdenum dioxide nanoparticles highly dispersed on nitrogen-doped carbon nanorods (Co–MoO2/NCND), are synthesized from anilinium trimolybdate dihydrate nanorods, for the performance improvement of microbial fuel cell based on a mixed bacterial culture. Electrochemical measurements demonstrate that the as-synthesized Co–MoO2/NCND exhibits excellent electrocatalytic activity for the charge transfer on anode, providing the cell with a maximum power density of 2.06 ± 0.05 W m−2, which is strikingly higher than the bare carbon felt anode (0.49 ± 0.04 W m−2). The excellent performance of Co–MoO2/NCND is ascribed to the increased electronic conductivity of carbon nanorods by N-doping, the high ability of MoO2 to enrich electroactive bacteria, as demonstrated by high-throughput sequencing, and the enhanced activity of MoO2 by Co-modifying toward redox reactions in electroactive bacteria. This report provides a new concept of anode electrocatalyst fabrications for the application of microbial fuel cells in electricity generation and wastewater treatment.

Encapsulated ultrafine and highly dispersed molybdenum dioxide nanoparticles in hollow mesoporous silica spheres as an efficient epoxidation catalyst for alkenes

A facile post-synthetic strategy was developed to functionalize the preformed hollow mesoporous silica spheres by encapsulating the molybdenum dioxide (MoO2) nanoparticles inside the interior cavity. Hollow mesoporous silica spheres were prepared and employed as carriers, and the encapsulation of MoO2 nanoparticles was achieved through a one-pot hydrothermal protocol. After characterization, the encapsulated MoO2 nanoparticles were certified to be ultrafine and highly dispersed, which greatly promoted the catalytic activity. The as-prepared catalysts were utilized in epoxidation of alkenes and exhibited as a promising catalyst in this reaction. After reacting for 10 h, the optimal catalyst MoO2@SiO2-1 achieved a conversion above 95% and selectivity above 95%, respectively. Moreover, the catalysts also exhibited good reusability, conversion of 78% and selectivity of 89% (reaction time 4 h) were still obtained after recycling for 5 times. Meanwhile, the employed facial and efficient hydrothermal approach could be expanded to other molybdenum modified heterogeneous catalysts in various applications.

High Power Energy Storage: New Materials for Large Format Supercapacitors

Electrochemical double layer capacitors are well known for their high power output. However, pseudocapacitors have recently demonstrated the ability to compete here, with hybrid devices being a compromise between high power and high energy, by way of combined battery and supercapacitor technologies. Metal oxides have shown promising performance within battery and supercapacitor operation. However, cost and low conductivity have limited the performance of many of these materials and has led to the need for doping the material and refining particle shapes and sizes.1 Molybdenum dioxide is a promising material, having many properties required for pseudocapacitance, including its electrical conductivity (atypical for a metal oxide.)2,3 Further to this it has a theoretical specific capacity of 838 mAhg-1 when undergoing a four electron redox reaction. The various niobium oxides have multiple oxidation states, chemical stability and a high potential window making them suitable for energy storage.4 As niobium pentoxide has a theoretical capacity of 200 mAhg-1, which is higher than lithium titanate, (a common anode5), these materials have been tested in batteries and supercapacitors. Yet there remains considerable room for investigation surrounding mixed and doped versions of these materials. Facile one-pot hydrothermal synthesis was used to make nanostructured pseudocapacitive materials. Molybdenum dioxides and niobium oxides were systematically synthesised with varied reaction conditions to gain shape and size control. Molybdenum dioxide nanoparticles were synthesised with the addition of a shape director to form spherical secondary particles. Upon doping the molybdenum dioxide with niobium, crystalline nanoparticles were formed with an average diameter of ~150 nm. Undoped niobium oxides form ‘flower-like’ particles, with the addition of a molybdenum precursor the reaction yields molybdenum dioxide/niobium oxide composite where molybdenum dioxide nanoparticles decorate the niobium oxide particles. All materials were manufactured into electrodes using conventional processing methods and activated carbon electrodes were made for asymmetric devices. The materials showed varying electrochemical properties directly influenced by characteristics gained through the synthesis conditions. Electrochemical testing was carried out on these materials vs. Li’Li+ in half-cells and in asymmetric supercapacitor cells to assess their suitability for hybrid devices. Y. Gogotsi and R. M. Penner, ACS Nano, 12, 2081–2083 (2018).Y. Liu, H. Zhang, P. Ouyang, and Z. Li, Electrochim. Acta, 102, 429–435 (2013) http://dx.doi.org/10.1016/j.electacta.2013.03.195.X. Li et al., J. Power Sources, 237, 80–83 (2013) http://dx.doi.org/10.1016/j.jpowsour.2013.03.020.P. Arunkumar et al., RSC Adv., 5, 59997–60004 (2015) http://xlink.rsc.org/?DOI=C5RA07895D.E. Lim et al., ACS Nano, 8, 8968–8978 (2014). Figure 1

Molybdenum Dioxide in Carbon Nanoreactors as a Catalytic Nanosponge for the Efficient Desulfurization of Liquid Fuels

AbstractThe principle of a “catalytic nanosponge” that combines the catalysis of organosulfur oxidation and sequestration of the products from reaction mixtures is demonstrated. Group VI metal oxide nanoparticles (CrOx, MoOx, WOx) are embedded within hollow graphitized carbon nanofibers (GNFs), which act as nanoscale reaction vessels for oxidation reactions used in the decontamination of fuel. When immersed in a model liquid alkane fuel contaminated with organosulfur compounds (benzothiophene, dibenzothiophene, dimethyldibenzothiophene), it is found that MoO2@GNF nanoreactors, comprising 30 nm molybdenum dioxide nanoparticles grown within the channel of GNFs, show superior abilities toward oxidative desulfurization (ODS), affording over 98% sulfur removal at only 5.9 mol% catalyst loading. The role of the carbon nanoreactor in MoO2@GNF is to enhance the activity and stability of catalytic centers over at least 5 cycles. Surprisingly, the nanotube cavity can selectively absorb and remove the ODS products (sulfoxides and sulfones) from several model fuel systems. This effect is related to an adsorptive desulfurization (ADS) mechanism, which in combination with ODS within the same material, yields a “catalytic nanosponge” MoO2@GNF. This innovative ODS and ADS synergistic functionality negates the need for a solvent extraction step in fuel desulfurization and produces ultralow sulfur fuel.

Highly stable molybdenum dioxide nanoparticles with strong plasmon resonance are promising in photothermal cancer therapy

Photothermal therapy (PTT) is one of promising cancer therapy with high efficiency and minimal invasiveness. Exploiting of perfect PTT agent is vital to improve the therapy. In this study, a new type of bow tie-like molybdenum dioxide (MoO2) nanoparticles was successfully synthesized. These nanobow-ties had strong localized surface plasmon resonance (SPR) effect from visible to near infrared regions, and exhibited ultrahigh chemical stability. They could not only withstand high temperature heating without oxidation, but also resist the corrosion of strong acid and alkali. Meanwhile, the MoO2 nanoparticles were highly stable in protein-containing biological medium, though they partly degraded in PBS solution. Both in vivo and in vitro experiments indicated that they exhibited inappreciable toxicity. Under illumination of near infrared laser, they showed excellent PTT effect, as revealed by significant inhibition of cancer cell viability in vitro and efficient destruction in tumor tissue growth in vivo. These MoO2 nanoparticles possessed highly chemical stability and low toxicity with high PTT efficiency, thus promising them high potential as nanoagent in cancer treatment.

Synthesis of Ni promoted molybdenum dioxide nanoparticles using solvothermal cracking process for catalytic partial oxidation of n-dodecane

Ni promoted MoO2 nanoparticles were synthesized by combining spray pyrolysis and solvothermal cracking process. First, polycrystalline MoO3 microparticles were prepared by spray pyrolysis at 600 °C. Then nano-sized Ni-MoO2 particles were formed by solvothermal cracking process after adding Ni precursor, which disassembled polycrystalline MoO3 microparticles into crystalline grains by thermal expansion and shattered them into Ni-MoO2 nanoparticles by the subsequent solvothermal polyol reduction process. TPR profiles of Ni-MoO2 nanoparticles presented the decrease of reducibility of MoO2 with addition of Ni promoter. Catalytic partial oxidation of n-dodecane was conducted at various temperatures from 450 °C to 850 °C using Ni-MoO2 nanoparticles and pure MoO2 nanoparticles. H2 yield of all the Ni-MoO2 nanoparticles was higher than that of pure MoO2 nanoparticles at 850 °C. Specially, 7 and 10 mol% Ni-MoO2 nanoparticles showed desirable catalytic performance of ca. 60% of H2 yield. This is mainly attributed to the existence of polymolybdate with addition of Ni and Ni2+ species partly located in the polymolybdate layer without formation of bulk Ni phase.

An efficient electrocatalysts for the hydrogen evolution reaction based on molybdenum dioxide nanoparticles embedded porous graphene nanocomposite

Molybdenum dioxide nanoparticles embedded porous reduced graphene oxide (MoO2-pGR) were prepared for catalyzing the hydrogen evolution reaction (HER) by a simple pyrolysis method. The as-prepared product was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The HER electrocatalytic property of MoO2-pGR in acidic solution was evaluated by linear sweep voltammetry (LSV). As expected, MoO2-pGR composites exhibit a high HER active with a low Tafel slope of 57.8 mV dec−1, a small onset potential (Eonset) of −72.53 mV vs. RHE and an outstanding long-term stability. These results provide a new thought for the synthesis of MoO2-pGR composites as an excellent HER catalysts.

Molybdenum dioxide-anchored graphene foam as a negative electrode material for supercapacitors

Molybdenum dioxide nanoparticles of diameter 100 nm were anchored uniformly to a three-dimensional (3D) graphene foam using an ultrasonication-assisted deposition method. X-ray diffraction and Raman spectroscopy indicated that the molybdenum dioxide nanoparticles had a monoclinic crystal structure. The 3D graphene/MoO2 nanoparticle composite showed excellent pseudocapacitive ability as its specific capacitance reached 404 F g−1 at a scan rate of 2 mV s−1 in the negative potential range, −1.0 to −0.2 V, in a neutral solution. Overall, the 3D graphene/MoO2 nanoparticle composite has great potential as an anode material for the next generation of high-performance supercapacitors.

Polygon Shaped Molybdenum Dioxide Nanoparticles as Anode Material for Lithium Ion Batteries

Polygon Shaped Molybdenum Dioxide Nanoparticles as Anode Material for Lithium Ion Batteries

Graphene decorated with molybdenum dioxide nanoparticles for use in high energy lithium ion capacitors with an organic electrolyte

An electrode material consisting of graphene decorated with molybdenum dioxide nanoparticles (G–MoO2) is developed. The material exhibits not only a high specific capacitance but also an excellent cycling performance as well as good rate capability in lithium ion capacitors (LICs). The specific capacitance of the G–MoO2 containing 10 wt% G reaches 624.0 F g−1 at a current density of 50 mA g−1, much higher than 269.2 F g−1 for the MoO2 particles alone. Even at a current density of 1000 mA g−1, a high specific capacitance of 173.2 F g−1 is obtained. The capacitance retention remains 91.2% after 500 cycles. Moreover, G–MoO2 provides a high specific energy density of 33.2 W h kg−1 at a power density of 3000 W kg−1. The influences of the synergistic effect of nanostructured MoO2 and conducting G on the electrochemical performance of the LICs are discussed.

Interplay Between Size and Crystal Structure of Molybdenum Dioxide Nanoparticles—Synthesis, Growth Mechanism, and Electrochemical Performance

A detailed study is presented on the formation of MoO(2) nanoparticles from the dissolution of the precursor to the final rodlike product, with a focus on the exploration of the inorganic reaction occurring ahead of the nucleation step, and interplay between size and crystal structure of MoO(2). In situ X-ray absorption spectroscopy experiments show that the crystallization and the growth process of MoO(2) nanorods is initiated by rapid reduction of the MoO(2) Cl(2) precursor in benzyl alcohol and acetophenone. This reaction triggers the nucleation of 2 nm MoO(2) particles with spherical shape and hexagonal crystal structure. The transformation from spheres into rods emerges as a complex process driven by oriented attachment. High-resolution transmission electron microscopy and X-ray diffraction results provide evidence that the 2 nm particles first aggregate into 5-20 nm-large oriented assemblies. The increase in particle size induces the phase transition from hexagonal to the less symmetrical monoclinic crystal structure, and finally the transformation into rods. Is it shown that electrodes for lithium-ion batteries based on MoO(2) nanorods have a long-term cycling life. The specific discharge capacity even after 200 cycles at a discharge rate of 1 C is about 300 Ah kg(-1) .

Fabricating random arrays of boron doped diamond nano-disc electrodes: Towards achieving maximum Faradaic current with minimum capacitive charging

Abstract We report the first construction of a random array of boron doped diamond (BDD) nano-disc electrodes (RAN BDD), formed by a simple three-step method. First molybdenum(IV) dioxide nanoparticles are electrodeposited onto a BDD substrate. Second the electrode surface is covered in an insulating polymer film by the electropolymerization of a 4-nitrophenyldiazonium salt. Third the molybdenum dioxide nanoparticles are dissolved from the BDD surface (removing the polymer layer directly above them only) using dilute hydrochloric acid to expose nano-discs of BDD, ca. 20 ± 10 nm in diameter surrounded by a polymer insulating the remainder of the BDD. This method produces up to 650 ± 25 million BDD nano-disc electrodes per cm 2 . Various RAN BDD electrodes were produced using this method with a similar distribution of nano-disc size and number density, confirming that this is a reliable and reproducible method of manufacturing such nanoelectrode arrays. At modest scan rates the RAN BDD array was found to produce peak currents approaching that of the Randles–Sevcik limit for the equivalent geometric electrode area despite the fact that most of the surface was insulated by the polymer as shown by voltammetry and atomic force microscopy. The experimental results are compared with simulations of both ordered and random arrays of nano-disc electrodes, the results of which demonstrate that the maximum current obtainable at such arrays is that predicted by the Randles–Sevcik equation. The array of BDD nano-discs shows a significantly reduced capacitive background current compared to the bare BDD electrode, suggesting that such devices may offer improved signal resolution in electroanalytical measurements.

The Effect of a Magnetic Field on a RAPET (Reaction under Autogenic Pressure at Elevated Temperature) of MoO(OMe)4: Fabrication of MoO2 Nanoparticles Coated with Carbon or Separated MoO2 and Carbon Particles

In this article, we present results of the RAPET dissociation of MoO(OMe)4 at 700 degrees C in a closed Swagelok cell. The reaction produces molybdenum dioxide nanoparticles (20 nm) coated with carbon (20 nm). We have also carried out the same reaction under an applied magnetic field of 10 T. This reaction yielded different products. It produces a mixture of comparatively larger (50 nm) molybdenum dioxide nanoparticles and separated uncoated carbon particles (20-30 nm).