Effect Of Mo Doping Research Articles

Effect of Mo doping and NiFe-LDH cocatalyst on PEC water oxidation efficiency

The NiFe-layered double hydroxide (LDH) nanosheets were decorated on the surface of doped BiVO4 to structure an integrating photoanode for improving solar photoelectrochemical (PEC) water splitting efficiency, which is a dynamic research topic to solve the energy crisis and remit environmental pollution caused by fossil fuel combustion. The fabricated photoanode exhibits rapid response to visible light, enhances photocurrent density and shows significant cathodic shift compared to BiVO4. Moreover, the measured incident photon-to-current efficiency (IPCE) of the photoanode is comparable to that reported in the literature. The amount of evolution oxygen was measured and the faradaic efficiency produced oxygen was also obtained by comparing the theoretical calculation value. The enhancement is attributed to the increase of the carrier density, the effective separation of photogenerated electron-hole and consuming of the photogenerated holes accumulated at the electrode surface, which has been confirmed by electrochemical impedance spectra (EIS) and the intensity modulated photocurrent spectra (IMPS). The work may offer a promising method for designing a high efficiency and low-cost photoanode.

Improving the cycling stability of Ni-rich cathode materials by fabricating surface rock salt phase

Mo doped Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode materials have been synthesized via coprecipitation followed by high-temperature solid state method. The effect of Mo doping on the structure, morphology, and electrochemical performances of Ni-rich cathode material has been investigated. The results reveal that Mo doping may promote the formation of surface rock salt phase and expand the Li+ diffusion channels for Ni-rich material. Benefit from which, the further transition of layered to rock salt structure during cycling has been alleviated. As a result, the optimal Mo doped material, with 1 wt% doping, exhibits enhanced cycling stability with superior electrochemistry performances, that is high reversible capacity of 215.7 mAh g−1 at 0.1C, and 184.1 mAh g−1 at 1C with an excellent 100th capacity retention of 92.4%. Even the cut-off voltage raises to 4.5 V, the 100th capacity retention of Mo-doped material still reaches as high as 85.2%. The results indicate that fabricating the Ni-rich materials with a surface rock salt phase is an effective strategy towards better structure stability and electrochemical performances.

Fabrication of Mo-Doped WO₃ Nanorod Arrays on FTO Substrate with Enhanced Electrochromic Properties.

Well-oriented and crystalline WO3 nanorod arrays (WNRAs) decorated with Mo were synthesized on fluorine doped tin oxide (FTO) substrate by the hydrothermal method. The effects of Mo doping, hydrothermal reaction time, and hydrothermal temperature on the morphologies and electrochromic properties of as-prepared WNRAs were studied thoroughly. Scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and chronoamperometry techniques were used to characterize the structures and properties of obtained WNRAs. The results demonstrate that the average diameter of the as-prepared WNRAs ranged from 30 to 70 nm. During the decoration of Mo on the WNRAs, the growth density of as-prepared WNRAs decreased and the surfaces became rough. However, the decorated Mo on WNRAs synthesized at 180 °C for 5 h with a Mo/W mole ratio of 1:40 exhibited better electrochromic properties than single WNRAs. They exhibited high optical modulation (61.7%), fast bleaching/coloring response times (3 s/9 s), high coloration efficiency values (73.1 cm2/C), and good cycling stability.

Understanding the oxidation behavior of a ZrB2–MoSi2 composite at ultra-high temperatures

This basic research investigates the microstructure evolution of a composite based on ZrB2-MoSi2 from the as-sintered features to the changes occurring upon oxidation at ultra-high temperatures, 1650 and 1800 °C, in a bottom-up loading furnace for 15 min. Scanning and transmission electron microscopy evidenced the formation of a matrix typified by ZrB2-cores surrounded by (Zr,Mo)B2-rims with dispersed MoSi2 particles and SiO2 glass trapped at the triple junctions. The oxidation at 1650 °C induced the migration of silica to the surface, which formed a continuous and protective scale. Below this scale, the matrix evolved into ZrO2 grains encasing MoB nano-inclusions, as a result of the oxygen and boron oxide partial pressures established in the subscales. Underneath, a MoSi2-depleted boride region, but substituted by SiO2 and MoB was found. The same phases were observed upon oxidation at 1800 °C, but a thicker and more turbulent oxidized layer formed as a consequence of the rapid evolution of MoO3, SiO and B2O3 gases from the scales beneath the outermost silica-layer.According to the observed phases and the calculated phase stability diagrams, the partial pressures gradient within the oxide layer were defined and the effect of Mo-doping in boride matrices on the oxidation behavior was compared to that of other transition metals to establish a criterion design for the realization of ceramics with improved oxidation resistance.

Effect of Mo doping on the structure and electrochemical performances of LiNi0.6Co0.2Mn0.2O2 cathode material at high cut-off voltage

Mo-doped nickel-rich LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode material is prepared by a solid-state method to enhance the high voltage electrochemical performances of the NCM622 material for lithium-ion batteries. The molybdenum element is proved to be homogeneously distributed inside the particles of the NCM622 material according to the result from the EDS mapping of the particle cross-section. The effects of Mo doping on the crystal structure, morphology, electrochemical properties and high-temperature performances of the NCM622 material are investigated in detail. The Mo-doped sample delivers a discharge capacity of 203.1 mAh/g and a capacity retention of 82.96% after 100 cycles at 1C under a high cut-off voltage of 4.6 V. Besides, the Mo-modified material exhibits a better rate performance of 159.9 mAh/g at 8C and lower voltage fading compared with the unmodified material. The significant improvements in electrochemical properties are ascribed to the fact that trace Mo ions doped into the transition-metal layer help to enlarge the lithium slab spacing, stabilize the crystal structure and suppress the electrode polarization. It is also demonstrated that Mo doping effectively suppresses the pulverization of particles and reduces the charge transfer resistance according to the SEM and EIS analyses.

The effect of Mo doping on the structural and dielectric properties of Co-Zn ferrite

The effect of Mo doping on the structural and dielectric properties has been investigated in detail for Co-Zn spinel ferrite. Solid state reaction technique has been used to prepare the CZMO. The structural analysis is performed using HRXRD technique which confirms the inverse spinel structure of the material. The frequency and temperature dependence of dielectric constant are studied which reveals that the dielectric dispersion is due to Maxwell-Wagner type polarization in agreement with Koop's phenomenological theory. The contribution of grain and grain boundary at high and low frequency respectively are evident in the dielectric constant. The variation of dielectric loss tangent with both the temperature and frequency has been studied. The room temperature and high frequency dielectric loss is observed to be very small. Also it is revealed that the dielectric loss tangent decreases with Mo substitution.

Molybdenum substitution at the B-site of lanthanum strontium titanate anodes for solid oxide fuel cells

The effects of Mo doping into the B-site of La0.3Sr0.7TiO3-δ perovskite on its ionic conductivity and catalytic activity as an anode material of solid oxide fuel cells have been investigated. The partial substitution of Ti by Mo reduces the bond energy between metal and oxygen ions in the perovskite. The concentration of Mo5+/Mo6+ redox couples increases with the rise of the content of Mo, while the oxygen ionic conductivity decreases simultaneously. The doping of Mo significantly reduces the anodic polarization resistance and improves the performance of the single cell. The cell with La0.3Sr0.7Ti0.97Mo0.03O3-δ anode and La0.8Sr0.2Ga0.8Mg0.2O3-δ electrolyte exhibits a maximum power density of 135 mW cm−2 at 850 °C with hydrogen as fuel.

Effects of Mo-doping on microstructure and near-infrared shielding performance of hydrothermally prepared tungsten bronzes

Both Mo and W belong to VIB-sub-group, and possess similar ionic radii, electronegativity and oxide lattice configuration. Herein, Mo-doped (0–80at.%) tungsten bronzes, MxWO3, were hydrothermally prepared to systematically explore the influence of Mo-doping on their micro-structure and optical performance. The products adopted a hexagonal structure within 6at.% Mo-doping, and transformed into a monoclinic phase with higher Mo-doping content. Further tests suggested that 1.5at.% Mo-doping is beneficial for the formation of pure hexagonal phase and uniform nano-rod morphology. Optical measures showed that all samples exhibited high and comparable visible transmittance (70–80%), but a very different near infrared (NIR) shielding ability. The sample doped with 1.5at.% Mo demonstrated the best NIR shielding ability with a transmittance minimum of 20% at 1300nm. Further increase of Mo-doping dosage remarkably deteriorated NIR shielding ability by depressing the absorption of localized surface plasmon resonance (LSPR). However, the optical absorption from small-polaron was less influenced by the introduction of Mo. As a result, Mo-doping caused an evident blue shift of the infrared absorption peaks from 1350 to 750nm.

The effect of Mo doping on the charge separation dynamics and photocurrent performance of BiVO4 photoanodes.

Doping with electron-rich elements in BiVO4 photoanodes has been demonstrated as a desirable approach for improving their carrier mobility and charge separation efficiency. However, the effect of doping and dopant concentration on the carrier dynamics and photoelectrochemical performance remains unclear. In this work, we examined the effects of Mo doping on the charge separation dynamics and photocurrent performance in BiVO4 photoanodes. We show that the photocurrent of BiVO4 photoanodes increases with increasing concentration of the Mo dopant, which can be attributed to both the improved carrier mobility resulting from increased electron density and charge separation efficiency due to the diminishing of trap states upon Mo doping. The effect of doping on the electronic structure, carrier dynamics and photocurrent performance of BiVO4 photoanodes resulting from W and Mo dopants was also compared and discussed in this study. The knowledge gained from this work will provide important insights into the optimization of the carrier mobility and charge separation efficiency of BiVO4 photoanodes by controlling the dopants and their concentrations.

Effects of molybdenum doping and thermal annealing on the physical properties of amorphous In–Zn–O films

Amorphous In–Zn–O (a-IZO) films doped with Mo were prepared on glass substrates by using magnetron co-sputtering technique. The Mo concentration was controlled by varying the sputtering power applied on the Mo target. The effects of Mo doping and thermal annealing on the electrical, optical and magnetic properties of the a-IZO films were studied. The electrical properties of a-IZO films were found to be strongly affected by Mo doping and thermal annealing. The optical transmission near the absorption edge of a-IZO films is enhanced by Mo doping due to the decrease in reflection. The optical bandgap estimated to be 3.2eV of a-IZO films is unaffected by Mo doping and thermal annealing. Moreover, some of Mo-doped films exhibit room-temperature ferromagnetism after annealing.

Mo-doped TiO2 with enhanced visible light photocatalytic activity: a combined experimental and theoretical study.

In this paper, the effects of Mo doping on the geometrical, electronic, optical, and photocatalytic properties of TiO2 have been investigated theoretically and experimentally. The density functional theory based calculations show that Mo doping creates impurity states (Mo 4d) below the conduction band of TiO2 and the Fermi level is pinned inside the conduction band verifying n-type doping nature of the Mo in TiO2, which enhances its visible light absorption. Anatase TiO2 particles with Mo contents of 0.08, 0.1, 0.5, 1.0, 1.5 and, 2.0 at.% were synthesized by hydrothermal method without any post heat treatment for crystallization. Experiment results show that Mo ions have been successfully doped into the TiO2 lattice. The morphology of TiO2 particles is nearly spherical and the grain size is uniformly distributed as about 10 nm. Synthesized sample with 0.1 at.% Mo doping concentration shows the best visible light photocatalytic activity due to the reduced band gap and improved electron-hole pairs separation. However, the photocatalytic activity of the sample with 2.0 at.% Mo is relatively low although its visible light absorption is the best among the samples. The enhanced recombination of electron-hole pairs caused by the excessive Mo doping concentration may account for it.

Effect of molybdenum doping on the electrochromic properties of tungsten oxide thin films by RF magnetron sputtering

Thin films of pure and molybdenum (Mo)-doped tungsten trioxide (WO3) were deposited on indium tin oxide (ITO)-coated glass and Corning glass substrates by RF magnetron sputtering technique. The effect of Mo doping on the structural, morphological, optical and electrochromic properties of WO3 films was studied systematically. The energy dispersive X-ray analysis (EDAX) revealed that the films consist of molybdenum concentrations from 0 to 2 at.%. X-ray diffraction (XRD) studies indicated that with the increase of Mo concentration the structural phase transformation takes place from polycrystalline to amorphous phase. The crystallite size of the films decreased from 24 to 12 nm with increase of doping concentration of Mo in WO3. Scanning electron microscope (SEM) analysis revealed that Mo dopant led to significant changes in the surface morphology of the films. The electrochemical and electrochromic performance of the pure and Mo-doped WO3 were studied. The WO3 films formed with 1.3 at.% Mo dopant concentration exhibited high optical modulation of 44.3 % and coloration efficiency of 42.5 cm2/C.

Effects of Mo Doping on Properties of Pt/C as Catalyst towards Electro-oxidation of Ethanol

Direct Ethanol Fuel Cells (DEFCs) have attracted lots of interest with the merits of high energy density and environmental benignity. Thus, development of novel efficient catalyst with high activity and excellent durability is of great importance for the future large-scale application of DEFCs. A series of Mo-doped Pt/C catalysts were synthesized with microwave assisted technology, and the effects of Mo content on the activity as well as durability of the resulted catalyst towards ethanol oxidation were comparatively investigated by using cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry. The result shows that the Pt2Mo/C catalyst demonstrates a comparable onset potential to Pt/C, the highest current density and the slowest deterioration towards ethanol oxidation, implying that the Pt2Mo/C catalyst is best one to achieve highest activity and best durability.

Marked enhancement in electron–hole separation achieved in the low bias region using electrochemically prepared Mo-doped BiVO4photoanodes

Mo-doped BiVO4 electrodes were prepared by an electrochemical route for use as photoanodes in a photoelectrochemical cell. The purpose of Mo-doping was to improve the electron transport properties, which in turn can increase the electron-hole separation yield. The poor electron-hole separation yield was known to be one of the main limiting factors for BiVO4-based photoanodes. The electrochemical route provided an effective way of doping BiVO4, and the optimally doped sample, BiV(0.97)Mo(0.03)O4, increased the electron-hole separation yield from 0.23 to 0.57 at 0.6 V vs. RHE, which is a record high separation yield achieved for BiVO4-based photoanodes. As a result, BiV(0.97)Mo(0.03)O4 generated impressive photocurrents, for example, 2 mA cm(-2) at a potential as low as 0.4 V vs. RHE for sulfite oxidation, which has fast oxidation kinetics and, therefore, the loss of holes by surface recombination is negligible. For photooxidation of water, BiV(0.97)Mo(0.03)O4 was paired with FeOOH as an oxygen evolution catalyst (OEC) to improve the poor catalytic ability of BiV(0.97)Mo(0.03)O4 for water oxidation. The resulting BiV(0.97)Mo(0.03)O4/FeOOH photoanodes generated a significantly improved photocurrent for water oxidation compared to previous reported results, but the photocurrent of BiV(0.97)Mo(0.03)O4/FeOOH for water oxidation could not reach the photocurrent of BiV(0.97)Mo(0.03)O4 for sulfite oxidation. In order to examine the cause, the effects of Mo-doping on the interaction between BiVO4 and FeOOH and the effects of FeOOH on the electron-hole separation yield of BiV(0.97)Mo(0.03)O4 were investigated in detail, which provided new insights into semiconductor-OEC interactions.

A New Family of Mo-Doped SrCoO3−δ Perovskites for Application in Reversible Solid State Electrochemical Cells

The effect of Mo doping on the crystal structure and thermal, electrical, and electrochemical properties of the SrCo1–xMoxO3−δ (x = 0.05, 0.1) system has been studied. The introduction of Mo as a substitution for Co in SrCoO3−δ leads to a change from a hexagonal to a tetragonal perovskite structure at room temperature. The electrical conductivity is largely enhanced by the introduction of Mo at intermediate temperature due to the stabilization of the 3D-perovskite structure. However, the increase in Mo content decreases the total conductivity probably due to partial disruption of the electronic pathway. The use of these materials as cathodes in a solid-oxide fuel cell (SOFC) and as anodes in a solid oxide electrolyzer (SOE) has been evaluated, showing low values of electrode polarization resistances in both configurations over the intermediate temperature range. Interestingly, better performance was obtained under anodic polarization conditions reaching overpotential values as low as 28 mV for a current density of 210 mA·cm–2 at 700 °C. The good performance of the SrCo1–xMoxO3−δ compounds in both cathodic and anodic conditions makes this system a promising candidate for reversible oxygen electrodes in cells that could operate as both SOFC and SOE.

The effects of Mo doping on 0.3Li[Li0.33Mn0.67]O2·0.7Li[Ni0.5Co0.2Mn0.3]O2 cathode material

Mo doped Li excess transition metal oxides formulated as 0.3Li[Li(0.33)Mn(0.67)]O(2)·0.7Li[Ni(0.5-x)Co(0.2)Mn(0.3-x)Mo(2x)]O(2) were synthesized using the co-precipitation process. The effects of the substitution of Ni and Mn with Mo were investigated for the density of the states, the structure, cycling stability, rate performance and thermal stability by tools such as first principle calculations, synchrotron X-ray diffraction, field-emission SEM, solid state (7)Li MAS nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), elemental mapping by scanning TEM (STEM), inductively coupled plasma atomic emission spectrometry (ICP-AES) and a differential scanning calorimeter (DSC). It was confirmed that high valence Mo(6+) doping of the Li-excess manganese-nickel-cobalt layered oxide in the transition metal enhanced the structural stability and electrochemical performance. This increase was due to strong Mo-O hybridization inducing weak Ni-O hybridization, which may reduce O(2) evolution, and metallic behavior resulting in a diminishing cell resistance.

Microstructure and mechanical properties of Mo/DLC nanocomposite films

Mo-doped diamond-like carbon (Mo/DLC) films were deposited on stainless steel and Si wafer substrates via unbalanced magnetron sputtering of molybdenum combined with inductively coupled radio frequency (RF) plasma chemical vapor deposition of CH 4/Ar. The effects of Mo doping and sputtering current on the microstructure and mechanical properties of the as-deposited films were investigated by means of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, atomic force microscopy (AFM), and nano-indentation. It was found that Mo doping led to increase in the content of sp 2 carbon, and hence decreased the hardness and elastic modulus of Mo/DLC films as compared with that of DLC films. The content of Mo in the films increased with the increasing sputtering current, and most of Mo reacted with C atoms to form MoC nanocrystallites at a higher sputtering current. Moreover, the Mo-doped DLC films had greatly decreased internal stress and increased adhesion to the substrate than the DLC film, which could be closely related to the unique nanocomposite structure of the Mo-doped films. Namely, the Mo/DLC film was composed of MoC nanoparticles embedded in the cross-linked amorphous carbon matrix, and such a kind of nanostructure was beneficial to retaining the loss of hardness and elastic modulus.

Effect of Mo substitution in then=3Ruddlesden-Popper compoundCa4Mn3O10

The effect of Mo doping on the structural, magnetic, electrical, and thermal transport properties of Ca4Mn3�xMoxO10 0x 0.3 compounds has been investigated. Our study indicates that Ca4Mn3O10 exhibits a weak ferromagnetism below TN = 115 K, which is due to the canting of antiferromagnetic sublattices. The slight Mo doping at Mn sites for x = 0.03, 0.06, and 0.1 induces ferromagnetic clusters. The induced ferromagnetism may be ascribed to the double-exchange DE interaction between Mn 4+ and Mn 3+ ions. For the x = 0.2 and 0.3 samples, experimental results show that a cluster-glass state dominates at low temperatures due to the competition between the ferromagnetic DE and the antiferromagnetic superexchange interactions. The small polaron hopping and variable range hopping mechanisms have been used to explain the conduction behavior of these samples. Under 7 T field and at 50 K, the maximum magnetoresistance value 45% is observed in the x = 0.1 sample. The observed negative thermopower S values indicate that the carriers present in all the samples are electrons. Furthermore, the thermal conductivity measurement results show the enhanced Jahn-Teller distortions of MnO6 octahedra and quenched structural disorder due to Mo doping.

Effect of Mo doping on magnetic and transport properties of La 0.5Sr 0.5CoO 3

The substitutional effect of Mo on the magnetic and transport properties of double exchange ferromagnets, La 0.5Sr 0.5Co 1− x Mo x O 3 (0⩽ x⩽0.2) has been investigated. Substitution of 10% Mo at the Co-site of La 0.5Sr 0.5CoO 3 decreases the Curie temperature by ∼60 K than that of the parent compound and the long-range ferromagnetic ordering disappears for x⩾0.2. The Mo-doped samples, however, undergo a transition from the parent metallic state to the insulating state below T c. The insulating state is found to obey Mott's variable range hopping of conduction. The effect of Mo substitution is attributed to the factors namely, (i) the dilution of magnetic Co sublattice, (ii) the reduction of Co 4+/Co 3+ ratio resulting in a reduced carrier concentration and (iii) disruption of the intermediate spin structure of Co, namely Co 3+: t 2g 5e g 1.

Effect of Mo-Doping on the Sol-Gel Prepared Catalysts for Synthesizing Multi-Wall Carbon Nanotube Bundles

Effect of Mo-Doping on the Sol-Gel Prepared Catalysts for Synthesizing Multi-Wall Carbon Nanotube Bundles