Mo Doping Research Articles

Effects of Molybdenum Doping on the Enhanced Electrocatalytic Nitrogen Reduction Reaction Performance of CeO2 Nanorods: Theoretical and Experimental Investigations.

As a green and sustainable strategy, the electrocatalytic N2 reduction reaction (NRR) has been considered the best potential approach to replace the traditional Haber-Bosch process under ambient conditions. The key is to exploit efficient and low-cost electrocatalysts according to the current situation. Herein, a series of Molybdenum (Mo) doped CeO2 nanorods (NR) catalysts were successfully fabricated via a hydrothermal reaction coupled with high temperature calcination. The nanorod structures were not altered after Mo atom doping. The obtained 5 %-Mo-CeO2 nanorods act as a superior electrocatalyst in neutral electrolytes of 0.1 M Na2 SO4 . Such electrocatalyst significantly enhances NRR performance with an NH3 yield of 10.9 μg h-1 mg-1 cat at -0.45 V vs reversible hydrogen electrode (RHE) and a Faradaic efficiency (FE) of 26.5 % at -0.25 V vs RHE. That outcome is 4 times higher than that of CeO2 nanorods (2.6 μg h-1 mg-1 cat ; 4.9 %). Meanwhile, density functional theory (DFT) calculation shows the characteristics after Mo doping: the band gap value lowers, the density of states increases, electrons are more easily excited, and N2 molecules are more easily adsorbed, thereby enhancing the activity of the electrocatalytic NRR.

Enhanced Photocatalytic Performance of Visible-Light-Driven BiVO4 Nanoparticles through W and Mo Substituting

Bismuth vanadate (BiVO4), W-doped BiVO4 (BiVO4:W), and Mo-doped BiVO4 (BiVO4:Mo) nanoparticles were synthesized at pH = 4 using a green hydrothermal method. The effects of 2 at% W or Mo doping on the microstructural and optical characteristics of as-prepared BiVO4 nanoparticles and the effect of combining particle morphology modification and impurity dopant incorporation on the visible-light-derived photocatalytic degradation of dilute Rhodamine B (RhB) solution are studied. XRD examination revealed that these obtained BiVO4-based nanoparticles had a highly crystalline and single monoclinic phase. SEM and TEM observations showed that impurity doping could modify the surface morphology, change the particle shape, and reduce the particle diameter to enlarge their specific surface area, increasing the reactive sites of the photocatalytic process. XPS and FL measurements indicated that W- and Mo-doped nanoparticles possessed higher concentrations of oxygen vacancies, which could promote the n-type semiconductor property. It was found that the BiVO4:W and BiVO4:Mo powder samples exhibited better photocatalytic activity for efficient RhB removal than that shown by pristine BiVO4 powder samples under visible light illumination. That feature can be ascribed to the larger surface area and improved concentration of photogenerated charge carriers of the former.

Effect of hydroxyl and Mo doping on activity and carbon deposition resistance of hydroxyapatite supported NixMoy catalyst for syngas production via DRM reaction

The doping of the second metal Mo is expected to further enhance the carbon deposition resistance of Ni-based catalysts for syngas production via dry reforming of methane (DRM). In this study, the hydroxyapatite (HAP) was used as the support and a small Mo dosage was doped in the Ni-based catalysts to investigate the effect of intrinsic hydroxyl and Mo doping on the catalytic activity and carbon deposition resistance in DRM reaction. The catalyst characterization results show that both Ni and Mo are doped into the HAP structure with relatively uniform dispersion. The basic site strength of Ni4Mo0.2-HAP catalyst containing Mo is significantly higher than that of without Mo. The Mo dopant significantly improves the initial catalytic activity, but has minimal effect on the stability enhancement. Whether the catalyst is pre-reduced or not is crucial to the initial activity of the DRM reaction, the non-pre-reduced catalysts will go through a “self-activation” stage at the beginning of the reaction, where the “hydroxyl group” are proved to play as an “oxygen supply” for the partial oxidation of CH4 or the oxidation of the carbon deposition in the initial stage. Only trace amount of carbon deposition is found after 100 h of DRM reaction on Ni3Mo0.2-HAP catalyst. The NiMo-HAP catalysts exhibit excellent initial activity and resistance to carbon deposition due to the synergistic effect of Ni–Mo alloy and hydroxyl groups in the hydroxyapatite support.

Co-sputtered Mo:BiVO4 thin film-based transparent photovoltaic and photoelectrochemical activity for see-through energy systems

Recently, the photovoltaic (PV) and photoelectrochemical (PEC) cell has engrossed cumulative attention for clean and low-cost sustainable energy. Here, we propose transparent PV (TPV) and PEC (TPEC) based on sputtered BiVO4 semiconducting thin films to unite electric power and hydrogen generation for see-through energy systems. The TPV and TPEC devices performed better under white light illumination when doped with Mo, and showed average visible transmittance of ∼60%. Such enhancements are due to the Mo doping in BiVO4, which offers better optoelectronic properties suitable to TPV and TPEC devices than BiVO4 thin films. Mo:BiVO4-based TPV-TPEC device shows a high open circuit voltage of 0.43 V with a fill factor value of 33.8% and a short-circuit current density of 0.415 mA/cm2, attributed to the enhanced absorption for blue wavelength photons, indicating stable and safe onsite power production. The structural, optical, and electrical performances of BiVO4 films were studied and compared with its Mo:BiVO4. These co-sputtered Mo:BiVO4-based TPV and TPEC devices can further enhance the robust power-generating systems for see-through onsite energy production.

Fabricating Heterostructures for Boosting the Structure Stability of Li-Rich Cathodes.

Li-rich Mn-based oxides are regarded as the most promising new-generation cathode materials, but their practical application is greatly hindered by structure collapse and capacity degradation. Herein, a rock salt phase is epitaxially constructed on the surface of Li-rich Mn-based cathodes through Mo doping to improve their structural stability. The heterogeneous structure composed of a rock salt phase and layered phase is induced by Mo6+ enriched on the particle surface, and the strong Mo-O bonding can enhance the TM-O covalence. Therefore, it can stabilize lattice oxygen and inhibit the side reaction of the interface and structural phase transition. The discharge capacity of 2% Mo-doped samples (Mo 2%) displays 279.67 mA h g-1 at 0.1 C (vs 254.39 mA h g-1 (pristine)), and the discharge capacity retention rate of Mo 2% is 79.4% after 300 cycles at 5 C (vs 47.6% (pristine)).

Effects of V and Mo dopants on electronic structures, magnetic and optical properties of ZrSe2: First-principles calculations

The electronic structures, magnetic and optical properties of pure ZrSe2, V, Mo mono-doped ZrSe2 (V–ZrSe2, Mo–ZrSe2) and (V, Mo) co-doped ZrSe2 are researched by the first-principles of density functional theory (DFT). The results show that V–ZrSe2 and Mo–ZrSe2 can become magnetism, and the total magnetic moments generated are 1.76 μB and 2.06 μB by V–ZrSe2 and Mo–ZrSe2, respectively. The stable ferromagnetism (FM) properties in (V, Mo) co-doped ZrSe2 are mainly derived from the hybridization of V:3 d, Se:4p and Mo:4 d orbitals. Due to the doping of V and Mo atoms, which improves electric conductivity and makes up the infrared absorption coefficient of pure materials. In addition, we find that biaxial strain changes the electronic structure of (V, Mo) co-doped ZrSe2 monolayer, and the ferromagnetism of the system be changed significantly. In conclusion, (V, Mo) co-doped ZrSe2 magnetic semiconductor has excellent potential in spin electronic devices.

Elucidating the role of Mo doping in enhancing the meta-Xylene ammoxidation performance over the CeVO4 catalyst

Vanadium-based oxides-catalyzed conversion of meta-xylene (m-X) directly to isophthalonitrile (IPN) through vapor phase ammoxidation is a short-flow, sustainable and economic process. Herein, effects of molybdenum promoter loadings are systematically studied on the ammoxidation performance over the SiO2 supported V-Ce composite oxide catalyst prepared by spray drying method. The roles of Mo addition were elucidated by series of structure characterizations. It had been revealed that the addition of Mo can promote the formation of specific crystal face of CeVO4 species which works as the active phase of the catalyst. Meanwhile, the Mo addition can suppress the surface V2O5 species formation, and thus lower the oxidation state and the acid strength of the catalyst. The Ce3+/Ce4+ ratio is also increased with the rising of Mo amount, and the chemisorbed oxygen amount is lowered, leading to a moderate activation of the reactants. The modified physicochemical properties originated from the Mo promoter doped on the CeVO4 surface. At last, the performances of the Mo-modified and Mo-free catalysts are evaluated in the fluidized bed under 415 °C. The oxidation degree of the feeding m-X of the Mo containing catalyst is obviously lower than the Mo-free catalyst, and as a result the yield of IPN is improved. However, the Mo/V cannot be excessively increased, because at high Mo/V, the weaker adsorption of reactant would cause the incomplete m-X conversion, and the selectivity for monocyano product, i.e., metatolunitrile, rises, lowering the selectivity of the main product (IPN).

Effect of Mo doping in NiO nanoparticles for structural modification and its efficiency for antioxidant, antibacterial applications

Novel molybdenum (Mo)-doped nickel oxide (NiO) Nanoparticles (NPs) were synthesized by using a simple sonochemical methodology and the synthesized NPs were investigated for antioxidant, and antibacterial applications. The X-ray diffraction (XRD) analysis revealed that the crystal systems of rhombohedral (21.34 nm) and monoclinic (17.76 nm) were observed for pure NiO and Mo-doped NiO NPs respectively. The scanning electron microscopy (SEM) results show that the pure NiO NPs possess irregular spherical shape with an average particle size of 93.89 nm while the Mo-doped NiO NPs exhibit spherical morphology with an average particle size of 85.48 nm. The ultraviolet–visible (UV–Vis) spectrum further indicated that the pure and Mo-doped NiO NPs exhibited strong absorption band at the wavelengths of 365 and 349 nm, respectively. The free radical scavenging activity of NiO and Mo-doped NiO NPs was also investigated by utilizing several biochemical assays. The Mo-doped NiO NPs showed better antioxidant activity (84.2%) towards ABTS. + at 200 µg/mL in comparison to their pure counterpart which confirmed that not only antioxidant potency of the doped NPs was better than pure NPs but this efficacy was also concentration dependant as well. The NiO and Mo-doped NiO NPs were further evaluated for their antibacterial activity against gram-positive (Staphylococcus aureus and Bacillus subtilis) and gram-negative (Pseudomonas aeruginosa and Escherichia coli) bacterial strains. The Mo-doped NiO NPs displayed better antibacterial activity (25 mm) against E. coli in comparison to the pure NPs. The synthesized NPs exhibited excellent aptitude for multi-dimensional applications.

Remarkable formaldehyde photo-oxidation efficiency of Zn2SnO4 co-modified by Mo doping and oxygen vacancies

Formaldehyde (HCHO) is one of the major volatile organic compounds (VOCs) contributing to both urban and indoor air pollution. It is emitted from several industrial activities and construction materials. Photocatalytic oxidation is a green promising technology aiming at HCHO removal. However, it still has some scientific challenges not fully addressed, like insufficient reaction active sites and not enough active species. This results in low HCHO removal efficiency, several toxic intermediates and poor stability. Therefore, the design of photocatalysis with surface-active sites, improved mineralization activity and recycling stability is of crucial importance. Herein, we report a facile one-pot hydrothermal method to prepare Zn2SnO4 (ZSO) with transition metal Mo doping (using Na2MoO4·2H2O as molybdenum source). Our experiments show that Mo is successfully incorporated into the ZSO lattice and contributes to the generation of oxygen vacancies (OVs). Moreover, the introduction of Mo enhances the separation and migration of photogenerated carriers and hinders their recombination. Furthermore, in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations reveal that switching the active sites from O terminals to Mo ones effectively improves adsorption and activation of the target molecules (O2, H2O, and HCHO), and promotes conversion of the reaction intermediates. Thus, ZSO co-modified by Mo doping and oxygen vacancies allows to achieve an efficient HCHO removal activity of 96%, which is much higher than pristine ZSO (21%) and other previously reported photocatalysts.

Novel cobalt-free perovskite PrBaFe1.9Mo0.1O5+δ as a cathode material for solid oxide fuel cells

Fe-based perovskite PrBaFe2O5+δ is inactive toward the oxygen reduction reaction (ORR) due to the sluggish oxygen-ion transport kinetics. Herein, Mo doping is developed as a simple and effective strategy to improve the ORR activity of PrBaFe2O5+δ. Mo-doped PrBaFe1.9Mo0.1O5+δ (PBFMO) is comparatively studied with undoped PrBaFe2O5+δ (PBFO) to reveal the effect of Mo doping on its crystal structure, thermal expansion behavior, electrical and electrochemical properties. PBFMO sample has a tetragonal structure with P4/mmm space group. Pr, Fe, and Mo in PBFMO sample exist as Pr3+/Pr4+, Fe2+/Fe3+, and Mo5+/Mo6+ mixed valence states. Mo doping reduces the average thermal expansion coefficient (TEC) from 18.8 × 10−6 K−1 down to 14.5 × 10−6 K−1, which is closer to the TEC of La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte. Moreover, Mo doping results in the increment of oxygen vacancy content and thus the enhancement of electrochemical performance. The polarization resistance (Rp) is 0.092 Ω·cm2 at 800 °C for PBFMO and is reduced by 27.0% after Mo doping. The peak power density is 0.68 W·cm−2 at 800 °C for PBFMO-based single cell. These obtained results indicate Mo doped PBFMO can be a good candidate for cathode material of intermediate temperature SOFC.

Mo doping and Se vacancy engineering for boosting electrocatalytic water oxidation by regulating the electronic structure of self-supported Co9Se8@NiSe.

Oxygen evolution reactions (OERs) are regarded as the rate-determining step of electrocatalytic overall water splitting, which endow OER electrocatalysts with the advantages of high activity, low cost, good conductivity, and excellent stability. Herein, a facile H2O2-assisted etching method is proposed for the fabrication of Mo-doped ultrathin Co9Se8@NiSe/NF-X heterojunctions with rich Se vacancies to boost electrocatalytic water oxidation. After step-by-step electronic structure modulation by Mo doping and Se vacancy engineering, the self-standing Mo-Co9Se8@NiSe/NF-60 heterojunctions deliver a current density of 50 mA cm-2 with an overpotential of 343 mV and a cell voltage of only 1.87 V at 50 mA cm-2 for overall water splitting in 1.0 M KOH. Our study opens up the possibility of realizing step-by-step electronic structure modulation of nonprecious OER electrocatalysts via heteroatom doping and vacancy engineering.

Optimising the synthesis of LiNiO2: coprecipitation versus solid-state, and the effect of molybdenum doping

A detailed study on the optimisation of the synthesis of LiNiO2 is reported, with further preliminary results showing improved performance on Mo doping.

NaCl template-assisted construction of a CoP-MoP heterostructured electrocatalyst for electrocatalytic nitrogen reduction.

The electrocatalytic nitrogen reduction reaction (NRR) to ammonia is a promising technology to store renewable energy and mitigate greenhouse gas emissions. However, it usually suffers from low ammonia yield and selectivity because of the lack of efficient electrocatalysts. Herein, we report that the construction of metal phosphide heterojunctions is an efficient strategy for NRR activity enhancement. A CoP-MoP heterojunction electrocatalyst, which is fabricated by a facile NaCl template-assisted strategy, exhibits a favorable ammonia yield rate of 77.8 μg h-1 mgcat-1 (38.9 μg h-1 cm-2) and a high faradaic efficiency of 11.16% at -0.50 V versus the reversible hydrogen electrode. The high NRR electrocatalytic activity can be attributed to the electronic coupling effects and interfacial synergistic effects of CoP and MoP at the heterojunction interface, which accelerates the electron transfer rate. Moreover, Mo doping changes the d-band centers of metal sites on the CoP surface, which is conducive to N2 adsorption and promotes N2* adsorption in the competition of occupying active sites, thus inhibiting the HER. This work manifests the high potential of phosphide electrocatalysts and opens an alternative route toward NRR electrocatalysis.

From the single-atom limit to the mixed-metal phase: finding the optimum condition for activating the basal plane of a FePSe3 monolayer towards HER.

Layered ternary transition metal tri-chalcogenides are some of the most promising candidates for hydrogen evolution reaction (HER) because of their ease of synthesis and affordability. However, majority of the materials in this category have HER active sites only at their edges, rendering a large portion of the catalyst useless. In this work, ways for activating the basal planes of one of these materials, namely, FePSe3, are explored. The effects of substitutional transition metal doping and external biaxial tensile strain on the HER activity of the basal plane of a FePSe3 monolayer are studied via first principles electronic structure calculations based on density functional theory. This study reveals that although the basal plane of the pristine material is inactive towards HER (value of H adsorption free energy, ΔGH* = 1.41 eV), 25% Zr, Mo, and Tc doping makes it more active (ΔGH* = 0.25, 0.22 and 0.13 eV, respectively). The effect of reducing the doping concentration, moving to the single-atom limit, on the catalytic activity is studied for Sc, Y, Zr, Mo, Tc and Rh dopants. For Tc, the mixed-metal phase FeTcP2Se6 is also studied. Among the unstrained materials, 25% Tc-doped FePSe3 gives the best result. Significant tunability of HER catalytic activity in the 6.25% Sc doped FePSe3 monolayer via strain engineering is also discovered. An external tensile strain of 5% reduces ΔGH* to ∼0 eV from 1.08 eV in the unstrained material, making this an attractive candidate for HER catalysis. The Volmer-Heyrovsky and Volmer-Tafel pathways are examined for some of the systems. A fascinating correlation between the electronic density of states and HER activity is also observed in most materials.

Influence of Mo doping on interfacial charge carrier dynamics in photoelectrochemical water oxidation on BiVO4

Intensity of photocurrent during water oxidation in BiVO4 is predominantly limited by charge transfer resistance (Rct), rather than semiconductor bulk resistance (Rbulk). Mo doping of BiVO4 can slightly reduce Rbulk but obviously decreases Rct.

In situ grown high-valence Mo-doped NiCo Prussian blue analogue for enhanced urea electrooxidation.

Mo-doped NiCo Prussian blue analogue (PBA) electrocatalysts self-supported on Ni foam are elaborately designed, which exhibit a low potential of 1.358 V (vs. RHE) to reach 100 mA cm-2 for catalyzing the urea oxidation reaction (UOR). The incorporation of high-valence Mo (+6) modifies the electronic structure and improves the electron transfer ability. Using X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) techniques, we confirm the effect of Mo doping on the NiCo PBA electronic structure.

Introducing high-valence molybdenum to stimulate lattice oxygen in a NiCo LDH cathode for chloride ion batteries.

Layered double hydroxides (LDHs) have been intensively investigated as promising cathodes for the new concept chloride ion battery (CIB) with multiple advantages of high theoretical energy density, abundant raw materials and unique dendrite-free characteristics. However, driven by the great compositional diversity, a complete understanding of interactions between metal cations, as well as a synergetic effect between metal cations and lattice oxygen on LDH host layers in terms of the reversible Cl-storage capability, is still a crucial but elusive issue. In this work, we synthesized a series of chloride-inserted trinary Mox-doped NiCo2-Cl LDH (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) with gradient oxygen vacancies as enhanced cathodes toward CIBs. The combination of advanced spectroscopic techniques and theoretical calculations reveals that the Mo dopant facilitates oxygen vacancy formation and varies the valence states of coordinated transition metals, which can not only tune the electronic structure effectively and promote Cl-ion diffusion, but improve the redox activity of LDHs. The optimized Mo0.3NiCo2-Cl LDH delivers a reversible discharge capacity of 159.7 mA h g-1 after 300 cycles at 150 mA g-1, which is almost a triple enhancement compared to that of NiCo2Cl LDH. The superior Cl-storage of trinary Mo0.3NiCo2Cl LDH is attributed to the reversible intercalation/deintercalation of chloride ions in the LDH gallery along with the oxidation state changes in Ni0/Ni2+/Ni3+, Co0/Co2+/Co3+ and Mo4+/Mo6+ couples. This simple vacancy engineering strategy provides critical insights into the significance of the chemical interaction of various components on LDH laminates and aims to effectively design more LDH-based cathodes for CIBs, which can even be extended to other halide-ion batteries like fluoride ion batteries and bromide ion batteries.

Mo-Pre-Intercalated MnO2 Cathode with Highly Stable Layered Structure and Expanded Interlayer Spacing for Aqueous Zn-Ion Batteries

Although manganese-based oxides possess high voltage and low cost, the sluggish reaction kinetics and poor structural stability hinder their applications in aqueous rechargeable Zn-ion batteries (ZIBs). Herein, a molybdenum (Mo) pre-intercalation strategy is proposed to solve the above issues of δ-MnO2. The pre-intercalated Mo dopants, acting as the interlayer pillars, can not only expand the interlayer spacing but also reinforce the layered structure of δ-MnO2, finally achieving enhanced reaction kinetics and superb cycling stability during carrier (de)intercalation. Moreover, oxygen defects, introduced due to Mo-pre-intercalation, play a critical role in the fast reaction kinetics and capacity improvement of the Mo-pre-intercalated δ-MnO2 (Mo-MnO2) cathode. Therefore, the Mo-MnO2 cathode displays a high energy density of 451 Wh kg-1 (based on cathode mass), excellent rate capability, and admirable long-term cycling performance with a high capacity of 159 mAhg-1 at 1.0 A g-1 after 1000 cycles. In addition, the energy storage mechanism of Zn2+/H+ stepwise reversible (de)intercalation is also revealed by ex situ experiments. This work provides an insightful guide for boosting the electrochemical performance of Mn-based oxide cathodes for ZIBs.

A first principles study on H-atom interaction with bcc metals

Solute hydrogen trapping has long been proposed as one of the mechanisms for hydrogen embrittlement in steel. It has been reported that the maximum hydrogen trapping energy of metallic solutes ranged from −0.7 eV to −0.9 eV. In this work, the mechanism of metal-H interaction in Cr-Mo steels was investigated with first principles calculations by modelling the binary alloy Fe-X (X = C, Si, Mn, Cr, Mo) system with reference to the chemical composition of Cr-Mo steels. The formation of hydrogen bonds in the case of H atoms located at different sites in Fe-X crystals was analyzed. Results indicated that various atomic doping had different roles in hydrogen effect in the steel, with C, Si and Mo doping making the solid solution of hydrogen in Fe crystals easier, while Mn and Cr doping was rather more difficult. In Fe-Mn and Fe-Cr crystals, the repulsion between Fe lattices was insignificant when H atoms were located in tetrahedral sites, which considerably reduced the binding energy in the crystal. When H atoms were dissolved into the crystal, the interatomic bonding interactions in Fe-X crystals were weakened, resulting in higher charge density fluctuations. The current work extends the understanding of H-atom diffusion and migration in steel from the microscopic scale to the atomic and electronic scales, which underpins the physics for tailoring chemical elements of bcc metals towards higher resistance to hydrogen embrittlement.

Novel Mo-doped WO3/ZnO nanocomposites loaded with polyvinyl alcohol towards efficient visible-light-driven photodegradation of methyl orange

The purpose of this work was to develop a molybdenum (Mo)-doped WO3/ZnO and polyvinyl alcohol (PVA) novel nanocomposite and then analyze and assess its photocatalyticperformance. The resulting composite was employed in a laboratory photoreactor to decompose methyl orange (OM) dye from synthetic wastewater. Fourier transform infrared (FT-IR) spectroscopy, UV–vis spectroscopy, and a transmission electron microscope (TEM)were utilized to analyze the preparednanocomposite. The impact of Mo dopant and PVA addition upon crystallinity, optical bandgap, and morphology was investigated. It was shown that 92 % of MO dye can be degraded by Mo-WO3/ZnO@PVA after 120 min of visible light irradiation.