Mo Doping Research Articles

Submerged Photosynthesis of Molybdenum–Tungsten Nanostructures for Supercapacitor Application

Research on electrochemical energy storage devices aims to produce supercapacitors via a facile and nonpolluting method. Because of unnecessary elemental doping and disordered morphologies of nano-oxides, impurities in raw materials during the conventional fabrication process would reduce the pseudocapacitance. Herein, we propose a submerged photosynthesis crystalline method for synthesizing oxygen vacancy (Vo)-enriched Mo–W oxide hydrates and Mo-doped tungsten oxide hydrate nanocomposites at 55 °C and normal pressure. In addition, this study describes the impact of Vos on pseudocapacitance using ab initio calculations based on density functional theory. Doping the WO3·0.33H2O lattice with Mo and Vos brings the conduction band closer to the Fermi energy level. The comparison of the ultraviolet–visible–near-infrared (UV–vis–NIR) irradiation spectrum and absorption coefficient calculation suggests that Mo and Vo doping is responsible for the NIR absorption. This study concludes that enriched Vos result in the highest specific capacitance and pseudocapacitive behavior of MoxW1–xO3·0.33H2O.

Polymerization State of Vanadyl Species Affects the Catalytic Activity and Arsenic Resistance of the V2O5-WO3/TiO2 Catalyst in Multipollutant Control of NOx and Chlorinated Aromatics.

The conventional V2O5-WO3/TiO2 catalyst suffers severely from arsenic poisoning, leading to a significant loss of catalytic activity. The doping of Al or Mo plays an important role in promoting the arsenic resistance on NH3 selective catalytic reduction (NH3-SCR), but their promotion mechanism remains in debate and has yet to be explored in multipollutant control (MPC) of NOx and chlorinated organics. Herein, our experimental characterizations and density functional theory (DFT) calculations confirmed that arsenic species preferentially adsorb on both Al and Mo to form arsenate, thereby avoiding bonding to the catalytically active V sites. More importantly, Al doping partially converted the polymeric vanadyl species into monomeric ones, thereby inhibiting the near-surface and bulk lattice oxygen mobility of the V2O5-WO3/TiO2 catalyst, while Mo doping resulted in vanadyl polymerization with an enriched V5+ chemical state and exhibited superior MPC activity and COx selectivity. Our work shows that antipoisoning catalysts can be designed with the combination of site protection and occurrence state modification of the active species.

Electrocatalytic removal of persistent organic contaminants at molybdenum doped manganese oxide coated TiO2 nanotube-based anode

Electrooxidation is an attractive technique that can be effectively applied for the treatment of persistent organic contaminants, but its implementation in practice is limited by the lack of efficient and low-cost anode material that would not lead to the generation of chlorinated by products. Herein, we developed a novel anode based on TiO2 nanotube array (NTA) coated with Mo-doped MnxOy, and applied it for electrooxidation of persistent organic contaminants. The Ti/TiO2 NTA–MnxOy-Mo anode outperformed the commercial Ti/IrOx-Pt anode and effectively oxidized organic contaminants, with a significantly reduced electric energy per order, and avoiding chlorine evolution reaction. Mo doping played a key role in the excellent performance of the synthesized anode as it favored the formation of oxygen vacancies in the host lattice and Mn and Mo species redox couples, which increased the oxidizing power of the anode and ensured its complete stability.

Significantly enhanced surface oxygen vacancies over W18O49 via Mo doping and plasma-induced surface reconstruction for oxidative desulfurization

The non-stoichiometric structure of tungsten oxide (W18O49) makes it easy to form oxygen vacancies near the low-valence W atoms, so the W18O49 can be applied to oxidative desulfurization. To further improve the desulfurization activity of W18O49 to meet the increasingly stringent environmental requirements, Mo doping and plasma-induced surface reconstruction cooperative strategies are developed. The incorporation of Mo species into the W18O49 surface by replacing W sites can adjust the atomic and electronic structure of the catalyst surface and form more oxygen vacancies. After Mo doping into the W18O49, the plasma bombarded the surface of material to destroy part of the surface structure, thus producing the reactive sites with low coordination numbers. This reconstructed atomic surface also accompany to generate more oxygen vacancies, thus greatly improving the catalytic activity. Compared to pure W18O49, significantly improves oxidative desulfurization performance can be achieved over Mo-W18O49-P, and deep desulfurization is realized within 3 h. Moreover, the optimal Mo-W18O49-P shows better stability than pure W18O49, which can be recycled for 12 times. This work provides an accessible pathway for cooperative enhancing the catalytic oxidative desulfurization activity of oxide catalysts.

Changes to Material Phase and Morphology Due to High-Level Molybdenum Doping of ZnO Nanorods: Influence on Luminescence and Defects.

The influence of Mo on the electronic states and crystalline structure, as well as morphology, phase composition, luminescence, and defects in ZnO rods grown as free-standing nanoparticles, was studied using a variety of experimental techniques. Mo has almost no influence on the luminescence of the grown ZnO particles, whereas shallow donors are strongly affected in ZnO rods. Annealing in air causes exciton and defect-related bands to drop upon Mo doping level. The increase of the Mo doping level from 20 to 30% leads to the creation of dominating molybdates. This leads to a concomitant drop in the number of formed ZnO nanorods.

Influence of a Mo interlayer on the oxidation behavior of a Cr coating on a Zr alloy substrate

Cr-based coatings with or without a Mo interlayer were deposited on a Zr substrate by multi-arc ion plating, and the effect of the Mo interlayer on the oxidation behavior of the coatings at different time lengths (maximum 90 min) at 1160 °C was investigated. Atomic scale characterization confirms that, on the one hand, the Mo interlayer prevents the Cr coating from reacting with the Zr substrate to form the ZrCr2 Laves phase and, on the other hand, the solid solution structure generated due to Mo doping effectively guarantees the integrity of the Cr2O3 oxide layer and the residual Cr coating.

Heterogeneous doping via charge carrier transport improves Photoelectrochemical H2O oxidative H2O2 synthesis

Photoelectrochemical (PEC) water splitting into H2O2 and H2 has attracted significant attention due to its low cost and sustainability. However, slow charge carrier transport and water oxidation kinetics limit the selectivity for H2O2 production and solar conversion efficiency. Herein, we propose a heterogeneous doping approach that combines surface gradient doping with bulk doping to improve the charge carrier transport in the photoelectrode. Inducing gradient Nb and homogeneous Mo doping into BiVO4 photoanode (G-Nb/Mo:BVO) can promote charge separation and carrier transfer, leading to the high selectivity for H2O2 generation and suppression of O2 production. Consequently, the heterogeneously doped G-Nb/Mo:BVO photoanode presents an average Faraday efficiency (FE) of over 80% for H2O2 production in a wide potential of 0.6–1.8 VRHE with the maximum FE of 83.7% at 1.2 VRHE under AM 1.5G illumination. More importantly, H2O2 production rate can reach 1.23 μmol min−1 cm−2 at 1.23 VRHE, representing the best H2O2 production rate reported for the photoelectrodes. Density functional theory calculations prove that Mo and Nb co-doping increases the reactivity of BiVO4 and improves 2e− water oxidation reaction activity and selectivity. This work demonstrates that heterogeneous doping provides a cost-effective strategy to break performance trade-offs by improving charge carrier separation and transport in light absorbers, and modulating the selectivity and activity of water oxidation reaction to generate H2O2, which can be extended to other photocatalytic reactions.

Insight into the enhanced tolerance of Mo-doped CeO2-Nb2O5/TiO2 catalyst towards the combined effect of K2O, H2O and SO2 in NH3-SCR

MoO3-doped CeO2-Nb2O5/TiO2 catalyst was synthesized by a sol–gel method. It was found that Mo doping observably enhanced the tolerance of CeO2-Nb2O5/TiO2 catalyst to the combined poisoning of H2O, SO2 and K2O. Mo doping could restrain the generation of ammonium sulfate and metal sulfate on the surface of the catalyst. This came down to the large specific surface area, strong acidity and superior redox performance of CeO2-MoO3-Nb2O5/TiO2 catalyst. In situ DRIFTS results indicated that K/S/H-CMNT catalyst still proceeded the SCR reaction according to the L-H and E-R mechanisms together, while K/S/H-CNT catalyst only followed the E-R mechanism. Mo doping could enhance the adsorption of NH3 and NOx species in the presence of K2O, H2O, and SO2.

Compositional mapping of Mo-doped ZnO thin films: Mechanical, nano-surface and ToF-SIMS analyses

ZnO and Mo-doped ZnO thin films were grown using the spray pyrolysis process with variations in Mo doping concentrations. The films were characterized with a comprehensive compositional analysis, including electron dispersive X-ray (EDX), X-rays photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS), along with grazing incidence X-ray diffraction(GIXRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and UV–Vis spectroscopy to investigate their structural, morphological, optical and chemical compositions. Micro-hardness analysis was performed on films as a function of the Mo content. GIXRD analysis detected the presence of characteristic peaks of ZnO along the (100), (002) and (101) planes. The presence of Zn, O, and Mo in the synthesized samples was revealed by EDX, XPS, and ToF-SIMS results, which matched the experimental values of a pure and Mo:ZnO-x composition. XPS analysis revealed the Mo6+ oxidation state of molybdenum present in Mo:ZnO films. From UV–Vis absorption spectroscopy, the bang gap was observed to increase with Mo content, up 5 at.%, and located in the 3.18 – 3.24 eV interval. These results will be helpful in the synthesis of Mo:ZnO films for relevant applications, including sensing, optoelectronics and antimicrobial.

Coupling of self-healing atomic layer CoAl-LDH onto Mo:BiVO4 photoanode for fast surface charge transfer toward stable and high-performance water splitting

Herein, Mo doping BiVO4/ultrathin-CoAl-LDH (Mo:BVO/CoAl-LDH-u) photoanode with self-healing property is firstly designed by using the atomic layer CoAl-LDH as cocatalyst to modify Mo:BVO through a simple dipping coating method. The Mo:BVO/CoAl-LDH-u photoanode presents a nearly 100% surface charge separation efficiency and extremely outstanding photocurrent density of 5.8 mA/cm2 at 1.23 V vs. reversible hydrogen electrode (VRHE) without any scavengers. The CoAl-LDH-u intimately contacted with BiVO4 photoanode significantly improves the surface charge transfer efficiency by passivating the surface state and rapidly extracting holes from Mo:BiVO4, and promotes the oxygen evolution reaction (OER) rate by conversion of Co2+ to Co3+ species. Interestingly, the Mo:BVO/CoAl-LDH-u photoanode has the self-healing peculiarity, due to the easy reparation of oxygen defects in CoAl-LDH-u by the cycle of Co3+/Co2+, and hence the photoelectrochemical (PEC) performance can be restored naturally in the air. This work presents a facile approach to fabricate high-efficiency BiVO4 photoelectrode for accelerating the PEC water splitting.

Unraveling the high catalytic activity of single atom Mo-doped TiO2 toward NH3-SCR: Synergetic roles of Mo as acid sites and oxygen vacancies as oxidation sites

Herein, the single-atom Mo doped TiO2 catalysts with abundant oxygen vacancies (OVs) were fabricated to get a deep insight into the roles of Mo species and OVs for selectivity catalytic reduction (SCR) of NOx. The single-atom Mo doping largely enhances the catalytic activity of TiO2 even with the presence of 5 vol% H2O. Surface Mo species remarkably enhance the strength of Brønsted acid sites on TiO2, which further facilitates the adsorption and activation of NH3 to –NH2. Meanwhile, the in-situ generated OVs largely increase the concentration of monatomic species (O-), which facilitate the oxidation of NO to NO2, thus promoting the catalytic activity below 350 °C. Additionally, the surface polymeric Mo would lead to the side reaction at high-temperature range above 350 °C. This work gives a new insight into the effect of Mo species, and the synergistic role of Mo and OVs in the SCR reaction over Mo-based catalysts.

High-valent bimetal Ni2P/Co2P heterostructures induced by Mo doping as an advanced electrode for hybrid supercapacitors

The development of advanced electrode materials with fast reaction kinetics and optimized morphology is key to achieving high-performance hybrid supercapacitors with high energy density and outstanding cycling performance. Herein, an ingenious strategy is developed to prepare M doped Ni2P/Co2P (M = Cu, Zn, Mo) bimetallic phosphide electrode materials with heterostructure. For the Mo-doped Ni2P/Co2P, the unique morphology of hollow nanocubes consisting of ultrathin nanosheets facilitates the availability of more electrochemical active sites and relieves the deformational effects. In addition, the formation of heterogeneous structures modulates the electronic structure and the causes redistribution of interfacial charges, while the introduction of Mo cation can promote the formation of more high-valent Ni/Co sites, which synergistically accelerate reaction kinetics. Consequently, the Mo-Ni2P/Co2P hollow nanocubes with heterogeneous interfaces exhibit an optimal specific capacitance of 2300 F g−1 at 1 A g−1. In addition, when combined with activated carbon (AC) as a hybrid supercapacitor (HSC), the Mo-Ni2P/Co2P //AC device displays an energy density of 35.56 Wh kg−1 at a splendid power density of 800.0 W kg−1 and a remarkable cycling performance (the capacitance retention of 84.83% after 15,000 cycles). This study reveals that the introduction of Mo cation induces the formation of high-valence Ni/Co, providing a meaningful reference for the construction of high-performance metal phosphides with unique morphology and massive phase boundaries.

Influence of Mo Doping on Electronic and Magnetic Properties of Monolayer CrX3: A First-Principles Study

In recent years two dimensional (2D) materials with intrinsic magnetism have drawn intense research interest due to their potential application in spintronic devices. Among them, chromium trihalide family has received much attention due to the exhibition of wide range of electronic and magnetic properties. Aiming to improve their spintronic properties, we have investigated the electronic and magnetic properties of mono-layer (ML) Mo-doped CrX3 (X = Cl, Br and I) using density functional theory (DFT) + Hubbard U approach. Our results show that substitution of Mo atom at the Cr site is energetically favorable. Magnetic ground state of all the members is found to be ferromagnetic (FM) which undergoes a transition to antiferromagnetic (AFM) state by applying both the compressive as well as the tensile strain. FM exchange interaction parameter and the estimated Curie temperature (T c ) of ML CrMoX6 are found to be significantly enhanced compared to the corresponding values of pristine CrX3. All the members of ML CrX3 show magneto-crystalline anisotropy energy (MAE) favoring an out-of-plane easy axis of magnetization. Our calculations further reveal that all three compounds exhibit semiconducting properties with reduced bandgap compared to the ML CrX3 family. This property can make them useful in spintronic applications.

Influence of molybdenum doping on the structural, electrical, and optical properties of germanium telluride thin films

This study investigates the influence of molybdenum (Mo) doping on the local atomic structure, morphology, and electrical properties of amorphous germanium telluride (GeTe) thin films. Structural and morphological studies show that Mo-doping inhibits the crystallization of amorphous GeTe thin films. Moreover, the crystallization temperature of the GeTe thin film increases from 197 to 317 °C with increasing Mo dopant concentration. The electrical properties of Mo-doped GeTe thin films are discussed in terms of the capacitance–voltage characteristics in temperatures range 27–357 °C. The optical bandgap values decrease from 0.67 to 0.55 eV when increasing Mo doping in GeTe thin film. Mo integration significantly impacts the Ge–Te bond lengths and structural symmetry, increasing the degree of disorder in amorphous GeTe thin films. This study demonstrates the effectiveness of Mo doping in enhancing the thermal stability of the amorphous phase of GeTe for its envisioned memory and brain-inspired computing applications.

Enhanced hydrogen storage properties of Ti–Cr–Nb alloys by melt-spin and Mo-doping

Ti–Cr–Nb hydrogen storage alloys with a body centered cubic (BCC) structure have been successfully prepared by melt-spin and Mo-doping. The crystalline structure, solidification microstructural evolution, and hydrogen storage properties of the corresponding alloys were characterized in details. The results showed that the hydrogen storage capacity of Ti–Cr–Nb ingot alloys increased from 2.2 wt% up to around 3.5 wt% under the treatment of melt-spin and Mo-doping. It is ascribed that the single BCC phase of Ti–Cr–Nb alloys was stabilized after melt-spin and Mo-doping, which has a higher theoretical hydrogen storage site than the Laves phase. Furthermore, the melt-spin alloy after Mo doping can further effectively increase the de-/absorption plateau pressure. The hydrogen desorption enthalpy change ΔH of the melt-spin alloy decreased from 48.94 kJ/mol to 43.93 kJ/mol after Mo-doping. The short terms cycling test also manifests that Mo-doping was effective in improving the cycle durability of the Ti–Cr–Nb alloys. And the BCC phase of the Ti–Cr–Nb alloys could form body centered tetragonal (BCT) or face center cubic (FCC) hydride phase after hydrogen absorption and transform to the original BCC phase after desorption process. This study might provide reference for developing reversible metal hydrides with favorable cost and acceptable hydrogen storage characteristics.

Rational Design of Molybdenum-Doped Cobalt Nitride Nanowire Arrays for Robust Overall Water Splitting.

Rational design of efficient electrocatalysts is highly imperative but still a challenge for overall water splitting. Herein, we construct self-supported Co3 N nanowire arrays with different Mo doping contents by hydrothermal and nitridation processes that serve as robust electrocatalysts for overall water splitting. The optimal Co3 N-Mo0.2 /Ni foam (NF) electrode delivers a low overpotential of 97 mV at a current density of 50 mA cm-2 as well as a highly stable hydrogen evolution reaction (HER). Density functional theory (DFT) calculations prove that Mo doping can effectively modulate the electronic structure and surface adsorption energies of H2 O and hydrogen intermediates on Co3 N, leading to improved reaction kinetics with high catalytic activity. Further modification with FeOOH species on the surface of Co3 N-Mo0.2 /NF improves the oxygen evolution reaction (OER) performance benefiting from the synergistic effect of dual Co-Fe catalytic centers. As a result, the Co3 N-Mo0.2 @FeOOH/NF catalysts display outstanding OER catalytic performance with a low overpotential of 250 mV at 50 1 mA cm-2 . The constructed Co3 N-Mo0.2 /NF||Co3 N-Mo0.2 @FeOOH/NF water electrolyzer exhibits a small voltage of 1.48 V to achieve a high current density of 50 mA cm-2 at 80 °C, which is superior to most of the reported electrocatalysts. This work provides a new approach to developing robust electrode materials for electrocatalytic water splitting.

Density-functional quantum computations on bandgap engineering and tuning of optoelectronic properties of MgH2 via Mo doping: Prospects and potential for clean energy hydrogen-storage fuel and optoelectronic applications

With the increasing depletion of conventional energy sources and their detrimental environmental hazards, it is imperative to search for sustainable alternative clean energy sources. In the recent decades, hydrogen has emerged as potential source of clean energy. One of the potential alternatives to achieve the objective is the designing and characterization of materials for hydrogen-storage energy applications. In this regard, metal-bearing hydrides are the most promising candidates. For instance, magnesium-bearing hydrides are the focus of current research work owing to high hydrogen capacity of 7.6 wt%. In this paper, we first time report density functional-based quantum theoretical analysis to explore the potential of Mo-doped magnesium hydrides MgH2:Mo for optoelectronic and hydrogen-storage applications. For the quantum computations of the required optoelectronics and energy storage properties, we employed all-electron methods within generalized gradient approximation (GGA). Besides applying GGA approximation to account for the electronic correlated effects, we employed the Hubbard potential U (= 4 eV) for onsite repulsive Coulomb force. We predict that 10% doping by weight of Mo into MgH2 suppresses its insulating band gap of 4.9 eV to semiconducting band gap of order 3.15 eV for spin up and 0.15 eV for spin down. As such the doping of Mo can tune the the bandgap, structural, electronic and optoelectronic properties of MgH2 considerably for potential applications.

Electronic structure reconfiguration of nickel–cobalt layered double hydroxide nanoflakes via engineered heteroatom and oxygen-vacancies defect for efficient electrochemical water splitting

The development of earth-abundant and high-efficiency bifunctional electrocatalysts is extremely desirable for electrochemical water splitting, but there are some critical challenges that need to be addressed. The coordinated tailoring of electronic structure and Bader charge transference by heteroatom doping and oxygen vacancy defects are one of the strongest tactics to enhance the oxygen and hydrogen evolution reactions (OER and HER) of catalysts. Herein, a novel Mo-decorated nickel–cobalt layered double hydroxides 3D honeycomb nanoflake on Ni foam (labeled as Mo-NiCo LDHs(Vo)) as bifunctional electrode materials with enriched oxygen vacancy defects, excellent geometric stability, and enriched active sites was successfully fabricated through a facile hydrothermal reaction strategy. Density functional theory computations and experimental results confirmed that the electrocatalytic intrinsic activity of Mo-NiCo LDHs(Vo) was optimized not only because of the provision of new active sites by the Mo dopants via the construction of defects and oxygen vacancies but also because of the activation of the local electronic structures of the surrounding Ni and Co sites. Consequently, Mo-NiCo LDHs(Vo) exhibited outstanding electrocatalytic performance with an overpotential of 258 mV for OER and 194 mV for HER at a current density of 10 mA/cm2 in an alkaline medium. In addition, the catalyst exhibited excellent long-term stability after 100 h of use as a bifunctional electrode for overall water splitting. This work provides a facile means to fabricate superior, efficient noble metal-free catalysts with well-designed defects at the atomic-level using electronic structure engineering for energy-related applications.

Performance enhancement of α-MnO2 through tunnel-size and morphology adjustment as pseudocapacitive electrode

As a typical pseudo-capacitive electrode material, α-MnO2 always suffers from low practical capacity and poor stability because of the low conductivity and unavoidable disproportionation reaction. In the work here, high valance Mo (Mo6+) doping followed by chemical reduction treatment is proposed to mitigate these issues. It is found that morphology of the α-MnO2 can be influenced by Mo-doping, and tunnel size is tuned by the following reduction. Without doping, α-MnO2 nanorods with good crystallization can be obtained. With the increase of Mo feed ratio, the length of the nanorods is gradually reduced and fine nanoparticles are formed when the Mo/Mn feed mole ratio reaches 1:20 (named as R-1:20). With this feed ratio, a largely increased capacity of 245 C g−1 at 0.5 A g−1 is achieved, much larger than that of the pure α-MnO2 nanorods (110 C g−1). Yet, there is a certain distortion of the crystal structure, resulting in decline of rate performance. Meanwhile, cycling performance also decays owing to the increase of active sites and hence disproportionation reaction. After reduction treatment, tunnel size of the R-1:20 are slightly enlarged, leading to the improvement of rate performance and cycling stability, and 93% of the initial capacity is maintained after 10,000 cycles. Mo-doping and the following reduction treatment can effectively increase the activity sites, increase the electronic and ionic conductivity, suppress the disproportionation reaction through the adjustment to morphology and tunnel size, and thus improve the charge storage capability of α-MnO2.

Interface and electronic structure regulation of Mo-doped NiSe2-CoSe2 heterostructure aerogel for efficient overall water splitting

Transition metal selenides (TMSes) with cubic pyrite-type crystal structure have been widely explored as electrocatalysts for oxygen evolution reaction (OER), but the insufficient hydrogen evolution reaction (HER) performance hinders the application of overall water splitting. Herein, we designed and prepared a Mo doped NiSe2-CoSe2 heterostructure aerogel as bifunctional electrocatalyst via facile spontaneous gelation and selenium vapor deposition. The active sites on the heterointerface possessed desirable Gibbs free energy of hydrogen adsorption, leading to better HER performance than single NiSe2 or CoSe2. Moreover, systematically experimental research and density functional theory (DFT) calculations revealed that fine regulated Mo doping improved the electropositivity of heterostructure, promoting the nucleophilic adsorption of water molecule. Benefit from those improvements, the optimal Mo doped NiSe2-CoSe2 aerogel exhibited an extremely low overpotential of 57 mV at the current density of 10 mA·cm−2 for HER with a small Tafel slope value of 38 mV·dec−1. Meanwhile, Mo doping provided higher electron transfer efficiency and better adsorptive property toward reaction intermediate in anodic reaction, resulting in low overpotential of 270 mV at the current density of 100 mA·cm−2 for OER with good electrocatalytic stability. This work provides an anticipated perspective of rational combination of metal doping and heterostructure for advanced electrocatalysts.