Mo Doping Research Articles

Regulating the Oxygen Vacancy and Electronic Structure of NiCo Layered Double Hydroxides by Molybdenum Doping for High-Power Hybrid Supercapacitors.

Amelioration of nickel-cobalt layered double hydroxides (NiCo-LDH) with a high specific theoretical capacitance is of great desire for high-power supercapacitors. Herein, a molybdenum (Mo) doping strategy is proposed to improve the charge-storage performance of NiCo-LDH nanosheets growing on carbon cloth (CC) via a rapid microwave process. The regulation of the electronic structure and oxygen vacancy of the LDH is consolidated by the density functional theory (DFT) calculation, which demonstrates that Mo doping narrows the band gap, reduces the formation energy of hydroxyl vacancies, and promotes ionic and charge transfer as well as electrolyte adsorption on the electrode surface. The optimal Mo-doped NiCo-LDH electrode (MoNiCo-LDH-0.05/CC) has an amazing specific capacity of 471.1mA h g-1 at 1 A g-1 , and excellent capacity retention of 84.8% at 32 A g-1 , far superior to NiCo-LDH/CC (258.3mA h g-1 and 76.4%). The constructed hybrid supercapacitor delivers an energy density of 103.3W h kg-1 at a power density of 750W kg-1 and retains the cycle retention of 85.2% after 5000 cycles. Two assembled devices in series can drive thirty LED lamps, revealing a potential application prospect of the rationally synthesized MoNiCo-LDH/CC as an energy-storage electrode material.

Synergy Effect of the Enhanced Local Electric Field and Built-In Electric Field of CoS/Mo-Doped BiVO4 for Photoelectrochemical Water Oxidation.

Bismuth vanadate is a promising material for photoelectrochemical water oxidation. However, it suffers from a low quantum efficiency, poor stability, and slow water oxidation kinetics. Here, we developed a novel photoanode of CoS/Mo-BiVO4 with excellent photoelectrochemical water oxidation performance. It achieved a photocurrent density of 4.5 mA cm-2 at 1.23 V versus the reversible hydrogen electrode, ∼4 times that of BiVO4. The CoS/Mo-BiVO4 photoanode also exhibited good stability, and the photocurrent density generated by the CoS/Mo-BiVO4 photoanode did not significantly decrease after light irradiation for 2 h. Upon replacement of part of the V with Mo doping in BiVO4, the local electric field around the Mo-O bond was enhanced, thus promoting carrier separation in BiVO4. The CoS was deposited on the surface of Mo-BiVO4, forming a built-in electric field at the interface. Under the action of the bias electric field and the built-in electric field, the carriers of CoS/Mo-BiVO4 were efficiently separated in the direction of the inverse type II heterojunction. In addition, CoS improved the light absorption and charge injection efficiency of the CoS/Mo-BiVO4 photoanode.

Spectral regulation with high-temperature resistance by Mo-doped HfO2 monolayer for thermophotovoltaic systems

Structured spectrally selective emitters show good spectral performance in thermophotovoltaic (TPV) systems, but most of them cannot maintain good spectral emittance at high temperatures as expected. A Mo-doped HfO2 monolayer structure was proposed to improve the thermal stability of the structured emitters. A simulation model based on the transfer matrix method and effective medium theory was used to design the doped monolayer emitters. Thermal annealing and characterization measurements were conducted to investigate the proposed emitter after 1273 K–1473 K thermal annealing, and a TPV system model was built to evaluate their spectral performance after thermal annealing. The results revealed that 20% Mo doping can improve the spectral performance of a 90 nm HfO2 monolayer structure, making the spectral efficiency up to 60.93% at 1273 K. Due to the combined action of the Mo oxidation, grain growth and phase transition of HfO2 during thermal annealing, the formation of holes and Mo oxides were observed. Consequently, the spectral emittance of the doped emitters changed. Nevertheless, no obvious decline in the system efficiency (approximately 1%) of the TPV system with the doped emitter after 1273K thermal annealing for 12 h was observed. The proposed Mo-doped HfO2 monolayer emitter shows good spectral performance compared with the undoped one. The investigation of the thermal degradation of the proposed emitters can lay a foundation for promoting their applications of TPV systems.

Structural, electronic, linear, and nonlinear optical properties of undoped and Mo (I, II)-doped LiNbO3 crystal

In this paper, density functional theory (DFT) calculations used to investigate the structural, electronic, linear and nonlinear optical properties of pure lithium niobate crystal (LiNbO3) and doped LiNbO3 by Mo (I) and Mo (I). The lattice constants were calculated by analysing the optimised unit cell, and the results were found to be in good agreement with both the experimental and theoretical values that were reported. The results indicate a clear distinction in the electronic characteristics of LiNbO3 and doped LiNbO3 (Mo-Nb), the band structures that have been computed indicate that the band gap of LiNbO3 can be narrowed by adding Mo (I) and Mo (II) dopants to 2.068 eV and 0.476 eV, respectively. Interesting results were obtained by this doping process, as these results showed that the effect of doping led to an improvement in some optical properties, such as the absorption spectrum of the material, and also led to an increase in the effect of second harmonic generation (SHG), which is considered a basic requirement for developing optical devices in many photonic applications such as laser, electro-optic applications and optical switches.

High thermal stability and optical contrast of Mo-doped Ge8Sb2Te11 films prepared by magnetron co-sputtering

In this work, Ge8Sb2Te11 (GST) films with high melting point element Mo doping were prepared by magnetron co-sputtering, and the influence of Mo content on the phase transformation and optical properties of the films was investigated. The results of GIXRD, XPS, and ellipsometry analysis show that Mo will occupy the lattice vacancy, promoting grain growth and accelerating phase transitions. With an increase in Mo content, the phase transition temperature of the films can reach 360 °C, and the amorphous thermal stability of the films can be enhanced by Mo doping. Meanwhile, the optical properties of the films are improved. The optical band gap of Mo-doped films is reduced, the absorption coefficient rises, and the refractive index contrast of GST films with low Mo-doping in the Vis-NIR band is as high as 2.27. This result will make it possible to apply Ge8Sb2Te11 thin films in structural color fields and broaden their color spectrum.

Bandgap tuning by controlled growth of Mo doped NiO nanoparticles and their functional role as excellent photocatalytic degradation agent

Semiconductor materials are in leading role for elimination of organic pollutants in water with an effective tuning of bandgap and improving their photocatalytic activity. Pristine and Mo-doped (0, 1, 2, 3, 4 and 6 %) NiO nanoparticles have been synthesized by sol–gel method. The synthesized nanoparticles were examined by XRD, SEM, EDS, UV–visible spectroscopy and photoluminescence (PL) analysis. The synthesized nanoparticles exhibit spherical morphology and their crystallite size decreases with an increase in Mo concentration. The average crystallite size decreases from 67 nm to 44 nm and the drastic reduction in band gap occurs from 3.5 eV to 2.9 eV at 3 wt% Mo doping. The photocatalytic activity against Rhodamine-B (RhB) and methylene blue (MB) showed that the Molybdenum doping improves the performance of NiO photocatalyst. The PL analysis revealed that the Molybdenum substitution in NiO host lattice specifically reduces the recombination rate with an improved photo-efficiency. The reaction kinetics examination showed pseudo-first-order kinetics with an improved rate constant. The sample containing 3 wt% Mo doped NiO showed highest efficiency among all the prepared samples. The sample with 3 wt% doping shows 90% degradation after 90 min when using against MB dye, whereas with RhB dye it shows 98% degradation in 120 min. The retention of high performance after five consecutive cycles confirms the reusability of synthesized nanoparticles.

Vermiwash-mediated synthesis of molybdenum doped TiO2 nanoparticles: Evaluation of photocatalytic and biomedical properties

Combined effects of molybdenum (Mo) doping and enzyme incorporation on the photocatalytic and certain biomedical activities (antibacterial, antioxidant and antidiabetic) of titanium oxide nanopowder were studied. A soft-chemical eco-friendly approach was adopted to prepare enzyme powered Mo doped TiO2 nanoparticles (MTV). The photocatalytic dye degradation study against MB dye showed that the Mo addition increases the degradation efficiency from 73 to 86%. The enzyme incorporation into the system through the addition of vermiwash improves the efficiency further to 97%. The doping of Mo and addition of enzymes effectively controlled the growth of the tested bacteria Proteus vulgaris, Bacillus subtilis, and Pseudomonas aeruginosa. The minimum inhibitory concentration (MIC) of bare TiO2 against the bacteria viz. P. vulgaris, B. subtilis and P. aeruginosa are 125, 125 and 250 µg/mL, respectively, whereas the MIC of vermiwash activated Mo doped TiO2 are as low as 15.62 µg/mL, 07.81 µg/mL and 15.62 µg/mL, respectively. The antioxidant capacity of the sample MTV expressed potential free radical scavenging effect by 2,2-diphenyl-1-picrylhydrazyl (DPPH) with an inhibition of 89.77% and 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) with an inhibition of 87.02% compared to the standard ascorbic acid. In addition, the MTV nanopowders exhibited significant anti-diabetic effect (89.29%) by inhibiting the α-glucosidase enzyme. The mechanism involved in the enhancement of efficiency of the synthesized material is elaborated in this article. The XRD, SEM, FT-IR, Raman, XPS and BET results support the discussions on the property enhancement of the prepared material.

Dielectric response and current-voltage characteristic of Mo-doped diamond-like carbon thin films at room temperature

Herein we have reported the effect of molybdenum (Mo) doping and acetylene (C2H2) gas flow rate, during deposition, on the electrical properties of diamond like carbon (DLC) films. The frequency dependent dielectric response of the undoped and doped DLC films has been discussed in details. Mo doping also increases the dielectric constant value owing to interfacial polarization and the corresponding change with C2H2 gas flow rate has been attributed to the formation of sp2 bonding over sp3 bonding, favoring the emergence of a graphite-like phase. The ac conductivity of DLC films has been observed to increase with frequency following a power law behavior. However, with 29 % Mo doping we have noticed two plateau regions having different slopes which has been explained on the basis of the jump relaxation model (JRM). The theoretical fitting of the experimental data indicates occurrence of ionic conduction along with polaron hoping. The dc contribution part (σdc) of the measured ac conductivity is found to vary with the acetylene (C2H2) gas flow dependent sp2 bonding formation. The σdc is extracted to be 2351 S/m for the 29 % Mo doped DLC films. From the Nyquist plot in impedance spectroscopy single relaxation phenomena have been observed for the no or low Mo doping but with 29 % Mo doping both the grain and grain boundary effect are prominent. This also suggests the presence of sp2 hybridization and formation of dangling bonds between the metal carbide and DLC film. From the current voltage characteristics, the development of high sp2 bonding and high electron injection into the DLC matrix with subsequent change in nature of the DLC from semiconducting to metallic with high Mo doping has been reported. From the capacitance voltage characteristics study it has been found that either increase in acetylene gas flow during deposition or Mo doping increases the space charge and trap carrier densities.

High-Valence Mo Doping and Oxygen Vacancy Engineering to Promote Morphological Evolution and Oxygen Evolution Reaction Activity.

The rational design of high-efficiency, low-cost electrocatalysts for electrochemical water oxidation in alkaline media remains a huge challenge. Herein, combined strategies of metal doping and vacancy engineering are employed to develop unique Mo-doped cobalt oxide nanosheet arrays. The Mo dopants exist in the form of high-valence Mo6+, and the doping amount has a significant effect on the structure morphology, which transforms from 1D nanowires/nanobelts to 2D nanosheets and finally 3D nanoflowers. In addition, the introduction of vast oxygen vacancies helps to modulate the electronic states and increase the electronic conductivity. The optimal catalyst MoCoO-3 exhibits greatly increased active sites and enhanced reaction kinetics. It gives a dramatically lower overpotential at 50 mA cm-2 (288 mV), much smaller than that of the undoped counterpart (418 mV) and comparable to those of the recently reported electrocatalysts. Density functional theory results further verify that the increased electronic conductivity and optimized adsorption energy toward oxygen evolution reaction intermediates are mainly responsible for the enhanced catalytic activity. Moreover, the assembled two-electrode electrolyzer (MoCoO-3||Pt/C) exhibits superior performance with the cell potential decreased by 233 mV to reach a current density of 50 mA cm-2 with respect to the benchmark counterpart catalysts (RuO2||Pt/C). This work might contribute to the rational design of effective, low-cost electrocatalyst materials by combining multiple strategies.

Modulating the Electronic Structure of Ni/NiO Nanocomposite with High‐Valence Mo Doping for Energy‐Saving Hydrogen Production via Boosting Urea Oxidation Kinetics

Electrocatalytic urea oxidation reaction (UOR) has emerged as a promising alternative to the anodic oxygen evolution reaction (OER) in water electrolysis. However, UOR faces challenges like slow kinetics, high energy barriers, and a complex mechanism, necessitating the development of efficient electrocatalysts. Herein, a rapid method is proposed for synthesizing Mo‐doped Ni/NiO (Ni/MNO) nanocomposite as a highly effective UOR electrocatalyst. Mo doping oxidizes Ni2+ to Ni3+, creating abundant active sites for UOR. The Ni/MNO catalyst exhibits remarkable activity for both OER and UOR due to Mo doping, structural modulation, increased active sites, and the presence of Ni3+ ions. Optimized Ni/MNO‐10 shows a low OER overpotential of 280 mV and a UOR working potential of 1.37 V versus reversible hydrogen electrode at 10 mA cm−2, with exceptional stability over 12 h of continuous electrolysis. Notably, urea‐assisted water splitting requires only 1.45 V for 10 mA cm−2, significantly less than the overall water splitting voltage (1.65 V), indicating energy‐efficient hydrogen production. Moreover, the Ni/MNO catalyst exhibits outstanding long‐term stability. This work presents a rapid and effective approach to synthesizing cost‐effective and efficient electrocatalysts for clean energy production and wastewater treatment.

Enhancement of electrochemical performance of SrFe0.5Co0.5O3-δ as air electrode for intermediate temperature solid oxide cells via Sb and Mo doping

Optimisation of the composition or rare-earth-free perovskites is of considerable interest for their application as air electrodes in intermediate temperature solid oxide cells (IT-SOCs). Herein, we report the effects of Mo and Sb doping (5 mol %) of SrFe0.5Co0.5O3-δ (SFC) on oxygen content, thermal behaviour, electrochemical properties and stability. Phase-pure, XRD-cubic perovskite is achieved on sintering powder derived from Pechini synthesis in the range 1000-1100 °C for SFC, SrFe0.475Co0.475Mo0.05O3-δ (SFCM) and SrFe0.475Co0.475Sb0.05O3-δ (SFCSb). Oxygen content determined by redox titration is greater for the Mo- and Sb-doped phases than for SFC, although oxygen loss occurring at > 350 °C is greatest for SFCSb. The higher total oxygen content of the Mo-doped phase is expected to increase the electron-hole content resulting in higher conductivity (σ = 340.5 S cm−1 at 300 °C in O2). In contrast, the greater oxygen-vacancy content with increasing temperature of the Sb-doped material is associated with the most competitive electrode-polarisation resistance (<0.1 Ω cm2 at 700 °C). The greater relative effect of cathodic and anodic polarisation on improving electrochemical performance at lower temperatures highlights the potential of the studied compositions as air electrodes in IT-SOCs.

Enhanced ammonia gas sensing by cost-effective SnO2 gas sensor: Influence of effective Mo doping

Metal oxide based semiconductors play a vital role in the development of cost-effective gas sensors. In this study, undoped and Mo-doped SnO2 films were deposited using nebulizer spray by varying Mo doping concentrations from 0 to 1.5 wt% (in steps of 0.5 wt%) at the substrate temperature of 350°C. Ammonia vapour was used as the test gas. The effect of Mo doping concentration on the gas sensing ability of SnO2 films was investigated. Among the tested samples, the SnO2: Mo film with 1 wt% of Mo doping exhibits the best response (21 s) and recovery (31 s) times. The XRD results revealed the tetragonal structure and a decrease in the crystallite size upon doping. The Mo doping caused noticable changes in oxygen vacancies (as observed from PL), surface morphology, grain size and surface roughness which are found to be favourable for effective gas sensing.

Static and dynamic evolution of CO adsorption on γ-U (1 0 0) surface with different levels of Mo doping using DFT and AIMD calculations

Static and dynamic evolution of CO adsorption on γ-U (1 0 0) surface with different levels of Mo doping using DFT and AIMD calculations

Optimizing 3d spin polarization of CoOOH by in situ Mo doping for efficient oxygen evolution reaction

AbstractTransition‐metal oxyhydroxides are attractive catalysts for oxygen evolution reactions (OERs). Further studies for developing transition‐metal oxyhydroxide catalysts and understanding their catalytic mechanisms will benefit their quick transition to the next catalysts. Herein, Mo‐doped CoOOH was designed as a high‐performance model electrocatalyst with durability for 20 h at 10 mA cm−2. Additionally, it had an overpotential of 260 mV (glassy carbon) or 215 mV (nickel foam), which was 78 mV lower than that of IrO2 (338 mV). In situ, Raman spectroscopy revealed the transformation process of CoOOH. Calculations using the density functional theory showed that during OER, doped Mo increased the spin‐up density of states and shrank the spin‐down bandgap of the 3d orbits in the reconstructed CoOOH under the electrochemical activation process, which simultaneously optimized the adsorption and electron conduction of oxygen‐related intermediates on Co sites and lowered the OER overpotentials. Our research provides new insights into the methodical planning of the creation of transition‐metal oxyhydroxide OER catalysts.

Synthesis of defective Ni-Mn layered double hydroxides nanosheets via alkali-assisted Mo doping for urea electro-oxidation

Urea oxidation reaction (UOR) with favorable thermodynamic potential provides a good application prospect in renewable energy infrastructure. However, the sluggish kinetics caused by 6e- transfer greatly hinders the usage of urea as fuel, efficient catalysts are urgently needed in consequence. In response, alkali-assisted Mo doped into Ni-Mn layered double hydroxides (Mo-NiMnLDH-OH) with laminate structure is synthesized via one-pot hydrothermal method. The alkali-assisted Mo doping contributes the modified morphology and microstructure, the tuned chemical states of Ni and Mn species, simultaneously generates defects and more active sites. The existence of alkali plays a vital role in promoting the Mo doping. Without alkali, the Mo doping should damage the laminate structure, and the chemical states of active sites cannot be efficiently tuned. When used as catalyst for UOR, the current density of 45.3 mA cm−2 and a specific current activity of 1132.8 mA cm−2 mg−1 for Mo-NiMnLDH-OH can be achieved at the potential of 1.623 V (vs. RHE), which is 4-fold higher than that for Ni-Mn layered double hydroxides without doping. Both indirect electrochemical and direct urea oxidation processes occur when using Mo-NiMnLDH-OH as catalyst, and the existence of Mo species will facilitate the occurrence of direct urea oxidation process. This work paves an effective way to synergistically engineer of Mo doping and defects into Ni-based layered double hydroxides for UOR.

(Digital Presentation) Mo Doped Nickel Sulfide with Enhanced Electrochemical Activity for Hybrid Supercapacitors

Global energy depletion has become an irreversible fact. Researchers have vigorously pursued the development of renewable energy sources. It is well known that once renewable energy is produced, energy storage devices are needed to store the energy. Supercapacitor (SC) is considered to be a very promising energy storage device because of its long cycle life, high performance, and cost-effectiveness. As emerging SC devices, a battery-type electrode and a double-layer capacitor-type electrode as the anode and the cathode assembles a hybrid supercapacitor (HSC) well [1, 2]. Using anode materials to provide high capacitance, the purpose of the high energy density of HSC devices is achieved [3]. Nickel sulfide (Ni3S2) has tremendous potential for energy storage and conversion due to its impressive theoretical capacitance and high redox rate. Previous studies have demonstrated that optimizing the electronic structure can enhance the electrical conductivity of transition metal sulfides [4]. Aggrandizing surface defects and introducing impurities are effective strategies to modulate the electronic structure. Interestingly, the generation of sulfur vacancies on metal sulfides can modulate their electronic structure and elevate electrical conductivity. On the other hand, introducing foreign metals into Ni3S2 materials is another promising strategy to modulate the electronic structure [5]. The doping of molybdenum ions can optimize the electronic structure configuration. Mo doping works in concert with the vacancies to achieve a dual regulation of the electronic structure. However, few reports have been devoted to modulating the electronic structure by combining the two effective strategies mentioned above. To our knowledge, studies on the optimal amount of Mo doping to achieve the best electrochemical properties in the synthesis of Ni3S2 have not been adequately considered so far [6].[Figure insert] Figure. 1 (a) Crystal structures of NS and MNS, (b) ESR spectra of 0.75-MNS, (c) Comparative plots of the split peaks of the Ni 2p curves of 0.5-MNS, 0.75-MNS and 1.0-MNS, (d) High resolution XPS spectra of Mo 3d, (e) CV curves at 2 mV s−1, (f) GCD curves at 1 A g− 1, and (g) Ragone plot.Here, we propose that prepared Mo-doped Ni3S2 (denoted as MNS) by a one-pot hydrothermal method, which achieves the simultaneous two strategies of introducing impurities and increasing surface defects and attains a double optimization of the electronic structure of Ni3S2 materials (Fig. 1). To further shorten the charge transfer distance, the MNS is grown on nickel foam while avoiding the need for large amounts of conductive additives and adhesives. The prepared MNS microscopic features exhibit coral-like nanoclusters with a specific capacitance of 1531.2 C g−1 at 1 A g−1 when the Mo salt is added at 0.75 mmol. Furthermore, an HSC device was fabricated by utilizing the activated carbon (AC) electrode and MNS electrode, showing satisfying energy density (32.85 Wh kg−1 at 800 W kg−1). This work demonstrates the potential of MNS electrodes as anodes for HSC.

Inhibiting in Situ Phase Transition in Ruddlesdenpopper Perovskite Via Tailoring Bond Hybridization for Oxygen Ion Conduction

Owing to the excellent physical and chemical properties, mixed ionic-electronic conducting (MIEC) oxide materials, especially Ruddlesden-Popper (RP) perovskite oxides with the chemical formula of An+1BnO3n+1, are interesting materials for gas separation, solid oxide fuel/electrolysis cells, polymer electrolyte fuel cells, lithium-ion battery, sodium-ion battery, zinc ion battery and metal-air battery. The in-situ phase transition at different temperatures is a common phenomenon for these MIEC oxide materials, which generally exerts a great influence on the properties and functionalities of these materials and finally determines their performance in various applications. However, the in-depth understanding of the mechanism of phase transitions is still limited so far. Element-doping has been recognized as a facile and efficient strategy to improve the oxygen ionic or electronic conductivity or to stabilize the crystal phase structure (inhibiting both ex-situ and in-situ phase transitions) favorable for oxygen ion conduction. Herein, the ex-situ collapse at room temperature of crystal structure together with the generation of impurities in orthorhombic Pr2NiO4 through Mo doping are observed as the rearrangement of praseodymium atoms-based lattice deformation, which could be attributed to the Mo-induced destabilization of the Pr2NiO4 systems. Noteworthy is that, such effect can be prohibited by controlling the doping contents, and the resultant materials would give rise to the inhibition of in-situ phase transition (high temperature) from low order Pr2NiO4 (An+1BnO3n+1 (n=1)) to high order Pr4Ni3O10 (An+1BnO3n+1 (n=3)) by adjusting bond hybridization at the phase interface. Mo-doping can influence the covalent interaction between praseodymium and oxygen and then promotes the mobility of interstitial oxygen. Pr2Ni1-xMoxO4+ δ were further developed as oxygen separation membrane to help further evaluate the performance of oxygen ion conductivity. In Pr2Ni1-xMoxO4+ δ, Mo doping level of x = 0.05 resulted in an oxygen permeation flux of 3.35 mL min-1 cm-2 at 1000 °C, comparing favorably with the literature. Furthermore, membranes made with Pr2Ni0.95Mo0.05O4+ δ showed high permeation stability in air or helium, and exhibits high CO2 tolerance without obvious decline of the oxygen permeation flux during 500 hours at round 900 °C. This work advances our understanding of the ex-situ and in-situ phase transitions of Pr2NiO4-based RP perovskite materials and shows how Mo doping can stabilizes the in-situ phase structure and improves the mobility of interstitial oxygen. Figure 1

Synthesis, mechanical properties and thermal conductivity of high-entropy (TiTaNbZrMox)(CN) ceramics

Novel high-entropy (TiTaNbZrMoX)(CN) (x = 0, 5, 10, 15, and 20 at%) carbonitride ceramics were synthesised using the carbothermal reduction-nitridation and spark plasma sintering methods. The effects of Mo doping on the microstructure, mechanical properties, and thermal characteristics of these high-entropy ceramics were investigated. The increase in Mo contents caused increased grain size, uniform distribution of elements, improved Vickers hardness and fracture toughness, and reduced thermal conductivity at the same temperature. High-entropy (TiTaNbZrMo0.2)(CN) ceramic displayed superior Vickers hardness of 21.41 GPa and fracture toughness of 4.34 MPa·m1/2, compared with 20.51 GPa and 3.94 MPa·m1/2 for (TiTaNbZr)(CN) ceramic, respectively. Density functional theory calculations indicated that adding Mo atoms promoted the hybridisation of metal and carbon elements, thereby preferentially enhancing electron filling in the bonding orbital due to high valence electrons. This, in turn, improved the mechanical properties of (TiTaNbZrMox)(CN) ceramics. Additionally, the increased Mo contents strengthened covalent bonding and induced lattice distortion, reducing the thermal conductivity of high-entropy ceramics.

Controlled synthesis of Mo and Ni codoped Co2P as environmentally friendly catalyst for urea, freshwater and seawater oxidation

The thermodynamic equilibrium potential of urea electrolysis (0.37 V) is lower than that of conventional water electrolysis (1.23 V). In this paper, the urea oxidation reaction performance of Ni-Co2P was regulated and enhanced by doping with different quantity of Mo. The growth characteristics of Mo doping Ni-Co2P were characterized and analyzed to reveal the electrochemical properties of the target catalysts, and finally the electrochemical performance tests were carried out. The experimental results show that MoNi-Co2P-0.12 electrode exhibits superior catalytic activity and durability at an iR compensation of 90. What is noteworthy is that at a current density of 10 mA cm−2, the MoNi-Co2P-0.12 catalyst showed an ultra-low voltage of 1.244 V with a small Tafel slope (79.52 mV dec−1) and stable catalysis for over 12 h, which is one of the best catalytic activities reported to date. Experimental results show that the increased activity of the MoNi-Co2P-0.12 catalyst is attributable to synergic catalytic effect of Mo and Co, electron regulation and exposure of more active sites. Density functional theory (DFT) calculations demonstrate the doping of Mo can increase the urea adsorption energy of the MoNi-Co2P material compared with the Ni-Co2P material, and is also conducive to the improvement of the conductivity of the MoNi-Co2P material. This work provides new research into the use of cheap transition metal catalysts as an alternative to precious metal catalysts for urea electrolysis.

Tunable optical topological transitions of plasmon polaritons in WTe2 van der Waals films

Naturally existing in-plane hyperbolic polaritons and the associated optical topological transitions, which avoid the nano-structuring to achieve hyperbolicity, can outperform their counterparts in artificial metasurfaces. Such plasmon polaritons are rare, but experimentally revealed recently in WTe2 van der Waals thin films. Different from phonon polaritons, hyperbolic plasmon polaritons originate from the interplay of free carrier Drude response and interband transitions, which promise good intrinsic tunability. However, tunable in-plane hyperbolic plasmon polariton and its optical topological transition of the isofrequency contours to the elliptic topology in a natural material have not been realized. Here we demonstrate the tuning of the optical topological transition through Mo doping and temperature. The optical topological transition energy is tuned over a wide range, with frequencies ranging from 429 cm−1 (23.3 microns) for pure WTe2 to 270 cm−1 (37.0 microns) at the 50% Mo-doping level at 10 K. Moreover, the temperature-induced blueshift of the optical topological transition energy is also revealed, enabling active and reversible tuning. Surprisingly, the localized surface plasmon resonance in skew ribbons shows unusual polarization dependence, accurately manifesting its topology, which renders a reliable means to track the topology with far-field techniques. Our results open an avenue for reconfigurable photonic devices capable of plasmon polariton steering, such as canaling, focusing, and routing, and pave the way for low-symmetry plasmonic nanophotonics based on anisotropic natural materials.