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One-step pyrolysis synthesis of nitrogen, manganese-codoped porous carbon encapsulated cobalt-iron nanoparticles with superior catalytic activity for oxygen reduction reaction
No full textReplacing precious metal catalysts with low-price and abundant catalysts is one of urgent goals for green and sustainable energy development. It is imperative yet challenging to search low-cost, high-efficiency, and long-durability electrocatalysts for oxygen reduction reaction (ORR) in energy conversion devices. Herein, three-dimensional low-cost Co3Fe7 nanoparticles/nitrogen, manganese-codoped porous carbon (Co3Fe7/N, Mn-PC) was synthesized with the mixture of dicyandiamide, cobalt (II) tetramethoxyphenylporphyrin (Co(II)TMOPP), hemin, and manganese acetate by one-step pyrolysis and then acid etching. The resultant Co3Fe7/N, Mn-PC exhibited excellent durability and prominent ORR activity with more positive onset potential (E-onset, 0.98 V) and half-wave potential (E-1/2, 0.87 V) in 0.1 M KOH electrolyte, coupled with strong methanol resistance. The pyrolysis temperature and optimal balance of graphite with pyridine-nitrogen are of significance for the ORR performance. The prepared Co3Fe7/N, Mn-PC displayed excellent ORR performance over commercial Pt/C in the identical environment. It was ascribed to the uniform 3D architecture, Mn- and N-doping effects by finely adjusting the electronic structures, coupled with the synergistic catalytic effects of multi-compositions and multi-active sites. This work provides some constructive guidelines for preparation of low-cost and high-efficiency ORR electrocatalysts. (C) 2021 Elsevier Inc. All rights reserved
Theoretical Insights into the Actinide-Silicon Bonding Nature and Stability of a Series of Actinide Complexes with Different Oxidation States
No full textThe electronic structures of a series of complexes (CpSiMe3)(3)AnSi(NCHMes)(2) ([An-Si], An = Th-Am) with different oxidation states (OS = II, III, and IV) of actinides were investigated using the relativistic density functional theory to explore the actinide-silicon bonding, which was evaluated based on the analyses of quantum theory of atoms in molecules (QTAIM) and electron localization function (ELF). The An-Si bond length variation for a series of [An-Si] with different oxidation states may be attributed to the synergistic effect of the steric hindrance and the ability of the actinide atom to accept electrons. The value of AnSi Mayer bond order (MBO) decreases across the actinide series with the same oxidation state. The values of An-Si MBO for the [An(II)-Si](-) (An = Th-Pu) are the largest in general among the complexes with three actinide oxidation states, except that for the Am-Si MBO of [Am-IV-Si](+) is the largest because of more covalent Am-Si bond in the [Am-IV-Si](+) complex. The An-Si bonds are highly polarized due to lone pair electrons located on the Si 3s orbital. Moreover, the An-Si bonds possess donor-acceptor interactions according to the analyses of QTAIM and ELF. In addition, the binding energies suggest that the tetravalent complexes [An(IV)-Si](+) are accessible, of which [U-IV-Si](+) and [Pu-IV-Si](+) are the most preferable. The electron affinity analysis suggests reaction of [An(III)-Si] -> [An(II)-Si](-) should become increasingly facile across the actinide series from Th to Am. the knowledge on the An-Si bonding, especially for the transuranium-silicon bonding, and guides synthesis of complexes with different oxidation states
Differentiation of Multiple Mechanical Stimuli by a Flexible Sensor Using a Dual-Interdigital-Electrode Layout for Bodily Kinesthetic Identification
No full textHuman bodily kinesthetic sensing is generally complicated and ever-changing due to the diversity of body deformation as well as the complexity of mechanical stimulus, which is different from the unidirectional mechanical motion. So, there exists a huge challenge for current flexible sensors to accurately differentiate and identify what kind of external mechanical stimulus is exerted via analyzing digital signals. Here, we report a flexible dual-interdigital-electrode sensor (FDES) that consists of two interdigital electrodes and a highly pressure-sensitive porous conductive sponge. The FDES can precisely identify multiple mechanical stimuli, e.g., pressing, positive bending, negative bending, X-direction stretching, and Y-direction stretching, and convert them into corresponding current variation signals. Moreover, the FDES exhibits other exceptional properties, such as high sensitivity, stretchability, large measurement range, and outstanding stability, accompanied by simple structural design and low-cost processing simultaneously. Additionally, our FDES successfully identifies various complex activities of the human body, which lays a foundation for the further development of multimode flexible sensors
Structural and electrochemical characterization of vanadium-excess Li3V2(PO4)(3)-LiVOPO4/C composite cathode material synthesized by sol-gel method
No full textTo improve capacity and electrochemical performance of the cathode of Li-ion batteries, non-stoichiometric, vanadium-excess (V-excess) Li3V2 (PO4)(3)-LiVOPO4/C (LVP-LVOP/C) composite cathode materials are synthesized by a single-step citric acid assisted sol-gel method and sintered at temperatures (300-900 degrees C). X-ray diffraction and transmission electron microscope results indicate that major Li3V2(PO4)(3) and minor LiVOPO4 phases coexist and X-ray photoelectron spectroscopy results also show that the valance state of vanadium is +4 and + 3. The sample sintered at 800 degrees C shows the best electrochemical performance with the highest discharge capacity of 140 mAh g(-1) at 0.2 C, higher than the theoretical capacity of Li3V2(PO4)(3) in the voltage range 2.8-4.3 V. The composite material displays remarkably improved stability exhibiting reversible capacity of 130, 115, and 108 mAh g(-1) after 300, 500, and 1000 cycles at the rate of 0.3 C, 0.5 C, and 1 C, respectively. Additionally, the composite LVP-LVOP/C shows superior rate performance at various current densities from 0.2 to 10 C. Our study reveals that the novel composite material considerably enhances electrochemical performance, electronic conductivity, Liion diffusion, and contribution of LiVOPO4 to capacity by accommodating extra Li-ions to enhance capacity. The results demonstrate that the study is highly promising for the development of V-excess cathodes as V-excess composite materials exhibit better performance than pure phase Li3V2(PO4)(3)
One-step epitaxy of high-mobility La-doped BaSnO3 films by high-pressure magnetron sputtering
No full textAs unique perovskite transparent oxide semiconductors, high-mobility La-doped BaSnO3 films have been successfully synthesized by molecular beam epitaxy and pulsed laser deposition. However, it remains a big challenge for magnetron sputtering, a widely applied technique suitable for large-scale fabrication, to grow high-mobility La-doped BaSnO3 films. In this work, we developed a method to synthesize high-mobility epitaxial La-doped BaSnO3 films (with mobility up to 121 cm(2) V-1 s(-1) at the carrier density of similar to 4.0 x 10(20) cm(-3) at room temperature) directly on SrTiO3 single crystal substrates using high-pressure magnetron sputtering. The structural and electrical properties of La-doped BaSnO3 films were characterized by combined high-resolution x-ray diffraction, x-ray photoemission spectroscopy, and temperature-dependent electrical transport measurements. The room-temperature electron mobility of La-doped BaSnO3 films achieved in this work is two to four times higher than the reported values of the films grown by magnetron sputtering. Moreover, in the high carrier density range (n > 3 x 10(20) cm(-3)), the electron mobility value of 121 cm(2) V-1 s(-1) achieved in our work is among the highest values for all reported doped BaSnO3 films. It is revealed that high argon pressure during sputtering plays a vital role in stabilizing the fully relaxed films and inducing oxygen vacancies, which facilitates high mobility at room temperature. Our work provides an easy and economical way to massively synthesize high-mobility transparent conducting films for transparent electronics
Numerical and experimental exploration towards a 26% efficiency rear-junction n-type silicon solar cell with front local-area and rear full-area polysilicon passivated contacts
No full textIn this work, structure designs and the corresponding energy loss analysis are conducted to achieve the highefficiency n-type rear-junction solar cells with polysilicon passivated contact. We focus on the front-side structure design of solar cells, considering that the primary efficiency loss of the conventional n-type polysilicon passivated contact cells with boron-diffusion emitter is from the front side. A well-designed rear-junction solar cell with front localized n-type and rear full-area p-type polysilicon passivated contacts is expected to overcome these problems. However, the efficiency of rear-junction solar cells is sensitive to the front-side electrode contact resistivity. To accurately assess the practically achievable efficiency that the current technology can reach, we develop a simple modified TLM with wet-chemical etching to measure the contact resistivity of the n-type polysilicon contact. This method does not require relatively expensive photolithography and reactive ion etching tools and is easy to be used. When the contact resistivity of the front-side localized n-type polysilicon contact reaches 0.002 omega.cm2 with a saturation current density of -10 fA/cm2 in the front-side un-diffused area, the efficiency of the rear-junction n-type solar cell is expected to be -26%, showing its potential for application in mass-production of high-efficiency crystalline silicon solar cells
Mechanical and electrical properties of borophene and its band structure modulation via strain and electric fields: a first-principles study
No full textThe basic electronic and mechanical properties of 2-Pmmn borophene and their strain and electric field-dependence are studied by the first-principles calculations. The Young's moduli are 236 and 89 GPa in the armchair and zigzag directions, respectively, indicating that the borophene has giant mechanical anisotropy. We also find that the borophene presents anisotropic electronic properties. The borophene is electroconductive in armchair direction but has a bandgap in the zigzag direction. To modulate the band structure, we applied strain and electric fields on borophene, and find that, the resistance of borophene decreases with the increase of applied strain, while the applied electric field has almost no effect on its band structure. The enhanced conductivity of borophene upon applied strain is ascribed to the expansion of the buckled structure through the analysis of the charge density of the strained borophene
Structure, mechanical and tribological properties in seawater of multilayer TiSiN/Ni coatings prepared by cathodic arc method (vol 493, pg 1177, 2019)
No full textSupporting nickel on vanadium nitride for comparable hydrogen evolution performance to platinum in alkaline solution
No full textThe hydrogen evolution reaction (HER) is an effective means to producing hydrogen from electrolytic water splitting. However the best-performing catalysts use expensive Pt-group metals. Cheaper non-precious metal alternatives have shown low activity as their mechanism of H-2 formation (Volmer-Heyrovsky) leads to high overpotentials. Here, we report an outstanding HER catalyst (Ni/VN) highly dispersed nickel supported on vanadium nitride that matches the turnover frequency of the platinum on carbon (Pt/C) benchmark material. It is more durable than Pt/C in alkaline solution. Ni/VN follows the low-overpotential (Volmer-Tafel) mechanism of H-2 formation, with a 43 mV overpotential at a current density of 10 mA cm(-2). This value is even below that of Pt/C (57 mV). The support of VN enhances the dispersion of nickel, weakens the surface oxidation, decreases the hydrogen binding energy, and therefore significantly improves the HER catalysis. This result removes one of the major barriers for scalability of electrolytic water-splitting by demonstrating that nitride-based materials can match and even surpass the efficiency and durability of precious metal catalysts
Stable CsPbBr3-Glass Nanocomposite for Low-etendue Wide-Color-Gamut Laser-Driven Projection Display
No full textUp-to-date laser-driven projection technology puts an urgent demand for green phosphor with stringent requirements on its performance. Herein, by virtue of a new architecture design based on CsPbBr3-glass nanocomposite, i.e., CsPbBr3 glass ceramic film sintered on sapphire plate, the application availability of this famous green-emitting phosphor is demonstrated in laser-driven projection. The mono-dispersed perovskite CsPbBr3 nanostructure in amorphous glass matrix and the negligible thermal corrosion during co-sintering with low-melting-glass ensure good luminescent properties. The robust glass host and the carried sapphire substrate with high thermal conductivity contribute to good resistances to thermal shock, moisture, and blue laser irradiation. It is revealed that the thermal accumulation effect is relieved due to the pulsed excitation of rotatory phosphor wheel, and so the luminescence saturation threshold gets increased. The constructed prototype lighting source yields a low etendue of approximate to 0.41 mm(2), a wide color gamut of 128.4% NTSC (95.9% Rec. 2020), and a moderate luminous flux of 174 lm. The present work highlights an unprecedented design that makes the seemingly impossible application of CsPbBr3 come true