Engineering topics
Publications and source records attributed to Wang, Yu.
Combinatorial synthesis combined with high throughput electrochemistry enabled discovery of 29 ternary oxide photoanodes, 15 with visible light response for oxygen evolution. Y 3 Fe 5 O 12 and trigonal V 2 CoO 6 emerge as particularly promising candidates due to their photorepsonse at sub-2.4 eV illumination.
Here, we report a comparison of the photocatalytic performance of WSe 2 -on-MoSe 2 and MoSe 2 -on-WSe 2 heterostructures. While built-in electric fields exist in these heterostructures on the order of 100 kV/cm due to band offsets between these two materials, the photocatalytic performance (i.e., photocurrent) is independent of the stacking order of the two materials. Solving Poisson’s equation under these conditions, we find that the built-in electric field produced in the heterostructure is at least 1 order of magnitude smaller than that produced in the electrochemical double layer (i.e., Helmholtz layer). Mott–Schottky measurements indicate that transition metal dichalcogenides (TMDCs) on ITO electrodes have similar capacitance to that of bare ITO, providing further evidence that the interfacial electric fields produced in the solid state heterostructure are negligible compared to the fields generated by the ions in solution. The photocatalytic performance of these heterostructures provided the largest relative enhancement in the heterojunction region under 920 and 785 nm irradiation compared with 532 and 633 nm wavelength excitation. Here, the 920 nm (1.35 eV) photons lie below the band gaps and produce very little photocurrent in the constituent monolayer materials but resonantly excite the interlayer optical transition in the heterostructure, producing a 5-fold enhancement in the measured photocurrent.
Goethite is a major iron-bearing sedimentary mineral on Earth. In this study, we conducted in situ high-pressure x-ray diffraction, Raman, and electrical impedance spectroscopy measurements of goethite using a diamond anvil cell (DAC) at room temperature and high pressures up to 32 GPa. We observed feature changes in both the Raman spectra and electrical resistance at about 5 and 11 GPa. However, the x-ray diffraction patterns show no structural phase transition in the entire pressure range of the study. The derived pressure-volume (P-V) data show a smooth compression curve with no clear evidence of any second-order phase transition. Fitting the volumetric data to the second-order Birch–Murnaghan equation of state yields V 0 = 138.9 ± 0.5 Å 3 and K 0 = 126 ± 5 GPa.
We have investigated magnetotransport properties of YRh 6 Ge 4 , which was recently predicted to be a triply degenerate nodal semimetal. We find it exhibits remarkable signatures of a chiral anomaly, manifested by large negative longitudinal magnetoresistance, the quadratic field dependence of magnetoconductance and the planar Hall effect. Furthermore, we have also observed Shubnikov-de Haas (SdH) quantum oscillations in the magnetoresistivity measurements on this material. The analyses of the SdH data reveal two pointlike Fermi surfaces and these pockets are found to host nearly massless fermions. The small size of these Fermi pockets is in a good agreement with the theoretical prediction that the triply degenerate point in YRh 6 Ge 4 is much closer to the Fermi level than previously demonstrated triply degenerate nodal semimetals such as MoP and WC. These results suggest YRh 6 Ge 4 may serve as a model system to probe exotic properties of three-component fermions and understand their underlying physics.
The intrinsic brittleness of poly(lactic acid) (PLA) has hindered its widespread use in many structural applications. Various strategies have been developed to toughen PLA; however, most of the methods lead to a trade-off in strength or modulus. In this study, a chain end engineering strategy was developed to toughen PLA via an industry-friendly melt processing method. Green acids with multifunctional groups, such as 1,2,3,4-butanetetracarboxylic acid (BTCA), were used to modify PLA chain ends/tails via a melt reaction. We report a remarkable improvement in toughness (16×) was achieved by the addition of a minimal amount of BTCA (0.5%). At the same time, the toughened PLA samples maintained the tensile strength and Young’s modulus of neat PLA, suggesting a unique toughening mechanism that is different from the plasticizing effect. Other acid–based modifiers with different numbers of functional groups were also studied in this work. To understand the toughening, we propose a chain end engineering picture that can improve the toughness via a reduction in the number density of chain ends or defects of entanglement and the formation of long-branch topological structures. This study demonstrates a unique and cost-effective strategy for toughening PLA via scalable melt reaction without sacrificing other mechanical properties of PLA, potentially broadening the applications.
In this paper, we synthesized HNbMoO{sub 6}/C composite through the calcination of octylamine-intercalated HNbMoO{sub 6} precursor. The resulting HNbMoO{sub 6}/C composite showed some new phases of MoO{sub 2}, MoO{sub 3}, NbO{sub 2}, Nb{sub 2}O{sub 5}, and carbon, which was fully confirmed via powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and X-ray photoelectron spectroscopy (XPS) technologies. Besides, the HNbMoO{sub 6}/C hybrid was coated on glass carbon electrode to construct an electrochemical sensor for sensitive determination of clenbuterol. The electrochemical behaviors of clenbuterol on the prepared electrode were tested by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) analysis. The results showed that the intercalated carbon can act as active sites to accelerate electron transfer. In addition, more exposed surface areas of the HNbMoO{sub 6}/C composite will facilitate the electrolyte to permeate. The oxidation peak current of clenbuterol was linearly related to its concentration in the range of 1.04 × 10{sup −5} to 7.51 × 10{sup −4} mol L{sup −1}, and the determination limit was calculated to be 3.03 × 10{sup −6} mol L{sup −1} (S/N = 3). This sensor exhibits excellent stability, reproducibility, specificity, and good recoveries when applied to monitor clenbuterol in real samples.
The regulation of catalytic activity in the oxygen reduction reaction (ORR) is significant to the development of metal–air batteries and other oxygen involving energy conversion devices. Herein, we propose an atomic interface strategy to construct a single atom copper catalyst (denoted as Cu-SA/SNC) which exhibits enhanced ORR activity with a half-wave potential of 0.893 V vs. RHE in alkaline media. Moreover, synchrotron-radiation-based X-ray absorption fine structure (XAFS) investigations together with density functional theory (DFT) calculations reveal that the isolated bond-shrinking low-valence Cu (+1)–N 4 –C 8 S 2 atomic interface moiety serves as an active site during the ORR process, and the synergistic mechanism between the Cu species and the carbon matrix at the atomic interface plays a critical role in boosting the ORR efficiency, by adjusting the reaction free energy of intermediate adsorption. Furthermore, this atomic interface concept may provide an alternative methodology for the rational design of advanced oxygen electrode materials and new probability to improve their catalytic performance.
Electrochemical CO 2 reduction to valuable products is a centerpiece of future energy technologies that relies on identification of new catalysts. Here, we present accelerated screening of Cu bimetallic alloys, revealing remarkable sensitivity to alloy concentration that indicates the migration of alloying elements to critical sites for hydrocarbon formation.
Transformative technologies are enabling the construction of three dimensional (3D) maps of tissues with unprecedented spatial and molecular resolution. Over the next seven years, the NIH Common Fund Human Biomolecular Atlas Program (HuBMAP) aims to develop a widely accessible framework for comprehensively mapping the human body at single-cell resolution by supporting technology development, data acquisition, and detailed spatial mapping. HuBMAP will integrate its efforts with other funding agencies, programs, and the biomedical research community at large towards the shared vision of a comprehensive, accessible 3D molecular and cellular atlas of the human body, in health and various disease settings.
Frank-Kasper phases, a family of ordered structures formed from particles with spherical motifs, are found in a host of materials, such as metal alloys, inorganic colloids and various types of soft matter. All the experimentally observed Frank-Kasper phases can be constructed from the basic units of three fundamental structures called the A15, C15 and Z phases. The Z phase, typically observed in metal alloys, is associated with a relatively large volume ratio between its constituents, and this constraint inhibits its formation in most self-assembled single-component soft-matter systems. We have assembled a series of nanosized shape amphiphiles that comprise a triphenylene core and six polyhedral oligomeric silsesquioxane cages grafted onto it through linkers to give a variety of unconventional structures, which include the Z phase. Finally, this structure was obtained through fine tuning of the linker lengths between the core and the peripheral polyhedral oligomeric silsesquioxane cages, and exhibits a relatively large volume asymmetry between its constituent polyhedral particle motifs.
The economic viability of the biofuel industry could be improved by adding a high-value revenue stream for biomass supply chains: bioderived composites for the rapidly expanding large-scale additive manufacturing industry (i.e., 3D printing). Using fibrillated fibers derived from biomass (e.g., Populus ) to reinforce polymers for 3D printing applications would be less expensive compared to using conventional carbon fibers. Poplar fibers of different mesh sizes (<180, 180–425, 425–850, and 850–2360 μm) were used to prepare poplar–polylactic acid (PLA) composites. The poplar/PLA composites were successfully printed using a large-scale 3D printer to create a podium support. The tensile strength of the composites increased from 34 to 54 MPa as the poplar fiber size decreased. Here, the fracture surfaces of composites derived from smaller poplar fibers (<180 μm) were more compact with fewer voids compared with the composites made with larger poplar fibers. Because of the porous and hollow microstructures, smaller poplar fibers contained more pores on their outer surfaces, which were available for the access and penetration of PLA. Poplar has potential for use as a thermoplastic reinforcement for large-scale 3D printing.
Here, we report spectroscopic measurements of the local electric fields and local charge densities at electrode surfaces using graphene-enhanced Raman spectroscopy (GERS) based on the Stark-shifts of surface-bound molecules and the G band frequency shift in graphene. Here, monolayer graphene is used as the working electrode in a three-terminal potentiostat while Raman spectra are collected in situ under applied electrochemical potentials using a water immersion lens. First, a thin layer (1 Å) of copper(II) phthalocyanine (CuPc) molecules are deposited on monolayer graphene by thermal evaporation. GERS spectra are then taken in an aqueous solution as a function of the applied electrochemical potential. The shifts in vibrational frequencies of the graphene G band and CuPc are obtained simultaneously and correlated. The upshifts in the G band Raman mode are used to determine the free carrier density in the graphene sheet under these applied potentials. Of the three dominant peaks in the Raman spectra of CuPc (i.e., 1531, 1450, and 1340 cm –1 ), only the 1531 cm –1 peak exhibits Stark-shifts and can, thus, be used to report the local electric field strength at the electrode surface under electrochemical working conditions. Between applied electrochemical potentials from -0.8 V to 0.8 V vs NHE, the free carrier density in the graphene electrode spans a range from -4 × 10 12 cm –2 to 2 × 10 12 cm –2 . Corresponding Stark-shifts in the CuPc peak around 1531 cm –1 are observed up to 1.0 cm –1 over a range of electric field strengths between -3.78 × 10 6 and 1.85 × 10 6 V/cm. Slightly larger Stark-shifts are observed in a 1 M KCl solution, compared to those observed in DI water, as expected based on the higher ion concentration of the electrolyte. Based on our data, we determine the Stark shift tuning rate to be 0.178 cm –1 / (10 6 V/cm), which is relatively small due to the planar nature of the CuPc molecule, which largely lies perpendicular to the electric field at this electrode surface. Computational simulations using density functional theory (DFT) predict similar Stark shifts and provide a detailed atomistic picture of the electric field-induced perturbations to the surface-bound CuPc molecules.
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Electrochemical conversion of carbon dioxide into valuable chemicals or fuels is an increasingly important strategy for achieving carbon neutral technologies. The lack of a sufficiently active and selective electrocatalyst, particularly for synthesizing highly reduced products, motivates accelerated screening to evaluate new catalyst spaces. Traditional techniques, which couple electrocatalyst operation with analytical techniques to measure product distributions, enable screening throughput at 1–10 catalysts per day. In this paper, a combinatorial screening instrument is designed for MS detection of hydrogen, methane, and ethylene in quasi-real-time during catalyst operation experiments in an electrochemical flow cell. Coupled with experiment modeling, product detection during cyclic voltammetry (CV) enables modeling of the voltage-dependent partial current density for each detected product. Here, we demonstrate the technique by using the well-established thin film Cu catalysts and by screening a Pd–Zn composition library in carbonate-buffered aqueous electrolyte. The rapid product distribution characterization over a large range of overpotential makes the instrument uniquely suited for accelerating screening of electrocatalysts for the carbon dioxide reduction reaction.
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MnB i 2 T e 4 has recently been established as an intrinsic antiferromagnetic (AFM) topological insulator—an ideal platform to create quantum anomalous Hall insulator and axion insulator states. We performed comprehensive studies on the structure, nontrivial surface state, and magnetotransport properties of this material. Our results reveal an intrinsic anomalous Hall effect arising from a noncollinear spin structure for the magnetic field parallel to the c axis. We observed negative magnetoresistance under arbitrary field orientation below and above the Néel temperature (T N ) , providing clear evidence for strong spin fluctuation-driven spin scattering in both the AFM and paramagnetic states. Furthermore, we found that the nontrivial surface state opens a large gap (~85 meV) even far above TN. Our findings demonstrate that the bulk band structure of MnB i 2 T e 4 is strongly coupled with the magnetic property and that a net Berry curvature in momentum space can be created in the canted AFM state. In addition, our results imply that the gap opening in the surface states is intrinsic, likely caused by the strong spin fluctuations in this material.
Vanadium diboride (VB{sub 2}) powders with low oxygen content are prepared via a molten-salt-assisted borothermal reduction reaction at 1123 K to 1273 K (850 °C to 1000 °C) using V{sub 2}O{sub 3} and boron powders as the raw materials. The effects of the amount of molten salt and reaction temperature on the phase transition and morphology of the final products are investigated. The results reveal that the addition of molten salt is beneficial for decreasing both the synthesis temperature and particle size of the final products. When the mass ratio of NaCl to reactants is 0.75:1, the VB{sub 2} powders prepared at 1173 K (900 °C) have a particle size lower than 100 nm. Too little or too high molten salt addition has a negative impact on the preparation of the VB{sub 2} powders. Furthermore, the reaction temperature has an important impact on the morphology and purity of the VB{sub 2} particles. An appropriate reaction temperature (1173 K (900 °C)) is beneficial for controlling the size of the VB{sub 2} particles in the order of nanoscale and improving the quality of the VB{sub 2} powders.