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Tuning intermediate adsorption energy by shifting the d-band center offers a powerful strategy to tailor the reactivity of metal catalysts. Here we report a potential sweep method to grow Pd layer-by-layer on Au with the capability to in situ measure the surface structure through an ethanol oxidation reaction. Spectroscopic characterizations reveal charge-transfer induced valence band restructuring in the Pd overlayer, which shifts the d-band center away from the Fermi level compared to bulk Pd. Precise overlayer control gives the optimal bimetallic surface of two monolayers (ML) Pd on Au, which exhibits more than 370-fold mass activity enhancement in oxygen reduction reaction (at 0.9 V vs. reversible hydrogen electrode) and 40 mV increase in half-wave potential compared to the Pt/C. Tested in a homemade Zn-air battery, the 2-ML-Pd/Au/C exhibits a maximum power density of 296 mW/cm2 and specific activity of 804 mAh/gZn, much higher than Pt/C with the same catalyst loading amount. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) This work was supported by the fund from the Singapore Ministry of Education Academic Research Fund (AcRF) Tier 1: RG4/20 and Tier 2: MOET2EP10120-0002, and Agency for Science, Technology, and Research (A*Star IRG: A20E5c0080).

A genetic algorithm was employed as a novel method to determine the best combination of materials for a double-layer electromagnetic shielding composite with good electromagnetic wave absorption efficiency at high frequencies from numerous magnetic materials. A carbonyl iron soft magnetic composite and a flaky FeNi soft magnetic composite were used to form the double-layer composite. The reflection and transmission parameters of the double-layer composite were measured using a vector network analyzer. The electromagnetic shielding effectiveness (SE) of the double-layer composite was calculated and analyzed. The double-layer composite was composed of two shielding materials with different electromagnetic parameters and demonstrated an excellent electromagnetic SE greater than 20 dB above 4 GHz; the ratio of the absorption efficiency (SEA) to SE (SEA/SE) was greater than 0.95, which indicates that more than 95% of the electromagnetic waves at high frequencies were attenuated by the shielding material, rather than being scattered into the surrounding environment. The double-layer composite exhibits excellent performance toward high electromagnetic waves absorption during the EMI shielding process.

While inheriting the exceptional merits of single atom catalysts, diatomic site catalysts (DASCs) utilize two adjacent atomic metal species for their complementary functionalities and synergistic actions. Herein, a DASC consisting of nickel-iron hetero-diatomic pairs anchored on nitrogen-doped graphene is synthesized. It exhibits extraordinary electrocatalytic activities and stability for both CO2 reduction reaction (CO2RR) and oxygen evolution reaction (OER). Furthermore, the rechargeable Zn-CO2 battery equipped with such bifunctional catalyst shows high Faradaic efficiency and outstanding rechargeability. The in-depth experimental and theoretical analyses reveal the orbital coupling between the catalytic iron center and the adjacent nickel atom, which leads to alteration in orbital energy level, unique electronic states, higher oxidation state of iron, and weakened binding strength to the reaction intermediates, thus boosted CO2RR and OER performance. This work provides critical insights to rational design, working mechanism, and application of hetero-DASCs., Diatomic site catalysts utilize two adjacent atomic metal species for their complementary functionalities and synergistic actions. Here, the authors report the orbital coupling of hetero-diatomic nickel-iron site boosts CO2 reduction reaction and oxygen evolution reaction.

In order to fracture shale gas reservoir with carbon dioxide as the working fluid, laboratory experiments were firstly conducted to measure the influence of carbon dioxide immersion on shale rock’s properties, and then the coupling mechanism between stress and seepage during hydraulic fracturing was simulated based on cohesive zone model. The fracturing ability of carbon dioxide and water was also compared under the same working conditions, and finally sensitivity analysis (including elastic modulus of shale, filtration coefficient, pump rate and viscosity of carbon dioxide) were conducted based on field application. The results show that, the elastic modulus of shale increased by 32.2%, the Poisson's ratio decreased by 40.3% and the compressive strength decreases by 22.9% after geothermal reaction with carbon dioxide under 30 MPa and 335.15 K for 2 hours. Compared with water fracturing, carbon dioxide fracturing induces longer fracture (increased by 25.3%) and narrower fracture (decreased to 40.8%). The fracture tends to get longer and narrower with increasing elastic modulus of shale. As filtration coefficient increases, the maximum width of fracture decreases significantly, whereas the length changes little. Both the length and maximum width of fracture increase with increasing pump rate, however the changing rate of length tends to decrease. The influence of viscosity of carbon dioxide on both fracture width and length is negligible, which validates the stable feasibility of carbon dioxide fracturing in different formation conditions.

During the process development of brigatinib, we have made an unusual observation about some impurities. Detailed investigation has led to the conclusion that impurity A is formed via the raw material 2 oxidation, impurity B is formed via the pyrolysis of DMF, impurity C is formed via raw material 4, and impurity D is formed via HCl-catalyzed decomposition of intermediate 3. The present work details a report of the journey toward the development of an efficient process for the commercial production of brigatinib substantially free from all the impurities.

This article presents a short-circuit and over current protection method using a new current sensor—tunnel magnetoresistance (TMR). The resistance of TMR changes with the magnetic flux density and a Wheatstone bridge circuit-based TMR can be used for current measurement. A toroid TMR current sensor is first proposed to measure the IGBT current, and the measured current is compared to references for protection. A prototype based on a 1200-V/200-A IGBT module is constructed to test the TMR sensor. A 120 A over-current can be detected in 604 ns. The measured current is also utilized to estimate the dc bus capacitance, experimental results show the maximum estimation error is 0.26%. Next, the TMR sensors are integrated into an IGBT module to expand the application scenario. The Calculation method and finite element method (FEM) are proposed to find optimal install locations of the TMR inside a 62-mm IGBT module. A differential TMR sensor circuit is employed to suppress the interference of the adjacent magnetic field. Experimental results based on a commercial IGBT with an integrated TMR sensor have been provided. The reaction time of the integrated TMR sensor is 530 ns and the maximum measurement error for the dc current is 0.85%. The detection and protection time for a 280-A short-circuit fault is 677 ns and 1.23 μ s, respectively.

The oxygen evolution reaction (OER) is crucial in electrochemical water splitting and metal-air battery, and demands a low cost, efficient and durable electrocatalyst. An ideal OER catalyst should ...

Electrochemical reduction of molecular O2 to hydrogen peroxide (H2O2) offers a promising solution for water purification and environmental remediation. Here, we design a hierarchical free‐standing single‐Co‐atom (with Co–N4 coordination) electrode for oxygen reduction reaction (ORR) via a two‐electron pathway to make H2O2 in acidic media. The current density of the single‐Co‐atom electrode reached 51 mA/cm2 at 0.1 V vs reversible hydrogen electrode, lasting for more than 10 hours of continuous operation with H2O2 selectivity greater than 80%. Toward practical application, the single‐Co‐atom electrode was directly used to assemble an electrochemical cell to produce H2O2 at a rate of 676 mol/kgcat/h with a cell voltage of about 1.6 V.

Fuel cells that use small organic molecules or hydrogen as the anode fuel can power clean electric vehicles. From an experimental perspective, the possible fuel cells' electrocatalytic reaction mechanisms are obtained through in situ electrochemical spectroscopy techniques and density functional theory calculations, providing theoretical guidance for further development of novel nanocatalysts. As advanced nanocatalysts for fuel cells' electrochemical reactions, alloy nanomaterials have greatly improved electrocatalytic activity and stability and have attracted widespread attention. Enhanced electrocatalytic performance of alloy nanocatalysts could be closely related to the synergistic effects, such as electronic and strain effects. Depending on the arrangement of atoms, alloys can be classified into random alloy and intermetallic compounds (ordered structure). Intermetallic compounds generally have lower heats of formation and stronger heteroatomic bonding strength relative to the random alloy, resulting in high chemical and structural stability in either full pH solutions or electrochemical tests. Here, we summarize the latest advances and the structure-function relationship of noble metal alloy nanocatalysts, among which Pt-based catalysts are the main ones, as well as comprehensively understand why they significantly affect the electrocatalytic performance of fuel cells. Novel alloy nanocatalysts with a robust three-phase interface to achieve efficient charge and mass transfer can obtain desirable activity and stability in the electrochemical workstation tests, and is expected to acquire a higher power density on fuel cell test systems with harsh test conditions.

High performance and durable bifunctional oxygen electrocatalysts are of great importance for the commercial application of environmentally friendly and sustainable energy through electrochemical d...

A high temperature microwave absorber with magnetic metal as an additive (Planar anisotropy Co@C/Na2SiO3 composite) was successfully fabricated. Following a C-coat treatment and complex formation with Na2SiO3, the composite worked stably at 673 K and showed outstanding high temperature stability. Evaluation of TG analysis results and static magnetic properties before and after sintering adequately illustrated that its antioxidant performance was outstanding. Its electromagnetic interference (EMI) shielding may reach 20 dB with a thickness of 10 mm, where absorption inside the composite was the main mechanism underlying attenuation. A reflection loss (RL) intensity below −8 dB may be obtained in the X band with a thickness of 1.7 mm at 673 K. The absorption strength of the composite was lower than −10 dB in the range of 8.7–11.8 GHz. Moreover, the composite showed excellent stability at high temperatures. Compared with dielectric loss absorbers, magnetic metallic absorbers have an obvious advantage in both absorption performance and price, and show irreplaceable potential for extensive use and commercialization in the field of high temperature absorbance.

Herein, we attempted to prepare MoS2/Fe@Fe3O4 nanocomposites capable of strongly absorbing broadband incident electromagnetic (EM) radiation and probed the effects of their composition on complex permittivity and permeability at 2–18 GHz. Calculations of normal-incidence reflection losses (RLs) based on EM parameters revealed that the Fe@Fe3O4 to MoS2 mass ratio strongly influenced the absorption peak intensity and bandwidth. Specifically, an RL peak of −31.8 dB@15.3 GHz and a bandwidth (RL

To investigate the flow field near fracture entrance and promote the development of sand fracturing with carbon dioxide as the working fluid, numerical simulation of multiphase flow was conducted with a 3D geological model considering the compressibility of carbon dioxide. The flow field of carbon dioxide alone was firstly investigated to lay the foundation for the analysis of multiphase flow, and then comparative analysis was conducted on the flow field of both the injecting sand from the pipe and the annulus. The results show that jet fracture with carbon dioxide can achieve a 4.46 MPa pressure boost at the fracture tip compared to the annulus pressure, which theoretically validates the feasibility of the mentioned technology. Sand fracturing can achieve a higher pressure boost in the cavity, while it needs greater pump pressure at the surface. Injecting sand from the annulus could decrease the need for pump pressure by 6.62 MPa at the condition of injecting 25% carbon dioxide from the annulus simultaneously, while the pressure difference between the cavity tip and the annulus decreases as a result.

Improving the slow kinetics of hydrogen evolution/oxidation reaction(HER/HOR) on Pt in the alkaline electrolyte is key to the development of water splitting and hydroxide exchange membrane fuel cells, which feature a potential cost advantage over their acid-operating counterparts. However, it is still unconfirmed whether adsorbed surface hydroxyl species (OHad) plays a significant role in determining HER/HOR activity. Moreover, the active sites should be different in the alkaline due to the sluggish reaction rate. In the present work, electrochemical tests have shown that for modified bulk Pt surface and Pt3Ni nanoalloy, HER rate is co-determined by the oxophilic effect and electronic effect, while the rate of HOR is associated with the electronic effect. Density functional theory (DFT) calculations reveal the fundamentally different HER and HOR mechanism of Pt-based nanoparticles, and the surface charge may account for such difference. Finally, the adsorption and oxidation of carbon monoxide (CO) as a novel descriptor are provided to predicate the activity of HER and HOR.

To satisfy impedance matching at low frequencies and obtain high microwave absorption performance, easy-plane anisotropy Fe–Si powders coated with SiO2 were produced by a ball milling technique and a chemical deposition method. Then, a scanning electron microscope, a transmission electron microscope, an X-ray photoelectron spectrometer, an X-ray diffractometer, a Mossbauer spectrometer, a vibrating sample magnetometer, and a vector network analyzer were used to characterize the samples. Compared to easy-plane anisotropy Fe–Si powders without surface modification, the dielectric constant of easy-plane anisotropy Fe–Si powders with SiO2 coating decreased dramatically and the microwave absorption performance was improved significantly. The reflection loss peak reached − 10 dB when the thickness was 1.4 mm and even reached − 34 dB when the thickness was 4.5 mm, exhibiting great potential for application in thin absorbers working in the frequency range of 0.1–4 GHz. In addition, the microwave absorption performance at oblique incidence was also investigated. A reflection loss peak of − 30 dB was obtained when the incident angle was 30°, and a reflection loss peak of more than − 10 dB can still be obtained even when the incident angle was 80°. The results show that the easy-plane anisotropy Fe–Si powders with SiO2 coating still possess high microwave absorption performance at oblique incidence.

In situ/operando characterization techniques are powerful to provide fundamental information about molecular structure–activity/selectivity relationships for various catalytic systems under controlled condition. However, the lack of model catalyst, as the major obstacle for deeper understanding on the nature of active sites and reaction mechanisms, hinders the further advancements in catalysis. Fortunately, the rapid development of single-atom catalysts (SACs) offers us new opportunities for capturing the reaction intermediates, identifying the active sites, and even monitoring the dynamic behaviors of both the geometric structure and electronic environment of the catalytic sites at atomic scale. In this Perspective, the recent advances on the in situ/operando characterization techniques including X-ray absorption spectroscopy, scanning tunneling microscopy, Fourier-transform infrared spectroscopy, among other methods, for the characterization of SACs are thoroughly summarized. The results from these in situ/operando measurements reveal the crucial role of SACs as model systems for sharpening our understanding on the nature of catalytic sites. Furthermore, the challenges and outlooks in developing in situ/operando techniques for single-atom catalysis are discussed. Ministry of Education (MOE) Accepted version This work was supported by the National Key R&D Program of China (2016YFA0202804), the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB17000000), Dalian National Laboratory for Clean Energy (DNL180401), the Youth Innovation Promotion Association CAS, Nanyang Technological University (M4080977.120), and Ministry of Education of Singapore (AcRF Tier 1 M4011021.120 and Tier 2 2015-T1-002-108).

Conversion the ethanol into CO2 at low potential through C C bond cleavage is vital to further improve the utilization of ethanol in direct ethanol fuel cells. The addition of Rh into Pt lattice is considered as an efficient route to improve the CO2 selectivity during ethanol electro-oxidation. In this work, PtRh alloy nanoparticles with different element ratios supported on reduced graphene oxide (RGO) were synthesized. Among them, Pt1Rh1/RGO shows an ultrahigh mass activity of 0.285 A mgpt−1 at 0.4 V (vs.SCE), 2.48 times as high as that of commercial Pt/C. Results of high-resolution transmission electron microscopy (HRTEM) reveal that the supported Pt1Rh1 alloy nanoparticles are in cubic shape with preferential (100) orientation and high-density of step sites. Results of in-situ FTIR spectra indicate that the addition of Rh greatly alleviates the COad poisoning on Pt surface. CO2 was generated at a low potential of −0.10 V, and the CO2 selectivity is 16.2 times as high as that of commercial Pt/C at 0.40 V. In-situ FTIR spectra using isotopically-labeled ethanol further confirm the superior CO2 selectivity on Pt1Rh1/RGO under low potentials is derived from the addition of Rh and high-density of step sites, which facilitates the C C bond cleavage and the oxidation of alcoholic groups.

In this study, thin Pr2Co17 flakes fractured along c crystal plane are successfully prepared by a surfactant-assisted high energy ball-milling technology and then oxidized by hydrogen peroxide (H2O2). The complex permittivity and permeability of the unoxidized and oxidized Pr2Co17 flakes/epoxy composites are measured. The measured results show that the oxidation of H2O2 can effectively decrease the permittivity and simultaneously suppress the eddy. For the oxidized sample with 40 vol% Pr2Co17, the real permeability at 8.2 GHz and 12.4 GHz can reach 1.65 and 1.42, respectively, and the natural resonance frequency can reach 11.0 GHz. If used as a microwave absorber, the oxidized sample with 20 vol% Pr2Co17 flakes exhibits a very excellent microwave absorption performance in x-band when the absorber thickness t is very thin (1.3 mm

Within a power electronics transformer (PET), the medium frequency transformer (MFT) is one of the key components for the whole system providing the required isolation and the voltage conversion between primary and secondary sides. A comprehensive design procedure is presented aiming to achieve high-voltage-insulation and high-efficiency. Referring to insulation standard, transformer insulation parameters are determined. To achieve the high efficiency, the number of turns is discussed considering both the calculated core loss and the estimated winding loss. A 30kVA transformer prototype is constructed and extensive measurements are performed including insulation tests, transformer loss and parasitic capacitance. The transformer prototype passes the IEEE Std. C57.12.01 standard in terms of insulation and performs well in a resonant DC-DC converter. The measured winding and core losses under rated voltage and current are 117.9W and 72.4W respectively.

In this work, repetitive surge current stress is applied on the body diode of SiC MOSFET to examine the degradation of the body diode. The repetitive surge tests are conducted at $25^{\circ}\mathrm{C}$ and $125^{\circ}\mathrm{C}$. Static characteristics and reverse recovery transient of the DUT’s body diode are measured after each 50 surge pulses to monitor the electrical parameter variations. Increase in body diode resistance and decrease in reverse recovery charge are observed after hundreds of stress cycles. Meanwhile, the transfer curve and I-V curve of the DUT are measured. No obvious shift of threshold voltage is observed, indicating no gate oxide degradation occurred. Based on the analysis of the resistance components of body diode and MOSFET, bipolar degradation is demonstrated to be the mechanism leading to the degradation.

Some applications are very sensitive to the weight of the robot, such as space manipulation or any untethered mobile manipulation. In this article, we designed a five-module unilaterally bending serial manipulator with length of 32 cm and a weight of only 18 g. The manipulator is driven by dielectric elastomer actuators (DEAs). Each module consists of a spatially closed tubular structure, which has the capability of large deformation while simultaneously maintaining torsional rigidity. The design is based on the buckling of columns. To achieve global deformation continuously, each module was controlled independently by a multichannel high-voltage power supply. As a demo, the manipulator was able to enter and exit a narrow L-shaped pipe. Experiments demonstrate that the manipulator driven by spatial DEAs can be super lightweight and can realize large continuous deformation.

Highly active oxygen evolution reaction (OER) electrocatalysts are important to effectively transform renewable electricity to fuel and chemicals. In this work, we construct a series of multimetal oxide nanoplate OER electrocatalysts through successive cation exchange followed by electrochemical oxidation, whose electronic structure and diversified metal active sites can be engineered via the mutual synergy among multiple metal species. Among the examined multimetal oxide nanoplates, CoCeNiFeZnCuOx nanoplates exhibit the optimal adsorption energy of OER intermediates. Together with the high electrochemical active surface area, the CoCeNiFeZnCuOx nanoplates manage to deliver a small overpotential of 211 mV at an OER current density of 10 mA cm-2 (η10) with a Tafel slope as low as 21 mV dec-1 in 1 M KOH solution, superior to commercial IrO2 (339 mV at η10, Tafel slope of 55 mV dec-1), which can be stably operated at 10 mA cm-2 (at an overpotential of 211 mV) and 100 mA cm-2 (at an overpotential of 307 mV) for 100 h. Ministry of Education (MOE) National Research Foundation (NRF) The authors gratefully acknowledge the financial support from Singapore MOE AcRF Tier 2 under Grant Nos. 2017-T2-2- 069 and MOE Tier 1 2017-T1-002-009 and 2020-T1-001-031, and National Research Foundation of Singapore (NRF) Investigatorship, Award No. NRF2016NRF-NRFI001-22. We also acknowledge the 111 project (D18023) from Zhengzhou University for their support for this work.

The oxygen evolution reaction (OER) is a key process involved in energy and environment-related technologies. An ideal OER electrocatalyst should show high exposure of active sites and optimal adsorption energies of oxygenated species. However, earth-abundant transition-metal-based OER electrocatalysts still operate with sluggish OER kinetics. Here, a cation-exchange route is reported to fabricate cobalt-vanadium-iron (oxy)hydroxide (CoV-Fe0.28) nanosheets with tunable binding energies for the oxygenated intermediates. The formation of an amorphous/crystalline heterostructure in the CoV-Fe0.28 catalyst boosts the exposure of active sites compared to their crystalline and amorphous counterparts. Furthermore, the synergetic interaction of Co, V, and Fe cations in the CoV-Fe0.28 catalyst subtly regulates the local coordination environment and electronic structure, resulting in the optimal thermodynamic barrier for this elementary reaction step. As a result, the CoV-Fe0.28 catalyst exhibits superior electrocatalytic activity toward the OER. A low overpotential of 215 mV is required to afford a current density of 10 mA cm−2 with a small Tafel slope of 39.1 mV dec−1, which outperforms commercial RuO2 (321 mV and 86.2 mV dec−1, respectively). Ministry of Education (MOE) National Research Foundation (NRF) M.K. and J.Z. contributed equally to this work. The authors gratefully acknowledge the financial support from Singapore Ministry of Education (MOE) AcRF Tier 2 under Grant Nos. 2017-T2-2-069 and 2018-T2-01-010 and National Research Foundation of Singapore (NRF) Investigatorship, Award No. NRF2016NRF-NRFI001-22. The authors would also like to acknowledge 111 project (D18023) from Zhengzhou University for their support for this work.

Nowadays, the optical data storage (ODS) has already become one of the most promising data storage technologies in this digital era. Optically stimulated luminescence (OSL) material has recognized as a considerable potential candidate for the new-generation ODS. The improvement of volatile memory performance and the increase of storage capacity are two critical challenges to be solved. In this work which is reporting on, a new novel Eu2+-doped orthosilicate phosphor has been studied showing both persistent luminescence and OSL. The trap density is significantly enhanced by 10-fold via Dy3+ codoping. Information can be reversibly written into the traps by UV light illumination and then read out by optical or thermal stimulus. The capture and release dynamics of electrons by traps are studied in detail to reveal the OSL-based ODS mechanism. Moreover, as a proof-of-concept, ODS flexible medium is fabricated using the as-obtained OSL material to certify the application feasibility for erasable optical data write-in and read-out.

Inspired by “water ripples” in nature and the flocculation phenomenon in colloid chemistry, a novel liquid drop/colloid flocculation approach is developed to fabricate an extremely flexible and compressible 3D macroscopic graphene-based architecture (hydrogels or aerogels), via a new coagulation-induced self-assembly mechanism. This facile and universal technique can be achieved in a neutral, acidic, or basic coagulation bath, producing microsized hydrogels with various structures, such as mushroom, circle, disc shapes, etc. The method also allows us to introduce various guest materials in the graphene matrix using transition metal salts as the coagulating bath. A mushroom-shaped NiCo oxide/GS hybrid aerogel (diameter: 3 mm) is prepared as an example, with ultrathin NiCo oxide nanosheets in situ grown onto the surface of graphene. By employing as binder-free electrodes, these hybrid aerogels exhibit a specific capacitance of 858.3 F g–1 at 2 A g–1, as well as a good rate capability and cyclic stability. The asymmetric supercapacitor, assembling with the hybrid aerogels as cathode and graphene hydrogels as anode materials, could deliver an energy density of 21 Wh kg–1 at power density of 4500 W kg–1. The ease of synthesis and the feasibility of obtaining highly flexible aerogels with varied morphologies and compositions make this method a promising one for use in the field of biotechnology, electrochemistry, flexible electronics, and environment applications.

The complex permeability and permittivity of the easy-plane anisotropic Co/polyimide composite at high temperature (293–673 K) in X band were measured. The results show that both the complex permeability and permittivity increase with the increase of temperature in the measured temperature range. The calculated absorption properties display that the intensity of the reflection loss (RL) peak first increases and then decreases with the increase of temperature, and reaches the maximum (−52 dB) at 523 K. At each temperature, the composite can achieve the RL exceeding −10 dB in the whole X band. The composite can even work stably for more than 20 min with the excellent absorption performance under 673 K. In addition, the RL performance of the composite at high temperature is better than that at room temperature.

Co@C nanofibers have been prepared by an electrospinning technique. Uniform morphology of the nanofibers and good dispersion of the magnetic cobalt nanoparticles in the carbon fiber frame were confirmed by field-emission scanning electron microscopy and high-resolution transmission electron microscopy. The electromagnetic parameters of a composite absorber composed of Co@C nanofibers/paraffin were measured from 2 GHz to 15 GHz. The electromagnetic wave absorption properties were simulated and investigated in the case of normal and oblique incidence. In the normal case, the absorber achieved absorption performance of − 40 dB at 7.1 GHz. When the angle of incidence was increased to 60°, the absorption effect with reflection loss (RL) exceeding − 10 dB could still be obtained. These results demonstrate that the reported Co@C nanofiber absorber exhibits excellent absorption performance over a wide range of angle of incidence.

Digital rock images may capture more detailed pore structure than the traditional laboratory methods. No explicit function can correlate permeability accurately for flow within the pore space. This has motivated researchers to predict permeability through the application of numerical techniques, e.g., using the finite difference method (FDM). However, in order to get better permeability calculation results, the grid refinement was needed for the traditional FDM and the accuracy of the traditional method decreased in pores with elongated cross sections. The goal of this study is to develop an improved FDM (IFDM) to calculate the permeabilities of digital rock images with complex pore space. An elliptical pore approximation method is invoked to describe the complex pore space. The permeabilities of four types of idealized porous media are calculated by IFDM. The calculated results are in sound agreement with the analytical solutions or semi-empirical solutions. What’s more, the permeabilities of the digital rock images after grid coarsening are calculated by IFDM in three orthogonal directions. These results are compared with the previously validated lattice-Boltzmann method (LBM), which indicates that the predicted permeabilities calculated by IFDM usually agree with permeabilities calculated by LBM. We conclude that the presented IFDM is suitable for complex pore space.

A magneto-dielectric substrate material with high permeability and low loss at high frequency is necessary for a miniaturized antenna. Keeping the loss low is essential, in order to restrain the eddy current effect and to possess a high magnetic resonance frequency. In this work, the effects of the NaOH concentration and soaking time on crystal structures and morphologies of Co80Ni20 alloy particles are studied based on a polyol process. The results reveal that the size of particles increase with the promotion of the concentration of NaOH and soaking time. The electromagnetic (EM) properties of Co80Ni20 alloy particles/ polyurethane composites with various soaking times are studied at the NaOH concentration of 1.5 mol/L. The results reveal that the real part of permeability ( μ ' ), the real part of permittivity ( e ' ), the magnetic loss tangent (tan δ μ ), the dielectric loss tangent (tan δ e ) of the composite with the soaking time of 3 h are 2.0, 11.0, 0.09, and 0.057 at 1 GHz, respectively, and the eddy current effect is suppressed effectively. The calculation of the permeability shows that the composite possesses a high domain wall resonance frequency. This work is significant for developing a magneto-dielectric substrate material using at 1 GHz.

There is a widely observed phenomenon in the microwave absorption field that an absorber always exhibits good oblique incidence absorption capacity if it has high performance at normal incidence. However, if a certain angle is exceeded, this kind of effective absorptive capacity will no longer be maintained. Besides, an absorber performs differently for incident transverse electric (TE) and transverse magnetic (TM) waves: for the TE case, the absorber can no longer obtain effective absorption; for the TM case, another efficient absorption region was observed at higher frequencies even when the incident angle exceeded 80°. These phenomena are widely found in the literature, which demonstrates that they are caused by physical laws rather than material properties. To demonstrate the underlying reason, in this study, the common spherical carbonyl iron-polyurethane composite absorbers were fabricated as a typical example. Their absorbing performance was investigated via both simulation and experiment. All the phenomena mentioned above were observed, studied in detail by employing the multiple reflection model, and explained quantitatively. Further, along with establishing the underlying mechanism of electromagnetic wave transmission in the absorber, two formulas were deduced to predict: (a) the maximum incident angle for efficient absorption of the TE polarized wave; and (b) the required absorber thickness for obtaining efficient absorption for a large incident angle of the TM polarized wave.

Numerous efforts have been made to investigate manganese oxides as active materials in the field of energy storage. To further explore the full use of MnO2 for supercapacitor in aqueous electrolyte, a facile two-step hydrothermal method are developed to synthesis T-Nb2O5@MnO2 composites supported by carbon cloth (CC). With the hierarchical nanostructure and rational synergistic effect, CC@T-Nb2O5@MnO2 exhibits a high specific capacitance (319 F g−1 at 0.2 A g−1) and a good cycling stability (85.7% retention after 2000 cycles). An asymmetric supercapacitor with CC@T-Nb2O5@MnO2 nanocomposite as positive electrode and activated graphene oxide as negative electrode yielded an energy density of 31.76 Wh kg−1 and a maximum power density of 2250 W kg−1. These delightful findings demonstrate CC@T-Nb2O5@MnO2 to be a nice electrode material, and meanwhile provide an idea to design novel structure with synergic mechanism for high-performance supercapacitors.

We have synthesized thin Fe3O4 microflakes by a simple hydrothermal method and prepared Fe3O4 microflake–paraffin composites without and with magnetic orientation using the method of simple ultrasonic mixing and rotating samples in a magnetic field. X-ray diffractometer, Mossbauer spectrum, scanning electron microscope and vibrating sample magnetometer were used to characterize the samples. The complex permittivity and permeability of Fe3O4 microflake–paraffin composites without and with magnetic orientation were measured in the frequency range of 0.1–18 GHz by a vector network analyzer using a coaxial method. The reflection loss (RL) was calculated by the measured electromagnetic parameters using transmission line theory. The measurement of electromagnetic parameters shows that magnetic orientation makes the complex permittivity and permeability increase. The calculated RL shows that the Fe3O4 microflake–paraffin composite with magnetic orientation has enhanced microwave absorption properties in the frequency range of 1–3 GHz and the thickness range of 2.9–3.5 mm, indicating that the Fe3O4 microflake–paraffin composite with magnetic orientation is a promising thin microwave absorption material in the L-S band.

In order to maximize the Pt utilization in catalysts and improve catalytic processes, we report a convenient strategy for preparation of Pt3Co with Pt-skin structured bimetallic nanocatalysts directly supported on porous graphitic carbon. Notably, the thickness of the Pt-skin is only 1–2 atomic layers, about 0.5 nm. Surprisingly, the bimetallic nanocatalysts composed of Pt3Co with Pt-skin are first used as ethanol electro-catalysts, with the mass activity of 0.79 mA μgPt–1, which is a 250% enhancement compared with commercial Pt/C (0.32 mA μgPt–1). On the basis of the results of electrochemical in situ Fourier transform infrared spectroscopy (FTIRS) and density functional theory (DFT), a new ethanol electro-oxidation enhancement mechanism is proposed in which Pt3Co with Pt-skin promotes partial oxidation of ethanol over C–C bond cleavage, thereby resulting in higher CH3COOH production than CO2 production.

In this paper, a resonant dc-dc converter with modular rectifier is proposed for high voltage gain and wide output voltage range applications such as interconnecting renewables to the medium voltage dc grid. The modular rectifier on the secondary side is used to support the high voltage and the number of submodules (SMs) can be chosen depending on the output voltage. Wide range of voltage regulation is achieved by regulating the frequency and the duty cycle of the SM gate signals. The proposed converter can achieve ZVS for the primary side switches and ZCS for the secondary rectifier. An 800W prototype with one SM in each arm is constructed to demonstrate the operating principle of the proposed converter. The efficiency under voltage gain 1, 1.25 and 1.5 are measured and the peak efficiency is 96.8%.

Breaking the symmetry in catalysts through interface engineering has emerged as a new dimension in enhancing the catalytic performances, while the long-range asymmetry (i.e. in nanometer scale) in catalysts can hardly be achieved by alloying or doping. Herein, we introduce asymmetrical gradient effect into NiFe layered double hydroxide (NiFe-LDH) at nano scale via a simple nanoarray construction strategy on Ni foam substrate. The electron energy loss spectroscopy, extended X-Ray absorption fine structure and other characterizations together revealed the concentration and valence states gradients in NiFe-LDH nanoarrays. Subsequently, the gradient effect leads to distinctly optimized binding strength of active sites to oxygen evolution intermediates, better electron transfers and boosted oxygen evolution performances, which are absent in non-gradient NiFe-LDH catalysts. Such long-range gradient effects in nanoarray materials provide new opportunities to understand their boosted catalytic performances and to rationally design better catalytic materials. Ministry of Education (MOE) Nanyang Technological University This work was financially supported by the National Natural Science Foundation of China , the Program for Changjiang Scholars and Innovative Research Team in the University , the Fundamental Research Funds for the Central Universities , the Long-Term Subsidy Mechanism from the Ministry of Finance and the Ministry of Education of China , the National Key Research and Development Project , the Singapore Ministry of Education Academic Research Fund (AcRF) Tier 1: RG10/16, RG9/17, RG115/17; Tier 2: MOE2016-T2-2-004, and the Nanyang Technological University internal funding.

Compared to rigid manipulators, soft robot has advantages in complex working environments. In this paper, a soft and super lightweight biomimetic elephant trunk is proposed. The biomimetic elephant trunk is driven by dielectric elastomer actuators (DEAs) and operates by the deformation of its structure. To realize a large structural deformation and balance the rigidity requirement, a novel design concept was proposed that is using a group of symmetrical driving actuator areas on the surface of the structure. The relationship between the deformation and the voltage-induced strain was analyzed. Limited by the experimental conditions, only two connected modules were fabricated. However, the output force of the two-module device increased noticeably with the number of DEA film layers; with only three layers of DEA films, the force output reached 41 times its own weight. The experimental results indicate that the module is suitable to make a full-length biomimetic elephant trunk, which has highly redundant degrees of freedom (DOFs).

In this study, spherical amorphous Fe–B submicron particles were synthesized via aqueous chemical reduction, and a composite with a mass fraction of 80% was prepared by compounding them with polyurethane. By measuring the electromagnetic parameters and calculating the microwave absorption properties, we found that the composite had excellent absorption performance in a frequency range of 18–26.5 GHz. When the absorber was 0.88 mm thick, the reflection loss (RL) peak reached a maximum (−47.94 dB) with a bandwidth (RL < −10 dB) of 5.01 GHz. The absorption mechanism of the composite in the K band was also investigated. The results showed that the Fe–B particle composite effectively reduced the absorber’s thickness, maintaining a good absorption performance in the K band.

Tailoring the near-surface composition of Pt-based alloy can optimize the surface chemical properties of a nanocatalyst and further improve the sluggish H2 electrooxidation performance in an alkaline electrolyte. However, the construction of alloy nanomaterials with a precise near-surface composition and smaller particle size still needs to overcome huge obstacles. Herein, ultra-small PtRu3 binary nanoparticles ( Pt-increased > Pt/PC. From the perspective of engineering a near-surface structure, this study may open up a new route for the development of high-efficiency electrocatalysts with a strong electronic effect and oxophilic effect.

A facile two-step hydrothermal method is modified to synthesize NiCo 2 S 4 nanosheets on activated multiporous carbon (AMC) for application in supercapacitors. The structure and performance of both NiCo 2 S 4 and the intermediate product, i.e. NiCo 2 O 4 on AMC are investigated in detail to clarify the effect of the sulfidation treatment. Owing to the high electronic conductivity of NiCo 2 S 4 , the unique designed nanostructure exhibits a high specific capacitance (651.1 F g −1 at 0.6 A g −1 ), good rate performance (88.1% retention for current increases around 17 times) and excellent cycling stability (87.4% retention after 2000 cycles). These results suggest this hybrid composite to be a promising electrode material for high-performance supercapacitors and the rational fabrication provides an approach to improve the electrochemical energy storage for other transition metal sulfides and oxides.

Carbon coating is an effective approach to enhance the electrochemical properties of transition metal oxide. Herein, we demonstrated that increasing rigidness of carbon coating by incorporating the analogue of Al oxide was able to improve the rate capability and cycling stability of Co3O4. Compared with carbon coating, a hybrid coating consisted of carbon and the analogue of Al oxide (COAl) showed increased rigidness and robustness, which can suppress the massive expansion of Co3O4 upon lithiation, and accordingly, a conductive linkage of carbon over the electrode surface could be well preserved by using a thin hybrid coating. In this way, good electrode integration was obtained together with fast electric conduction and short Li+ diffusion distance. AFM force curve, SEM observation and impedance measurement were carried out to demonstrate the feasibility of our strategy. During the tests of Li-ion batteries, C@Co3O4@COAl exhibited significantly improved rate capability (0.2–20 A g−1) and cycling stability (4000 cycles at 5 A g−1) as compared with C@Co3O4@C, thus manifesting the significant role by increasing the rigidness of carbon coating.

To use the silicon carbide (SiC) metal–oxide–semiconductor field-effect transistor (MOSFET) intrinsic diode as a freewheeling diode in a power converter, its reverse recovery characteristics should be carefully evaluated from the point view of application. The intrinsic diode is based on the p–i–n junction structure, thus the minority carrier will inject into the drift layer during the forward conduction period, which leads to reverse recovery current when it switches off. The turn-off voltage, forward current, current commutating slope (di/dt) and junction temperature are major factors affecting the turn-off process of a diode, and are mostly concerned in practical applications. Therefore, in this study, the reverse recovery characteristics of the intrinsic diode are systematically evaluated based on these four factors. The experimental results are presented and discussed. The reverse recovery characteristics of an SiC Schottky barrier diode (SBD) and two types of silicon (Si) p–i–n diode are also presented for a quantitative comparison. In terms of the reverse recovery performance, although not as good as the SiC SBD, the SiC MOSFET intrinsic diode is much better than the Si p–i–n diode.

An oil/water separation film with excellent durability and stable recyclability is highly desired for the treatment of oil containing effluents, like industrial oily wastewater. Herein, a novel superhydrophobic nanofibrous film (SNF) was fabricated by growing TiO2 on a collagen fiber membrane (CFM), followed by surface coating of vinyl triethoxysilane. The as-prepared SNF was well characterized by SEM, SEM-EDS and XPS. Due to the unique structure, the SNF featured superhydrophobicity with a water contact angle (WCA) of 153°. When applied in the separation of oil/water mixtures, SNF exhibited a high separation efficiency of ∼97% in 5 circles, and it showed more effective oil/water separation efficiency compared to the commercial PTFE film. SNF was also effective for the separation of gasoline/water or diesel oil/water mixtures with varied volume ratios, and all the corresponding separation efficiencies were higher than 97% even after 5 cycles. In addition, SNF could still maintain superhydrophobicity with WCA around 150° after being treated by high temperature (120 °C), ultraviolet irradiation, water or organic solvent immersion for 24 h, manifesting an excellent durability.

In this study, flaky carbonyl iron powder (CIP)@SiO2 particle/polyurethane (PU) composites with different steric configurations were prepared using a rotating magnetic field and different cutting methods. The effects of the angle between the easy magnetization plane and the vector of incident electromagnetic (EM) waves on the EM parameters and microwave absorption characteristics were studied. In order to investigate the influences of different steric configurations of the flaky CIP@SiO2 particles on the EM parameters of the composites, the complex permeability of the samples was calculated using the Landau-Lifshitz-Gilbert equation and Bruggeman’s effective medium theory combined with consideration of the shape anisotropy. The calculated results agreed well with the experimental results. In addition, it was revealed that the complex permeability of the composites was dominated mainly by the steric configuration of the flaky CIP@SiO2 particles, which was significant for the development of an excellent absorber in oblique incident conditions.

Broadband absorbing coating in the case of large-angle incidence is rarely studied. In this paper, the high filling ratio graphene-paraffin composite absorbing coatings which are capable of absorbing large-angle incident transverse magnetic (TM) waves in an ultra-wide frequency band were prepared. By increasing the filling ratio, the optimum absorbing angle was found to increase. In particular, the bandwidth of the absorber with 15% mass fraction covers 3.6-18 GHz when the incident angle is 86° at the thickness of 1.5 mm. The dependence of absorbing properties on the thickness of the absorbing coating was also studied. Different from the variation pattern in the case of normal incident, in the case of oblique incidence, with the increase of the thickness, the absorption bandwidth will expand to the low frequency, while the original absorption performance remains unchanged. Through the multi-reflection model, this phenomenon was investigated comprehensively and the underlying physical mechanism of the change of the absorption performance was explained.

High-efficiency microwave absorption materials are widely used in electronic equipment and communication facilities. This study aims to develop a broad-bandwidth metamaterial absorber based on the magnetic substrate with a central frequency selective surface (FSS). It is however, different from the strategy of expanding the bandwidth for metamaterial absorbers reported in other literatures, in this study, a unique development strategy that involves selecting the most suitable magnetic substrate from a database using genetic algorithm is adopted. By adding an optimized FSS layer to the magnetic substrate, its loss performance and impedance matching performance are considerably improved, and the resulting metamaterial absorber exhibits excellent absorption properties. At a thickness of 3.1 mm, the reflection loss in the range from 2.5 to 17.2 GHz is below –10 dB, which is significantly better than the values reported in previous studies. In addition, the prepared metamaterial absorber possesses excellent absorption characteristics under oblique incidence conditions. The strategy proposed in this study leads to the successful development of a high-efficiency metamaterial absorber and represents a more effective approach than those previously used in the field.

PtRu bimetal is of particularly attractive in various electrocatalytic reactions owing to its synergistic effect, ligand effect and strain effect. Here, PtRu nanoalloy supported on porous graphitic carbon (PC) has been successfully prepared via a very facile method involving co-reduction the precursors of Pt and Ru at 300 °C by H2 (PtRu/PC L) followed by thermal treatment at high temperature (700 °C, PtRu/PC–H). Specifically, the electrocatalytic performance of PtRu/PC nanoalloy could be dramatically enhanced through high-temperature annealing. This strategy has synthesized smaller Pt and PtRu nanoparticles (ca. L and Pt/PC nanocatalysts. The mass activity and specific activity on PtRu/PC–H nanoalloy can be increased to 1674.2 mA mg−1Pt and 4.4 mA cm−2 for MOR, it is 4.08 and 8.80 times higher than that of the Pt/PC nanocatalyst, respectively. From in-situ FTIR spectra, we can discover PtRu/PC–H nanoalloy generates CO2 at a lower potential of −150 mV than those on PtRu/PC–L (0 mV) and Pt/PC (50 mV) nanocatalysts, dramatically improves the ability of cleavage C–H bond and alleviates the COads poisoning on active sites. The PtRu/PC H nanocatalyst exhibits maximum power density of 83.7 mW cm−2 in single methanol fuel cell test, which more than threefold than that of commercial Pt/C as the anode catalyst. Those experimental results open an effective and clean avenue in the development and preparation of high-performance Pt-based nanocatalysts for direct methanol fuel cells.

Soft magnetic composites (SMCs) are effective as magnetic powder cores in power transformers. Currently, SMCs used in transformers are mostly prepared from NiZn ferrites. One example of this type of material is NiZnCu ferrite, whose working frequency limit is 40 MHz. Above this frequency, its large magnetic loss angle tangent ( tan δ m), approximately equal to 0.29 at 100 MHz, seriously impairs the property of transformers. Generally, the magnetic losses in the MHz frequency band result from eddy-current loss, domain wall resonance, and natural resonance, specifically the high natural resonance loss. A way to decrease it is by increasing the resonance frequency ( f r). However, the increase in f r is very difficult for the uniaxially anisotropic NiZnCu ferrite due to the Snoek limit. We present a composite of oriented Ce2Fe17N3 microflakes and polyurethane in this letter. Although its true permeability is not as high as that of NiZnCu, the f r reaches 7.5 GHz. As a result, the tan δ m at 100 MHz is decreased to 0.015. This indicates that our material has a higher working frequency than NiZnCu and should make fabrication of a 100 MHz transformer possible.

The electromagnetic wave can be efficiently absorbed by coating absorbing materials in the frequency of absorption peak, which has been experimentally proved deriving from destructive interference of electromagnetic waves reflected from different interfaces of the absorber in that frequency. However, except at the peak frequency, the absorption mechanism is still controversial. In this paper, the symmetry model of absorbing materials has been proposed and the reflected waves originated from different interfaces were separated. The separated waves’ amplitude and phase were extracted, which provides direct evidence to explain the absorption performance at different frequencies. Three common fillers, namely magnetic materials, ferrite materials, and carbon materials, were selected to prepare polyurethane composite absorber material. Their absorbing properties were simulated by the finite element method, and the information of separated waves was obtained. The superposition result of the separated waves is the same as the reflection loss, which reveals the dependence of absorption performance and the waves reflected from different interfaces, validates the correctness of the quarter-wave model, and proves that not only the reflection loss at peak frequency, the absorption performance at all the frequency range are dependent on the interference.