查看更多>>摘要：A binder-free positive electrode material of 3D starfish-like Co_3O_4/Ni forest is fabricated via a novel and facile hydrothermal process followed by thermal treatment. The morphological studies clearly showed the construction of starfish-like micro-flowers of Co_3O_4 nanostructure forest densely covered on the entire Ni current collector. The 3D-Co_3O_4/Ni electrode displayed an areal capacity as high as 143.28 mC cm~(-2) at 0.5 mA cm~(-2) and higher stability of 88.4% after 5000 cycles. Moreover, the fabricated 3D-Co_3O_4/Ni||3D-Bi_2O_3/Ti supercapattery delivered a maximum areal capacitance of 24.73 mF cm~(-2), the energy density of 6.73 uWh cm~(-2) and power density of 5250 uW cm~(-2) with good cycling stability > 71% capacity retention after 5000 cycles. The higher electrochemical performance of the electrode is delivered due to the availability of abundant electrochemically active sites in the 3D starfish-like Co_3O_4 microflower, which facilitates a higher electrochemical reaction. The starfish-like forest architectures allow rapid ion diffusion, and the binder-free electrode reduces the contact resistance, which fasten the electron transport. These tolerable results prompt the as-prepared electrode with 3D starfish-like Co_3O_4 microflower morphology as an auspicious positive electrode material for electrochemical energy storage devices.
查看更多>>摘要：A novel temperature stable (l-x)MgZr_(0.85)Sn_(0.15)Nb_2O_8-xBa_3Ti_4Nb_4O_(21) -2wt% BaCu(B_2O_5) (MZSN-BTN-BCB, x = 0.12, 0.14, 0.15, 0.16, 0.18 in molar) composite ceramic was fabricated via a conventional solid-state reaction method. MZSN and BTN phase can coexist in the sintered ceramics due to the different crystal structures from the results of X-Ray diffraction and scanning electron microscopy. The sintering temperature and phase composition are especially relevant to the microwave dielectric properties. The optimal sintering temperature of MZSN-BTN ceramics was successfully reduced to 1125 °C due to the formation of BCB liquid phase. The temperature coefficient of the resonant frequency was successfully adjusted to near zero by adding an appropriate amount of BTN due to its opposite-sign τf value. Excellent microwave dielectric properties of er = 33, Q×f= 53,950 GHz (at 6.079 GHz), τf = -4.3 ppm/°C were obtained in 0.88MZSN-0.12BTN-2 wt% BCB composite ceramics when sintered at 1125 °C for 4 h.
查看更多>>摘要：Spinel metal oxides, prepared at high temperature, have shown excellent gas sensing properties among metal oxide sensing materials. Herein, a series of porous spinel gallate nanospheres, including CdGa_2O_4, NiGa_2O_4, CoGa_2O_4, CuGa_2O_4, ZnGa_2O_4, and MgGa_2O_4 were prepared by solvothermal method and followed low temperature calcination. XRD, SEM, XPS and N_2 adsorption-desorption have been carried out to determine their structure, morphology, chemical state and surface area, respectively. These nanospheres are all composed of tiny nanoparticles, giving meso-porous characters. Furthermore, the sensor based on CdGa_2O_4 exhibits excellent formaldehyde sensing performance, including good selectivity, short response time, and excellent stability at the low working temperature of 120 °C.
查看更多>>摘要：A series of NaYF_4:0.2Yb/0.02Ho microcrystals co-doped with various K~+ and Gd~(3+) concentrations were synthesized by hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM), and upconversion (UC) spectroscopy were used to study the effects of co-doped ions on the phase structure, morphology, size and up-conversion luminescence (UCL) properties of microcrystals in detail. The results show that the K~+ and Gd~(3+) co-doping do not evoke the change in crystal structure, but the UCL intensities of NaYF_4:0.2Yb/0.02Ho are significantly enhanced. Compared to K~+ and Gd~(3+)-absent sample, UCL intensities of green emission (541 nm) and red emission (643 nm) in NaYF_4:0.2Yb/0.02Ho microcrystals via 15 mol% K~+ and 15 mol% Gd~(3+) co-doping are increased by 2.4 times and 3.3 times, respectively. The temperature sensing characteristics and thermal quenching properties of the microcrystals were also explored. Significantly, the maximum relative sensitivity of the studied sample reaches 0.0127 K~(-1) at 298 K, which indicates that NaYF_4:0.2Yb/0.02Ho phosphors can be suitable for temperature sensing.
查看更多>>摘要：Semiconductor catalyst with high photocatalytic activity can be exploited via heterojunction. In this study, a new S-scheme SrTiO_3/porous ZnO composite was rationally devised, successfully prepared by utilizing a two-step pyrolysis of SrTiO_3/ZIF-8, and analyzed by various characterization technologies including XRD, SEM, TEM, BET, XPS, PL, UV-vis DRS, and photoelectrochemical and DFT theoretical calculations. A porous structure, tight contact, and a heterojunction formed between SrTiO_3 and porous ZnO (ZnOT) can be observed by SEM and TEM images. BET testing indicates that the SrTiO_3/porous ZnO composite (S3ZT) shows the highest specific surface area (30.37 m~2/g). The band gap values (E_g) of SrTiO_3 and ZnOT are around 3.17 and 2.95 eV, which agree with those obtained from DFT calculations. Compared to other samples, the SrTiO_3/porous ZnO composite (S3ZT) shows higher light absorption and lower transfer resistance as demonstrated by UV-vis DRS and EIS results. S3ZT presents a superior photocatalytic efficiency of 48.8% in degrading 5 mg/L methyl orange (MO) irradiated by 1 h UV-vis light, which are 7- and 1.5-fold higher than pristine SrTiO_3 and ZnOT, respectively. Moreover, based on Mott-Schottky theory, active species trapping experiments, XPS determination, and DFT calculations (energy band gap and work function), it was shown to be reasonable to utilize the S-scheme charge migration process for an explanation regarding the better photocatalytic activity of SrTiO_3/porous ZnO composite. Overall, this work will provide an effective protocol for devising and preparing semiconductor photocatalysts with S-scheme heterojunction by utilizing the superior characteristics of MOFs.
查看更多>>摘要：The chemical doping of carbon and heteroatoms is expected to be a promising strategy for enhancing the absorption properties of electromagnetic waves. In this work, N-doped C/ZnO composites (CN/ZnO_x-Ts) were originally designed and synthesized by using temperature-controllable calcination engineering with zinc-based acrylate resins containing N atoms as precursors. The best electromagnetic wave absorption (EMWA) performance for the composites was obtained by changing the composition and calcination temperature of the acrylate resin precursor. A CN/ZnO_(0.064)-900 composite prepared using a precursor containing acrylonitrile (0.4 mol) and ZnO (0.064 mol) calcined at 900 °C showed a minimum reflection loss (RL_(min)) of - 43.15 dB at 3.0 mm and 9.68 GHz, with an effective absorption bandwidth (EAB) ranging from 5.1 GHz to 18 GHz achieved by adjusting the thickness of the absorber. This method for preparing novel N-doped carbon-based materials provides the possibility for the mass production of highly efficient absorbers.
查看更多>>摘要：Biomass carbon is a potential alternate for commercially expensive graphene and carbon nanotubes to fabricate nanocomposites as electromagnetic (EM) wave absorbers. Here, we systematically prepared porous biomass carbon/ferrite nanocomposites with different chemical compositions, particle sizes, and structures using rice husk ash, carbonized luffa sponge, carbonized kapok and cotton fibers. All the prepared nanocomposites show limited dielectric losses, indicating the permittivity is less affected by the micro-morphologies, chemical compositions, and structures of biomass carbon. The magnetic loss of microwaves by most samples is caused by eddy current effect. Both smaller and wider range sized particles would contribute additional natural resonance for the magnetic loss of ferrite nanoparticles. The EM wave absorption performance of the nanocomposites are controlled by both the impedance matching between the absorber and air and their magnetic/dielectric losses for incident EM waves. The maximum bandwidth of RL < -10 dB of the as-prepared nanocomposites is about 4.8 GHz, covering most of the K_u-band. Due to their low density and good impedance matching with air, the biomass carbon/ferrite nanocomposites could be promising green light-weight EM wave absorbers by adjusting the particle sizes of ferrite nanoparticles.
查看更多>>摘要：This article reports the significantly improved piezoelectric and ferroelectric properties of Cu/W co-doped Ca_2Bi_2Nb_(2-x)(Cu_(1/4)W_(3/4))_xO_9 (CBNCW-x, where 0≤ x ≤ 0.150) high Curie temperature lead-free piezoelectric ceramics. The crystal structure, microstructure, and electric properties of CBNCW-x ceramics have been systematically analyzed. The results show that ceramic samples have a bismuth layered structure of m- 2, which is a single-phase of CBN. The ceramic grains show the typical plate-like structure of the bismuth layer. Cu/W co-doped CBN ceramics increased the distortion of NbO_6 octahedron, and significantly enhanced the piezoelectric constant and the remnant polarization. When x = 0.075, it shows better comprehensive properties with an excellent d_(33) of 13.8 pC/N, a high remnant polarization of 12.10 uC/cm2, the Tc of 918 °C, a dielectric loss value of 0.57%, and the Ωm value of 7099. Moreover, CBNCW-0.075 ceramic simple maintains the d_(33) of 12.7 pC/N after annealing 900 °C for 30 min, which shows good high-temperature stability. It suggests that the Cu/W co-doped CBN ceramics have good application prospects in the high-temperature piezoelectric field.
查看更多>>摘要：The configurations of nitrogen species have a crucial influence on the transition metal-nitrogen-doped carbon catalysts (M-N-C). Whereas, how to build more sp2 hybrid N (including pyridinic and graphitic N) to enhance the catalytic activity and charge transfer rate of the carbon-based ORR catalysts remains a challenge. Herein, Co-embedded nitrogen-enriching platanus bark-derived porous carbon (PBPC) material (Co-N-C) was developed from the pyrolytic platanus bark, assisted by impregnating cobalt salt and ethylene-diamine nitriding strategy. The synthesized catalyst exhibits a high nitrogen content of 5.02%, of which over 2/3 are high conductivity sp2 hybrid N (consist of pyridinic and graphite-N), suggesting the unity of high activity and conductivity. Thus, it delivers a competitive half wave potential and a lower Tafel slope (69.55 mV dec~(-1)) than Pt-C-20% catalyst. The ZAB with Co-N-C-900 catalyst exhibits a higher open-circuit potential and a peak power density up to 3.5 times (186.17 mW cm~(-2)) higher than that of the Pt-C-20%. During the durability test for 100 cycles (16.7 h), the voltage gap only increased by 4.2%, nevertheless, the Pt-C-20%-based ZAB encountered a catastrophic polarization surge in less than 16 h. When assembling a flexible ZAB, it performs excellent flexibility in bending tests, and the voltage gap merely increased by 1.7% after 100 cycles (16.7 h).
查看更多>>摘要：The paper presents a review of the authors' studies of advanced functional composites of graphene based materials with metals, alloys, intermetallic compounds and their hydrides, and on the creation on their basis of hydrogen-storage materials for a compact and safe hydrogen storage, electrode materials for nickel-metal hydride batteries, highly efficient catalysts for the hydrogenation of metals and organic compounds as well as their integration into the hydrogen energy systems for the backup electric power and for the H-based energy storage.
NSTL
Elsevier