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Supercapacitors suffer from lack of energy density and to achieve better energy density, a new class of hybrid architectures with controlled morphology is prerequisite. Here, a facile polyol method is successfully used for the synthesis of MnCo2O4/nitrogen doped graphene 2D/2D hybrid nanoarchitectures and this combination successfully avoids the restacking and agglomeration of nitrogen−doped graphene nanosheets. The formation of MnCo2O4/NG 2D/2D hybrid nanoarchitectures are confirmed by state−of−art techniques. This combination leads to a large conducting network that improves the exposure of active sites at the electrode−electrolyte interface for the transportation of electrons and ions. The synergistic effect of 2D MnCo2O4 nanoflakes over the 2D nitrogen−doped graphene serves the capacitance of ca. 1170 F g−1 at 1 A g−1 with an excellent rate capability of 818 F g−1 at 20 A g−1. An asymmetric supercapacitor is successfully fabricated using these MnCo2O4/NG 2D/2D hybrid nanoarchitectures as the cathode and 2D nitrogen−doped graphene as the anode electrodes, which exhibits better performance than previously reported spinel metal oxide materials. The asymmetric supercapacitor exhibits excellent energy density (∼48.5 Wh kg−1 at ∼808 W kg−1) and power density (∼16000 W kg−1 at ∼32.1 Wh kg−1), with an outstanding cyclic durability of 85.9% retention after 10,000 cycles.

Transition-metal-based nanomaterials are preferred for electrochemcial supercapacitor applications owing to their low purchasing cost, facile synthesis process and high theoretical electrochemcial performance. However, these materials can not translate their excellent theoretical performance into commendable experimental values. In these circumstances, supercapacitors based on new class of highly conductive and electroactive hybrid nanomaterial are recommended. Herein, for the first time, 2D CuMnO2-MnxOy@graphene foam (GF) hybrid nanomaterial is constructed as a novel electrode material for asymmetric supercapacitor application. The CuMnO2-MnxOy@GF hybrid nanomaterial displays an excellent areal capacitance of 7.82 F cm−2 at a current density value of 3 mA cm−2, while it also maintains maximum areal capacitance of 67.51% at 60 mA cm−2. The CuMnO2-MnxOy@GF hybrid nanomaterial retains a high capacitance of 92.15% after maximum 10,000 cycles. A high-performance asymmetric supercapacitor device is assembled based on CuMnO2-MnxOy @GF and sulfur-nitrogen-codoped graphene nanosheets (SN-GNs) as positive and negative electrode materials, respectively. The CuMnO2-MnxOy @GF//SN-GNs ASC device shows an ultra-high energy density value of 81.4 W h kg−1 at a minimum power density of 809.5 W kg−1. The CuMnO2-MnxOy @GF//SN-GNs ASC device retains a specific capacitance of 88.88% after 10,000 cycles. The CuMnO2-MnxOy@GF hybrid nanomaterial is beneficial to promote asymmetric supercapacitor device with an excellent electrochemcial performance.

The freestanding hierarchical core-shell nanoarchitectures exemplify the substantial interest in the development of next-generation electrode materials for energy storage systems . Herein, the hierarchical 3D CoS@MoS2 nanowire arrays (NWAs) are synthesized through a cost-effective hydrothermal process and followed by an effective sulfurization. The structural and morphological investigations of hierarchical 3D CoS@MoS2 NWAs are carried out for each stage. The 3D CoS@MoS2 NWAs yields a high specific capacity of 374.75 mA h g−1 and an areal capacity of 1.39 mA h cm−2 at a current density of 4 mA cm−2, exceptional rate capability (∼70.1% retention of the capacity at 20 mA cm−2), and remarkable cycling performance (∼96.2% retention of the capacity after 10,000 consecutive charge-discharge cycles), which are superior to the corresponding CoS nanowires and MoS2 nanosheets counterparts. The assembled CoS@MoS2//Fe2O3@rGO asymmetric supercapacitor (ASC) exhibits a broader working potential window of 1.7 V, ultrahigh energy density of 95.7 W h Kg−1 at the power density of 711.2 W kg−1, and super-long cycling stability (∼95.5% retention of capacity after 10,000 cycles), demonstrating that the hierarchical 3D CoS@MoS2 NWAs are promising as potential candidates for hig-performance SCs.

Nanocrystalline Cr-doped lithium ferrites have been synthesized at different pH values through sol–gel process. Dielectric properties of the synthesized samples were studied via impedance measurements in the frequency range of 100 Hz–7 MHz at room temperature. It was found that the dielectric properties strongly depended on the pH value, and the sample synthesized at pH 3.5 exhibited the highest dielectric constant, on the order of ∼107. In contrast, the sample synthesized at pH 11.5 exhibited the lowest dielectric constant. The occurrence of a peak in the dielectric loss spectra was found to be pH dependent, whereas the AC conductivity increased with frequency and was the highest in the sample synthesized at pH 3.5. The impedance spectroscopy and modulus formulism were also employed to investigate the charge transfer and relaxation dynamic properties. Consequently, dielectric properties of the samples were easily tuned by varying the pH during the synthesis process.

In this paper we report the synthesis of multiferroic BiFeO3 (BFO)–CoFe2O4 (CFO) nanocomposites. The XRD and SEM data confirm the formation of both the parent compounds and the composite. All the composite samples show typical frequency dispersion at low frequency. The composite samples possess low dielectric loss. The frequency dependence of ac electrical conductivity curves of the composite samples were fitted using the relation σ ( f ) = σ dc + A ( T ) f n ( T ) . It is observed that at lower frequency range the curve is not well fitted suggesting the contribution of small ac conductivity due to electrode polarization effect along with dc conductivity; however at higher frequency the curves are well fitted confirming the frequency dependence of ac conductivity at higher frequency. Frequency dependent of ac conductivity indicates that conduction occurs due to hopping of small polarons among the localized states. BFO shows weak ferromagnetism with coercivity, Hc = 374 Oe and magnetization, Ms = 0.06 emu/g at 21 kOe. All the composite samples show ferrimagnetic nature and found that there is a decrease in both saturation and remanence magnetization with increase in BFO content. However, there is a variation in coercivity with increase in BFO content and the sample 0.8(BFO)–0.2(CFO) (BF8–CF2) shows maximum Hc.

Lithium-based ferrites are promising and potential magnetic materials for microwave applications. They possess a spinel (AB 2 O 4 ) type crystal structure, where the distributions of metal cations over the tetrahedral (A) and octahedral (B) voids play a crucial role for exhibiting different physical properties. Among various parameter of synthesis, pH is an important factor that influences the cation distribution over A and B voids, overall growth of the nanoparticles and different physical properties. In the present work single phase Cr substituted lithium ferrite nanoparticles have been synthesized by the sol–gel method at different pH. The phase identification and crystallite size have been probed by X-ray diffraction studies. The crystallite size changes by 44.2–48.8 nm upon varying the pH from 3.5 to 11.5. In order to investigate the cations distribution at A/B sites, Mossbauer spectroscopic measurements were done. The values of magnetic hyperfine field obtained from the Mossbauer data for the A and B sites are ≈49.5 T and 51 T, respectively. Moreover, it is observed that the area ratio of B site to A site increases with increasing the pH. This observation further suggests that the B site is more preferable for Fe 3+ cations at higher pH than the A site. The magnetic parameter such as saturation magnetization ( M s ), remanent magnetization ( M r ), coercive field ( H C ) and squareness ( S ) are determined by vibrating sample magnetometer (VSM) measurements, which show a consistent increase with increasing pH. The reason for the variation in magnetic properties has been explained on the basis of increased Fe 3+ cation occupancies at the B site and size effect, which is well supported by Mossbauer spectroscopic and XRD studies.

NiCo 2 O 4 nanoparticles dispersed on reduced graphene oxide (RGO) are prepared by simultaneously reducing graphene oxide (GO), nickel and cobalt nitrate via a hydrothermal method assisted by post annealing at low temperature. The method involves formation of hydroxides on GO using ammonia under hydrothermal conditions. Subsequent thermal treatment at 300 °C led to the conversion of hydroxides into single-phase NiCo 2 O 4 atop the RGO. The synthesized products are characterized through several techniques including X-ray diffraction (XRD), ultraviolet–visible spectroscopy (UV–Vis), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (RS), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The FE-SEM investigations reveal the growth of a layer by layer assembly of NiCo 2 O 4 –RGO (2:1) nanocomposite, where the NiCo 2 O 4 nanoparticles are tightly packed between the layers of RGO. Further, the catalytic properties of the NiCo 2 O 4 –RGO nanocomposite are investigated for the oxygen evolution reaction (OER) through cyclic voltammetry (CV) measurements. It is observed that the special structural features of the NiCo 2 O 4 –RGO (2:1) nanocomposite, including layer by layer assembly, integrity and excellent dispersion of the NiCo 2 O 4 nanoparticles atop the RGO, produced a synergistic effect and therefore significantly improved the electrochemical performance. The oxidation potential (0.135 V) of NiCo 2 O 4 –RGO (2:1) nanocomposite was observed to be lower than that of bare NiCo 2 O 4 nanoparticles (0.33 V), whereas the corresponding current densities were measured to be 4.1 mA/cm 2 and 3.11 mA/cm 2 , respectively.

Manganese (Mn) substituted nanocrystalline Bismuth Ferrite (BiFe1−xMnxO3) thin films were deposited on quartz substrates by sol–gel process and the effect of the substitution on the structural and optical properties of BiFe1−xMnxO3 system was studied. With the increase in Mn content up to 30%, a distortion in crystal lattice constants and contraction in unit cell volume was observed without any formation of secondary phase. From the AFM photograph ran increase in grain size with the increase in Mn contents was observed. Optical transmittance spectra showed a decrease in transmittance (T%) with the increase in Mn content. Further, it was observed that the presence of Mn lead to the decrease in optical energy band gap of the samples. The effect of Mn substitution on the photoluminescent properties of BiFe1−xMnxO3 system was also studied in order to exploit their possible application in nanoscale optoelectronic devices.

Polyvinyl alcohol (PVA) films doped with different concentrations viz., 0.5, 1.0, and 2.0 wt.% of the carbon coated zinc oxide (C-ZnO) nanoparticles were prepared by solution casting method in order to investigate the effect of C-ZnO addition on the electrical, optical, structural and morphological properties of PVA matrix. The electrical properties such as dielectric constant (e′), dielectric loss (e″), dissipation factor (Tan δ), electrical modulus (M′, M″) and AC conductivity (σac) of the PVA/C-ZnO nanocomposites have been performed with reference to weight percentage of nanofiller (i.e., 0.5, 1.0, and 2.0 wt%) and frequency (20 Hz to 1 MHz). It is observed that the dielectric constant, dielectric loss, and electrical conductivity gradually decrease with filler concentration. Microstructural property of the nanocomposites is studied by using X-ray diffraction. XRD profiles demonstrated the semi crystalline nature of the composites. SEM photomicrographs of the PVA/C-ZnO nanocomposites reveal the uniform distribution of nanoparticles within the polymer matrix. Differential scanning calorimetry (DSC) thermograms of nanocomposites clearly indicates that the influence of nanofillers on their melting temperature (Tm) is insignificant.

Ionic and non-ionic surfactant functionalized, water dispersible graphene were prepared to investigate the effects on the dispersion stability and electrical conductivity of graphene. In this study, sodium dodecyl benzene sulfonate (SDBS), sodium dodecyl sulfate and 4-(1,1,3,3-tetramethylbutyl) phenyl-polyethylene glycol (Triton X-100) were used as ionic and non-ionic surfactants. The effects of surfactant concentrations on the dispersibility and electrical conductivity of the surface modified graphene were investigated. The dispersion stability of SDBS functionalized graphene (SDBS-G) was found to be best in water at 1.5 mg ml −1 . X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analysis indicate that the presence of surfactants does not prevent the reduction of graphene oxide (GO). These measurements also demonstrated that the surfactants were present on the surface of graphene, resulting in the formation of functionalized graphene. The thickness of different functionalized graphene was measured by Atomic force microscopy and varied significantly with different surfactants. The thermal properties of the functionalized graphene were also found to be dependent on the nature of the surfactants. The electrical conductivity of SDBS-G (108 S m −1 ) was comparatively higher than SDS and Triton X-100 functionalized graphene.

In the present study, the effect of plasma treatment on the bonding strength of CFRP/aluminum foam composites was investigated. CFRP and aluminum foam were surface-treated in a plasma cleaner using oxygen gas. To determine the optimal plasma treatment time, contact angles were measured as a function of treatment time. Treatment effects were determined by comparing the bending and shear strength of three cases: untreated CFRP/aluminum foam (case 1), untreated CFRP/plasma-treated aluminum foam (case 2), plasma-treated CFRP/untreated aluminum foam (case 3). Fracture surfaces of specimens from the three cases were investigated after bending and shear tests. Our results showed when the CFRP was plasma-treated using oxygen gas, and that the bending and shear strength was improved by 7.5% and 650%, respectively, compared to the case without plasma treatment. The improved bonding strength of the plasma-treated CFRP/aluminum foam composites was attributed to the increased surface roughness of the CFRP and the newly formed functionalities on the CFRP. The surface roughness of the CFRP was increased by more than 20% and two functional groups, namely, C O and O C O, were newly formed.

The structure, piezoelectric properties and ferroelectric properties of (Na0.5Bi0.5)1−xBaxTiO3 ceramics were investigated. A gradual change in crystalline structure and microstructure with the increase of BaTiO3 (BT) concentration was observed. It was ascertained that the rhombohedral–tetragonal morphotropic phase boundary (MPB) of the ceramics lies in the composition range of 0.04