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Eco-friendly, nontoxic and high-energy storage materials are very important for flexible electrode materials. Bi₄Ti₃${\text{O}}_{12}$ lead-free, perovskite phase may prove suitable as filler in composites for electrode materials because of its large spontaneous polarization. We have synthesized Bi₄Ti₃${\text{O}}_{12}$/polystyrene (BTO/PS) composites and carried out their structural, morphological and bonding studies with the help of X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR), in that order. Dielectric measurements in the broad frequency range of synthesized composites determined by Impedance analyzer. We observed that the dielectric constant of composites increased with filler concentration and decreased with applied field frequency. Bi₄Ti₃${\text{O}}_{12}$/PS composites can be good electrode materials.

The resistive switching effect in TiO_2-x memory devices is thoroughly investigated in order to obtain optimum memory performance, in terms of switching ratio, uniformity of the switching characteristics and multilevel capability. As a result, various fabrication procedures were followed with the aim to enhance the above properties. The main body of our devices was TiO_2-x thin film, with constant thickness of 45 nm, while different approaches were implemented during the fabrication process, such as increasing the oxygen content during film growth, depositing top electrodes with different thicknesses, inserting a layer of nanocrystals (NCs) within the middle of the dielectric and using two various oxygen contents during film deposition in order to create a homobilayer structure. The common feature of these techniques is to control the regions where oxygen vacancy creation will take place in order to control the formation/rupture of the conducting filaments (CFs). Conductive-Atomic Force Microscopy (C-AFM) results support the localized nature of the switching effect. The gradual transition during the SET process, which allows precise CF control through proper external stimulus, as well as the self-rectification effect, which alleviates the sneakpath issue in crossbar architecture, are also important assets of our experimental approach.

In this research, manganese cobaltite (MCO) nanoparticles with different morphologies were synthesized by a simple hydrothermal method with excellent electrochemical properties. To investigate the physical features of prepared samples, XRD analysis was used to study the crystalline structure. The SEM and TEM proved that the morphology of synthesized materials formed as flake and nanoplane structures. The electrode of samples was prepared using the hydrothermal method and the electrochemical properties of samples were investigated by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), electrochemical impedance spectroscopy (EIS) and cyclic stability analysis. Results showed that the flake structures of nanoparticles revealed the highest capacitance of 1971.98$\mathrm{\text{F}}\cdot {\mathrm{\text{g}}}^{-1}$ at 0.5Ag${}^{-1}$ as well as longer stability compared to the others with the nanoplane structure. The high cyclic stability of 91.47% after 5000 cycles introduces this electrode as a durable and promising electrode for use in energy storage devices.

The ZnCo₂O₄ nanorods and nanosheets were grown on nickel foam by a facile and effective hydrothermal method, respectively. The effect of the morphologies of the nanostructures on electrochemical performance was investigated. Importantly, ZnCo₂O₄ nanorod electrodes with a high specific surface area exhibited a higher specific capacitance of 2457.4 F g${}^{-1}$ at 2 A g${}^{-1}$ and remarkable cycling stability with capacitance retention of 97.7% after 1000 cycles, which are superior to those of ZnCo₂O₄ nanosheet electrodes. Such a result is well explained. The investigation on the electrochemical properties of these two nanostructures as electrodes confirmed that the morphology of active materials has an important impact on electrochemical properties.

Micro-porous activated carbons (ACs) with a narrow pore size distribution of 0.4–0.6nm and high specific surface areas (1160–1315m²$\cdot$ g${}^{-1})$ are prepared from environment-friendly, low-grade potassium humate (HA-K, carbon resource) and mild activating agent potassium acetate (CH₃COOK). Microstructure characterizations indicate that the introduction of activating agent CH₃COOK is a key step to achieve high specific surface area and carbonization degree. These ACs contain small amount of oxygen and nitrogen, and show obvious pseudo-capacitance besides double layer capacitance. As a result, the optimized ACs achieve high specific capacitances of 311F$\cdot$g${}^{-1}$ and 317F$\cdot$g${}^{-1}$ at 0.1A$\cdot$g${}^{-1}$ in 2M KOH and 1M H₂SO₄ aqueous electrolytes, respectively. This sample also shows a good charge-discharge cycling stability within 10 000 cycles.

Cobalt–nickel oxide electrode materials with three-dimensional hexagon films or flower-shaped structures have been synthesized by a chemical precipitation method at different thermal decomposition temperatures. Nickel ions enter into the lattice of Co₃O₄ by forming solid solution and promote primary nanoparticles partly self-assemble into three-dimensional hexagon films which interlace with each other to form a flower-like structure. Consequently, cobalt–nickel oxide with a Ni/Co mole ratio of 1:6 at 220${}^{\circ }$C displays a highest capacitance of 796.16F/g at 200mA/g and cobalt–nickel oxide with a Ni/Co mole ratio of 1:3 at 200${}^{\circ }$C exhibits a highest capacitance of 290F/g at 10A/g, which significantly improve the electrochemical properties of Co₃O₄.

Hierarchically porous carbons are obtained by a facile process of carbonizing the precursor of diblock copolymer xPS-$b$-polymethylmethacrylate (PMMA). In the diblock copolymer, there is a carbon source of cross-linked polystyrene (xPS) and a sacrificial block of PMMA. The atom transfer radical polymerization was used to synthesize the diblock copolymer with controlled molecular weight and narrow polydispersity in dimethylformamide at 120^∘C. The obtained hierarchically porous carbons (HPCs) exhibit remarkable electrochemical properties, such as higher specific capacitance of 204Fg${}^{-1}$ at the current density of 0.5Ag${}^{-1}$ in 6molL${}^{-1}$ aqueous KOH electrolyte. In addition, it also presents an excellent rate performance of 64% capacitance retention as the current density increases to 10Ag${}^{-1}$ and a superior cycling stability of 98% capacitance retention after 5000 cycles at the current density of 1Ag${}^{-1}$.

The hausmannite phase manganese oxide nanoparticles (NPs) were prepared by a simple chemical reflux method. Powder X-ray diffraction shows the well-crystalline structure of Mn₃O₄ spinel. Fourier-transform infrared spectroscopy study exhibited the Mn–O functional group vibrations in the hausmannite NPs. UV–visible spectroscopy study reveals that the optical bandgap energy of the manganese oxide nanoparticles is about 3.1eV. The scanning electron microscopy (SEM) analysis shows that the surface morphologies of the manganese oxide nanoparticles are wrinkle structures. Cyclic voltammetry studies were carried out to the electrode of Mn₃O₄ NPs in KOH and Na₂SO₄. The charge–discharge analysis and impedance spectroscopy method analysis were made on Mn₃O₄ NPs to understand the electrochemical performance. The ability of synthesized Mn₃O₄ NPs electrodes was analyzed and compared with the existing materials for the supercapacitor applications.

CaMoO₄ nanoparticles/graphene oxide (CaMoO₄/GO) composites are prepared by a facile hydrothermal method. CaMoO₄ nanoparticles are adsorbed on the GO sheets by in situ reduction. Along with the synergistic effect between the CaMoO₄ and GO sheets, the CaMoO₄/GO nanocomposites exhibited high performances as electrodes for supercapacitors. The specific capacity ($Q_s)$ of the CaMoO₄/GO electrodes could be up to 571.82F$\cdot$g${}^{-1}$ at 0.5A$\cdot$g${}^{-1}$. Furthermore, asymmetric supercapacitors (ASCs) are mainly composed of CaMoO₄/GO composite and activated carbon (AC), respectively. The fabricated CaMoO₄/GO//AC devices display an energy density of 25.18W$\cdot$h$\cdot$kg${}^{-1}$ at 1710.3W$\cdot$kg${}^{-1}$. A blue LED is powered using two series-connected two ASC devices. These results indicate the considerable potential of CaMoO₄/GO for use in high-performance energy storage devices.

Mild chemical bath route at 60–80°C led to the redox reaction between MnSO₄ and KMnO₄ to form MnO₂. The as-synthesized MnO₂ was a mixture of both α- and δ-phases, which has enhanced electrochemical capacitance performances. Pure α-, δ- and γ-MnO₂ were also chemically prepared in the current solution system. The electrochemical performances of the as-prepared MnO₂ samples were evaluated as an electrode for supercapacitor by recording cyclic voltammograms and galvanostatic charge-discharge curves. The crystallographic structure of MnO₂ was found to be determined by the chemical bath reaction temperature and time. In the current work, we purposefully designed the optimum reaction parameters to synthesize high performance mixed-phase MnO₂ through mild chemical bath route, ultimately for enhancing the capacitance of powder-based electrodes.

The paper reports a kind of NiCo₂O₄ material with urchin-like morphology. This material was prepared using a facile strategy of hydrothermal process followed by calcinations, and exhibits an excellent electrochemical performance. For example, it delivers a specific capacitance high up to 1167Fg${}^{-1}$ at 1Ag${}^{-1}$ and still retains a value of 1095Fg${}^{-1}$ at 10Ag${}^{-1}$, showing a good rate capability; after suffering from 3000 cycles at 10Ag${}^{-1}$, the specific capacitance has only a decay of 12%, presenting a good cycling stability.

A porous organic framework as electrode material for supercapacitor was prepared successfully. It exhibited the remarkable specific capacitance of $170.66\mathrm{\text{F}}\cdot {\mathrm{\text{g}}}^{-1}$ at current density of $1.0\mathrm{\text{A}}\cdot {\mathrm{\text{g}}}^{-1}$, and 100% of capacitance retention after successive charge–discharge 10,000 cycles in an alkaline aqueous electrolyte solution. At the same time, we explored the electrochemical performance of porous N-doped carbon derived from the template of porous organic framework as supercapacitor electrode material. Impressively, it possessed the higher specific capacitance and better cycling stability, which showed specific capacitance of $180.88\mathrm{\text{F}}\cdot {\mathrm{\text{g}}}^{-1}$ at the current density of $0.4\mathrm{\text{A}}\cdot {\mathrm{\text{g}}}^{-1}$ and retained 100% of initial capacitance after 30,000 cycles.

The resistive switching effect in TiO_2-x memory devices is thoroughly investigated in order to obtain optimum memory performance, in terms of switching ratio, uniformity of the switching characteristics and multilevel capability. As a result, various fabrication procedures were followed with the aim to enhance the above properties. The main body of our devices was TiO_2-x thin film, with constant thickness of 45 nm, while different approaches were implemented during the fabrication process, such as increasing the oxygen content during film growth, depositing top electrodes with different thicknesses, inserting a layer of nanocrystals (NCs) within the middle of the dielectric and using two various oxygen contents during film deposition in order to create a homobilayer structure. The common feature of these techniques is to control the regions where oxygen vacancy creation will take place in order to control the formation/rupture of the conducting filaments (CFs). Conductive-Atomic Force Microscopy (C-AFM) results support the localized nature of the switching effect. The gradual transition during the SET process, which allows precise CF control through proper external stimulus, as well as the self-rectification effect, which alleviates the sneakpath issue in crossbar architecture, are also important assets of our experimental approach.