•3D flower-like NiCo2O4 electrode material has been fabricated via a modified solvothermal method combined with calcination.•Rarely used guanidine hydrochloride was applied to produce hydroxyl anions.•The as-prepared NiCo2O4 sample possesses hierarchical mesopores and large specific surface area.•The composite displays a high specific capacitance, i.e. 1609 F g−1 at current density of 1 A g−1.Novel 3D hierarchical mesoporous flower-like NiCo2O4 electrode material was prepared by water-ethanol mixed solvothermal method combining the calcination process. Nickel sulfate hexahydrate (NiSO4·6H2O), cobalt sulfate heptahydrate (CoSO4·7H2O), rare-used guanidine (CH6ClN3) were used as nickel and cobalt sources, precipitant of weak base, respectively. The resultant samples were characterized by X-ray diffraction, scanning electron microscopy, N2 adsorption and desorption and transmission electron microscopy. The prepared NiCo2O4 material exhibited excellent electrochemical performance-with a high specific capacitance of 1609 F g−1 at 1 A g−1, and high capacity retention of 85% after a 1000-cycle charge-discharge at 10 A g−1.

Novel 3D flower-like CoNi2S4/carbon nanotube composites with a porous structure were designed through a facile precursor transformation approach as electrode materials for supercapacitors. The resulting samples are characterized by X-ray diffraction, Raman spectra, energy dispersive spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption–desorption. Their electrochemical performance was investigated by means of cyclic voltammetry, galvanostatic charge–discharge, impedance spectra and cycle life. By selecting carbon nanotubes as the conductive support for the growth of CoNi2S4, the as-obtained CoNi2S4/carbon nanotube composites displayed an ultrahigh specific capacitance of 2094 F g−1 at 1 A g−1 and a good rate capability (72% capacity retention at 10 A g−1). These results above suggest the great potential of the unique flower-like CoNi2S4/carbon nanotube composites in the development of high-performance electrode materials for supercapacitors.

A novel hydrothermal emulsion method is proposed to synthesize mesoporous NiMoO4 nanosphere electrode material. The size of sphere-shaped NiMoO4 nanostructure is controlled by the mass ratio of water and oil phases. Nickel acetate tetrahydrate and ammonium heptamolybdate were used as nickel and molybdate precursors, respectively. The resultant mesoporous NiMoO4 nanospheres were characterized by X-ray diffraction, N2 adsorption and desorption, scanning electron microscopy, and transmission electron microscopy. The electrochemical performances were evaluated by cyclic voltammetry (CV), cyclic chronopotentiometry (CP), and electrochemical impedance spectroscopy (EIS) in 6 M KOH solution. The typical mesoporous NiMoO4 nanospheres exhibit the large specific surface area of 113 m2 g−1 and high specific capacitance of 1443 F g−1 at 1 A g−1, an outstanding cyclic stability with a capacitance retention of 90 % after 3000 cycles of charge-discharge at a current density of 10 A g−1, and a low resistance.

•Ribbon-like NiO was prepared by using mesoporous carbon as a hard template.•Typical ribbon-like NiO possesses the hierarchical mesoporous nanostructure.•High specific capacitance of 1260 F g−1 is obtained at a current density of 1 A g−1.•Excellent electrochemical stability of 95% after 5000 charge–discharge cycles.In this paper, nanostructured hierarchical mesoporous ribbon-like NiO was synthesized by a hard-template method combining the calcination process. Nickel sulfate hexahydrate, guanidine hydrochloride and mesoporous carbon were used as nickel precursors, precipitant of weak base and template, respectively. The resultant NiO samples were characterized by Raman spectroscopy, energy dispersive spectrometer, X-ray diffraction, N2 adsorption and desorption, scanning electron microscopy and transmission electron microscopy. The electrochemical performances were evaluated by cyclic voltammetry (CV), cyclic chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS) in 6 M KOH solution. The typical hierarchical mesoporous ribbon-like NiO shows a good electrochemical performance: a high specific capacitance of 1260 F g−1 at 1 A g−1, 748 F g−1 at high current density of 20 A g−1 and 95% capacity retention at a current density of 10 A g−1 in a testing range of 5000 cycles.The ribbon-like NiO was synthesized by a hard-template method combining the calcination, using mesoporous carbon as a hard templat and guanidine hydrochloride as precipitant of weak base, respectively. The nanostructured hierarchical mesoporous ribbon-like NiO exhibits the high specific capacitance of 1260 F g−1 at the current density of 1 A g−1, and 95% capacity retention at a current density of 10 A g−1 in a testing range of 5000 cycles.

A novel electrode material of three-dimensional (3D) hierarchical NiCo2S4@NiMoO4 core/shell nanospheres for high-performance supercapacitors was successfully synthesized by a two-step method. First, ball-like NiCo2S4 was obtained by controlling the morphology through a hydrothermal method using diethanol amine as a new precipitant; second, the interconnected uniform NiMoO4 nanosheets were allowed to efficiently grow on the NiCo2S4 backbone by the hydrothermal method to form NiCo2S4@NiMoO4 core/shell nanospheres. The resultant hierarchical NiCo2S4@NiMoO4 core/shell nanospheres were characterized by X-ray diffraction, energy dispersive spectrometry, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy and N2 adsorption and desorption. The electrochemical properties of the samples were evaluated though cyclic voltammetry, charge–discharge and electrochemical impedance spectroscopy in 6.0 M KOH electrolytic solution. The results showed that the hierarchical NiCo2S4@NiMoO4 core/shell nanospheres exhibited a very large specific capacitance of 1714 F g−1 at 1 A g−1, an outstanding cyclic stability with a capacitance retention of 96% after 5000 cycles of charge–discharge and a low resistance.

One-dimensional NiMoO4 · xH2O nanorods were synthesized by a facile template-free hydrothermal method as a potential electrode material for supercapacitors. The influences of reaction temperature, reaction time, and nickel source on the properties of resultant samples were investigated. Electrochemical data reveal that the as-synthesized one-dimensional NiMoO4 · xH2O nanorod superstructures can deliver a remarkable specific capacitance (SC) of 1131 F g−1 at a current density of 1 A g−1 and remain as high as 914 F g−1 at 10 A g−1 in a 6 M KOH aqueous solution. Moreover, there is only 6.2 % loss of the maximum SC after 1000 continuous charge–discharge cycles at the high current density of 10 A g−1. Such outstanding electrochemical performance may be owing to the unique one-dimensional hierarchical structures, which can facilitate the electrolyte ions and electrons to easily contact the NiMoO4 nanorod building blocks and then allow for sufficient faradaic reactions to take place, even at high current densities.

A novel electrode material of the three-dimensional (3D) multicomponent oxide NiCo2O4@NiMoO4 core–shell was synthesized via a facile two-step hydrothermal method using a post-annealing procedure. The uniform NiMoO4 nanosheets were grown on the seaurchin-like NiCo2O4 backbone to form a NiCo2O4@NiMoO4 core–shell material constructed by interconnected ultrathin nanosheets, so as to produce hierarchical mesopores with a large specific surface area of 100.3 m2 g−1. The porous feature and core–shell structure can facilitate the penetration of electrolytic ions and increases the number of electroactive sites. Hence, the NiCo2O4@NiMoO4 material exhibited a high specific capacitance of 2474 F g−1 and 2080 F g−1 at current densities of 1 A g−1 and 20 A g−1 respectively, suggesting that it has not only a very large specific capacitance, but also a good rate performance. In addition, the capacitance loss was only 5.0% after 1000 cycles of charge and discharge tests at the current density of 10 A g−1, indicating high stability. The excellent electrochemical performance is mainly attributed to its 3D core–shell and hierarchical mesoporous structures which can provide unobstructed pathways for the fast diffusion and transportation of ions and electrons, a large number of active sites and good strain accommodation.

LiFePO4/C cathode materials were prepared from different lithium and iron sources, using glucose as the carbon source and the reducing agent, via a solid state reaction. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), galvanostatic charge–discharge test and cyclic voltammetry (CV). The results showed that the LiFePO4/C is olivine-type phase, and composed of relatively large particles of about 400 nm and some nano-sized particles, which favor the electronic conductivity. The LiFePO4/C cathode material synthesized from Li2CO3 and Fe2O3 had the smallest particles and the highest uniformity. It delivered the capacity of 145.8 mA h/g at 0.2 C, and had good reversibility and high capacity retention. The precursor of LiFePO4/C was characterized by thermogravimetry (TG) to discuss the crystallization formation mechanism of LiFePO4.Highlights► Two lithium resources and two iron resources are used for preparation of LiFePO4/C. ► LiFePO4/C using Li2CO3 and Fe2O3 have the smallest particles and highest uniformity. ► Reactants play a key role on electrochemical performance. ► Correlations between crystallinity and performance are explored.

Mesoporous electrode materials of spinel Co3O4 were synthesized by hydrothermal method using polyethylene glycol-6000 (PEG-6000) as dispersant and subsequent calcination at different temperatures in air. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), nitrogen adsorption and electrochemical measurements. The results showed that the dispersant PEG-6000 had a distinct effect to control the porosity, particle size and homogeneity of Co3O4; the calcination temperature had a significant influence on the crystal structure, surface area, porosity and morphology, and indeed electrochemical performance. The resultant Co3O4 sample calcinated at 350° C possessed a narrow mesopore distribution around 4 nm and exhibited excellent electrochemical performance. It had the specific capacitance as high as 348.7 F/g, increased by 21.5% over that of pure Co3O4 and showed good cyclical charge–discharge stability.

Olivine LiFePO4, as a cathode material for lithium ion batteries, was prepared by a novel optimized hydrothermal method; afterwards, the product mixed with glucose was two-step (350°C and 700°C) calcinated under high-purity N2 atmosphere to obtain the LiFePO4/C composite. The study on the hydrothermal preparation method, which focused on the influences of molar ratios, initial pH value, reaction temperature, and duration, was made to promote the resultant performances and to investigate the relations between the performances and the reaction conditions. The resultant samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical tests, which include charge-discharge, electrochemical impedance spectroscopy, and cyclic voltammetry. The result shows that the optimal hydrothermal condition is to set the Li:Fe:P molar ratio at 3:1:1 and the reaction temperature at 180°C for 5 h duration with an initial pH value of 7. The optimized sample, with an average particle size of 100 to 300 nm and a discharge capacity of 118.2 mAh·g−1 at 0.1C, exhibits a stable and narrow-gapped charge-discharge platform and small capacity losses after cycles.

The olivine-type LiFePO4/C cathode materials were prepared via carbothermal reduction method using cheap Fe2O3 as raw material and different contents of glucose as the reducing agent and carbon source. Their structural and morphological properties were investigated by X-ray diffraction, scanning electron microscope, transmission electron microscope, and particle size distribution analysis. The results demonstrated that when the content of the carbon precursor of glucose was 16 wt.%, the synthesized powder had good crystalline and exhibited homogeneous and narrow particle size distribution. Even and thin coating carbon film was formed on the surface of LiFePO4 particles during the pyrolysis of glucose, resulting in the enhancement of the electronic conductivity. Electrochemical tests showed that the discharge capacity first increased and then decreased with the increase of glucose content. The optimal sample synthesized using 16 wt.% glucose as carbon source exhibited the highest discharge capacity of 142 mAh g−1 at 0.1C rate with the capacity retention rate of 90.4% and 118 mAh g−1 at 0.5C rate.

A polymeric activated carbon (PAC) was synthesized from the carbonization of a resorcinol–formaldehyde resin with KOH served as an activation agent. The nitrogen adsorption–desorption at 77 K, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the prepared PAC. Compared with the commercial activated carbon (Maxsorb: Kansai, Japan), PAC shows superior capacitive performance in terms of specific capacitance, power output and high energy density as electrode materials for supercapacitors. PAC presents a high specific capacitance of 500 F g−1 in 6 mol l−1 KOH electrolyte at a current density of 233 mA g−1 which remained 302 F g−1 even at a high current density of 4.6 A g−1. The good electrochemical performance of the PAC was ascribed to well-developed micropores smaller than 1.5 nm, the presence of electrochemically oxygen functional groups and low equivalent series resistance.

A simple process was proposed based on a combination of chemical and physical activation for the production of activated carbon. The process was expected to improve the mesoporosity in activated carbons. The KOH- or ZnCl2-chemical activation coupled with CO2-physical activation of lignocellulosic materials, such as coconut shells and palm stones, were used as a simultaneously chem-physical activation for increasing the mesoporosity. The porosity of the resultant activated carbons was characterized by nitrogen adsorption isotherms at 77 K. Both chemicals and CO2 had effects on the formation of mesopores. Intensified activation conditions, such as high chemical ratio to the precursors, long soaking time, elevated temperature, increased the mesoporosity in activated carbons. The surface area and the nature of the porosity can be controlled by means of the experimental parameters. By changing the ratio of activating agent to carbon precursor, it is possible to control the pore size from supermicropore (1.5–2.0 nm) to mesopore (2–3.49 nm). The BET-surface area of the carbons can be over 2100 m2/g; the mesopore content (ratio of mesopore volume to total pore volume) is 71%. Furthermore, the activated carbon from palm stones possesses mesopore content as high as 94%.

An improved ZnCl2-chemical activation method is proposed to produce highly porous activated carbons. The novel process can produce either microporous carbons or mesoporous carbons from lignocellulosic materials, such as coconut shells and palm seeds. The porosity of the resultant activated carbons was characterized by nitrogen adsorption isotherms at 77 K. The BET-surface area of the carbons can be over 2400 m2/g; the mesopore content (ratio of mesopore volume to total pore volume) is 71%. Furthermore, the activated carbon from palm seeds possesses mesopore content as high as 94%. Thermogravimetric analysis (TGA) was used to monitor the course of pyrolysis of coconut shell and ZnCl2-impregnated coconut shell. The adsorptive properties for phenol and dyes were tested.

A novel electrode material of the three-dimensional (3D) multicomponent oxide NiCo2O4@NiMoO4 core–shell was synthesized via a facile two-step hydrothermal method using a post-annealing procedure. The uniform NiMoO4 nanosheets were grown on the seaurchin-like NiCo2O4 backbone to form a NiCo2O4@NiMoO4 core–shell material constructed by interconnected ultrathin nanosheets, so as to produce hierarchical mesopores with a large specific surface area of 100.3 m2 g−1. The porous feature and core–shell structure can facilitate the penetration of electrolytic ions and increases the number of electroactive sites. Hence, the NiCo2O4@NiMoO4 material exhibited a high specific capacitance of 2474 F g−1 and 2080 F g−1 at current densities of 1 A g−1 and 20 A g−1 respectively, suggesting that it has not only a very large specific capacitance, but also a good rate performance. In addition, the capacitance loss was only 5.0% after 1000 cycles of charge and discharge tests at the current density of 10 A g−1, indicating high stability. The excellent electrochemical performance is mainly attributed to its 3D core–shell and hierarchical mesoporous structures which can provide unobstructed pathways for the fast diffusion and transportation of ions and electrons, a large number of active sites and good strain accommodation.