The environmental degradation and hazard to human life caused by the depletion of fossils fuels and the urgent need for sustainable energy sources to meet the rising demand in energy has led to the exploration of novel materials that are environmentally friendly, low cost and less hazardous to human life for energy storage application using the green chemistry approach.Herein, we report on the transformation of the readily abundant pine cone biomass into porous carbon via KOH activation and carbonization at 800 °C as electrode materials supercapacitor.The porous carbon material exhibited a mesoporous framework with a specific surface area of

The construction and design of novel porous carbons for electric double-layer capacitors (EDLCs) application to meet the increasing demand and supply of energy is eminent. This is important because the pore volume (PV)/micropore volume (MV) in the porous network architecture of the carbon is mostly responsible for the ion traps in energy storage. Three dimensional carbon materials based on graphene materials with relatively high specific surface area (SSA) represents a promising material candidate for EDLCs applications. In this work, we synthesized highly porous carbon from graphene foam (GF) and polyvinyl alcohol PVA as a sacrificial template, and investigate their performance as electrodes for EDLCs applications. The as-produced carbons present a fairly large surface area (502 m 2 g -1 ), and a highly porous interconnected framework with mesopore walls and micropore texture which are suitable as electrode for energy storage. As electrode material in a symmetric configuration the activated graphene foam (AGF) showed a specific capacitance of 65 F g -1 , energy density of 12 Wh kg -1 , power density of 0.4 kW kg -1 , good rate performance and excellent long term stability in 1 M Na 2 SO 4 aqueous with no capacitance loss after 3000cycles.

Activated carbon from tree bark (ACB) has been synthesized by a facile and environmentally friendly activation and carbonization process at different temperatures (600, 700, and 800 °C) using potassium hydroxide (KOH) pellets as an activation agent with different mass loading. The physicochemical and microstructural characteristics of the as-obtained material revealed interconnected micro/mesoporous architecture with increasing trend in specific surface area (SSA) as carbonization temperatures rises. The SSA values of up to 1018 m 2 g -1 and a high pore volume of 0.67 cm 3 g -1 were obtained. The potential of the ACB material as suitable supercapacitor electrode was investigated in both a three and two electrode configuration in different neutral aqueous electrolytes. The electrodes exhibited EDLC behaviour in all electrolytes with the Na 2 SO 4 electrolyte working reversibly in both the negative (-0.80 V to -0.20 V) and positive (0.0 V to 0.6 V) operating potentials. A specific capacitance (C S ) of up to 191 F g -1 at a current density of 1 A g -1 was obtained for the optimized ACB electrode material in 1 M Na 2 SO 4 electrolyte. A symmetric device fabricated exhibited specific C S of 114 F g -1 at 0.3 A g -1 and excellent stability with a coulombic efficiency of a 100% after 5000 constant charge-discharge cycles at 5.0 A g -1 and a low capacitance loss for a floating time of 70 h.

In this work, we present the synthesis of low cost carbon nanosheets derived from expanded graphite dispersed in Polyvinylpyrrolidone, subsequently activated in KOH and finally .This electrical double layer capacitor electrode also exhibits excellent stability after floating test for 120 h in 6 M KOH aqueous electrolyte. These results suggest that this activated expanded graphite (AEG) material has great potential for high performance electrode in energy storage applications.

In this study, porous activated carbons (AC) were synthesized by an environmentally friendly technique involving chemical activation and carbonization, with an in-depth experimental study carried out to understand the electrochemical behaviour in different aqueous electrolytes (KOH, LiCl, and Na 2 SO 4 ). The electrochemical performance of the AC electrode was evaluated by different techniques such as cyclic voltammetry, galvanostatic charge/discharge and impedance spectroscopy. The results obtained demonstrate that the AC materials in different electrolytes exhibit unique double layer properties. In particular, the AC electrode tested in 6 M KOH showed the best electrochemical performance in terms of specific capacitance and efficiency. A specific capacitance of 129 F g À1 was obtained at 0.5 A g À1 with a corresponding solution resistance of 0.66 U in an operating voltage window of 0.8 V, with an efficiency of $100% at different current densities.

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VS 2 nanosheets as the positive electrode and the activated carbon (AC) as the negative electrode with a 6 M KOH solution as electrolyte were fabricated as an asymmetric supercapacitor. These materials were combined to maximize the specific capacitance and to enlarge the potential window, therefore improving the energy density of the device. A specific capacitance of 155 F g -1 at 1 A g -1 with a maximum energy density as high as 42 Wh kg -1 and a power density of 700 W kg -1 was obtained for the asymmetric supercapacitor within the voltage range of 0 -1.4 V. The supercapacitor also exhibited a good stability with ∼ 99% capacitance retention and no capacitance loss after 5000 cycles at a current density of 2 Ag -1 .

Highly c-axis oriented zinc oxide (ZnO) thin films with a wurtzite structure have been grown on glass substrates by metal organic chemical vapor deposition. The influence of growth parameters on the luminescent properties of the ZnO layers is investigated. It is shown that the growth temperature and VI/II ratio strongly influence the luminescent properties of ZnO thin films. For the films grown at low temperatures (250–325°C) a broad violet emission band at about 3.1eV has been observed. As the growth temperature increases, ultraviolet emission dominates the spectra and deep level emission is suppressed. It is suggested that the violet emission depends on grain size and hence the width of the free-carrier depletion region at the particle surface; the narrower the depletion width compared to the grain size, the higher the intensity. The result suggests that the mechanism responsible for the violet emission is recombination of delocalized electrons close to the conduction band with holes trapped in neutral zinc vacancy (VZn0) centers. For films grown under different VI/II ratios, the spectra are increasingly dominated by deep level emission as the VI/II ratio is increased. This broad emission is resolved into three bands at ∼2.0, ∼2.3, and ∼2.5eV. Based on the growth conditions, possible origins are proposed and discussed.