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.

Highlights • Thin Co-Mn LDH nanoflakes was synthesized by a facile solvothermal technique. • AC was synthesized by a two-step eco-friendly hydrothermal synthesis. • A device was fabricated using Co-Mn LDH as positive and AC as negative electrode. • The electrode materials exhibited good electrochemical performance.

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First principles density functional theory (DFT) calculations have been performed to explore the stability, structural and electronic properties of Be and S codoped graphene sheets. The band-gap of graphene has been tuned by co-doping with beryllium and sulphur at different sites. The results show that by codoping graphene with Be and S, the band-gap increases from zero up to 0.58 eV depending on the doping sites. The cohesive and the formation energies of the systems were also determined. All the isomers formed by exploring different doping sites differ notably in stability, bond length and band-gap. Nevertheless, the planar structure of all the systems investigated was preserved even after geometry optimisation. Majority of the isomers that correspond to co-doping at non-equivalent sites favour higher band-gap opening, but lesser stability, than the other set of isomers with equivalent doping sites. Bader charge analysis was adopted to account for charges distribution in the systems. As a result of the difference in electronegativity among carbon atoms and the impurities, it was observed that electrons accumulation occurred more on the carbon atoms in the proximity of Be and S than at any other position in the graphitic systems investigated.