Biogas-slurry derived mesoporous carbon for supercapacitor applications

This research article published by Elsevier Ltd., 2017This study reports on the transformation of biogas slurry into mesoporous carbon for supercapacitor electrodes. Pore structures have been modified by altering activation time, temperature and KOH/carbon mass ratio. The mesoporous carbons are successively developed as evidenced by type IV isotherms obtained in nitrogen sorption studies. BET, micropore and mesopore surface area of 515, 350, and 165 m2 g−1, respectively as well as a narrow pore width distribution of 3–4.5 nm are obtained. X-ray photoelectron results have confirmed the presence of functional groups of oxygen and nitrogen in the samples which facilitates the pseudocapacitance. The electrochemical measurements in 6 M KOH using a three electrode cell with Ag/AgCl as reference electrode and platinum as counter electrode has been performed. The materials activated at 700 °C, 3:1 KOH to carbon mass ratio, and for 120 min exhibit high specific capacitance of 289 F g−1 at a scan rate of 5 mV s−1. Shortening activation time to 30 and 60 min reduces specific capacitance to 163 and 182 F g−1, in that order. Additionally, at 3:1 KOH to carbon mass ratio and 60 min activation time, specific capacitances of 170 and 210 F g−1 at 600 and 800 °C, respectively are obtained. Moreover, specific capacitance increases with increasing the KOH to carbon mass ratio from 148 F g−1 for 1:1–163 F g−1 for 3:1 at 700 °C. Electrochemical impedance spectroscopy studies demonstrate that material has high conductivity. In addition; capacity retention of 96% after 20,000 cycles is shown at scan rate of 30 mV s−1. The study shows that high performance electrodes can be designed from biogas slurry derived porous carbon

Supersalts Na2AlX5 (X = F, Cl): Quantum Chemical Study of the Structure, Vibration Spectra and Thermodynamic Properties

This research article published by the Current Journal of Applied Science and Technology, 2017Theoretical investigation, prediction and design of novel supersalts Na2AlX5 (X = F, Cl) have been performed. The formation of the supersalts was considered through association reactions between different building blocks: Superalkalies and superhalogens, ionic (Na2X+ and AlX4−), as well as dimers Na2X2 and traditional salts AlX3. The optimization of geometrical structures, and determination of vibrational spectra of supersalts and their respective building blocks was carried out by the DFT/B3P86 and MP2 methods; The McLean-Chandler basis set and the extended basis set (cc-pVTZ for Na, Al; aug-cc-pVTZ for F, Cl) were used. Different possible geometrical configurations for the supersalts Na2AlX5 were considered. Consequently, two structures were proved to be isomers: A structure with two cycles in perpendicular planes with a tail (C2v symmetry) and a compact structure with a tail (Cs symmetry). Evaluation of their relative concentrations in equilibrium vapour was done, and the energies and enthalpies of the association reactions were determined. The enthalpies of formation ∆fH°(0) of gas-phase supersalts are: -2250±45 kJ×mol-1 (Na2AlF5) and -1380 ±20 kJ×mol-1 (Na2AlCl5)