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In recent years, extensive investigations have focused on the study and improvement of supercapacitor electrode materials. The electric devices produced with these materials are used to store energy over time periods ranging from seconds to several days. The main factor that determines the energy storage period of a supercapacitor is its self-discharge rate, i.e., the gradual decrease in electric potential that occurs when the supercapacitor terminals are not connected to either a charging circuit or electric load. Self-discharge is attenuated at lower temperatures, resulting in an increased energy storage period. This paper addresses the temperature-dependence of self-discharge via a systematic study of supercapacitors with nominal capacitances of 1.0 and 10.0 F at DC potentials of 5.5 and 2.7 V, respectively. The specific capacitances, internal resistances, and self-discharge characteristics of commercial activated carbon electrode supercapacitors were investigated. Using cyclic voltammetry, the specific capacitances were determined to be 44.4 and 66.7 Fg−1 for distinct carbon electrode supercapacitors. The self-discharge characteristics were investigated at both room temperature and close to the freezing point. The internal resistances of the supercapacitors were calculated using the discharge curves at room temperature. The microstructures of the electrode materials were determined using scanning electron microscopy.

Graphene has attracted significant interest because of its excellent electrical properties. However, a practical method for producing graphene on a large scale is yet to be developed. Graphene oxide (GO) can be partially reduced to graphene-like sheets by removing the oxygen-containing groups and recovering the conjugated structure. GO can be produced using inexpensive graphite as the raw material via cost-effective chemical methods. High vacuum and temperature (10−7 mbar and 1100°C, respectively) conditions are well-known to enable the preparation of reduced powder at the laboratory scale. However, a large-scale high vacuum reduction system that can be routinely operated at 10−7 mbar requires considerable initial capital as well as substantial operational and maintenance costs. The current study aims at developing an inexpensive method for the large-scale reduction of graphene oxide. A stainless steel vessel was evacuated to backing-pump pressure (10−2 mbar) and used to process GO at a range of temperatures. The reduction of GO powder at low vacuum pressures was attempted and investigated by X-ray diffraction and Fourier transform infrared spectroscopy. The experimental results of processing GO powder at various temperatures (200–1000°C) at relatively low pressures are reported. The microstructures of the processed materials were investigated using scanning electron microscopy and chemical microanalyses via energy dispersive X-ray analysis.

This paper presents the results obtained from the hydrogenation and decrepitation of three LaNi-based alloys, La0.7Mg0.3Al0.3Mn0.4Co0.5Ni3.8, La0.7Mg0.3Al0.3Mn0.4Cu0.5Ni3.8and La0.7Mg0.3Al0.3Mn0.4Sn0.5Ni3.8, in the as-cast condition. The procedure for decrepitating the alloys to be used in the negative electrode of the batteries was carried out using a combination of various hydrogen pressures (2-9 bar) at room temperature. At 2 bar of H2it was revealed that Co, Cu and Sn have influence on the microstructures of the hydrogenated alloys and on the efficiency of hydrogen decrepitation. None of these alloys required thermal heating to activate and start the hydrogen absorption process. The decrepitated materials were characterized by scanning electron microscopy (SEM). The electrochemical measurements were performed using the tested negative electrode between two Ni (OH)2electrodes as a battery cell.