Self-discharge of heterogeneous electrochemical supercapacitor of PbO2 vertical bar H2SO4 vertical bar C related to manganese and titanium ions

The paper contains the results of the research of the mechanism of shuttle self-discharge determined by the manganese and titanium ions in the electrolyte of a PbO2 vertical bar H2SO4 vertical bar C heterogeneous electrochemical supercapacitor (HES). Research was made with respect to the effect of the shuttle self-discharge determined by the manganese and titanium ions on the energy, capacity parameters, and the charge and discharge voltage of HESs. Using the methods of the research of the energy, capacity parameters, self-discharge of the capacitors, and optical spectra of their electrolytes, it was established that, in the process of the shuttle, self-discharge of the capacitors with the electrolytes containing manganese and titanium, mostly MnO4-, Mn2+ and Ti3+ and TiO2+ ions, respectively, is involved. It is shown that the shuttle self-discharge determined by the manganese ions brings about the self-discharge of an HES down to the minimal allowable voltage, and the titanium ions to the voltage of 1.62 V. It was established experimentally that the self-discharge current and the power of energy losses during the self-discharge related to the manganese ions in the electrolyte depend nonlinearly on the concentration of the manganese ions. When the concentrations of iron, titanium, and manganese are identical in the electrolyte of HES, the value of the capacitors' self-discharge decreases during the transition from the iron to the manganese. In the spectra of the optical density of HESs electrolyte containing manganese and titanium in the wave band of 200-1100 nm, absorption bands are discovered which are related to the ions of the manganese, titanium, and the level of the capacitors' state of charge. During the charge and discharge of an HES with the electrolyte which contains the titanium, Ti2+ ions whose concentration is substantially lower than the concentration of Ti3+ ions are also formed in the electrolyte. (C) 2008 The Electrochemical Society.