Abstract: Capacitors employing liquid or gel electrolytes have their useful lifetime significantly extended by including, in the electrolyte, a binary mixture of transition metal ion species. Each species has at least two distinct oxidation states when dissolved in the electrolyte. The interaction of the mixture of ion species reduces the potential of the cathode and maintains the potential of the cathode below the hydrogen potential to prevent the reduction of hydrogen ions and the formation of hydrogen. The binary mixture of transition metal species reduces the cathode potential by oxidation of the transition metal species at the anode and reduction of the transition metal species at the cathode. Thus, the rate of decrease in capacitance, increase in equivalent series resistance, and swelling of the capacitor are suppressed. In addition, the ratio of capacitor aging to the quantity of charge passed by the capacitor is decreased by at least a factor of two as compared to previous known extended life capacitors.