Long-term cycling of carbon-based supercapacitors in aqueous media

The behaviour of mesophase-derived electrodes on long-duration cycling conditions was studied in 1 M sulfuric acid and 6 M potassium hydroxide. Variation in the specific capacitance values with the number of cycles shows a good cycling life performance in acidic media but very poor in an alkaline electrolyte. The total loss of capacitance after 7000 cycles in acidic media is 8% at 0.6 V and 16% at 1 V, whereas in the basic electrolyte the reduction in the capacitance values is 72%, even at a very small operating voltage (0.6 V). This behaviour was associated to the strong oxidation of the positive electrode caused by the progressive shift of the working potential towards very positive potential values during cycling.