Fourier transform infrared spectroelectrochemistry has been used to study the vibrational spectrum of a thin layer of the organic electrolyte in contact with a divided carbon supercapacitor electrode. Variations in the absorption of peaks characteristic of the solvent and of the support electrolyte during an anodic potential scan have been observed. The presence of adsorbed water was detected. The formation of a stable adduct of CH 3 CN and BF 3 under anodic potential was identified.Electrical energy produced by renewable sources such as wind power or photovoltaic devices is fluctuant by nature. In order to use it reliably, it is necessary to have a means of storing electricity. These storage devices are also of prime importance in systems where surges of power are frequent; e.g. applications such as transportation and regenerative braking.Storage of electrical energy can be accomplished in an elegant way through the use of lightweight capacitors. Recently, devices based on the use of the electrochemical double-layer capacitor ͑EDLC͒ have been developed: the supercapacitors. 1 Supercapacitors are intermediate systems between electrochemical batteries, which can store high energy associated with medium power values, and dielectric capacitors, which can deliver very high power during times of the order of a few milliseconds. Supercapacitors are used for energy storage over time periods ranging from seconds to minutes; their peak power is up to 10-20 times higher than that of batteries, but their energy density is 20-50 times lower.Their principle relies on the use of high specific area electrodes placed in an electrolyte and separated by a thin inert microporous membrane. This work focuses on organic electrolyte capacitors with electrodes manufactured using carbon dispersed in an aqueous solvent. To be useful, these devices must be able to remain charged in open-circuit conditions for great lengths of time. This implies that no irreversible reactions induced by the variation of the potential of each electrode should occur; thus, it is important to understand the mechanisms occurring during charge and spontaneous discharges.During the charge of the EDLC, several phenomena can occur. 2 An increase in the number of ions forming the double layer can be caused by the application of a voltage. A local increase in ionic concentration near the carbon surface, but not directly connected with the double layer, can also be produced if a current flows through the capacitor at or above the electrolyte potential range.Self-discharge processes are complex and involve mechanisms occurring on a short or a long time scale. When the supercapacitor is fully charged, its removal from the power supply induces a fast relaxation phenomenon. This process is reversible at short times. An irreversible process corresponding to faradaic reactions can also be observed on the same time scale. Another reason for self-discharge are the faradaic reactions of various groups at the surface of the carbon during ca. the first 500 h of use of the device...