Self-discharge mechanisms in electrochemical capacitors

Electrochemical capacitors, or "supercapacitors", can store the energy produced by intermittent alternative energy sources (e.g. solar panels or windmills). They can also complement fuel cells and batteries for hybrid car applications, where the battery or fuel cell provides the energy required to drive long distances, and the capacitor delivers the high power needed for acceleration. Electrochemical capacitors are essentially maintenance free and have a much higher cycle life than batteries (they can be charged millions of times, rather than hundreds or thousands of times for batteries), making them ideal for remote applications. One poorly understood aspect of electrochemical capacitor behaviour is self-discharge, the spontaneous loss of voltage as the electrochemical capacitor sits for long periods of time. This is of practical importance as one would like to know that the electrochemical capacitor is ready for use, whether it has been unused for a day or a year. At this point, it is unclear why and how it loses this voltage, and this is under study in the Andreas laboratory. This program is based on fundamental, basic scientific research into the causes of electrochemical capacitor self-discharge and the factors which affect the rate of this discharge. Electrochemical methods (using electricity to study the properties of a system) will be used in this research. This research will include studies of: the state of the surface and bulk material of the electrochemical capacitor electrode and the redox active functional groups on the electrode surface; the effect of the highly porous nature of the electrode material; the effect of impurities (such as iron and oxygen) in the capacitor electrolyte; and the stability of the electrolyte. This will lead to very important fundamental knowledge about electrochemical capacitor self-discharge, and will then lead to the minimization or prevention of self-discharge in commercial systems. Given present economic (fuel prices) and societal (environmental movement) factors, the field of energy storage is expected to grow and this research will aid both academic and industrial researchers in the quest to reduce or eliminate self-discharge in electrochemical capacitors.