The prevailing low-cost electrochemical capacitor technology consists of carbon electrodes in an organic electrolyte. To increase the energy storage of this system, it is proposed to functionalize the carbon surface with a group which undergoes reversible electron transfers in organic electrolytes. The procedure for attaching this group to carbon has already been demonstrated, and the electrochemistry of the group itself is known. Its associated faradaic processes should provide a two-electron pseudocapacitance, and based on our past experience with another pseudocapacitive system, this is expected to increase the carbon's energy storage by 80 to 400%. The greatest enhancements are anticipated when certain varieties of nanofiber carbon are functionalized. The proposed surface-modification procedure involves no special equipment; it is straightforward and practical. The Phase I work includes the preparation and testing of carbon materials enhanced with this pseudocapacitive scheme.
Benefits: The proposed pseudocapacitance may well double the capacitance of the original carbon, and it would be applicable to almost all varieties of carbon. The greatest potential benefits will come from enhancing tailored carbon nanofibers which exhibit high frequency capacitance. We have evidence that pseudocapacitance can add energy even at high frequencies in some nanofibers (at >1000 Hz in aqueous systems), so that a relatively high-frequency pseudocapacitance may also be realized in organic electrolytes when nanofiber substrates are used. The result would be enhanced power as well as energy from surface functionalization
