Demand of electrical energy storages is increasing quickly with market expansion of cell phones, electrical vehicles, and stationary energy storage. Supercapacitor is an alternative choice of rechargeable batteries because of their low cost for fabrication and maintenance, high cycle life, high charge rate, and high specific power. Using mediators to enhance the performance of the carbon materials based supercapacitors is more effective than using conductive polymer or metal oxide materials. In this study, we improved the performance using metal complex mediators. Several different mediators were synthesized and compared in this work. The active electrode material consisted of 10% mediator, 90% high specific surface area active carbon (AC). An EDLC made by AC only was also fabricated as a reference. To qualify the industrial requirements, current collector, electrolyte and separator are all commercial. The prototypes were fabricated in the glove box and sealed under vacuum. The calculation of specific energy (SE) was based on total mass of both electrodes and cyclic voltammetry (CV) curves and glvanostatic charge/discharge curves (GCDs). Typical CVs were shown in Figure 1. The mediator supercapacitor exhibited high energy densities (˃40 Wh kg^-1), high charge/discharge efficiency (˃99%) and high reversibility (˃90% after 10000 cycles). The effect of the rare earth and transition metals on the effectiveness of the mediators is investigated. As shown in Table 1, for mediators containing rare earth metals, Pr, La, Y are more effective than Ho. For mediators containing transition metals, Mn, Fe, and Co are more effective than Zn. The authors explain the phenomenon with the notions of molecular configurations, electronic structures, and interactions between charged mediators.