ABSTRACT The energy density of carbon based supercapacitors (CBSCs) was significantly increased by the addition of an inorganic redox species [Ce2(SO4)3] to an aqueous electrolyte (H2SO4). The development of the faradaic processes on the positive electrode not only significantly increased the capacitance but also the operational cell voltage of these devices (up to 1.5V) due to the high redox potentials at which the Ce3+/Ce4+ reactions occur. Therefore, in asymmetric CBSCs assembled using an activated carbon as negative electrode and MWCNTs as the positive one, the addition of Ce2(SO4)3 moderately increases the energy density of the device (from 1.24Whkg−1 to 5.08Whkg−1). When a modified graphite felt is used as positive electrode the energy density of the cell reaches values as high as 13.84Whkg−1. The resultant systems become asymmetric hybrid devices where energy is stored due to the electrical double layer formation in the negative electrode and the development of the faradaic process in the positive electrode, which acts as a battery-type electrode.