The paper reports on electrochemical characterization of several supercapacitors operating in aqueous electrolytes and discusses a strategy for enhancing their performance. Various electrolytes such as alkaline (6 mol L-1 KOH), acidic (1 mol L-1 H2SO4) and neutral (1 mol L-1 KI and 1 mol L-1 Na2S2O3) were investigated in terms of electrochemical stability and redox activity. A new concept of capacitor with two electrodes operating in different electrolytes is demonstrated. The positive electrode worked in KI solution whereas KOH solution served as an electrolytic medium for the negative electrode. As a result, improved capacitance values and energy density for a capacitor with a combined electrolyte have been obtained because of the beneficial redox phenomena on both electrodes. (C) The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. All rights reserved.