The electrochemical performance of a carbon-based hybrid energy storage system, with Ce-2(SO4)(3)/H2SO4 as inorganic redox electrolyte, was enhanced by optimizing several parameters of the device. A mass balance of the two electrodes forming the system together with the selection of a suitable activated carbon as negative electrode allowed the cell voltage to be increased up to 1.9 V. In addition, the use of a cation-exchange membrane significantly enhanced the electrochemical performance of the system by minimizing secondary reactions of cerium ions on the negative electrode. The optimized device reached energy and power density values up to similar to 20 W h kg(-1) and 524 W kg(-1) respectively. Moreover, the system showed a good long-term electrochemical performance over 20,000 cycles. (C) 2016 Elsevier B.V. All rights reserved.