We introduce a novel bipolar assembly of ion-exchange membranes as the separator for aqueous supercapacitors. The new bipolar separator enables the positive electrode and the negative electrode to operate in acidic electrolyte and alkaline electrolyte, separately. The bipolar separator increases the theoretically stable voltage window from 1.23 to 1.76 V for the device when pH 1 and pH 10 are selected for the positive and negative electrode, respectively, based on the pH tolerance of commercial ion exchange membranes. By considering the results from comprehensive electrolyte stability investigation, we charge the cells to 1.8 V, which increases the maximum cell discharge voltage to 1.77 V. A specific energy of 12.7 Wh/kg is achieved based on the electrodes' mass, which is twice the value of the comparative best performing single electrolyte. The new cell configuration with the three-compartment bipolar separator effectively prevents the acid/base electrolyte cross diffusion, where after 10,000 cycles, the capacitance retention is 97% with coulombic efficiency maintained above 99.6% all through cycling. The design here may open up a new avenue toward high-energy aqueous energy storage devices. (C) 2016 The Electrochemical Society. All rights reserved.