NOVELTY - The asymmetric supercapacitor comprises a first electrode comprising a first porous active material and having a first operating window, a second electrode comprising a second porous active material and having a second operating window, a separator disposed between the first and second electrodes, and basic and acidic aqueous electrolyte. The first active material comprises a metal nitride, a metal oxynitride, a metal carbide, a metal oxycarbide, a metal boride and/or a metal oxyboride, where the metal consists of Groups III, IV, V, VI, or VII of the Periodic Table.    USE - The transition metal carbide, nitride and boride based asymmetric supercapacitor such as an electrochemical energy-storage device is useful for load-leveling and regenerative braking in hybrid and electric vehicles, for powering devices for the modern soldier and exoskeleton system for human universal load carrier, for powering electromagnetic armor and extended range vehicles and in advanced auxiliary power units and buffering for peak power associated with renewable energy sources such as wind turbines.    ADVANTAGE - The transition metal carbide, nitride and boride based asymmetric supercapacitor exhibits enhanced energy performance and high capacitance, energy density and stability.    DETAILED DESCRIPTION - The asymmetric supercapacitor comprises a first electrode comprising a first porous active material and having a first operating window, a second electrode comprising a second porous active material and having a second operating window, a separator disposed between the first and second electrodes, and basic and acidic aqueous electrolyte. The first active material comprises a metal nitride, a metal oxynitride, a metal carbide, a metal oxycarbide, a metal boride and/or a metal oxyboride, where the metal consists of Groups III, IV, V, VI, or VII of the Periodic Table. The first and second operating windows overlap by less than 60% based on the voltage. A total operating window for the supercapacitor is greater than 1.5-2.2 V. The first active material is a pseudocapacitive material, and the second active material is an electrical double layer capacitive material. The second active material consists of a metal oxide, where the metal of the metal oxide is different than the metal of the first active material. The second active material has a high over-potential for oxygen evolution. The first and second active materials have a pore size of 2-50 nm. The first active material has a specific surface area of 100 m2/g. An INDEPENDENT CLAIM is included for a method of selecting an electrode pairing for use in an asymmetric supercapacitor.