NOVELTY - An energy-harvesting device comprises: a positive electrode capable of storing and donating ions and electrons and of reducing oxygen; a negative electrode capable of storing and donating ions and electrons and of oxidizing hydrogen; and an electrolyte that permits transport of oxygen and hydrogen in contact with the positive electrode material and negative electrode material different from the positive electrode material.    USE - For supplying power to electronic device(s) (claimed).    ADVANTAGE - The invention can supply nW/cm2 to muW/cm2 levels of power and/or continuous energy by harvesting energy from the environment. It can convert hydrogen and oxygen harvested from the atmosphere into electricity via a fuel cell mechanism. Because of the electrode design. the device is also capable of storing charge and delivering the stored energy in a pulse and serve as an electrochemical capacitor (or ultra capacitor). The device has been demonstrated in several environments, including laboratory grade dilute acid, seawater, tap water, and humid air.    DETAILED DESCRIPTION - An energy-harvesting device comprises: a positive electrode (2) comprising a positive electrode material, preferably metal, metal oxide, hydrous metal oxide, semiconductor, and/or their alloys, where the positive electrode is capable of storing and donating ions and electrons and of reducing oxygen; a negative electrode (6) comprising a negative electrode material, preferably a metal, a metal oxide, a hydrous metal oxide, semiconductor, and/or their alloys, where the negative electrode material is different from the positive electrode material and capable of storing and donating ions and electrons and of oxidizing hydrogen; and an electrolyte that permits transport of oxygen and hydrogen in contact with the positive electrode material and the negative electrode material.    An INDEPENDENT CLAIM is also included for a method of harvesting energy comprising allowing an energy-harvesting device to charge and discharging the device.    DESCRIPTION OF DRAWING(S) - The figure shows an energy-harvesting device.    Positive electrode (2)    Positive electrode current collector (4)    Negative electrode (6)    Negative electrode current collector (8)    Separator (10)    Additional metal that can enhance water splitting into oxygen and hydrogen (12)