NOVELTY - An iron-air rechargeable battery (100) comprises: composite electrode including iron electrode (12) and hydrogen electrode (20) integrated with it; air electrode (30) spaced from the composite electrode; and an electrolyte (10) in contact with the composite electrode and air electrode. The battery further comprises self-assembling organic sulfur-based additives in the electrolyte; nano-structured whisker substrate as a catalyst support for the air electrode; and carbon dioxide management system (36) that rapidly adsorbs carbon dioxide from air that is supplied to the air electrode.    USE - As iron-air rechargeable battery (claimed) useful in grid-scale energy storage applications; and in electric vehicle applications.    ADVANTAGE - The iron-air rechargeable battery has a moderate energy density (preferably 50-75 Wh/kg), moderate cycle life (preferably 2000-5000 cycles) and low cost (preferably less than 100 dollars/kWh); is environmentally friendly; is constructed from abundant raw materials; is easily scalable; is an excellent candidate for grid-scale energy storage; has the round-trip energy efficiency of 50-80%; and has an open circuit cell voltage of 1.28V and a theoretical energy density of 764 Wh/kg. The specially-designed bilayer composite electrode structure is integrated into the iron electrode for generating electricity from the hydrogen evolved during charge and self-discharge, thus minimizing the loss in round-trip energy efficiency due to self-discharge and inefficient charging.    DETAILED DESCRIPTION - An iron-air rechargeable battery (100) comprises: composite electrode including iron electrode (12) and hydrogen electrode (20) integrated with it; air electrode (30) spaced from the composite electrode; and an electrolyte (10) in contact with the composite electrode and air electrode. The battery further comprises self-assembling organic sulfur-based additives in the electrolyte; nano-structured whisker substrate as a catalyst support for the air electrode; and carbon dioxide management system (36) that rapidly adsorbs carbon dioxide from air that is supplied to the air electrode. The whisker substrate is prepared from at least one of carboximide pigments and phthalocyanines. The nano-structured whisker substrate is coated with a thin catalytically active oxide layer, where the oxide layer includes at least one of perovskite oxide, pyrochlore oxide, or spinel oxide. The iron electrode comprises a bismuth additive. The air electrode includes a thin film nano-structured catalyst layer (32) supported on a gas diffusion layer (34). The carbon dioxide management system includes a carbon dioxide absorbent that is regenerated between the charge and discharge operations on the battery, where the absorbent includes nano-structured silica-supported organo-amine absorbent through which incoming air is passed and which weakly binds carbon dioxide. An INDEPENDENT CLAIM is included for charging the iron-air battery involving charging the iron electrode while allowing the hydrogen electrode to discharge at the same time; and isolating the iron electrode and the hydrogen electrode during discharge so that only the iron electrode is involved in power delivery.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic representation of an iron-air battery.    Electrolyte (10)    Iron electrode (12)    Hydrogen electrode (20)    Air electrode (30)    Nano-structured catalyst layer (32)    Gas diffusion layer (34)    Carbon dioxide management system (36)    Iron-air rechargeable battery (100)