An on-board aircraft electrochemical system, comprising: a stack of electrochemical cells comprising a cathode and an anode separated by an electrolyte separator; a cathode fluid flow path in fluid communication with the cell cathodes that discharges nitrogen-enriched air; a nitrogen-enriched air flow path that receives nitrogen-enriched air from the cathode fluid flow path and delivers it to a fuel tank, a fire suppression system, or both a fuel tank and a fire suppression system; a first anode fluid flow path configured to controllably direct water or air to the cell anodes; a second anode fluid flow path configured to controllably direct fuel to the anodes; an electrical connection in controllable communication between an electric power source and the cell cathodes and anodes; an electrical connection in controllable communication between an electric power sink and the cell cathodes and anodes; and a controller configured to alternatively operate the electrochemical cell in either: a first mode in which water or air is directed to the anode from the first anode fluid flow path, electric power is directed from the power source to the cell anodes and cathodes to provide a voltage difference between the anodes and the cathodes, and nitrogen-enriched air is directed from the cathode to the fuel tank, the fire suppression system, or both the fuel tank and the fire suppression system, or a second mode in which fuel is directed to the cell anodes from the second anode fluid flow path, electric power is directed from the anodes and cathodes to the power sink, and nitrogen-enriched air is directed from the cathodes to the fuel tank, the fire suppression system, or both the fuel tank and the fire suppression system. a stack of electrochemical cells comprising a cathode and an anode separated by an electrolyte separator; a cathode fluid flow path in fluid communication with the cell cathodes that discharges nitrogen-enriched air; a nitrogen-enriched air flow path that receives nitrogen-enriched air from the cathode fluid flow path and delivers it to a fuel tank, a fire suppression system, or both a fuel tank and a fire suppression system; a first anode fluid flow path configured to controllably direct water or air to the cell anodes; a second anode fluid flow path configured to controllably direct fuel to the anodes; an electrical connection in controllable communication between an electric power source and the cell cathodes and anodes; an electrical connection in controllable communication between an electric power sink and the cell cathodes and anodes; and a controller configured to alternatively operate the electrochemical cell in either: a first mode in which water or air is directed to the anode from the first anode fluid flow path, electric power is directed from the power source to the cell anodes and cathodes to provide a voltage difference between the anodes and the cathodes, and nitrogen-enriched air is directed from the cathode to the fuel tank, the fire suppression system, or both the fuel tank and the fire suppression system, or a second mode in which fuel is directed to the cell anodes from the second anode fluid flow path, electric power is directed from the anodes and cathodes to the power sink, and nitrogen-enriched air is directed from the cathodes to the fuel tank, the fire suppression system, or both the fuel tank and the fire suppression system. a first mode in which water or air is directed to the anode from the first anode fluid flow path, electric power is directed from the power source to the cell anodes and cathodes to provide a voltage difference between the anodes and the cathodes, and nitrogen-enriched air is directed from the cathode to the fuel tank, the fire suppression system, or both the fuel tank and the fire suppression system, or a second mode in which fuel is directed to the cell anodes from the second anode fluid flow path, electric power is directed from the anodes and cathodes to the power sink, and nitrogen-enriched air is directed from the cathodes to the fuel tank, the fire suppression system, or both the fuel tank and the fire suppression system.