An onboard electrochemical system of an electrochemical cell including a cathode and an anode separated by an electrolyte separator is selectively operated in either of two modes. In a first mode of operation, water or air is directed to the anode, electric power is provided to the anode and cathode to provide a voltage difference between the anode and the cathode, and nitrogen-enriched air is directed from the cathode to an aircraft fuel tank or aircraft fire suppression system. In a second mode of operation, fuel is directed to the anode, electric power is directed from the anode and cathode to one or more aircraft electric power-consuming systems or components, and nitrogen-enriched air is directed from the cathode to a fuel tank or fire suppression system.