A vehicle comprising an on-board inert gas-generating system, the system comprising: a protected space selected from a fuel tank ullage space, a cargo hold, or an equipment bay; an electrochemical cell comprising a cathode and an anode separated by a separator comprising a proton transfer medium; a cathode fluid flow path in operative fluid communication with the cathode between a cathode fluid flow path inlet and a cathode fluid flow path outlet; a cathode supply fluid flow path between an air source and the cathode fluid flow path inlet, and an inerting gas flow path in operative fluid communication with the cathode fluid flow path outlet and the protected space; an anode fluid flow path in operative fluid communication with the anode between an anode fluid flow path inlet and an anode fluid flow path outlet; an anode supply fluid flow path between a water source and the anode fluid flow path inlet, and an ozone flow path in operative fluid communication with the anode fluid flow path outlet and an ozone storage or distribution system; and an electrical connection between a power source and the electrochemical cell; a hydrogen source in operative fluid communication with the anode fluid flow path inlet; an electrical connection between the electrochemical cell and a power sink; and a controller configured to operate the system in alternate modes of operation selected from a plurality of modes including: a first mode in which process water is directed to the anode fluid flow path inlet, electric power is directed from the power source to the electrochemical cell to provide a voltage difference between the anode and the cathode, and a gas comprising ozone is directed from the anode fluid flow path outlet to the ozone storage or distribution system, and a second mode in which hydrogen is directed from the hydrogen source to the anode fluid flow path inlet, electric power is directed from the electrochemical cell to the power sink, and the ozone storage or distribution system is isolated from the anode fluid flow path outlet. a protected space selected from a fuel tank ullage space, a cargo hold, or an equipment bay; an electrochemical cell comprising a cathode and an anode separated by a separator comprising a proton transfer medium; a cathode fluid flow path in operative fluid communication with the cathode between a cathode fluid flow path inlet and a cathode fluid flow path outlet; a cathode supply fluid flow path between an air source and the cathode fluid flow path inlet, and an inerting gas flow path in operative fluid communication with the cathode fluid flow path outlet and the protected space; an anode fluid flow path in operative fluid communication with the anode between an anode fluid flow path inlet and an anode fluid flow path outlet; an anode supply fluid flow path between a water source and the anode fluid flow path inlet, and an ozone flow path in operative fluid communication with the anode fluid flow path outlet and an ozone storage or distribution system; and an electrical connection between a power source and the electrochemical cell; a hydrogen source in operative fluid communication with the anode fluid flow path inlet; an electrical connection between the electrochemical cell and a power sink; and a controller configured to operate the system in alternate modes of operation selected from a plurality of modes including: a first mode in which process water is directed to the anode fluid flow path inlet, electric power is directed from the power source to the electrochemical cell to provide a voltage difference between the anode and the cathode, and a gas comprising ozone is directed from the anode fluid flow path outlet to the ozone storage or distribution system, and a second mode in which hydrogen is directed from the hydrogen source to the anode fluid flow path inlet, electric power is directed from the electrochemical cell to the power sink, and the ozone storage or distribution system is isolated from the anode fluid flow path outlet. a first mode in which process water is directed to the anode fluid flow path inlet, electric power is directed from the power source to the electrochemical cell to provide a voltage difference between the anode and the cathode, and a gas comprising ozone is directed from the anode fluid flow path outlet to the ozone storage or distribution system, and a second mode in which hydrogen is directed from the hydrogen source to the anode fluid flow path inlet, electric power is directed from the electrochemical cell to the power sink, and the ozone storage or distribution system is isolated from the anode fluid flow path outlet.