A system for providing inerting gas to a protected space, such as a fuel tank ullage space, a cargo hold, or an equipment bay, the system comprising: an electrochemical cell comprising a cathode and an anode separated by a separator comprising a proton transfer medium; a power source arranged to provide a voltage differential between the anode and the cathode; 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; 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; 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 supply fluid flow path between a process water source and the anode fluid flow path inlet; a process water fluid flow path in operative fluid communication with the anode fluid flow path inlet and the anode fluid flow path outlet, including a gas outlet that discharges gas from the process water fluid flow path; a liquid-gas separator on the process water fluid flow path, wherein the liquid-gas separator includes an inlet and a liquid outlet each in operative fluid communication with the process water fluid flow path; and a gas discharge valve in fluid communication with the gas outlet, said gas discharge valve operative to allow fluid communication between the process water fluid flow path and a discharge side of the gas outlet in response to gas on the process water fluid flow path, and to block fluid communication between the process water fluid flow path and the discharge side of the gas outlet in response to a lack of gas on the process water fluid flow path; and characterized by a sensor configured to directly or indirectly measure dissolved oxygen content of process water that enters the gas-liquid separator; a controller configured to provide a target response of the sensor through control of a pressure differential between the process water fluid flow path and the discharge side of the gas outlet. an electrochemical cell comprising a cathode and an anode separated by a separator comprising a proton transfer medium; a power source arranged to provide a voltage differential between the anode and the cathode; 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; 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; 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 supply fluid flow path between a process water source and the anode fluid flow path inlet; a process water fluid flow path in operative fluid communication with the anode fluid flow path inlet and the anode fluid flow path outlet, including a gas outlet that discharges gas from the process water fluid flow path; a liquid-gas separator on the process water fluid flow path, wherein the liquid-gas separator includes an inlet and a liquid outlet each in operative fluid communication with the process water fluid flow path; and a gas discharge valve in fluid communication with the gas outlet, said gas discharge valve operative to allow fluid communication between the process water fluid flow path and a discharge side of the gas outlet in response to gas on the process water fluid flow path, and to block fluid communication between the process water fluid flow path and the discharge side of the gas outlet in response to a lack of gas on the process water fluid flow path; and characterized by a sensor configured to directly or indirectly measure dissolved oxygen content of process water that enters the gas-liquid separator; a controller configured to provide a target response of the sensor through control of a pressure differential between the process water fluid flow path and the discharge side of the gas outlet.