An aircraft fuel tank ullage gas management system is disclosed. The system includes an electrochemical cell having a membrane electrode assembly that includes a cathode and anode separated by an electrolyte separator. A cathode fluid flow path is in fluid communication with the cathode, and receives the flow of cabin air from the cabin air fluid flow path and discharges nitrogen-enriched air. An anode fluid flow path is in fluid communication with the anode, and discharges oxygen or oxygen-enriched air. The electrochemical cell also includes water in fluid communication with the anode. The system includes an electrical power source and electrical connections to the anode and cathode for providing an electric potential difference between the anode and cathode. An ullage flow path receives nitrogen-enriched air from the cathode fluid flow path and delivers it to the fuel tank. An optional flow path delivers humidified oxygen-enriched air back to the cabin.