Hybrid Life Support with integrated PEM Fuel Cells

Abstract

To realize human long-term habitation in space, regenerative, sustainable and reliable life support systems (LSS) with low resupply masses have to be developed. Regenerating the main life support media (oxygen, water, carbon) and demonstrating a closed loop are the crucial factors. Until bioregenerative LSS become available in a few decades, hybrid LSS are being investigated and used. The following study considers a hybrid LSS characterized by a crosslinked integration of a proton exchange membrane fuel cell (PEMFC) as a physicochemical component and a photobioreactor (PBR) for algae cultivation as a biological component. Algae convert carbon dioxide exhaled by the crew into oxygen and edible biomass under illumination. The oxygen is directed into a unitized oxygen or air infrastructure, from which the crew cabin and the PEMFC are supplied. The PEMFC generates electricity and pure water. The algal emission gas contains contaminants in low concentration that are dispersed in the gas infrastructure of the space system if no filtration is provided. The algal emission gas is analyzed by gas chromatography, mass spectrometry, flame ion detection and optical emission spectrometry in order to specify organic and inorganic compounds. PEMFC performance and degradation under influence of the algal emission gas on the cathode side are investigated during a total operation time of 300 hours. Results are demonstrated by comparison of characteristic curves (voltage-current) and electrochemical impedance spectroscopy on different operation times. Algal emission gas specification and PEMFC diagnostics results reflect the interrelationship between electrochemical and biochemical processes. Identified gas compounds and required filtration methods for the crosslinked integration are evaluated. Preliminary estimations of mass, energy and resupply of such a hybrid system are done and compared to a regenerative physico-chemical system in order to point out advantages but also requirements of a hybrid system.