Concurrent CO2 Control and O2 Generation for Advanced Life Support

The electrochemical reduction of carbon dioxide (CO2) using ceramic oxygen generators (COGs) is well known and widely studied, however, conventional devices using yttria-stabilized zirconia (YSZ) electrolytes operate at temperatures greater than 700 C. Operating at such high temperatures increases system mass compared to lower temperature systems because of increased energy overhead to get the COG up to operating temperature and the need for heavier insulation and/or heat exchangers to reduce the COG oxygen (O2) output temperature for comfortable inhalation. Recently, the University of Florida developed novel ceramic oxygen generators employing a bilayer electrolyte of gadolinia-doped ceria and erbia-stabilized bismuth for NASA's future exploration of Mars. To reduce landed mass and operation expenditures during the mission, in-situ resource utilization was proposed using these COGs to obtain both lifesupporting oxygen and oxidant/propellant fuel, by converting CO2 from the Mars atmosphere. The results showed that oxygen could be reliably produced from CO2 at temperatures as low as 400 C. These results indicate that this technology could be adapted to CO2 removal from a spacesuit and other applications in which CO2 removal was an issue. The strategy proposed for CO2 removal for advanced life support systems employs a catalytic layer combined with a COG so that it is reduced all the way to solid carbon and oxygen. Hence, a three-phased approach was used for the development of a viable low weight COG for CO2 removal. First, to reduce the COG operating temperature a high oxide ion conductivity electrolyte was developed. Second, to promote full CO2 reduction while avoiding the problem of carbon deposition on the COG cathode, novel cathodes and a removable catalytic carbon deposition layer were designed. Third, to improve efficiency, a pre-stage for CO2 absorption was used to concentrate CO2 from the exhalate before sending it to the COG. These subsystems were then integrated into a single CO2 removal system. This paper describes our progress to date on these tasks

In-situ surface monitoring of charge transfer during oxidation of zirconia at elevated temperatures

This work considers the reactivity at the gas/solid interface for energy conversion systems based on ZrO2, such as solid oxide fuel cells, SOFCs, and the related charge transfer. We consider the effect of a quasi-isolated surface structure, QISS, on the reactivity of yttria-stabilized zirconia, YSZ, with oxygen at elevated temperatures. The charge transfer associated with oxidation of both YSZ and Nb-doped YSZ in the range 973 K - 1173 K was determined by in situ surface monitoring using work function, WF, measurements. We show that the reactivity at the O2/YSZ interface can be enhanced by incorporation of pentavalent cations, such as Nb5+ ions, into the QISS that exhibits the functions of both fast ionic oxygen conductor and metallic electrode. It has been documented that surface doping of YSZ with niobium results in removal of oxygen chemisorption-related surface potential barrier that prevents oxygen incorporation into the lattice of YSZ. This finding paves the way for the development of novel materials for energy conversion devices, such as SOFCs, with enhanced performance through surface processing

Free-Standing Na2/3Fe1/2Mn1/2O2@Graphene Film for a Sodium-Ion Battery Cathode

The development of high-performance cathodes for sodium-ion batteries remains a great challenge, while low-cost, high-capacity Na2/3Fe 1/2Mn1/2O2 is an attractive electrode material candidate comprised of earth-abundant elements. In this work, we designed and fabricated a free-standing, binder-free Na2/3Fe1/2Mn 1/2O2@graphene composite via a filtration process. The porous composite led to excellent electrochemical performance due to the facile transport for electrons and ions that was characterized by electrochemical impedance spectroscopy at different temperatures. The electrode delivered a reversible capacity of 156 mAh/g with high Coulombic efficiency. The importance of a fluorinated electrolyte additive with respect to the performance of this high-voltage cathode in Na-ion batteries was also investigated. © 2014 American Chemical Society.