(315c) Redox-Active Y0.5Ba0.5CoO3-? As Thermochemical Oxygen Pump for O2-Inert Gas separations

Authors: 
Michalsky, R., ETH Zurich
Ezbiri, M., ETH Zurich
Steinfeld, A., ETH Zurich
To develop a thermochemical oxygen pump driven by solar-thermal process heat, we screen perovskites for their oxygen reduction- and oxidation-activities using electronic structure computations. Materials with high predicted redox-activity, La0.5Ba0.5CoO3-δ, Pr0.5Ba0.5CoO3-δ and Y0.5Ba0.5CoO3-δ, are synthesized and evaluated for reversible oxygen exchange in up to 50 redox cycles. Each cycle consist of endothermic perovskite reduction, that absorbs heat from 1 bar air at 500°C to form oxygen vacancies and O2, and exothermic perovskite oxidation, that refills oxygen vacancies with O2 stripped from O2-Ar mixtures at 0.01 bar O2, 1 bar, and 290°C. We demonstrate as well producing pure O2 via pressure-temperature swing from 1 bar O2 at 600°C to 1 bar air at 300°C. Evaluating mixed Y0.5Ba0.5CoO3-δ powder/SiO2 sand and porous Y0.5Ba0.5CoO3-δ granules at these conditions in a packed bed reactor gives oxygen exchange capacities of 64 mmol lattice oxygen per mol perovskite for decreasing pO2 from 0.01 to 0.001 bar and 114 mmolO molperovskite-1 for increasing pO2 from 0.2 to 1 bar, exchanged at about 12-19 μmolO2 gperovskite-1 min-1. Y0.5Ba0.5CoO3-δ thereby outperforms the CuO/Cu2O benchmark, active in reduction with air only above 1030°C, and SrCoO3-δ, reaching 88 mmolO molperovskite-1 in air at 627°C. With the measured heat capacities and reduction enthalpies we solve the energy balance for the Ar purifcation and O2 production modes, outlining the conditions at which thermochemical oxygen pumping might be a viable alternative to cryogenic distillation and vacuum pumping.