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

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, La_0.5Ba_0.5CoO_3-δ, Pr_0.5Ba_0.5CoO_3-δ and Y_0.5Ba_0.5CoO_3-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 Y_0.5Ba_0.5CoO_3-δ powder/SiO₂ sand and porous Y_0.5Ba_0.5CoO_3-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 mmol_O mol_perovskite^-1 for increasing pO₂ from 0.2 to 1 bar, exchanged at about 12-19 μmol_O2 g_perovskite^-1 min^-1. Y_0.5Ba_0.5CoO_3-δ thereby outperforms the CuO/Cu₂O benchmark, active in reduction with air only above 1030°C, and SrCoO_3-δ, reaching 88 mmol_O mol_perovskite^-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.