Thermochemical Energy Storage Using The Phase Transitions Brownmillerite-2h Perovskite - Cubic Perovskite In The Caxsr1-Xcoo3-Delta (X=0 And 0.5) System

The oxides Ca0.5Sr0.5CoO3-delta and SrCoO3-delta, which present perovskite or perovskite-related phases in different temperature domains, have been tested as materials for thermochemical energy storage. The first one, Ca0.5Sr0.5CoO3-delta, experiences a reversible phase transition upon consecutive cycles under an airflow at a maximum operating temperature of 1196 K. Unfortunately, the heat stored in this process, associated with an oxygen loss/gain and a structural phase transition, is very small, hindering its use for thermochemical heat storage. The as-prepared oxide SrCoO(3)(-)d, which displays a brownmillerite structure like the Ca-containing compound, in the first heating step irreversibly segregates some Co3O4 at 823 K to yield a 2H hexagonal perovskite. This phase reversibly transforms at 1073 K into a cubic perovskite. These 2H reversible arrow C transitions occur from the 2nd to, at least, 30th cycle. The average absorbed and released heat is similar to 104.1 +/- 0.06 and similar to 68.8 +/- 1.8 J/g, respectively, and therefore, SrCoO3-delta presents a high exo/endo ratio. The exergy efficiency is, on average for the 30 cycles performed, as high as 63.9 +/- 1.2%. The mechanism of the phase 2H reversible arrow C transition of SrCoO3-delta explains the good performance of this material for thermochemical energy storage.