Enthalpy increments and redox thermodynamics of SrFeO3−δ

Abstract

Abstract

Redox Thermochemistry, Thermodynamics, and Solar Energy Conversion and Storage Capability of Some Double Perovskite Cobaltites

“…This is the main reason why among RBaCo 2 O 6−δ double perovskites (R = Pr, Eu, Sm, or Gd) PrBaCo 2 O 6−δ , having a generally lower oxygen storage capacity (OSC), possesses a higher Δ H total ◦ , and also why SrFeO 3−δ with a greater specific heat capacity is an ≈20–30% more “capacious” energy storage material than RBaCo 2 O 6−δ (R = Pr, Eu, Sm, or Gd). The equilibrium OSC of strontium ferrite SrFeO 3−δ is higher than that of RBaCo 2 O 6−δ (R = Pr, Eu, Sm, or Gd), as shown in the inset of Figure , making Δ H red ◦ of SrFeO 3−δ greater despite the slightly lower (by absolute value) partial molar enthalpy of O 2 in this oxide. , …”

“…In the notation employed in this work, the enthalpy increments are denoted as Δ 298 T H °( T ), which corresponds to the enthalpy required to heat 1 mol of sample from 298.15 K to T and is equal to ∫ 298 T C p d T . The shape of Δ 298 T H °( T ) experimental dependences is typical of the oxides that are reduced upon being heated: the higher-temperature upward deviation from the near linear low-temperature trend is due to the additional contribution from the oxygen loss. ,,, In other words, the Δ 298 T H °( T ) values were actually measured for the RBaCo 2 O 6−δ (R = Eu or Sm) samples of variable oxygen content. To recalculate them for constant-composition samples, EuBaCo 2 O 5.56 and SmBaCo 2 O 5.6 , the following equation was used: where δ 0 = 0.44 for EuBaCo 2 O 5.56 and δ 0 = 0.40 for SmBaCo 2 O 5.6 and δ 1 is the nonstoichiometry of the sample at temperature T in air.…”

“…Δ H sens ◦ in eq is sometimes calculated with density functional theory (DFT) because of the lack of experimental thermodynamic data . Though useful, this approach requires extreme caution, because modern DFT is known to yield erroneous C p ( T ) dependences, especially when there are phase transitions to consider. ,, …”

“…This oxide has been found recently to be a very promising oxygen pumping and chemical looping material − ,, and for this reason was chosen herein as a reference compound. The information about the high-temperature heat capacity and defect structure of SrFeO 3−δ was taken from our previous works. , …”

“…The shape of Δ 298 T H°(T) experimental dependences is typical of the oxides that are reduced upon being heated: the highertemperature upward deviation from the near linear lowtemperature trend is due to the additional contribution from the oxygen loss. 55,56,78,79 In other words, the Δ 298 T H°(T) values were actually measured for the RBaCo 2 O 6−δ (R = Eu or Sm) samples of variable oxygen content. To recalculate them for constant-composition samples, EuBaCo 2 O 5.56 and SmBa-Co 2 O 5.6 , the following equation was used:…”