Standard Gibbs free energy of formation for Cu₂O, NiO, CoO, and Fe_xO: High resolution electrochemical measurements using zirconia solid electrolytes from 900-1400 K

Galvanic cells with oxygen-specific solid electrolytes made of calcia-stabilized zirconia have been used to make equilibrium measurements of the standard Gibbs free energy of formation, Δ_fG⁰_m,(T), for copper (I) oxide (Cu₂O), nickel (II) oxide (NiO), cobalt (II) oxide (CoO), and wüstite (Fe_xO) over the temperature range from 900-1400 K. The measured values of Δ_fG⁰_m at 1300 K are -73950, -123555, -142150, and -179459 J · mol^-1 for Cu₂O, NiO, CoO, and Fe_0.947O, respectively. The precision of these measurements is ± 30-60 J · mol^-1, and their absolute accuracy is estimated to be ± 100-200 J·mol^-1. Using values of -76.557, -94.895, -79.551, and -71.291 J · K^-1 · mol^-1 for the entropies of formation, Δ_fS_m⁰, (298.15 K), the calculated enthalpies of formation, Δ_fH_m⁰, (298.15 K), are -170508, -240110, -237390, and -266458 J · mol^-1 for Cu₂O, NiO, CoO, and Fe_0.947O, respectively. These values of Δ_fS_m⁰ (298.15 K) and Δ_fH_m⁰ (298.15 K) are in good agreement with the best available calorimetric measurements.