Determination of the standard Gibbs energy of formation of Rh2O3(s) and IrO2(s) from solid oxide electrolyte electromotive force measurements

  • Mallika C
  • Sreedharan O
  • Chandrasekharaiah M
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Abstract

The standard Gibbs energies of formation of Rh2O3(s) and IrO2(s) were determined in the temperature ranges 769-1263 K and 762-1260 K respectively using the galvanic cells Pt, Rh, Rh2O3|15 wt.% YSZ|air (PO2= 0.21 atm), Pt and Pt, Ir, IrO2|15 wt.% YSZ|air (PO2= 0.21 atm), Pt (YSZ, yttria-stabilized zirconia). After correcting for the standard oxygen content in the air reference electrode, the standard Gibbs energies of formation of Rh2O3(s) and IrO2(s) were calculated to be ΔGof(Rh2O3(s)) = -352 090 + 244.54T ± 1480 J mol-1and ΔGof(IrO2(s)) = -236 051 + 166.83T ± 1900 J mol-1The galvanic cell data for IrIrO2using NiNiO and CuCu2O as reference electrodes (reported in the literature) were also employed in calculating the data for ΔGofof IrO2(s). The reliability of oxygen potential measurements in this range of oxygen partial pressure employing oxide electrolyte galvanic cells with air as the reference electrode material was demonstrated by electromotive force measurements on CuCu2O electrodes. Third-law treatment of data on ΔGofof Rh2O3(s) and IrO2(s) yielded values of -360 ± 3 kJ mol-1and -247.8 ± 1.9 kJ mol-1respectively for ΔGof(298.15 K). By combining the standard Gibbs energy of formation data with the heat capacity data in the literature, values of 104.8 J K-1mol-1and 58.6 J K-1mol-1were derived for So298of Rh2O3(s) and IrO2(s) respectively. The Gibbs energy data in the present study were cross checked with dissociation temperature measurements on Rh2O3(s) and IrO2(s) employing thermogravimetry. © 1985.

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Authors

  • C. Mallika

  • O. M. Sreedharan

  • M. S. Chandrasekharaiah

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