Determination of the standard free energy of formation of PdO(s) from the solid oxide electrolyte e.m.f.

Abstract

The standard free energy of formation of PdO(s) was determined in the temperature range 699–1060 K using the galvanic cell Pt, Pd, PdO¦15 wt.% YSZ¦air ( P o 2 = 0.21 atm), Pt (YSZ  yttria-stabilized zirconia). After correcting for the standard oxygen content in the air reference electrode, the standard free energy of formation of PdO(s) was calculated to be ΔG f °( PdO( s)) = −112789.8 + 99.81 T ± 274 J mol −1. This value is consistent with experimental values of the dissociation temperatures of PdO(s) in air and in pure oxygen determined from thermogravimetry measurements. Thus the validity of the expression obtained here can be extended to 1130 K which is the thermodynamic dissociation temperature of PdO(s) in pure oxygen. This free-energy expression is compared with other measurements reported in the literature. Combining the data for PdO(s) with the values for S 298° and C p of PdO(s) reported in the literature gives a value of −116.248 ± 0.41 kJ mol −1 for ΔH f °( PdO( s), 298.15K).