Thermodynamic properties of RhO2

A solid-state electrochemical cell, with yttria-stabilized zirconia as the electrolyte and pure O2 gas at 0.1 MPa as the reference electrode, has been used to measure the oxygen chemical potential corresponding to the equilibrium between β-Rh2O3 and RhO2 in the temperature range from 850 to 1050 K. Using standard Gibbs energy of formation of β-Rh2O3 available in the literature and the measured oxygen potential, the standard Gibbs free energy of formation of RhO2 is derived as a function of temperature:ΔGf°(RhO2)(±71)/J mol−1=−238,418+179.89TUsing an estimated value of ΔCp ° for the formation reaction of RhO2 from its elements, the standard enthalpy of formation, standard entropy and isobaric heat capacity of RhO2 at 298.15 K are evaluated: ΔHf ° (298.15 K)( ± 164)/kJ mol−1 = − 244.94, S ° (298.15 K)( ± 3.00)/J mol−1 K−1 = 45.11 and Cp ° (298.15 K)( ± 2.6)J mol−1 K−1 = 64.28.