Oxygen Exchange Kinetics of the IT-SOFC Cathode Material Nd2NiO4+δ and Comparison with La0.6Sr0.4CoO3-δ

For the promising intermediate temperature solid oxide fuel cell (IT-SOFC) cathode material Nd 2 NiO 4+δ , chemical surface exchange coefficients k chem and chemical diffusion coefficients D chem of oxygen have been determined by conductivity relaxation measurements and compared with results for La 0.6 Sr 0.4 CoO 3-δ between 575 and 725°C. At 725°C and an oxygen partial pressure of 0.1 bar, k chem and D chem of Nd 2 NiO 4+δ amount to 1×10 -3 cm s -1 and 2 x 10 -6 cm 2 s -1 , respectively, which are higher than those for La 0.6 Sr 0.4 Co0 3-δ . However, due to high activation energies, a strong decrease of both kinetic parameters is observed for Nd 2 NiO 4+δ upon temperature reduction. Activation energies of k chem and D chem are lower for La 0.6 Sr 0.4 CoO 3-δ , leading to faster oxygen exchange compared to Nd 2 NiO 4+δ at 600°C. Electronic conductivities of Nd 2 NiO 4+δ amount to 100-125 S cm -1 while those of La 0.6 Sr 0.4 CoO 3-δ are between 1600 and 2200 S cm -1 in the investigated temperature and oxygen partial pressure range. Ionic conductivities and surface exchange resistances, which were calculated from the kinetic parameters, further show superior oxygen transport properties of La 0..6 Sr 0.4 CoO 3-δ compared to Nd 2 NiO 4+δ in pure O 2 -Ar atmospheres.