Oxygen Reduction Reaction Kinetics in Sr-Doped La2NiO4+δ Ruddlesden-Popper Phase as Cathode for Solid Oxide Fuel Cells

In this paper, electro-catalytic reduction of oxygen in Sr-doped lanthanum nickelates, La2-xSrxNiO4+delta (0 <= x <= 0.4) Ruddlesden-Popper (R-P) phase, has been investigated. The oxygen reduction reaction (ORR) kinetics is evaluated via electrochemical impedance spectroscopy (EIS) with the symmetric cell configuration. The maximum performance is achieved with the un-doped La2NiO4+delta, similar to 0.13 Omega cm(2) at 800 degrees C. Sr doping decreases the electrode performance progressively. Further detailed analysis indicates that bulk ionic diffusion and surface oxygen exchange co-limit the ORR of those cathodes. Sr substitution leads to both lowered bulk diffusion and surface exchange rates. With high Sr content (x = 0.3, 0.4), oxygen ion transfer resistance between nickelate/electrolyte is observed. As for the surface exchange process, oxygen adsorption is suggested to be the main rate-limiting step (RLS) according to the reaction orders, which is retarded further by the oxidation of Ni2+ to Ni3+ as Sr content increases. The possible role of incorporation process in determining the overall reaction rate is also discussed. (C) 2015 The Electrochemical Society. All rights reserved.