Abstract
Oxygen surface exchange properties of lanthanum nickelates La2NiO4+δ, La3Ni2O7-δ and La4Ni3O10-δ (LNOs) have been investigated using the Pulsed Isotope 18O/16O Exchange (PIE) technique in the temperature range 300–700 °C. The evaluation of the oxygen exchange rate from these lanthanum nickelates was conducted by measurement of isotope fractions 18O2, 16O18O, and 16O2 in the effluent pulse at the exhaust from the reactor with a packed bed. The rates of oxygen heterogenous surface exchange (rH), dissociative adsorption (ra) and incorporation (ri) were calculated. The oxygen surface exchange was found to vary between the three nickelates, with rH decreasing between samples La3Ni2O7-δ > La4Ni3O10-δ > La2NiO4+δ, which was attributed to a decreasing presence of Ni cations on the particle surfaces. Despite possessing the lowest oxygen surface exchange, La2NiO4+δ had the best electrode electrochemical performance, which was attributed to highly mobile interstitial oxygen atoms leading to the largest ri (surface oxygen incorporation rate into the bulk) of the nickelates. This study reveals the key limiting factors determining lanthanum nickelate cathode performance in SOFCs, and we suggest avenues to improve these materials towards functional cathodes in devices.
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