Non-stoichiometric La(1-x)NiO(3-delta) perovskites produced by combustion synthesis

Abstract

La(1-x)NiO(3-delta) perovskites present high metallic conductivity and Pauli-paramagnetism, and could be used as electrodes in electrochemical devices such as SOFCs, PEMFCs and MCFCs. Additionally, due to its sigma* conducting band, this material shows a very high electrocatalytic activity, particularly in oxygen reduction processes, with an efficiency comparable to that of platinum. This work describes the combustion synthesis of La(1-x)NiO(3-delta) perovskite powders (x=0 and 0.1) from mixtures of La(NO3)(3). 6H(2)O and Ni(NO3)(2). 6H(2)O as cation precursors, and urea as fuel. The as-prepared combustion product, characterized by XRD, DTA/TG, SEM/TEM, BET and dilatometry (after compaction), shows a much higher specific surface area than powders obtained via alternative routes and contains La2NiO4 with a typical K2NiF4-type structure, together with small amounts of NiO. The usual subsequent heat treatments for 1 to 12 h at successively higher temperatures showed that full conversion to La(1-x)NiO(3-delta) can be readily achieved in air at 750 degrees C and that the perovskite, after the 12 h heat treatment, remains stable up to 1100 degrees C. These results show that the combustion technique is a better and much simpler route to the synthesis of perovskite powders.