Synthesis and characterisation of a green NiO/La(Sr)PO4−δ cermet anode for phosphate based solid oxide fuel cells

Abstract

Cermets are commonly used as anode in fuel cells. Ni/La(Sr)PO4−δ has not been synthesized before and it could be a good anode for hightemperature protonic fuel cells. In this article, the preparation of Ni/La(Sr)PO4−δ by combustion synthesis using nitrates, ammonium phosphate and urea is described. In this preliminary work, we are more concerned to understand the calcined powder reduction pattern with in situ Electrochemical Impedance Spectroscopy (EIS) experiments. The as-prepared powder is structurally analysed by XRD, also after each calcination treatment in air and in reducing atmosphere, and before and after the electrical measurements were carried out. The electrical characteristics of a green pellet of NiO/La(Sr)PO4−δ are studied by impedance spectroscopy as a function of temperature (50–800 ◦C) in a reducing atmosphere (10−20 atm). The reducing process of NiO to Ni is also followed by EIS. Finally, the morphology of this composite material analysed by EIS was observed by means of SEM/EDX. The morphology of this composite material indicates the presence of two compatible phases. One corresponds to the La(Sr)PO4 phase and the second one to a Ni phase, according to EDX data. The low electrical conductivity values indicate that nickel agglomerates are not totally percolated in the calcined pellet as it was expected. Higher conductivity values are expected when total Ni percolation occurs after sintering.