Influence of Ni-Content on Crystallographic Parameters and Electrochemical Performance of the La0.25Sr0.25Ca0.4NixTi1 - xO3 - d SOC Fuel Electrode

Abstract

The search for alternative fuel electrode materials to Ni-cermets is very active in the solid oxide cell (SOC) field due to several reasons. Metallic Ni is very sensitive to oxygen partial pressure (p O2) and reoxidizes to NiO if p O2 rises above the threshold level (temperature dependent). Ni-cermets are also prone to sulphur poisoning 1,2 and coking 3 if carbonaceous fuel without sufficient steam is used. Even if gases are carefully purified from sulphur, and correct steam to carbon ratio is used, metallic Ni centres still has a tendency to coarsen over time, which leads to performance losses 4,5.Full ceramic anodes are envisaged as redox stable materials when compared to metal-cermets – there is no immense expansion relating to metal oxidation reduction cycles and these materials are more resistant to coking and sulphur depositions 6–8. La0.2Sr0.7 - xCaxTiO3 - d (LSCTA-) has been demonstrated to be promising ceramic fuel electrode due to excellent electrical conductivity and stability if x ≤ 0.45 9.In this work, we investigated the influence of Ni concentration on the crystallographic properties of La0.25Sr0.25Ca0.4Ti1 - xNixO3 - d (LSCNT-x) (x = 0, 0.02, 0.05, 0.1, 0.2) using in situ X-ray diffraction. Sr mobility during the processing of electrodes with different Ni contents was demonstrated. The electrochemical performance of each synthesized electrodes was evaluated with electrochemical impedance spectroscopy (EIS) using a 3-electrode setup in LSCNT-x/GDC|GDC/ScCeSZ/GDC|LSC cell (LSC is La0.6Sr0.4CoO3 - d ). Two-electrode measurements were also conducted with the most stable and electrochemically active electrode in order to assess its performance in working systems. Additionally, steam electrolysis experiments were performed to establishx the best electrode’s performance in electrolysis mode.