Investigation of Nickel exsolution perovskite electrodes for solid oxide cells (SOC) for high temperature CO2 and H2O co-electrolysis

Abstract

ABO3 type perovskites have been researched as an alternative to the current state of the art fuel electrode material for SOCs. High temperature solid oxide cells are one of the extensively researched Power-to-X technologies for directly converting chemical energy into electricity. Their ability to operate in electrolysis mode by converting energy into hydrogen and fuel cell mode by generating power, make them an attractive candidate. The purpose of the current work is to study the performance of an electrocatalyst based on a strontium doped lanthanum chromite doped with 15% of nickel (L65SCN), which has been developed at the German Aerospace Centre (DLR) in Stuttgart, as fuel electrode of an electrolyte-supported-cell (ESC) for high temperature hydrogen oxidation on Solid Oxide Fuel Cells (SOFC) and co-electrolysis operation on Solid Oxide Electrolysis Cells (SOEC). Cells were prepared by screen printing of fuel and air electrode inks on commercial 3YSZ electrolytes with double-coated CGO20 barrier layer. Pre-assessment of L65SCN was initially performed in H2O and CO2 co-electrolysis. The performance of L65SCN was then evaluated in SOFC mode by varying the sintering temperature of the fuel electrode and by performing Electrochemical Impedance Spectroscopy (EIS) and polarization studies. Durability test and redox cycling in SOFC mode were also evaluated. Porosity analyses via Scanning Electron Microscopy (SEM) were performed to characterize the morphology and determine the optimum fuel electrode sintering temperature along with the electrochemical characterization. The electrochemistry of the fuel electrode material was further analyzed by studying L65SCN in symmetrical cell configuration. The EIS spectra of symmetrical cells were further deconvoluted by means of Distribution of Relaxation Times (DRT) and Equivalent Circuit Model (ECM), in order to understand the different processes taking place within the L65SCN fuel electrode specifically. Temperature dependence of the symmetrical cells was also evaluated by means of Arrhenius studies. The main outcomes from the current work were identifying the optimum sintering temperature of L65SCN and studying its electrochemistry. 1100°C was identified as the optimum sintering temperature for L65SCN. The calculated activation energy barriers for L65SCN were 0.85eV and 0.82eV, which are consistent with the activation energy values reported in literature for other Mixed Ionic and Electronic Conducting (MIEC) electrodes.