Ceria-Nickel Fuel Electrode for Reversible and Fuel Flexible Operation: Scaling-up from Electrolyte- to Electrode-Supported Cell

Abstract

Solid oxide cells are devices that figure great versatility of fuels whilst in fuel cell mode like biogas, bioalcohols, or hydrogen with no need of high purification, and are also reversible, meaning that the same equipment can operate as an electrolyser being thus capable of converting water/steam or carbon dioxide into fuel for strategic reserve purposes. The FleXelL project, aims to develop a fuel electrode material based on nickel, cerium oxide and yttria-stabilised zirconia to accommodate such virtues – flexibility and reversibility. The physical assessment of the materials was done via X-ray diffraction analysis, which confirmed the phases integrity, and dilatometry outputs that allowed the fabrication of the fuel electrode and electrolyte layers by the tape casting technique with minimum thermal mismatches. The gadolinium-doped ceria protective layer and the lanthanum-strontium cobalt ferrite oxygen electrode were both deposited by spin coating. After the successful manufacturing, the cells were tested electrochemical by polarisation both in fuel cell mode whilst hydrogen or anhydrous methane served as fuels reaching peak power densities as high as 0.7 W.cm-2, or under electrolysis mode achieving current densities above 2 A.cm-2 with a voltage of 1.25 V. The high efficiencies of the cells specially under electrolysis is attributed to the ability of ceria to act as an oxygen buffer, which avoided the deactivation/oxidation of the nickel catalyst under high electrical currents. After operation, the microstructure was investigated with scanning electron microscopy and energy dispersive X-ray spectroscopy to confirm the suitability of the microstructure even after the harsh operation.