Kinetic investigation of the oxygen reduction reaction on LSCF-GDC composite cathodes for use in IT-SOFCs

A kinetic investigation of the Oxygen Reduction Reaction (ORR) was performed on LSCF-GDC composites cathodes spanning a wide range of operating conditions. EIS tests were carried out on symmetric cells between 700°C and 550°C under OCV conditions, with O2/N2 mixtures at varying the O2 molar fraction (5-100%). A dynamic, one-dimensional and physically-based model of the LSCF-GDC cathode was applied to rationalize the experimental results. The model simulates the spectra by solving mass and charge conservation equations, including terms for gas diffusion inside the electrode pores and solid state transport of oxygen vacancies inside the bulk of LSCF and GDC. A detailed kinetic scheme was chosen to describe the ORR mechanism, which took into account steps for adsorption and desorption, first and second electronation at the gas/electrode interface, interfacial and lattice ion transfer. An advanced numerical approach allowed to cut the computational times. Novel insights supporting the 2PB reaction pathway were provided by means of a sensitivity analysis on the kinetic parameters.