Design of BaZr_0.8y_0.2O_3-δ protonic conductor to improve the electrochemical performance in intermediate temperature solid oxide fuel cells (IT-SOFCs)

BaZr_0.8Y_0.2O_3-δ, (BZY), a protonic conductor candidate as an electrolyte for intermediate temperature (500-700°C) solid oxide fuel cells (IT-SOFCs), was prepared using a sol-gel technique to control stoichiometry and microstructural properties. Several synthetic parameters were investigated: the metal cation precursors were dissolved in two solvents (water and ethylene glycol), and different molar ratios of citric acid with respect to the total metal content were used. A single phase was obtained at a temperature as low as 1,100°C. The powders were sintered between 1,450 and 1,600°C. The phase composition of the resulting specimens was investigated using X-ray diffraction (XRD) analysis. Microstructural characterisation was performed using field emission scanning electron microscopy (FE-SEM). Chemical stability of the BZY oxide was evaluated upon exposure to CO₂ for 3 h at 900°C, and BZY showed no degradation in the testing conditions. Fuel cell polarisation curves on symmetric Pt/BZY/Pt cells of different thicknesses were measured at 500-700°C. Improvements in the electrochemical performance were obtained using alternative materials for electrodes, such as NiO-BZY cermet and LSCF (La_0.8Sr_0.2Co_0.8Fe_0.2O₃), and reducing the thickness of the BZY electrolyte, reaching a maximum value of power density of 7.0 mW cm^-2 at 700°C.