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)

Abstract

BaZr0.8Y0.2O3–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 (La0.8Sr0.2Co0.8Fe0.2O3), and reducing the thickness of the BZY electrolyte, reaching a maximum value of power density of 7.0 mW cm–2 at 700 °C.

Properties and applications of perovskite proton conductors

“…Applying their feedback on thin films deposition of proton conductors with perovskite structure, F. B. Prinz et al 84 have recently evaluated the structural and microstructural properties of BYZ films with 100 nm thickness, approximately, as well as the fuel cell performance. In general, the power densities of the cells with ultrathin membranes supported on Si substrates and covered by platinum electrodes were higher in magnitude than reported thicker cells 85,86 . Considering the thickness of the proton membrane consisting of a few grains, the ohmic loss across the electrolyte was negligible at 450 °C, as presented in the polarization curve.…”

Wet chemical synthesis and characterisation of Ba 0.5 Sr 0.5 Ce 0.6 Zr 0.2 Gd 0.1 Y 0.1 O 3−δ proton conductor

“…On the contrary, doped-BaZrO3 e.g. BaZr0.8Y0.2O3 -δ, possesses very high chemical stability in CO2 and H2O containing atmospheres due to high covalence of the Zr -O bond [1,9,15]. However, though it has high symmetry (cubic) as compared to cerates (orthorhombic) it still shows lower ionic conductivity than the latter, due to high grain boundary contributions, limiting its practical applications [16].…”

Optimizing the Manufacturing Method of Half-Cell Fuel Cell Based on Solid Electrolyte with Hydrogen Ion Conductivity

“…These conditions lead to high costs due to the need for using ceramic interconnects, expensive raw materials and materials degradation [5]. In addition, this high operating temperature represents the main drawback for SOFC practical applications, because of long start-up time, large energy input to warm up the cell, and the occurrence of thermal stresses that reduce the cell lifetime.…”

“…Because of the activation energy for proton transfer with smaller ionic radius is generally lower than that for oxygen-ion conducting electrolytes [5]. Therefore proton conducting ceramics have the capability to be used as an electrolyte in IT fuel cells [3,4].…”

“…Therefore, the use of proton conductors as electrolytes is a promising alternative that might solve the limits of SOFCs [5].…”