Effect of ionic size of dopants on the lattice structure, electrical and electrochemical properties of La_(2-x)M_xNiO_(4+δ) (M = Ba, Sr) cathode materials

摘要

La_(2-x)M_xNiO_(4+δ) (M = Ba, Sr; x = 0.1, 0.3), with a formula of A_2BO_4, has been prepared and investigated as cathode for solid oxide fuel cells to understand the influence of A-site dopants on the lattice structure, electrical conductivity and electrochemical properties of La_2NiO_(4+δ). All the compositions belong to tetragonal I4/mmm space group. La_(2-x)Ba_xNiO_(4+δ) shows larger lattice parameters than La_(2-x)Sr_xNiO_(4+δ) due to the large ionic radius of Ba~(2+) compared with Sr~(2+). For both Ba and Sr, the parameters a and b decrease while the c increases with increasing doping level. Rietveld refinement demonstrates that the increase in c parameter is partially originated from the increase in rocksalt layer thickness (La-O2( × 1) bond), which makes the adsorbed oxygen on particle surface much easier to enter the lattice and form interstitials, and thereby promoting the electrode reaction. The electrical conductivity of La_(2-x)M_xNiO_(4+δ) increases with doping level but decrease with increasing ionic radius of dopants. Both Ba and Sr doping decrease the electrode polarization and increase the power density of single-cell. La_(1.7)Ba_(0.3)NiO_(4+δ) exhibits superior electrochemical properties than La_(1.7)Sr_(0.3)NiO_(4+δ). The La_(1.7)Ba_(0.3)NiO_(4+δ) electrode exhibits the best performance with an ASR of 0.13 Ω cm~2 and a maximum power density of 310 mW cm~(-2) at 800 ℃ under electrolyte (La_(0.8)Sr_(0.2)Ga_(0.83)Mg_(0.17)O_(3-δ), 300 μm) - supported configuration.