Bismuth-doped La1.75Sr0.25NiO4+δ as a novel cathode material for solid oxide fuel cells

Bismuth has been doped into mixed ionic-electronic conducting La1.75Sr0.25NiO4+delta (LSN) with the 2D K2NiF4-type structure to evaluate its influence on various properties of the host material, which include its potential use as a SOFC cathode. X-ray powder diffraction indicates that LSN retains its tetragonal structure after doping with 5 mol% bismuth to form La1.65Bi0.1Sr0.25NiO4+delta (LSN-Bi). Bismuth doping profoundly lowers (by similar to 150 degrees C) the sintering temperature of LSN. Both LSN and LSN-Bi show excellent compatibility with electrolytes yttria-stabilized zirconia (YSZ) and samaria-doped ceria (SDC) in terms of thermal expansion and chemical reactivity (<900 degrees C). The electrical conductivity of both materials is metallic like and reaches values of 99.3 S cm(-1) and 100.3 S cm(-1) at 550 degrees C for LSN and LSN-Bi, respectively. The data from electrical conductivity relaxation (ECR) measurements demonstrate that the substitution of lanthanum by bismuth enhances the chemical diffusion coefficient (D-chem) and surface exchange coefficient (k(chem)) by factors of 2-3. The faster kinetics of oxygen transport exhibited by LSN-Bi relative to parent LSN is reflected by a lower polarization resistance of the former when the electrode performance of both materials is compared in symmetric cells. The corresponding values at 700 degrees C are 4.2 Omega cm(2) and 0.61 Omega cm(2) for LSN and LSN-Bi, respectively. High peak power densities are achieved (328 mW cm(-2) and 131 mW cm(-2) at 700 and 600 degrees C, respectively), when LSN-Bi is incorporated as the cathode in a fuel cell operated with humidified hydrogen as the fuel and air as the cathode gas. The material is considered a promising candidate for further study.