Effects of transition metal ion dopants on the performance of Ca2.9Bi0.1Co4O9-delta cathode

Abstract

A systematic study of 10 transition metal ions (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) doping in Ca2.9Bi0.1Co4O9-delta cathode for solid oxide fuel cells is performed by measuring their crystal structures, electrical conductivities and electrochemical performances. The presence of metal ion dopants in the Ca2.9Bi0.1Co4O9-delta matrix significantly influences its crystal structure and electrochemical performances. The electrochemical performances of metal ion-doped Ca2.9Bi0.1Co4O9-delta cathodes are quantified in terms of the electrical conductivity, impedance and power density of button cells. Doping with small amounts of ions for cobalt has negligible effect on the structure of powder samples as all of them form single-phase solid solutions with monoclinic misfit layered structure. However, the bar type samples of doping with Ti, Cr, Mn, Fe, Co, Ni, Cu and Zn keep the structure intact while those of doping with Sc and V slightly decompose after sintering. It is proposed that the metal dopants are located at different sites of double layered Ca2.9Bi0.1Co4O9-delta matrix due to their different ion radii, which mainly accounts for the difference of conductivity of doped samples. Among them, the Cu doped Ca2.9Bi0.1Co4O9-delta sample (Ca2.9Bi0.1Co3.9Cu0.1O9-delta) shows the highest electrical conductivity in the whole temperature range and has the lowest area specific resistance at 750 and 800 degrees C. The Ca2.9Bi0.1Co3.9Cu0.1O9-delta vertical bar Ce0.8Sm0.2O2+gamma vertical bar NiO + Ce0.8Sm0.2O2+gamma button cell shows obvious improvement than Ca2.9Bi0.1Co4O9-delta vertical bar Ce0.8Sm0.2O2+gamma vertical bar NiO + Ce0.8Sm0.2O2+gamma button cell. The maximal power densities of the Ca2.9Bi0.1Co3.9Cu0.1O9-delta cathode-cell were 689, 465 and 331 mW cm(-2) at 800, 750 and 700 degrees C respectively. (c) 2012 Elsevier B.V. All rights reserved.