Preparation And Performance Of BaFeO₃-based Cathodes For Solid Oxide Fuel Cells

Solid Oxide Fuel Cell (SOFC) is attracting more and more attention as an idealchemical-to-electrical energy conversion device for its unique virtues like solid-statestructure, high-efficiency, environmental friendly, etc. Conventional cobalt-basedcathode materials which are expensive and poor in long term stability. Concequently,it is urgently necessary to develop alternative cobalt-free cathode materials for SOFC.Research on SOFC cathode and DCFC were investigated systematically in thisthesis. Cathode properties including structural stability, high thermal expansioncoefficient and relatively low electrical conductivity of BaFe0.95-xLaxZr0.05O3(BFLZ,0≤x≤0.1) prepared by sol-gel method was demostrated. Furthermore, influencecaused by catalysis was also discussed on internal reforming DCFC.XRD suggest that the crystal phase structure is much better if BFLZ powderswere synthesized by citric acid-EDTA sol-gel method. Meanwhile chemicalcompatibility of high temperature shows better performance of BFLZ betweenSm0.2Ce0.8O2(SDC) and Gd0.2Ce0.8O2(GDC), as well, and there is no impurity phaseformation undergone co-calcind at1200oC for5h. The polarization resistances ofBFLZ(x=0.05) on SDC and GDC is smaller prepared by sol-gel method. Thepolarization resistances of0.44,0.21,0.11,0.06and0.03Ω cm2were obtained at700,750,800,850and900oC, respectively, based on SDC. The polarization resistances of0.442,0.211,0.117,0.06and0.032Ω cm2were obtained at700,750,800,850and900oC, respectively, based on GDC. A single electrolyte-supported cell with theconfiguration of (anode) Ni-SDC|YSZ|SDC|BFLZ (cathode) was adopted, and themaximum power densities of60,120and217mW cm-2were obtained at750,800and850oC, respectively, where molarity of La was0.05of BFLZ.A novel direct carbon fuel cells (DCFCs) were designed and fabricated. SOFCswere directly operated with the gaseous products of steam gasification from carbonblack which was arranged in the tubular solid oxide fuel cells. The characters andperformance were considered under following cells:(1) use pure carbon black;(2)Prior addition of Ca(OH)2to carbon black for a treatment at600oC before loading theferric nitrate and Potassium nitrate;(3) directly loading the Ca(OH)2, Fe(NO3)3andKNO3on the carbon black, to investigate the cell performances and effect of catalystaddition. Comparing with the pure carbon black, carbon black with addition ofCa(OH)2for pretreatment at600oC can obviously improve the cell performance, themaximum power densities of cell were47.4,62.3and77.9mW cm-2at800,850and 900oC, respectively. Furthermore, heat treatment with prior addition of Ca(OH)2helps to reduce the deactivation of catalysts in the operation process of cell.