Development of ceramic protonic conductors for solid oxide fuel cells operation under methane and hydrogen fuels

Author(s)

Olavo Rodrigues de Oliveira

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Pesquisas Energéticas e Nucleares (IPEN/BT)
• Defense date: 2009-06-26

Examining board members

Reginaldo Muccillo; Daniel Zanetti de Florio; José Roberto Martinelli

• Advisor: Reginaldo Muccillo

Abstract

Yttrium-doped barium zirconate ceramic solid electrolytes were prepared by mixing and heat treating barium, zirconium and yttrium oxides. An alternative route, based on the addition of barium to yttria-stabilized zirconia, was also followed. The compositions studied were BaZr0.92Y0.08O3- and BaZr0.85Y0.15O3-. The starting materials were analyzed by X-ray diffraction (crystalline phases) and laser scattering (distribution of particle size). Simultaneous thermogravimetric and differential thermal analyses were performed for the study of the thermal behavior during the formation of the compounds. Pressed powders were sintered and characterized by determining a) apparent density by the Archimedes method with kerosene as liquid medium, b) crystalline phases by X-ray diffraction, c) morphology by scanning electron microscopy of fracture surfaces. Densification was best achieved for BaZr0.92Y0.08O3-. Unitary planar electrochemical cells of the type anode (Pt)/protonic conductor/cathode (Pt or La0.6Ca0.4Fe0.8Co0.2O3-) were assembled for evaluation of open circuit voltage (OCV) in the 300-600 C range, current density at 600 ºC, both under methane and hydrogen and electrical measures of impedance spectroscopy at 600 ºC. The La0.6Ca0.4Fe0.8Co0.2O3- (LCFC) compound was prepared by mixing lanthanum oxide, iron oxide, cobalt oxide and calcium carbonate and sintering. The electrochemical cells with BaZr0.8Y0.2O3- protonic conductors showed the highest OCV and current density values under methane. Keywords: protonic conductor, barium zirconate, methane. (AU)