In situ X-ray Rietveld analysis of Ni–YSZ solid oxide fuel cell anodes during NiO reduction in H2

• Published in: Journal of physics. D, Applied physics Applied physics, 2005-07, Vol.38 (13), p.2276-2282
• Main Authors: Reyes Rojas, A, Esparza-Ponce, H E, Fuentes, L, López-Ortiz, A, Keer, A, Reyes-Gasga, J
• Format: Article
• Language: English
• Subjects: Applied sciences; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Materials and auxiliary equipments used in energy engineering
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/0022-3727/38/13/029

A synthesis and characterization of solid oxide fuel cell (SOFC) anodes of nickel with 8%mol yttrium stabilized zirconia (Ni-YSZ) is presented. Attention was focused on the kinetics and phase composition associated with the transformation of NiO-YSZ to Ni-YSZ. The anodes were prepared with an alternative synthesis method that includes the use of nickel acetylacetonate as an inorganic precursor to obtain a highly porous material after sintering at 1400 deg C and oxide reduction (NiO-YSZ - > Ni-YSZ) at 800 deg C for 8 h in a tubular reactor furnace using 10% H2/N2. The obtained material was compressed by unidirectional axial pressing into 1 cm-diameter discs with 15-66 wt% Ni and calcinated from room temperature to 800 deg C. A heating rate of 1 deg C min-1 showed the best results to avoid any anode cracking. Their structural and chemical characterization during the isothermal reduction were carried out by in situ time-resolved X-ray diffraction, refined with the Rietveld method (which allowed knowing the kinetic process of the reduction), scanning electron microscopy and X-ray energy dispersive spectroscopy. The results showed the formation of tetragonal YSZ 8%mol in the presence of nickel, a decrement in the unit cell volume of Ni and an increment of Ni in the Ni-YSZ anodes during the temperature reduction. The analysis indicated that the Johnson-Mehl-Avrami equation is unable to provide a good fit to the kinetics of the phase transformation. Instead, an alternative equation is presented.