No abstract

Gadolinium-doped cerium oxide (GDC) is an attractive ceramic material for solid oxide fuel cells (SOFCs) both as the electrolyte and in composite electrodes operating at low and intermediate temperatures. GDC exhibits high oxygen ion conductivity at a wide range of temperatures and displays a high resistance to carbon deposition when hydrocarbons are used as fuels. However, an inconvenience of ceria-based oxides is the high sintering temperature needed to obtain a fully dense ceramic body. In this study, a green chemistry route for the synthesis of 10 mol% GDC nanoparticles is proposed. The aqueous precipitation method starts from the nitrates of both cerium and gadolinium and uses excess hexamethylenetetramine (HMT) to produce crystalline GDC at 80 ºC. Such a low temperature synthesis provides control over particle size and sinterability of the material at low temperatures.

Electrodes for electrolyte-supported solid oxide fuel cells (SOFC's) were fabricated by spin coating. Strontium-doped lanthanum manganite (LSM) cathode and nickel yttria-stabilized zirconia cermet anodes were synthesized and processed for enhanced deposition conditions. The influence of electrode microstructural parameters was investigated by a systematic experimental procedure aiming at optimized electrochemical performance of single cells. Polarization curves showed a strong dependence on both electrode thickness and sintering temperature. By a systematic control of such parameters, the performance of single cells was significantly enhanced due to decreasing of polarization resistance from 26 Ω cm² to 0.6 Ω cm² at 800°C. The results showed that spin-coated electrodes can be optimized for fast and cost effective fabrication of SOFCs.

Carbon resistant and redox stable anodes have been intensively studied aiming at effective fuel-flex solid oxide fuel cells. Previous studies have demonstrated that La 0.75 Sr 0.25 Cr 0.50 Mn 0.50 O 3 (LSCM) perovskite has comparable performance in both hydrogen and methane fueled SOFCs. In the present study, LSCM compounds with partial substitutions of either Mn or Cr by Ru (LSCM-Ru) were synthesized and characterized. Thermal analysis and X-ray diffraction were used to study the thermal evolution of precursor resins and phase formation. The electrical properties were investigated by 4-probe measurements in the 25-800°C temperature range. X-ray diffraction data evidenced that single phase compounds were obtained at 1200°C, without significant structural distortions up to ~ 10 at.% Ru. The electrical resistivity data showed that the transport properties depend on the substituted cation. In addition, the formation of Ru nanoparticles on the surface of LSCM-Ru grains suggests that LSCM-Ru compounds have enhanced catalytic activity for carbon containing fuels.

Pr 0.5 Ba 0.5 MnO 3 was studied as the precursor phase of the double perovskite PrBaMn 2 O 5+δ (PBMO) anode material for solid oxide fuel cells (SOFC). The general properties were studied in both the pristine compound and Ru-doped samples Pr 0.5 Ba 0.5 Mn 1-x Ru x O 3 (PBMRu). Ru substitution at the B-site is expected to enhance the catalytic properties of the ceramic towards ethanol or methane fuels. The studied compounds were synthesized by the polymeric precursor method and characterized by thermogravimetric analyses, X-rays diffraction (XRD), and electrical transport properties. The experimental data show PBMO phase formation occurring at ~800°C and single phase compounds at ~1100°C up to ~10 at.% of Ru substituted. Similar ionic radius of Ru 3+ and Mn 3+ results in little effect on both the crystalline structure and electrical conductivity as compared to the pristine compound.

No abstract