Synthesis of NiO-SDC Based Composite and Influence of La and H2O2 Addition on its Structural and Thermal Performance for Intermediate Temperature SOFCs /

Abstract

Solid oxide fuel cells (SOFCs) conventionally operate in the temperature range of 800 – 1000 °C. The barriers for full-scale commercialization of SOFCs are the high cost and relatively poor long-term stability due to the high temperatures used in current state-of-the-art SOFCs. One solution is to decrease the operating temperature from high to intermediate, e.g. to 550-750 °C but this requires developing new electrolytes and electrode materials. Also, to increase efficiency and practicality, the anode should be able to internally reform hydrocarbon fuels especially methane because it is the most common hydrocarbon in natural gas. In this respect, Nickel Oxide-Samarium Doped Ceria (NiO-SDC) is the suitable candidate for its robust stability and performance in the recent past for SOFC applications. Various parameters were studied, such as pH, NiO concentration by volume, calcination temperature, addition of Lanthanum (La) and Hydrogen Peroxide (H2O2), to develop enhanced NiO-SDC composite. Observations from the X-ray diffraction results demonstrates that crystallites show an increment in their size with the rise in pH and calcination temperature but the alteration of NiO concentration influenced the average crystallite size. The average crystallite size in both the phases (NiO and SDC) show an increment at higher concentration of NiO. Furthermore, no impurity phases have been found in the crystalline structure of synthesized NiO-SDC composite material. SEM results demonstrated that NiO-SDC powder samples are well dispersed but the particles exhibit irregular shape and size of the particles ranges from 50-65 nm. Two different methods have been used to improve the NiO-SDC cermet. Firstly, NiO-SDC composite anode material by adding Lanthanum (La), Ni(La)O-SDC, was prepared by co-precipitation route. Cubic fluorite structure was observed and crystallite sizes, of both NiO and SDC, fall in the size ranges of 25 nm – 48 nm. La mix and disperse in the compound finely and no chemical reaction was observed with 10 mol% La or even with 15 mol% La. However, with 20 mol% La, there appears the onset formation of La2NiO4 and LaNiO3. Secondly, NiO-SDC was synthesized via altered co-precipitation method with the inclusion of Hydrogen Peroxide (H2O2). Cubic fluorite structures was also observed in NiO-SDC prepared using H2O2 and crystallites of NiO and SDC were found in the size ranges of 20 nm - 48 nm. Addition of H2O2 promotes somewhat earlier crystallization and it also resulted in formation of ii refined crystals. Furthermore, the conductivity of NiO-SDC was also calculated at 650 °C and found to be 3.494×10-3 S/cm. Last part contains chemical compatibility test of Neodymium Doped Ceria (NDC) electrolyte composite material and NiO-SDC. XRD characterization showed that both NDC and NiO-SDC remained separate at the elevated temperature of 800 °C and no mixed phase was found between the two composites. That is why it can be depicted that both of these materials can be used in SOFC applicaitons. Therefore, these research results can broaden the opportunities for applications in intermediate temperature solid oxide fuel cells (IT-SOFCs).