Novel nanostructured materials for anodes in solid oxide fuel cells

Abstract

Materials for heterogenous catalysis as well as in anodes for solid oxide fuel cells are two innovative and relevant areas of research. The search for a replacement of traditional Ni-based anodes in solid oxide fuel cells has been an increasing area of study over the last 20 years. The use of template materials such as ordered mesoporous silica to provide higher surface area materials for heterogenous catalysis are also a hot topic. In this thesis nanocubic doped-ceria oxides (for anodes in SOFCS) and lanthanum ferrite (as a good catalyst for the oxidation of hydrocarbons), were synthesised and studied separately for their electrochemical, structural, and catalytic properties, respectively.

Three different nanocubic ceria candidate materials were synthesised and tested by impedance spectroscopy for their electrochemical properties (Nanocubic ceria, La-doped ceria, and Pr-doped ceria). These materials were studied to determine the effect of dopants and nanostructure of the material on the resistances and conductivities. The electrochemical studies, by impedance spectroscopy yielded that La-doped ceria has the lowest resistance of the three materials. Problems were encountered both with the testing apparatus, as well as the printing and durability of the ink electrodes and this area of research was not pursued further.

For the lanthanum ferrite (LFO) materials, different preparation methods were explored by using ordered mesoporous carbon (OMC) templates to nanocast 19 ordered mesoporous products with high surface areas and improved catalytic performance. The use of OMC templates is a novel, safer, and easier route for nanocasting than its ordered mesoporous silica (OMS) counterparts. The preparation methods included a citrate complexation method, two solid-liquid methods – one of which included the preparation of these materials with OMC templates calcined at different temperatures – and a vacuum impregnation method.

These materials were characterised using x-ray diffraction, transmission (and scanning transmission) electron microscopy, and nitrogen physisorption. They were evaluated catalytically by temperature programmed reduction and light-off experiments. The crystallite size, BET specific surface area, particle size, pore volume, pore diameter, degree of nanorod-like and ordered mesoporous structure, the reducibility, and light-off temperatures were obtained for each material.

The vacuum impregnation method was the most successful method out of the four tested, with the highest specific surface areas reported as well as the best catalytic activity for the oxidation of methane in light-off experiments. The citrate complexation method was ranked second behind this with high specific surface areas and improved catalytic activity. The solid-liquid methods reported the lowest surface areas and worst catalytic activity, as well as having high impurity phases in the final products.