Microstructural tailoring of nanocomposite electrodes for solid oxide fuel cells

Abstract

The high demand for electrical energy induced by the rapid population growth has arisen the necessity to develop sustainable and environmentally friendly energy sources. In this context, fuel cells are one of the most promising technologies to obtain electrical energy from a wide variety of fuels with good efficiencies and lower emission of pollutants. In particular, Solid Oxide Fuel Cells (SOFCs) have attracted great attention in recent years due to their fuel flexibility, good tolerance to impurities in the fuel and higher efficiencies.

However, the high operating temperatures of SOFCs (600-800 ºC) needed to achieve a good electrode performance and a sufficient ionic conductivity for the electrolyte, negatively affect the long-term stability of these devices. For this reason, decreasing the operating temperature is one of the main goals for the wide implementation of SOFCs. It is well known that the crystal structure and composition of the electrodes play a key role in the electrochemical performance; nevertheless, the microstructural optimization of the electrodes has demonstrated to be crucial to boost the electrochemical properties at low operating temperatures in both oxidizing and reducing conditions. In this PhD thesis, different nanostructured and nanocomposite electrode layers based on the combination of perovskite-type electrodes, i.e. LaCrO3, SrTiO3 or LaFeO3 and the ionic conductor Ce0.9Gd0.1O1.95 (CGO) with fluorite-type structure have been prepared and tested for their implementation in SSOFCs. The electrode layers were prepared directly onto Zr0.84Y0.16O1.92 (YSZ) or La0.9Sr0.1Ga0.8Mg0.2O2.85 (LSGM) electrolytes by spray-pyrolysis. Additionally, pulsed laser deposition (PLD) was employed for the preparation of active layers. For comparison purposes, the same electrode compositions were prepared as powders from freeze-dried precursors and then deposited onto the electrolyte by screen-printing method.