Reduction and Reoxidation Processes of NiO∕YSZ Composite for Solid Oxide Fuel Cell Anodes

Abstract

Solid oxide fuel cells (SOFCs) are an emerging technology in hydrogen-based energy production, thanks to their high performance, high power density, high efficiency, and reduced emissions over conventional power generation technologies. For these reasons, a great attention has been addressed in these years to SOFCs materials and technologies. An important issue related to the utilization of SOFCs as power generators is the capability of SOFCs materials to resist to thermal cycles in different atmospheres. The present work proposes an experimental investigation on the reduction process of NiO∕YSZ anode into Ni∕YSZ cermet, which is the best candidate for anode material in SOFCs, its reoxidation into NiO∕YSZ and the following rereduction into Ni∕YSZ. Anodes with different NiO∕YSZ ratios were analyzed through different physical and chemical techniques, such as scanning electron microscopy (SEM) and porosity measurements. The reduction, reoxidation and rereduction behaviors were studied by thermogravimetric analysis (TGA) in a unique long experiment, at different temperatures in the range of 700–800°C. The kinetics of the processes was studied and thermodynamic parameters such as activation energy were also calculated and correlated to the compositions and microstructure of the materials. The study clears up the effect of anode composition and microstructure on the reduction, reoxidation, and rereduction processes.