1.1 Introduction

A Solid Oxide Fuel Cell (SOFC) is typically composed of two porous electrodes, interposed between an electrolyte made of a particular solid oxide ceramic material. The system originates from the work of Nernst in the nineteenth century. In his patent ^[1], Nernst proposed that a solid electrolyte could be made to electrically conduct, using a heater; the system then "glowed" by the passage of an electric current. The systems originally studied by Nernst were based on simple metal oxides. In 1937, Bauer and Preis ^[2] operated the first ceramic fuel cell at 1000 C, showing that the so-called "Nernst Mass" (85% zirconia and 15% yttria), and other zirconia-based materials present a reasonable ionic conduction at high temperature (600 1000 C). These works were really the prelude to the modern SOFC.

In Figure 1.1, a schematic representation of an SOFC is depicted.

Figure 1.1: Schematic representation of a Solid Oxide Fuel Cell

At the cathode the reduction of oxygen occurs via

The dense structure of the electrolyte does not allow the passage of the cathodic gas through it, while the high ionic conductivity and the high electrical resistance allow only O ^2? ions to migrate from the cathode to the anode. At the anode, O ^2? reacts with hydrogen producing water:

As reaction [1.2] occurs, electrons are released at the anode and migrate from the cathode through an external electric circuit, thus generating an electric current.

The overall reaction...