Solid oxide fuel cells research

Introduction

In recent times, environmental concerns have driven research into more efficient, less polluting and renewable energy sources. Solid oxide fuel cells (SOFCs) represent one potential technology, converting a fuel directly into energy using air. In a SOFC, O₂ gas, present in air, reacts at the cathode to gain four electrons and form two O^2- ions, which diffuse through the electrolyte to react with the fuel at the anode of the cell. By ensuring that the electrolyte is an electrical insulator, the electrons return to the cathode through an external circuit, thereby generating electricity. Fuel cells are uniquely capable of overcoming combustion efficiency limitations (i.e. the Carnot cycle) and hence are theoretically capable of over 80% efficiency in combined heat and power systems.

SOFCs are an attractive alternative for electricity generation for a number of reasons. Not only are they cleaner than conventional methods, they also have low noise pollution and can utilise a range of different fuels, not being solely limited to H₂, meaning they are relevant for both present and future use. The present generation of SOFCs are typically composed of an electronically-conducting cathode which can reduce O₂, such as La_1-xSr_xMnO₃ (LSM); a good O^2- ion-conducting electrolyte, such as Y₂O₃-stabilised ZrO2 (YSZ); and an electronically-conducting anode with catalytic activity for oxidising fuels, such as Ni/YSZ cermet. The components also need to be thermally stable and have similar thermal expansion coefficients. However, due to the electrolyte and cathode requirements, the present generation of high temperature SOFCs operate at temperatures of ~1000°C, which is needed to achieve high O^2- ion conductivity and is also required for the oxygen reduction reaction to occur at the cathode. This high temperature makes cell construction more difficult and increases the cost due to the necessity for materials which are stable at such temperatures.

In order to reduce the operating temperatures of these devices into the intermediate temperature range (500-800°C) it is necessary to focus on optimization of current materials and the development of alternative materials for the electrolyte and cathode. Links to our work on these materials are below.

SOFC electrolyte research

SOFC cathode research