The promise of direct and efficient conversion of chemical to electrical energy makes fuel cell development an area of great technological interest. The advantages over traditional power generation systems include increased efficiency, decreased emissions, high energy density and a scalable, modular, design.
The operating principle of a Solid Oxide Fuel Cell is quite straight-forward. Air is supplied to the cathode of the cell where oxygen is reduced to form oxygen anions
These oxygen anions then diffuse through the ion conducting but electronically insulating electrolyte to the anode.The oxygen anions react in the anode, oxidizing the fuel. For a general alkane hydrocarbon:
Of course, if hydrogen is used as the fuel, no carbon dioxide is formed. The liberated electrons travel around the external circuit, completing the circuit and providing electrical power.
The driving force for the ion transport is the oxygen electrochemical potential gradient between the cathode and anode compartments. This difference in electrochemical potential is related to a difference in electrical potential through the Nernst equation.
From the previous description, some of the requirements for SOFC materials may be deduced. For example, the anode must be both electron and oxygen anion conducting and catalytically active towards the combustion of fuel. These goals are currently met using composite electrodes. The study of the SOFC electrode processes, and how individual material properties interact in composite electrodes, forms an important part of our research. In addition, we strive to develop new materials to increase SOFC performance and enable the commercial application of this technology.
A significant limitation of current fuel cell technologies is the requirement for hydrogen fuel. The hydrogen economy is still some way off and increasing the efficiency with which we use our remaining hydrocarbon fuels is essential. As the ion species transported in SOFC is an oxygen anion, SOFC can, in principle, operate on any combustible fuel. Realizing this goal requires the development of novel anode materials and composites.
Some results from a recent neutron diffraction study. More to follow soon.