Development of nano-catalysts for use in solid oxide fuel cells

Contacts:

Martin Søgaard, ABF-Risø-DTU, 4677-5807 (martin.soegaard@risoe.dk)

Mogens Mogensen, ABF-Risø-DTU, 4677-5726 (mogens.mogensen@risoe.dk)

http://www.sofc.dk

Working principle of a fuel cell. On the cathode side oxygen from the air is reduced to oxide ions, which are transported through the electrolyte. On the anode side of the fuel cell the oxide ions combine with hydrogen and form water. The electrons needed for the redox processes are transported through an external circuit as useful power.

A fuel cell (FC) is a device that converts chemical energy into electric energy with very high efficiency. FCs have several advantages compared to the traditional ways of generating electrical power. These include high efficiency, scalability, fuel versatility and low noise operation. If the current operation temperature of the solid oxide FC (approximately 700 - 800°C) can be lowered, less expensive materials can be used in a FC stack increasing the likelihood of commercialization of the technology. When reducing the temperature the electrochemical activity of the electrodes decreases together with the ionic conductivity of the electrolyte. Especially the activity of the oxygen electrode (cathode) is severely decreased when decreasing the temperature. The polarization resistance of the cathode is approximately 75% of the overall resistance of the 2nd generation FC at 650°C. Great effort has therefore been put into finding more efficient materials for the oxygen reduction reaction at lower temperature.

The present project consists of three parts, a fundamental science part, a more development oriented project and finally a modelling part. In the first part of the project nano-catalysts will be infiltrated into cathodes and the electrochemical performance of the electrode will be measured before and after infiltration using detailed impedance spectroscopy. The infiltrated nano-particles will be characterized thoroughly using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and possibly time of flight-secondary ion mass spectrometry (TOF-SIMS). A second part of the project will deal with a recently new electrode material (Ba_0.5Sr_0.5Fe_0.5Co_0.5O_3-δ). This electrode material has an extraordinary high catalytic activity for oxygen reduction and would thus be an ideal choice as a cathode. However, present knowledge indicates that the surface of the material is not particularly stable over longer periods of time. In this project infiltration with nano-catalysts will be used to see if it is possible to enhance the stability of the surface. As a final part of the project a model that can describe the performance of infiltrated electrodes will be developed in MATLAB®. This model builds on already existing models available within Risø-DTU.