Understanding and minimizing anode degradation in hydrogen and natural gas fuelled SOFCs.
The development of Solid Oxide Fuel Cells (SOFCs) as viable energy conversion systems is still prevented by cost, which is several times higher than that required for economic feasibility, and by insufficient durability, especially concerning that of the anode cermet electrode. The main factors affecting anode degradation in hydrogen fuelled SOFCs comprise microstructural changes due to thermal and/or electrochemical sintering, which result in decrease of the gas exposed metal area and of the three phase (gas/electrode/electrolyte) boundary length as well as oxidation/reduction of the anode (redox cycles), due to disruption of the fuel supply as a result of thermal cycling or system failures. Anode degradation problems are even more severe in SOFCs using natural gas or other hydrocarbon fuels, especially those with high sulphur impurities, due to carbon deposition and sulphur poisoning which result in severe degradation of both the electrocatalytic activity of the anode and the catalytic activity for internal reforming or direct oxidation of the carbon containing fuel. In view of the fact that natural gas is a key energy vector in European Union while the role of renewable biofuels becomes increasingly important, minimizing anode degradation in SOFCs where such fuels are used is important in order to operate these fuel cells under internal reforming or direct oxidation conditions and, thus, improve the process economics.
Remedies proposed so far for reducing the effect of the aforementioned degradation factors suffer from severe technical and economic drawbacks, while there is not sufficient knowledge concerning the mechanism of the phenomena causing anode degradation.
The ROBANODE project proposes an integrated strategy for understanding the mechanism of processes which cause anode degradation in hydrogen and natural gas fuelled SOFCs by combining robust theoretical modelling with experiments over an extended range of operating conditions, using a large number of modified state-of-the-art Ni-based anodes.
Figure 1: Top view SEM images of Au-NiO/GDC anodes on different electrolyte-supported cells, prepared and tested in the frame of the ROBANODE project.