Impregnation Based Electrodes for Solid Oxide Fuel and Electrolysis Cells, the State-of-the-Art and Perspectives

Increasing the density of the triple phase boundary (TPB) sites has been the main focus of the microstructural optimization of the electrodes in solid oxide fuel and Electrolysis Cells (SOCs). TPB is the interface between the catalyst/electronic conductor, the ionic conductor, and the gas phase where the electrode reactions occur. Better electrode performance is achieved with increasing the TPB surface.  Classically, electrodes are prepared by mixing powders of the solid phases and then depositing them to form porous films after appropriate heat treatments. Optimizing the composition and particle size distribution of starting powders, as well as the deposition and sintering processes have led to a substantial increase in the TPB density. However, this has reached an optimum maturity. In the recent years impregnation based processes were developed to achieve larger TPB and better performance. In this scenario, one solid phase, usually the electrolyte, is sintered to form a porous backbone structure to be impregnated with a liquid precursor of the second phase. After drying and heating, the second solid phase is usually formed as a very fine structure on the top of larger particles of the porous backbone. This ensures a significant increase in the TPB, and good percolation of both solid phases. Very interesting results have been reported with a large number of cathode and anode materials in SOCs.

In this paper we will review the progress performed in our laboratories in impregnation based SOCs electrodes, including methods, materials, and results. In addition, the optimization of inkjet printing impregnation process will be presented and discussed in terms of controllability, reproducibility, and scalability.