The main objective of nextgenFCmat is to facilitate the development of fuel cells with low weight, compact design and low cost. To achieve this, we have to develop solid oxide fuel cell (SOFC) materials with higher performance at lower temperatures (400-600 °C) than the state-of-the-art materials. To reduce the ohmic loss, nextgenFCmat will develop thin film (0.1-3 µm) ceramic electrolytes by implementing genuine thin film techniques. The focus will be on proton-conducting electrolytes, but oxygen ion conductors will be fabricated for comparison. Proton-conducting perovskite type materials have one of the highest ionic conductivities among oxide-based materials at low temperatures. Analogue to the traditional oxygen ion-conducting SOFC, protonic ceramic fuel cells (PCFC) offers fuel flexibility, but it also has an important additional advantage compared to SOFCs. In a PCFC, the reaction product (water vapour) is evolved at the cathode side instead of at the anode (fuel side) as is the case for oxygen ion-conducting SOFC. Hence, no dilution of the fuel takes place in the PCFC, resulting in significantly higher efficiency
PCFC electrolytes are currently at a less advanced state than the traditional oxygen ion-conducting SOFC electrolytes. The same is true for the PCFC electrodes. In nextgenFCmat we will focus on the cathode in addition to the electrolyte. High performance PCFC cathodes are lacking completely. In nextgenFCmat, we will develop high performance (high chemical diffusion and oxygen exchange coefficient) thin film cathodes based on promising perovskite-type materials. A full fuel cell is beyond the ambitions of nextgenFCmat, we will focus on the electrolyte, the cathode, and the interfaces between them.
The use of genuine thin film technology will reduce the thickness of the individual layers and in turn reduce the ohmic loss. State-of-the-art SOFC electrolytes are 10-20 μm thick. They are produced by powder processing or by thick film techniques, such as tape-casting. To reduce the thickness of the electrolyte (and thereby the ohmic loss), nextgenFCmat will use genuine thin film techniques (chemical solution deposition, pulsed laser deposition, etc.). Such techniques are well known from the semiconductor industry and are used to process high quality metal oxide thin films for a range of applications. In addition, the thin film techniques also lower the sintering temperatures during processing and might, in the extreme case, remove the need of sintering entirely. This could lead to electrolyte-electrode assemblies with substantially higher performance, as the interfaces between electrolyte and electrodes suffer much less damage during processing. The use of thin film techniques also opens up a totally new range of possibilities for “nano-engineering” of the materials including possibilities for introducing fast ion-conducting interfaces.
In nextgenFCmat, extensive characterization will performed and used to increase our possibility to understand and thereby control the crucial processes at the “nano”-level. Structural/microstructural characterization of the films will be done with particular emphasis on texture, grain boundaries, interfaces and pores, using HRTEM, XEDS, EELS, EFTEM, FIB, SEM, in-situ XRD, and XPS. Electrochemical characterization will be done by various methods and serve as a measure for the performance for the fabricated thin films and the interfaces between electrolyte and cathode. Together with the microstructural characterization and modelling of the cathode activity, the electrochemical characterization will result in an enhanced understanding of the materials and the electrochemical processes taking place, again facilitating optimization of the thin films.
Published November 22, 2010