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Micro-Solid Oxide Fuel Cells based on highly catalytic ceramic oxide thin films nanostructures

Periodic Reporting for period 1 - Micro-SOLUTION (Micro-Solid Oxide Fuel Cells based on highly catalytic ceramic oxide thin films nanostructures)

Reporting period: 2015-07-01 to 2017-06-30

The continuous growing demand for mobile technologies as well as APUs and medical devices has become a constant in our society. In parallel to the development of all these 'gadgets', simultaneous development of small-scale energy delivering systems must occur to improve their run-time and functionality. An emerging alternative for portable power supply are Micro Solid Oxide Fuel Cells (micro-SOFCs) due to their high volumetric power density and energy-per-unit-mass. Micro-SOFCs presents an outstanding power density which will allow increasing the limited off-grid autonomy. A common strategy for enhancing micro-SOFC development implies lowering their operating temperature. Nevertheless, this approach will hinder their capacity to reform directly hydrocarbon-based fuels. Therefore, the development of micro-SOFCs capable to operate at temperatures higher would bring great benefits in terms of integration and utilisation of non-noble metals in the fuel electrode and feasible integration in hydrocarbon fueled systems. Bearing in mind this, Micro-SOLUTION project explores new strategies to incorporate nanostructured ceramic materials as electrodes and integrate them in the silicon microtechnology to increase the overall power density and total power of the system. The overall project objectives can be summarized as follows:
- Designing novel strategies for the incorporation of catalytically active materials in thin films deposited electrodes able to operate at high temperatures.
- In-depth characterization of the new engineered materials in order to make a rational selection.
- Integration of the novel engineered materials in real micro-SOFC systems.
Within Micro-SOLUTION we have successfully developed high-throughput methodologies that allow easy and fast preparation and characterization of materials, enabling the smart selection of optimum electrodes with complex composition. Moreover, highly active fuel electrodes have been prepared by infiltration employing techniques compatible with microfabrication processes which will help to their industrial application. Integration of the new engineered materials is being achieved and performance measurements will be carried out. In conclusion, all the major objectives of the action are almost attained. Benefits of this work will be shown in upcoming publications and/or patents.
The project started by working in parallel in the development of both electrodes: oxygen (cathode) and fuel (anode) electrode. In the case of the cathode, large-area combinatorial ternary deposition was fabricated generating a compositional map with the general formula: La0.8Sr0.2Mn1-x-yCoxFeyO3-d. Then, large-area samples were characterised in detail. After, symmetrical large-area combinatorial samples have been fabricated in order to characterise electrochemically the whole map generated in only one experiment. Adding this measuring approach to the fabrication by combinatorial deposition, which allows obtaining in a single experiment a huge plethora of compositions distributed throughout the wafer, it will reduce drastically the time needed for the fabrication and analysis of the properties of such a huge number of compositions.
Regarding the anode, within the project deposition of SDC ceramic thin films with optimised morphology on YSZ substrates was accomplished. Previously, an initial optimisation of PLD parameters was carried out, followed by morphological and structural as well as electrochemical characterisation. Then, incorporation of catalytically active materials have been tested by different methodologies, i.e. wet impregnation and atomic layer deposition (ALD), being successful the latter. By using ALD, a precise control of the layer thickness is achieved, avoiding agglomerations of material and getting the desired full coverage thanks to the layer-by-layer deposition. It is worth mentioning that ALD is a process that would allow the easy integration of the infiltration stage in the fabrication flow of the micro-SOFCs. An additional output of the utilisation of this technique is the possibility of the preparation of composites by ALD with unusual homogeneity which of great interest for SOFC and many other fields.
Subsequently, deposition of YSZ electrolyte by ALD was studied. Several precursors as well as diverse deposition parameters were tested. After fabricating each thin film, characterisation of its crystalline structure, morphology and composition was accomplished. According to prior experience, microfabrication of µSOFC platforms was carried out. In this regard, modification of microfabrication processes was made and new designs implemented allowed us to increase the survival rate close to 100%.
At this moment integration of new engineered electrodes into the μSOFC platforms is being carried out. Then, power output measurements will be done.
The work carried out has been presented in several internationally recognised scientific conferences (e.g. MRS, SSI, SOFC&SOE Forum,...) as well as in internal technical meetings. The scientific quality of the results is high, as it can be extracted from the prize received (Christian Friedrich Schönbein Bronze medal) in the Solid Oxide Fuel Cell and Electrolyser Forum in 2016.
Regarding the commercial exploitation of research results, two different incubator/acceleration programs were attended where commercialization of the technology employed in Micro-SOLUTION was studied, being well acknowledged.
Many attempts have been made in order to find the optimum composition for SOFC electrodes, in particular, in the cathode side where a large number of articles based on the modification of LSM composition by addition of transition metals can be found in the literature of the last 20 years. These works usually required considerable time and effort because researchers need to prepare, characterise and evaluate the performance of every sample individually. Micro-SOLUTION project takes advantage of an approach that allows fabricating, in a single experiment, up to thousands of different compositions: Combinatorial PLD. By this technique, a ternary compositional phase diagram was produced. Subsequently, structural, compositional, morphological and electrochemical analysis at wafer level has been accomplished, aiming for mapping the structure-composition-activity relationships. This is the first time that this methodology is implemented for studying SOFC material properties.
In the anode side, the utilisation of atomic layer deposition (ALD) for the infiltration of active components in a porous matrix is a novelty as well. ALD provides precise control on the morphology of the deposited layer and the amount of material added. Additionally, ALD is a common technique in microfabrication processes and can be easily integrated in a fabrication flow. This approach opens the possibility to the ALD fabrication of composites applicable as SOFC electrodes.
These two technological advances together with the improvements accomplished in the microfabrication processes anticipate a great impact in the results obtained within Micro-SOLUTION project.
Ternary combinatorial PLD sample