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Breaking the temperature limits of Solid Oxide Fuel Cells: Towards a newfamily of ultra-thin portable power sources

Periodic Reporting for period 2 - ULTRA-SOFC (Breaking the temperature limits of Solid Oxide Fuel Cells: Towards a newfamily of ultra-thin portable power sources)

Reporting period: 2017-10-01 to 2019-03-31

Solid Oxide Fuel Cells (SOFCs) are one of the most efficient and fuel flexible power generators. However, a great limitation on their applicability arises from temperature restrictions. Operation approaching room temperature (RT) is forbidden by the limited performance of known electrolytes and cathodes while typical high temperatures (HT) avoid their implementation in portable applications where quick start ups with low energy consumption are required.

The ULTRASOFC project aims breaking these historical limits by taking advantage of the tremendous opportunities arising from novel fields in the domain of the nanoscale (nanoionics or nano photochemistry) and recent advances in the marriage between micro and nanotechnologies. From the required interdisciplinary approach, the ULTRASOFC project addresses materials challenges to (i) reduce the operation to RT and (ii) technological gaps to develop ultra-low-thermal mass structures able to reach high T with extremely low consumption and immediate start up.

A unique μSOFC technology fully integrated in ultrathin silicon will be developed to allow operation with hydrogen at room temperature and based on hydrocarbons at high temperature. Stacking these μSOFCs will bring a new family of ultrathin power sources able to provide 100 mW at RT and 5W at high T in a size of a one-cent coin. A stand-alone device fuelled with methane at HT will be fabricated in the size of a dice.

Apart from breaking the state-of-the-art of power portable generation, the ULTRASOFC project will cover the gap of knowledge existing for the migration of high T electrochemical devices to room temperature and MEMS to high T. Therefore, one should expect that ULTRASOFC will open up new horizons and opportunities for research in adjacent fields like electrochemical transducers or chemical sensors. Furthermore, new technological perspectives of integration of unconventional materials will allow exploring unknown devices and practical applications.
The activity of the project has been focused on:

i) developing low temperature electrolytes able to be integrated in microtechnologies. So far, a new concept electrolyte have shown the potentiality to be used at temperatures as low as 150ºC in thin film form.

ii) understanding the effect of grain boundaries on the ionic conductivity and the catatytic properties of mixed-ionic electronic conductors with applicability in Solid Oxide Fuel Cells. We have shown an increase in several orders of magnitude of the mass transport properties compared to the bulk counterpart proving the origin of the effect. We have been able to engineer the mass transport properties of thin film cathodes by tuning local nonstoichiometry in the grain boundaries.

iii) designing and fabricating ultra-thin microdevices able to host micro-SOFCs. Moreover, systematic work on sealing, encapsulation by 3D printed ceramic parts and stacking of cells is under development.
The major achievements of the project represent clear advances beyond the state of the art. In particular, reducing the operating temperature of electrolytes below 100ºC is a target approached with a novel concept of thin film electrolyte. Moreover, proposing a new strategy for generating high diffusion pathways based on grain boundary engineering represents a breakthrough in the topic of nanoionics and has a great potentiality for thin-film based devices such as microSOFCs. Finally, the already defined ULTRASOFC cell design based on ultra-thin devices will reduce the thermal mass of the final stack reducing its start-up time while increasing dramatically its specific power.