Interview with Sonia Fiorilli, Associate Professor Department of Applied Science and Technology (DISAT), Politecnico di Torino.

In BEST4Hy, the Politecnico di Torino is working on the recovery and recycling technologies for SOFC. As a specific group, you have been in charge of selecting, validating, and demonstrating existing technologies for the recovery materials from the electrode and electrolyte components of the fuel cells. The first step was focused on the lab scale optimisation process. What kind of technologies did you choose to perform the recovery material and how did you work on optimising them?

At Polito, we develop multiple recycling pathways to recover valuable ceramic materials from electrode and electrolyte components of EoL and scrap cells, with the final goal to use the recovered materials in the re-manufacturing of SOC cell.

In particular, for End of Life cells, yttria-stabilised zirconia (YSZ) and nickel oxide have been recovered through a multi-step procedure, based on sequential milling, hydrothermal treatment and acidic-assisted leaching of Nickel and YSZ composite materials. The process parameters (step duration, acidic leaching, temperature) have been optimised to obtain ceramic powders with defined targeted specifications, in terms of particle size, specific surface area, and chemical purity to allow their re-use for SOC manufacturing and at the same time to minimise the demand of energy and chemicals.

In parallel, we optimised an easy and scalable approach based on multiple milling and sieving steps to recover composite Ni-YSZ materials from half-cells that due to structural defects are discarded by the manufacturer company. The number and duration of the sequential steps have been identified to obtain powders for direct re-use in the re-manufacturing of SOC components.

Sequential steps of the recovery process from EoL SOCs

Recovery of YSZ from end-of-life SOCs

After the lab scale, the further step is the design and build of a small-scale plant at TRL5. What are the results until now and the main challenges?

Currently, we are dealing with a scaling-up phase of the developed recovery pathway for EoL cells. We have installed a hydrothermal reactor that allows us to process ten times larger amounts of powders than the TRL3 process. The powders obtained resulted in satisfying properties when compared  to the specifications defined by the manufacturer company.

However, the main open challenge is to prove the economic and environmental potential of the proposed recycling strategies for ceramic fractions of EoL cells and lay the ground for circularity in the field of SOC technologies.  With this perspective, we are taking advantage of Design of Experiment tools for selecting the best combination of process parameters and providing the most efficient procedure in terms of energy consumption and produced liquid wastes.

Small-scale plant at TRL5

The recycling analysis also considers an open loop strategy to maximise the value of the recovered materials – strategic critical raw materials – in other markets besides fuel cells remanufacturing. Which applications do you consider could be targeted for the recovered materials not used in fuel cell remanufacturing?

We are exploring alternative uses of recovered materials, with a specific focus on nickel precursors obtained from the metal selective leaching of the Ni-YSZ composite. In particular, nickel can be precipitated from acid-leaching solutions as precursors (oxides, oxalates) for manufacturing layered cathodes used in second-generation lithium-ion batteries. We are considering different synthesis routes for cathode preparation and, besides nickel-based precursors, our next goal is to include cobalt precursors obtained from WP4 activities focussed on lanthanum strontium cobaltite electrode.