Scaling up ceramic recovery from end-of-life solid oxide cells: Process optimization and evaluation of recovered materials

This study introduces a scalable and sustainable method for recovering yttria-stabilized zirconia (YSZ) and nickel (as NiO) from end-of-life (EoL) solid oxide cells (SOCs). The process combines hydrothermal disaggregation at 200 °C with acid leaching into a single-step treatment, enabling whole-cell recycling and eliminating the need for complex layer separation. Optimised conditions – 50 g of SOC powder treated with 1 M HNO₃ for 1 h – achieved ≈92 wt% YSZ recovery while minimizing reagent use and processing time. The recovered YSZ showed a particle size distribution (445 ± 140 nm) comparable to virgin 3YSZ (470 ± 90 nm), with minimal Ni contamination (0.1 wt%) and preserved yttria content. When sintered at 1300 °C for 3 h, the material reached 95.5% relative density and an ionic conductivity of 7.9 × 10−3 S cm−1 at 800 °C, closely matching virgin 3YSZ (97.8%, 9.4 × 10−3 S cm−1). A residual monoclinic phase (17.4 wt%), which may slightly reduce transformation toughening, did not significantly affect ionic transport. Reuse pathways for recovered YSZ include closed-loop reintegration into SOC electrolytes or supports, and open-loop valorisation such as thermal barrier coatings or catalytic substrates. Concurrently, ≈99 wt% of Ni has been recovered in the form of NiO, with Co and La contamination below 1 wt%, further supporting circular economy strategies.