Hydrothermally-assisted recovery of Yttria- stabilized zirconia (YSZ) from end-of-life solid oxide cells

Effective and scalable recycling strategies for the recovery of critical raw materials are yet to be validated for solid oxide cells (SOCs) technologies. The current study aimed at filling this gap by developing optimized recycling processes for the recovery of Yttria-stabilized Zirconia (YSZ) from End-of-Life (EoL) SOC components, in view of using the recovered ceramic phase in cell re-manufacturing. A multi-step procedure, including milling, hydrothermal treatment (HT), and acidic-assisted leaching of nickel from composite Ni-YSZ materials, has been implemented to obtain recovered YSZ powders with defined specifications, in terms of particle size distribution, specific surface area, and chemical purity. The overall optimized procedure includes a pre-milling step (6 h) of the EoL composite materials, and a hydrothermal (HT) treatment at 200 °C for 4 h to further disaggregate the sintered composite, followed by selective oxidative leaching of Ni2+ by HNO3 solution at 80 °C for 2 h. In particular, the intermediate HT step was assessed to play an essential role in promoting the disaggregation of the sintered powders, with a related increase of specific surface area (up to 13 m2 g−1) and the overall reduction of the primary particle aggregates. The acid-assisted leaching allowed to fully extract Nickel from the composite Ni-YSZ powders, with retention of YSZ crystallinity and negligible loss of Zr and Y, as revealed by ICP analysis on the recovered supernatants. The developed multi-step pathway offers a promising strategy to recover valuable YSZ materials for the re-manufacturing of SOCs components, with the aim to boost a circular economy approach in the field of fuel-cell and hydrogen (FCH) technologies.