Development of multi-step acid/redox-based process for recovery of solid oxide cells components

Recycling pathways for end-of-life cells or waste production must be established to improve the lifecycle of solid oxide cells and develop more sustainable hydrogen production systems. This work details a multi-step procedure allowing the separation and recovery processes of a commercial cell based on the different solubility and redox properties of its constituent materials, i.e. LSCF, NiO, GDC, and YSZ. Commonly used nitric acid solutions or mixed nitric acid and hydrogen peroxide solutions at varying concentrations are the only necessary reagents. Each recovered material was fully characterized by X-ray powder diffraction, ICP-AES and EDX. This innovative step-by-step method allows the treatment of more than 95 % of the initial mass of the cell, the separation of YSZ and GDC, and the recovery of NiO and YSZ at respective commercial grade purities of 99 and 95 wt%. The method follows three main processes inspired by hydrometallurgy and the recycling industry, transitioning from an end-of-life cell to recycled products. The mechanical grinding of the cell into a mixed powder is performed using planetary milling. Selective chemical leaching involves solutions of pure nitric acid or mixtures with hydrogen peroxide, followed by the separation of the leachate and the remaining solid through centrifugation. This process is repeated step by step as many times as necessary to separate each material. Finally, thermal treatment of the leachates or solids enables the recovery of each material in commercially viable forms. • Scalable recycling method applied on a complete SOC. • Treatment using only nitric acid and hydrogen peroxide as chemical agents. • Selective separation of GDC and YSZ achieved via redox-assisted leaching. • Recovery of GDC from single and composite layers of a solid oxide cell. • The strategic nickel material recovery with high purity (99 wt%).