Recycling and Reuse Strategies for Ceramic Components of Solid Oxide Cells

Abstract

Fuel Cell and Hydrogen (FCH) applications will become crucial to enable the transition towards decarbonatization and meet the EU's zero net greenhouse gas emission targets to be achieved by 2050 (The European Green Deal, European Commission, 2019). As one part of novel FCH technologies, Solid Oxide Cells (SOCs) can be used as fuel cells and electrolyzers, enabling a fuel-flexible and adaptable range of applications. However, the Technology Readiness Level (TRL) of SOCs is currently assessed at 5–7 (H2-international, October 2022), which is lower compared to most of the technologies mentioned above. In order to achieve their market breakthrough, SOCs require scalable and cost-efficient manufacturing trails. This involves an adequate End-of-Life (EoL) material treatment, minimizing environmental impact, and avoiding landfill disposals. EoL strategies for FCH applications (including the SOC) are currently in the early stages and have not been adequately addressed. Until now, existing novel technologies and their materials are reviewed based on hazardousness, scarcity and cost. Initial considerations directly for SOC material recovery are given in two very recent publications. In these two studies, the focus was on the ceramic cell part of an SOC, aiming for the recovery of the most valuable cell fractions in a (semi-) closed loop scenario. Challenges in cell recycling arise from the diversity of structures and materials of established stack and cell designs. For industrial applications, planar stack geometry is likely to prevail, further subdivided based on the mechanical support used (fuel electrode-supported cells, FESC; electrolyte-supported cells, ESCs; metal-supported cells, MSCs). As a part of the German government-funded technology platform “H2Giga”, we are working on the re-integration of EoL FESC-type SOCs into the cell manufacturing process. The concept for FESC-recycling (Figure 1.) is based on the separation of the air-side perovskite materials (air-side electrode and contact layer) from the remaining predominant cell fraction (mechanical support, fuel electrode, electrolyte, and diffusion barrier layer). [1] Separation can be achieved by exploiting the chemical resistance of NiO and YSZ to suitable leachants such as hydrochloric acid or nitric acid. In comparison, the structure of the conventional perovskites used is more vulnerable to acid corrosion. The remaining solid fraction then undergoes a re-dispersion step and is incorporated into newly manufactured substrate. The recycled substrate is characterized in terms of electrical conductivity, mechanical stability, and microstructure. Critical components (Co, La) in the separated perovskite liquid fraction are to be recovered from the solution by precipitation. The presentation will guide the audience through the concept of multi-step recovery of the predominant cell fraction Ni(O)/YSZ, and will provide insides of the experimental results, ranging from the hydrometallurgical separation of cell fractions to suitable reprocessing techniques. [1] Sarner, S., Schreiber, A., Menzler, N. H., & Guillon, O. (2022). Recycling Strategies for Solid Oxide Cells. Advanced Energy Materials , 12 (35), 2201805. Figure 1