Water-based 8YSZ electrolyte suspension optimised by design of experiments

Solid oxide cells are approaching commercial viability, with most of the currently used materials representing state-of-the-art advancements. However, widespread market adoption hinges on reducing costs. In this context, manufacturing improvements – particularly those that minimise material waste during production – can play a crucial role in lowering the capital expenditure (CAPEX) of solid oxide cells, ultimately influencing the levelised cost of fuel for end users. This study presents an optimisation of electrolyte slurry formulation for tape casting. By controlling variables such as solid loading, binder content, milling parameters, and casting conditions, we achieved reproducible results in electrolyte thickness, porosity, and electrical conductivity. The slurries were prepared by ball milling, employing a range of compositions that included both low and high solid and binder contents. The resulting rheological profiles, tape quality, thickness, and porosity were carefully evaluated. The experimental design culminated in an optimised composition, for which electrical conductivity was measured using electrochemical impedance spectroscopy. The impedance data were deconvoluted into grain bulk and grain boundary contributions, enabling further refinement of the sintering temperature and subsequent microstructure.