Development of an oxygen ion conducting solid oxide electrolysis cell based on gadolinium-doped cerium oxide as fuel electrode and electrolyte material

The global transition toward CO2-neutral energy systems requires a significant expansion of hydrogen technologies, with solid oxide electrolysis cells (SOECs) offering a highly efficient route for hydrogen production via high-temperature electrolysis. However, despite their superior efficiency, SOECs remain technologically less mature than low-temperature alternatives such as alkaline or proton exchange membrane electrolyzers. Advancing SOEC development therefore demands innovation in both cell design and manufacturing strategies to achieve high performance, mechanical stability, and costefficiency. This dissertation focuses on the development and investigation of fully screen-printed, fuel electrodesupported solid oxide cells featuring a co-sintered tri-layer electrolyte architecture. The work was conducted within the framework of the ElChFest project, which aims to model the electro-chemomechanical behavior of gadolinium-doped ceria based solid oxide cells and understand crack formation phenomena in the electrolyte during operation. A key objective was to fabricate mechanically robust and electrochemically efficient cells by optimizing the interplay between powder properties, paste formulation, sintering behavior, and final microstructure. Particular attention was paid to residual stresses induced during manufacturing. The fabrication strategy centered around screen printing as a scalable and cost-effective deposition method. The project included the transition of previously sputtered barrier layers to screen-printed alternatives. A comprehensive study of powder processing (encompassing pre-calcination and milling) was carried out to tailor the sintering behavior and enable co-sintering of the multi-layer cell. Rheological characterization of screen-printing pastes revealed strong correlations between print quality and parameters such as damping factor, yield point, and particle distribution asymmetry. These findings highlighted the critical role of paste rheology in achieving defect-free and reproducible ceramic layers. The sintering behavior of gadolinium-doped ceria (GDC) and yttria-stabilized zirconia (YSZ) powders was evaluated using both bulk pellets and screen-printed layers. Gadolinium-doped ceria exhibited an earlier onset of sintering and higher shrinkage than yttria-stabilized zirconia. While co-doping and precalcination effectively modified sintering kinetics, translating these findings to printed layers required further adaptation due to the mechanical constraints induced by the support. Co-sintering trials showed that substrate shrinkage behavior had a significant influence on electrolyte densification. Pre-calcined NiO-8YSZ substrates often inhibited proper densification, leading to increased porosity and cell warping. The development of the tri-layer electrolyte revealed additional microstructural challenges. Interfacial porosity driven by interdiffusion and Kirkendall effects was observed at the GDC/YSZ interfaces, when screen printing was used. This porosity was not present in cells with sputtered barrier layers. Consequently, optimizing the sintering temperature became a balancing act between achieving sufficient densification and suppressing interdiffusion-related degradation. Electrochemical characterization confirmed that cells with Ni-GDC fuel electrodes outperformed conventional Ni-YSZ cells in terms of stability, validating the choice of doped ceria. While the best electrochemical performance was achieved in cells with sputtered barrier layers, the fully screen-printed cells showed competitive initial current densities and area-specific resistances comparable to the stateof- the-art Jülich Type III reference design. These results underscore the viability of screen printing for fabricating high-performance SOECs, provided that careful attention is paid to interfacial engineering and sintering conditions. In summary, this work demonstrates that fully screen-printed, fuel electrode-supported SOECs with trilayer electrolytes can be fabricated with high quality and performance but require tightly controlled processing conditions. The findings emphasize the need for compatible sintering behaviors, advanced paste rheology control, and substrate design tailored for co-sintering. Future work should focus on developing novel, shrinkage-matched substrates to reduce sintering temperatures without compromising densification. Additional research into long-term stability under realistic electrolysis conditions, reversible operation, and varying steam concentrations is also essential to enable the broader deployment of this technology in hydrogen production and energy conversion.