Magnetron Sputtering Deposition of Rare-Earth-Doped Ceria Interlayers to Enhance Long-Term Performance of Solid Oxide Electrolysis Cells

Despite its high efficiency, SOEC technology faces a critical challenge: maintaining long-term stability, often undermined by interfacial degradation and unwanted chemical interactions between air electrodes and the electrolyte. During cell operation, strontium is segregated from the electrode and diffuses towards the electrode-electrolyte interface, where it reacts with zirconium, forming insulating layers. The introduction of rare-earth-doped ceria interlayers at the interface has been proven to prevent strontium migration and improve long-term performance of the cell, enhancing air electrode-electrolyte compatibility. High density and absence of defects are crucial properties for these layers, in order to effectively prevent strontium diffusion towards the interface, limiting cell degradation. In this line, this work explores the deposition of dense, thin, homogeneous and defect-free rare-earth-doped ceria layers at the air electrode-electrolyte interface. The impact of different dopants on the interlayer: samarium, lanthanum and gadolinium, was analyzed. The films were deposited by means of magnetron sputtering techniques: direct current (DC) and high power impulse magnetron sputtering (HiPIMS). Magnetron sputtering offers precise control over the films’ properties: thickness, composition, uniformity and finishing, allowing for the deposition of high-quality and efficient films. Additionally, the scalability of magnetron sputtering makes it compatible with potential large-scale manufacturing. The implications of magnetron sputtering parameters on coating-surface interface and coating properties were examined. Scanning electron microscopy (SEM) was used to evaluate the film’s physical features. Focused ion beam (FIB) was employed for high resolution interface visualization. Energy dispersive spectroscopy (EDS) was used to verify the chemical composition of the coatings. X-ray diffraction (XRD) was employed to determine ceria’s adequate doping. In order to test the quality of the developed ceria interlayers, anode supported half cells of NiO-YSZ/YSZ were supplied by INMA, different deposition conditions for the interlayers were tested, and finally standard LSCF/CGO air electrodes were deposited by screen-printing. Electrochemical impedance spectroscopy (EIS) and current-voltage (I-V) characterization in both fuel cell and electrolysis mode were performed to evaluate electrochemical performance, including long-term stability. Glow discharge optical emission spectrometry (GDOES) was employed to verify the prevention of strontium migration after electrochemical testing. Overall, the study focuses on the deposition and optimization of rare-earth-doped ceria interlayers to enhance air electrode-electrolyte compatibility, addressing the degradation challenge SOEC technology faces. Tackling this issue by means of magnetron sputtering, it aims to produce superior quality films, and compare these results to those achieved by other deposition techniques. In this way, the study aspires to further explore and contribute to the optimization of SOEC technology, supporting its transition to industrial-scale applications.