Solid oxide electrolysis cells (SOECs) represent a promising avenue for sustainable energy storage, conversion, and the synthesis of fuels and chemical components. While state-of-the-art nickel and yttria-stabilised zirconia (Ni|YSZ) cermet cathodes exhibit high efficiency for CO₂ and H₂O electrolysis, they are plagued by issues such as coking and morphological degradation. In contrast, ceria-based cathodes, such as nickel and gadolinium-doped ceria (Ni|GDC) cermets, and particularly single-phase GDC cathodes, emerge as compelling alternatives as the mixed conductivity of GDC under reducing conditions leads to a high electrochemical activity. A major benefit of especially single phase GDC cathodes is their high coking resistance during CO₂ electrolysis. However, the notable drawback of ceria-based electrodes lies in their pronounced chemical expansion, causing mechanical stress, fractures, and potential cell failure. Furthermore, similar to Ni|YSZ, morphological transformations under intense electrochemical polarisation are anticipated for Ni|GDC due to solid-state (de)wetting phenomena, yet the intricate details of these transformations need further investigations.

In this study, our objectives are two-fold: (i) Investigate the (de)wetting behaviour of nickel on YSZ and GDC (ii) Unravel the intricacies of the chemical expansion observed in GDC under electrochemical polarisation.

For our first topic, dense Ni thin film electrodes are sputter deposited onto bare YSZ single crystals or YSZ substrates that have previously had a GDC film grown using pulsed laser deposition (PLD). Employing techniques such as electron microscopy, focused ion beam cutting, and electron backscatter diffraction, we examine the wetting behaviour under varying atmospheres and polarisations. The data obtained were matched with a computational phase field model and thus form the basis for understanding and predicting the morphological changes in SOEC cermet electrodes.

To fulfil our second goal, single phase, PLD grown GDC thin film electrodes are investigated by the means of in-situ X-ray diffraction (XRD) to study their chemical expansion behaviour under electrochemical polarisation. Electrochemical impedance spectroscopy is employed to simultaneously obtain the chemical capacitance of GDC electrodes, which provides us with the minority point defect concentration related to the expansion. Correlating in-situ XRD results with the material’s defect chemistry, establishes the groundwork for tailoring the electro-chemo-mechanics of SOEC cathodes, that will be done in forthcoming doping-variation experiments.