Recent model system studies by C. Nicollet [1] and C. Riedl [2] have demonstrated that surface modifications with basic binary oxides can improve the chemical surface exchange coefficient of oxygen (k_chem) by  ~1000 times and reduce the surface exchange resistance by a factor ~4, respectively. In both studies, an inverse correlation between the Smith acidity of the surface-modification oxides and the surface exchange kinetics for the oxygen reduction/evolution reaction (ORR/OER) was revealed. Motivated by these studies and reported benefits of modifying oxide surfaces with basic oxides [3-5], we conducted a screening study to explore the impact of basic binary oxide infiltration on technologically relevant oxygen electrode materials/structures in solid oxide cells (SOC).

In this work, symmetrical cells with porous electrodes composed of (La_0.6Sr_0.4)_0.98FeO_3-δ/Ce_0.9Gd_0.1O₂ (LSF/CGO), (La_0.6Sr_0.4)_0.98FeO_3-δ (LSF) and La_0.6Sr_0.4Co_0.2Fe_0.8O/Ce_0.9Gd_0.1O₂ (LSCF/CGO), were subjected to two infiltration cycles with selected basic binary oxides from groups 1 and 2 of the periodic table, including BaO, CaO, K₂O , Li₂O, MgO and SrO.

The findings regarding LSF/CGO indicate that, on average, infiltration with basic binary oxides reduce the polarization resistance (R_p) by a factor of 1.55 to 1.95 at 650°C in air. X-ray photoelectron spectroscopy (XPS) observations suggests that these improvements can be attributed to alterations in the distribution of Sr between the perovskite phase and secondary Sr rich phases in the outermost layers. No correlation between R_p and Smith acidity of the oxides used for surface modification were identified after two infiltration cycles. However, the number of cycles, an important factor from a technical standpoint, may not accurately reflect the infiltration footprint, thereby resulting in different OER/ORR active area footprints for each infiltrate. It is therefore believed that further improvements can be achieved by optimizing the loading, calcination- and heat treatment temperature. [6]

Basic binary oxides, such as BaO with a high boiling point, were discovered to stabilize LSF/CGO and decrease the degradation rate by a factor of 3 at 650°C. Oxides with a boiling point lower than the operating temperature initially enhanced the electrode performance but degraded rapidly over time.

In recent years, the research focus has shifted towards the fuel electrode, as area-specific-resistance (ASR) contributions from cobalt-containing oxygen electrodes are negligible under current operating conditions. However, to realize a more affordable SOC technology, the operating temperature must be reduced and the use of critical materials such as cobalt must be reduced/eliminated. This calls for research to also concentrate on the sluggish kinetics of cobalt-free oxygen electrodes and the development of materials for low-temperature operation. The findings of this study demonstrate that surface modification with basic binary oxides, especially BaO, can enhance the performance and durability of oxygen electrodes at intermediate temperatures. However, understanding the true mechanism behind the improvements observed in this study is crucial for fully exploiting the potential of surface modification by precipitation of basic binary oxides.