Solid oxide cells (SOCs) are efficient electrochemical systems for electrical power generation in fuel cell mode (SOFC) and hydrogen production in electrolysis mode (SOEC). One solution to increase the lifetime consists of decreasing the operating temperature to 650-750 °C but the electrode reaction kinetics become relatively insufficient [1]. One of the main challenges is to improve the oxygen electrode efficiency by enhancing the oxygen reduction/evolution reaction (ORR/OER). To tackle this issue, it is important to choose suitable materials with adequate physicochemical properties and to optimize the microstructure and architecture to further increase the electrochemical performances [2].

This work aims to design novel optimized oxygen electrodes with improved mixed ionic-electronic properties to be used as more efficient oxygen electrodes in SOCs. Indeed, it is of high importance to control the electrode microstructure and composition to obtain large surface areas. These properties are essential to increase the number of active sites for the ORR/OER and to enhance the ionic transfer at the electrode/electrolyte interface.

Here, we report recent advances in the design of the state-of-the-art La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF) [3, 4], La_2-xPr_xNiO_4+δ (LPNO), [5, 6] with 0 ≤ x ≤ 2, and Pr₆O₁₁ [7] oxygen electrodes with grain size and porosity at the nanometre length scales. These active functional layers are fabricated using electrostatic spray deposition (ESD), a unique bottom-up method capable of depositing films with original morphologies by a nano-texturing approach. 

This talk will show our latest electrochemical performance results of these innovative oxygen electrodes investigating the role of the nanostructure and the electrode/electrolyte interface. The correlation between microstructure, composition, grain size, interfaces, and electrochemical properties is discussed in detail for the different investigated oxygen electrodes.

Our investigations suggest that the ESD process is a suitable low-cost method to manufacture unique optimized porous and nanostructured oxygen electrodes with reproducibility. Three MIEC oxygen electrodes have shown one of the lowest values of polarization resistances in the literature and excellent performances in single-cell tests. To conclude, the suitability of these mixed ionic and electronic conductors (MIEC) with innovative and controlled microstructure as durable air electrodes for SOECs has been proven to be promising.