Electrochemical performance and stability of PrO1.833 as an oxygen electrode for solid oxide electrolysis cells

Significant efforts have recently been undertaken to develop highly efficient solid oxide cells for high-temperature steam electrolysis (SOEC). Implementing new materials and microstructures that would improve the performance and durability of this technology remains a major issue. For this purpose, a nano-structured PrO1.833 material coated by the electrostatic spray deposition (ESD) technique was studied as a promising active oxygen electrode for SOEC application. The study was performed considering the PrOx as the functional layer and strontium-doped lanthanum manganite (LSM) as the current collecting layer on a standard half-cell supported by a typical Ni-YSZ cermet, a YSZ electrolyte, and a gadolinium-doped ceria (GDC) barrier layer. The electrochemical characterizations showed promising initial performance at 700 °C in SOEC mode (− 1 A cm−2 at 1.4 V with H2O/H2 = 90 vol%/10 vol%). In addition, a reasonable degradation rate of ∼5.8% kh−1 was obtained at 700 °C within 1000 h of SOEC operation. The structural and elemental evolutions were analyzed with micrometer size resolution all along the functional layer thickness using synchrotron μ-X-ray diffraction and fluorescence. The electrode degradation was primarily attributed to the phase transitions of PrO1.833. In particular, the structural analyses of the sample aged under applied current revealed a small quantity of PrO1.5≤x≤1.7 phase at the GDC/AFL (active functional layer) interface which is expected to be less conductive than PrO1.833, along with PrO1.714 and GDC phases. Finally, additional structural characterizations were performed on samples annealed at different temperatures and dwell times: 700 °C for 1000 h and 800 °C for 700 h, respectively. The results are discussed to provide a better understanding of the stability of the praseodymium oxide.