Optimizing oxygen vacancies and electrochemical performance of CeO2−δ nanosheets through the combination of di- and tri-valent doping

Abstract

Ceramic fuel cells presently hold an important position in the future of sustainable energy. However, new concepts and designs are vital for each individual cell's component materials to improve the overall power output and stability. The limited ionic conductivity of the electrolyte component is one major challenge among these. In the present work, we developed nanosheets with a cubic fluoride structure of CeO₂ and introduced the di- and tri-valent doping of La and Sr to study their impact on oxygen vacancies and its ionic transport, keeping in mind the fact that CeO₂ is reduced when exposed to a reducing atmosphere. The attained La- and Sr-doped fluorite structures of CeO₂ exhibited good ionic conductivity of >0.05 S cm⁻¹ at low temperature, and their use in a fuel cell resulted in achieving a power output of >900 mW cm⁻² while operating at 550 °C. Therefore, we have found that laterally combining di- and tri-valent doping could be textured to give a highly oxygen-deficient CeO₂ structure with high ionic transport. Furthermore, various microscopic and spectroscopic analyses, such as HR-TEM, XPS, Raman, UV-visible, EIS, and density functional theory, were applied to investigate the change in structural properties and mechanism of the ionic transport of the synthesized La and Sr co-doped CeO₂ electrolyte. This work provides some new insights for designing high-ionic-conductivity electrolytes from low-cost semiconductor oxides for energy storage and conversion devices.