Gd-doped ceria with extraordinary oxygen-ion conductivity for low temperature solid oxide fuel cells

Doped ceria has been extensively explored as an efficient electrolyte material for intermediate to low temperature solid oxide fuel cell. Among other ceria electrolytes, gadolinia doped ceria (GDC) is one of the most extensively studied electrolyte materials for low temperature SOFC applications. Here, co-precipitation method is employed to synthesize GDC nanoparticles with stoichiometric ratio of Gd_xCe_1-xO_2-δ (with 0 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>≤</mml:mo></mml:math> x <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>≤</mml:mo></mml:math> 0.20). In this process, the molecular water of the precursors has been utilized during the co-precipitation to avoid possible agglomeration caused by hydrogen bonding. The cubic phase formation was examined using X-ray diffraction (XRD) and Raman profile ascribing absence of other phases. XRD along with Reitveld refinement confirm the presence of cubic phase of ceria and Raman profile confirms the oxygen vacancies due to the non-stoichiometry created in CeO₂ lattice. The granularity of the sample was observed using field emission scanning electron microscopy (FESEM) with elemental mapping by EDS. It is observed from FESEM that the grains are compact in nature and the density observed was around 98% of the theoretical density. The electrochemical behavior was investigated using electrochemical impedance spectroscopy (EIS), which was taken between the temperature ranges of 350-700 °C. It is observed from the EIS study that ceria doped with 15 mol % Gd³⁺ (Gd_0.15Ce_0.85O_2-δ) is having highest grain boundary ionic conductivity of about 0.104 S cm^-1 at 700 °C with an activation energy of 0.81 eV. This work demonstrates the correlation between oxygen vacancy generation and the enhancement of ionic conductivity with Gd³⁺ doping in ceria.