Development by Mechanochemistry of La_0.8Sr_0.2Ga_0.8Mg_0.2O_2.8 Electrolyte for SOFCs

In this work, a mechanochemical process using high-energy milling conditions was employed to synthesize La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-δ (LSGM) powders from the corresponding stoichiometric amounts of La₂O₃, SrO, Ga₂O₃, and MgO in a short time. After 60 min of milling, the desired final product was obtained without the need for any subsequent annealing treatment. A half solid oxide fuel cell (SOFC) was then developed using LSGM as an electrolyte and La_0.8Sr_0.2MnO₃ (LSM) as an electrode, both obtained by mechanochemistry. The characterization by X-ray diffraction of as-prepared powders showed that LSGM and LSM present a perovskite structure and pseudo-cubic symmetry. The thermal and chemical stability between the electrolyte (LSGM) and the electrode (LSM) were analyzed by dynamic X-ray diffraction as a function of temperature. The electrolyte (LSGM) is thermally stable up to 800 and from 900 °C, where the secondary phases of LaSrGa₃O₇ and LaSrGaO₄ appear. The best sintering temperature for the electrolyte is 1400 °C, since at this temperature, LaSrGaO₄ disappears and the percentage of LaSrGa₃O₇ is minimized_. The electrolyte is chemically compatible with the electrode up to 800 °C. The powder sample of the electrolyte (LSGM) at 1400 °C observed by HRTEM indicates that the cubic symmetry Pm-3m is preserved. The SOFC was constructed using the brush-painting technique; the electrode-electrolyte interface characterized by SEM presented good adhesion at 800 °C. The electrical properties of the electrolyte and the half-cell were analyzed by complex impedance spectroscopy. It was found that LSGM is a good candidate to be used as an electrolyte in SOFC, with an Ea value of 0.9 eV, and the LSM sample is a good candidate to be used as cathode.