Dominant Factors Influencing the Electrochemical Performance of Plasma-Sprayed LSGM Electrolyte

Mg/Sr-doped lanthanum gallate (LSGM) is one of promising electrolyte materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) because of its high ionic conductivity. However, a main challenge in the application of LSGM is how to fabricate dense and thin LSGM electrolytes on electrode substrates at relatively low temperature since it is difficult to sinter LSGM to full density below 1500 °C. In this study, low-cost atmospheric plasma spraying (APS) is used to fabricate the thin and dense LSGM electrolyte. The effects of deposition temperature and particle size on the phase composition, microstructure, and electrochemical performance of LSGM electrolyte were investigated. It was found that the deposited LSGM presents a dense microstructure with well bonded lamellar interfaces with a porosity of ~2.3% when the deposition temperature is >300°C. Besides, the electrochemical performance depends sensitively on the particle size of LSGM powders because Gallium (Ga) may evaporate during plasma spraying. It was revealed that when the particle size is <30 μm, Ga evaporation loss increases rapidly with the decrease of particle size, which dramatically reduces the ionic conductivity of the LSGM deposits. The ionic conductivity of a dense LSGM deposit was only ~4.2% of the bulk conductivity. It was found that using LSGM powders with particle sizes >30 μm, plasma-sprayed LSGM reaches an ionic conductivity of ~0.075 S cm^-1 at 800 °C, ~78% of the bulk value. Test cells based on the plasma-sprayed LSGM electrolyte show excellent performance. At 800°C, a maximum output power density of over 700W/cm² was obtained with a APS ~60um thick LSGM under test condition of H_²/Air, indicating that atmospheric plasma spraying is a promising approach for large-scale manufacturing of high-performance IT-SOFCs.