Investigation of plasma sprayed Sr_0·7La_0·3TiO₃ / La_0·2Sr_0·8MnO₃ Bi-layer interconnector performance and its application in high power tubular solid oxide fuel cells

Atmospheric plasma spraying (APS) has been demonstrated as an efficient and rapid method for manufacturing high-performance solid oxide fuel cells (SOFCs), with interconnects serving as the “wires” for large-scale integration of SOFCs. However, the challenge of producing highly conductive and stable interconnects through plasma spraying remains unresolved. This study developed a Bi-layer perovskite interconnect for segmented-in-series solid oxide fuel cell (SIS–SOFCs). It involved APS-prepared dense N-type interconnects of Sr_0·7La_0·3TiO₃ (LST), achieving low porosity, low leakage rate, and high conductivity LST coatings. The element of Ti valence state changes and conductivity of LST powders, hydrogen-treated powders, LST coatings, and hydrogen-treated coatings were quantitatively analyzed through phase detection and elemental valence state analysis under different oxygen partial pressure conditions to explore the variation of LST coating conductivity. Simultaneously, bi-layer interconnector model using La_0·2Sr_0·8MnO₃(LSM)as the P-type interconnect was established to elucidate the electron transport mechanism within the Bi-layer interconnect under operating conditions and propose optimization schemes for the structural design of tubular serial-connected cell interconnects. The tubular dual-cell combination using LST/LSM Bi-layer interconnectors exhibited a maximum power density of 360 mW/cm² at 800 °C, with only 33% interconnector loss compared to the maximum power density of 540 mW/cm² achieved by a single cell at 800 °C. Additionally, it attained the highest open circuit voltage (1.9 V) at 650 °C. This Bi-layer interconnectors has been successfully applied in serial-connected tubular cells with more than 5 cells. Furthermore, the dual-cell combination showed almost no performance loss under 100 h of constant current discharge (0.3 A/cm²) testing. These research findings indicate that the LST/LSM Bi-layer interconnectors prepared using atmospheric plasma spraying is an ideal material system for the functional layer of interconnects in high-power tubular segmented-in-series solid oxide fuel cell structures.