Shan-Lin Zhang

Atmospheric plasma-sprayed La0.8Sr0.2Ga0.8Mg0.2O3 electrolyte membranes for intermediate-temperature solid oxide fuel cells

La0.8Sr0.2Ga0.8Mg0.2O3 (LSGM) is considered a promising electrolyte material 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 membranes on electrode substrates at relatively low temperature (it is difficult to sinter LSGM to full density below 1500 °C). In this study, we report our findings on the preparation of thin LSGM electrolyte membranes using the low-cost atmospheric plasma spraying (APS) process. The phase composition, microstructure, and ionic conductivity of LSGM membranes deposited on an anode substrate depend sensitively on the particle size of LSGM powders because gallium (Ga) may evaporate during the APS process. When the particle size is 80% inter-lamellar bonding ratio), as referred from the thermal conductivity measurement of the LSGM deposit (>80% of the bulk thermal conductivity). Using LSGM powders with particle sizes >30 μm, we have fabricated LSGM membranes having ionic conductivity of ∼0.075 S cm−1 at 800 °C, ∼78% of the bulk value. Test cells based on plasma sprayed LSGM electrolyte membranes show excellent performance at 600–800 °C, suggesting that atmospheric plasma spraying is a promising approach for large-scale manufacturing of high-performance IT-SOFCs.

Controlling grain size in columnar YSZ coating formation by droplet filtering assisted PS-PVD processing

Grain size is important to the effect of material performance, particularly when reduced to nanoscale size. Generally, ionic conductivity in solid electrolytes can be remarkably enhanced by the nanostructure ceramics. In this study, a shrouded plasma torch was used on plasma spray-physical vapor deposition (PS-PVD) process. Multi-stage shielding was used to realize the controlling of grain size during the deposition process. The deposition behavior of YSZ was studied. The surface and cross-sectional morphology of the coating layer were also investigated. An island structure consisting of nano particle was seen on the coating layer surface, and the particle size becomes smaller with increased shielding stage. The cross section morphology of fracture coatings showed columnar structure. In this work, the grain size of the YSZ coating layer can be successfully controlled minimum to 25 nm by PS-PVD process. The effect of YSZ grain size on the coating properties is also discussed.

Thermally sprayed high-performance porous metal-supported solid oxide fuel cells with nanostructured La0.6Sr0.4Co0.2Fe0.8O3−δ cathodes

While porous metal-supported solid oxide fuel cells (PMS-SOFCs) have potential to dramatically reduce the cost while enhancing the durability of SOFC technology, the available fabrication processes are still cumbersome and unsuitable for commercial applications. Here, we report our findings in exploring low-cost, additive, thermal spray processes suitable for large-scale manufacturing of PMS-SOFCs. The additive fabrication process starts with a porous metal support, on which a porous nickel-based anode layer and a dense electrolyte membrane are sequentially deposited. Then, a nanostructured La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) cathode layer is applied using a liquid precursor high velocity oxygen fuel flame (LP-HVOF) spraying process. The polarization resistance of the LSCF cathode is reduced to 0.15 Ω cm2 at 600 °C and 0.025 Ω cm2 at 750 °C. The PMS-SOFCs display excellent performance, demonstrating peak power densities of 0.23, 0.65, 1.1, and 1.5 W cm−2 at 500, 600, 700, and 750 °C, respectively, while maintaining impressive stability (no observable change for more than 600 h at 650 °C). Our results suggest that thermal spraying has potential to be a low-cost and flexible process suitable for large-scale fabrication of commercial PMS-SOFCs.