This work focuses on optimizing the coating of a GDC blocking layer and LSCF cathode layer on SOFC half cells with NiO,YSZ anode support, NiO,YSZ anode functional layer, and YSZ electrolyte using RSDT. RSDT is an open-atmosphere, flame-based deposition process that uses inexpensive solvents and precursors (i.e. toluene and metal acetylacetonates) and performs a direct deposition of GDC and LSCF layers onto the cell [4]. By using RSDT, a dense GDC layer with good adhesion can be achieved at ~1000°C, which is a relatively low temperature compared to the ~1400°C at which GDC is traditionally processed. This lower temperature allows for reduced production costs and limits the inter-diffusion of the YSZ and GDC. Image (a) of the attached figure shows plan-view SEM of the RSDT-fabricated GDC layer on a half cell. This thin, dense GDC layer is expected to be transparent in SEM [2]; the large grains are the underlying YSZ. Energy Dispersive X-Ray Spectroscopy indicates the presence of cerium. Gadolinium is not detected, which is likely the result of its intended low mole ratio. The cathode is fabricated by simultaneously spraying a slurry of pre-synthesized LSCF nanoparticles and spraying LSCF nanoparticles synthesized directly in the flame. Preliminary testing shows that cells with the RSDT-fabricated cathode have less mass-transfer resistance at high current densities than cells with traditional LSCF cathodes (plot (b) of attached figure). These performance tests were conducted by FuelCell Energy at 750°C with humidified hydrogen on the anode and air on the cathode.
To improve the performance of a cell with RSDT-fabricated GDC blocking layer and LSCF cathode, it is important to decrease the ohmic resistance of the cell. This can be achieved by increasing the ionic and electronic conductivity of the LSCF cathode and by increasing the area of the triple phase boundary (TPB). In this work, the LSCF cathode morphology is tailored to optimize its ionic and electronic conductivity, TPB, and mass transfer resistance. The surface morphology of the dense GDC is also adjusted to optimize TPB. As part of the optimization, the morphology of the deposited layers is analyzed by X-Ray Diffraction and Scanning Electron Microscopy. Additionally, performance testing and electrochemical testing is carried out on the cells. This establishes a correlation among RSDT processing parameters, cell morphology, and cell performance.
References
[1] B. Timurkutluk, et al. Renewable and Sustainable Energy Reviews. 56 (2016) 1101-1121
[2] R. Maric, et al. Journal of Power Sources. 195 (2010) 8198-8201
[3] R. Maric, et al. Journal of Thermal Spray Technology. 20(4) (2011) 696-718