Microstructure and Performance Analysis of Low-Temperature Solid Oxide Fuel Cells Synthesized on Inert Al2O3 Substrates

Abstract

In order to lower the SOFCs operating temperatures new electrolyte materials should be used instead of yttria-stabilized zirconia (YSZ) and the thickness of electrolyte should be decreased to the low micrometer range. To prepare the thin electrolyte, physical vapour deposition methods, such as magnetron sputtering, leading to dense, pinhole-free thin films, are ideal. If, additionally, also the anode and cathode materials are kept thin, low-temperature cells are obtained, also called micro-SOFCs.To demonstrate the possibility of creating such thin-film layers, model anodes and anode/electrolyte systems were prepared on porous anodic aluminum oxide (AAO) substrates. As electrolyte material, Ce0.8Gd0.2O1.9-x (GDC) was used. The composite consisted of NiO and GDC was used as anode. The main advantage of GDC electrolyte for solid oxide fuel cells is four to five times higher ionic conductivity compared to YSZ in the temperature range 500-800°C.The microstructure of NiO-GDC thin-film anode after reduction in hydrogen at temperatures of 450 and 600°С was studied. It was found that at these temperatures there is also agglomeration of Ni particles and segregation on the film surface in the form of small particles as in [1] at 850°C. It is also shown that annealing of the deposited NiO-GDC anode layer at 1000°С allows stabilizing its structure and excluding subsequent agglomeration of Ni particles during operation in a hydrogen atmosphere. Figure 1 shows the microstructure of NiO anode/GDC electrolyte system deposited on AAO substrate.Button cells with a diameter of 13 mm and with different thicknesses of the anode and electrolyte were fabricated. A La0.6Sr0.4CoO3 cathode (Kceracell Co., Korea) was screen printed on the electrolyte surface and sintered in situ during cell testing in temperature range of 500–600°C. First investigations showed promising results, namely high open-circuit voltage values (0.8 V) and a power density up to 100 mW/cm² at 550°C in pure hydrogen. However, the impedance analysis of the cells points out that further anode and cathode optimization would be beneficial for the overall cell performance.[1] F.J. Garcia-Garcia et al., Int. J. Hydrog. Energy, 40(23), 7382 (2015) Figure 1: The microstructure of anode/electrolyte system deposited on AAO substrate (scanning electron microscopy) Figure 1