Improvement of Mechanical Strength and Long-Term Durability on Anode Support for Solid Oxide Fuel Cells by Adding Nanomaterials

Abstract

Ni-8YSZ is widely used as an anode support for Solid Oxide Fuel Cells (SOFC). However, because of its low mechanical strength and high price, it is essential to develop an improved anode support material for commercialization. It has been reported that 3YSZ, which is used for bioceramics (implants) or refractory materials (for metallurgical metals), has more than twice as high mechanical strength as 8YSZ. In addition, since it is about 20 % cheaper than 8YSZ, it is under study as an anode support material. However, it has the disadvantage of significantly degrading the mechanical strength in the high-temperature humidified hydrogen atmosphere, which is the operating condition of the SOFC. In this study, we tried to improve this by adding nano-ZrO2 and nano-WO3. According to the Hall-Petch equation, it has been reported that the addition of nanoparticles has the effect of reducing the grain size and thus improving the mechanical strength. ZrO2 is the same material as the anode support and will not affect the material properties. According to the report, when WO3 is reduced that it will exhibit high mechanical strength in the form of a Ni-W alloy. For uniform dispersion, NiO and 3YSZ powders were ball-milled for 100 hours, and nano-ZrO2 and nano-WO3 were also added, respectively. At that same time, a binder and a pore former were added to secure the same porosity as the SOFC anode support. The mixed slurry was dried for 24 hours in the oven, then sieved, and pelletized. The powders were sintered at 1400 oC for 5 hours. Sintered samples were reduced at 750 oC in a hydrogen atmosphere for 8 hours. The reduced samples were heat treated in a reducing atmosphere (at 900 oC in a humidified hydrogen) for 500 and 1000 hours, respectively, which is an accelerated atmosphere. The three-point bending method was used to evaluate the mechanical strength and SEM microstructure analysis was conducted to analyze the cause of the improvement. As a result, the mechanical strength and long-term durability of the Ni-3YSZ anode support were greatly improved in the case of the sample with nano-ZrO2 added.