HANG Qi ¹, XU Xu ^{1, 3}, WANG Leying ^{1, 3}, CHENG Liang ^{2, 3},ZHANG Shuangshuang ¹, CAO Xiwen ¹, XIONG Bin ¹, LIU Fan ¹

(1. School of Materials Science and Engineering, Jingdezhen Ceramic University, Jingdezhen 333403, Jiangxi, China;2. National Engineering Research Center for Domestic & Building Ceramics, Jingdezhen Ceramic University, Jingdezhen 333001, Jiangxi, China; 3. Jiangxi Key Laboratory of Advanced Ceramic Materials, Jingdezhen Ceramic University, Jingdezhen 333001, Jiangxi, China)

Extended Abstract:[Background and purpose] Ni-YSZ, as one of the most commonly used metallic ceramics, has demonstrated a wide range of applications, due to its unique physical and chemical properties. However, Ni based anode materials suffer from carbon deposition, resulting in irreversible loss of fuel cell performances. It has been shown that Ni nanocatalysts on YSZ surface (Ni@YSZ), made through reduction precipitation, exhibited excellent resistance to particle aggregation and carbon deposition in methane catalytic reactions. In this study, NiO-YSZ powders were prepared by using sol-gel method, and the solid solution of NiO in YSZ was examined. By controlling the precipitation conditions, uniformly distributed nanoparticles were precipitated on surface of the YSZ matrix, while the effect of Ni on anticarbon deposition performance was evaluated.[Methods] The precursor sols of 3 mol% NiO YSZ and 10 mol% NiO YSZ were prepared by sol-gel method, according to the stoichiometric ratios of Ni(NO₃)₂·6H₂O:Y(NO₃)₃·6H₂O:ZrO(NO₃)_2·xH₂O to be 0.03:0.08:0.89 and 0.10:0.08:0.82, respectively. After calcining at 1650 ℃, 3 mol% and 10 mol% NiO-YSZ powders were obtained, denoted as 2S and 10S, respectively, in which S stands for solid solution. For chemical analysis of composition, the powders were dispersed in diluted HNO₃ solution, while observing the change in color. Phase composition was characterized by using XRD (D8-Advance, Germany), with Cu Kα radiation (λ= 0.15478 nm), over 10°–80°, at a scanning rate of 6 (°)·min⁻¹. The powders were heated in H₂ to identify mass loss ratios before and after reduction. Subsequently, heat treatment was carried out in CH₄ at 800 ℃, while the relative mass gain was recorded. An SU8010 emission scanning electron microscope (SEM, Hitachi, Japan) was used to analyze the powder particles and compare the precipitation status of the Ni particles prepared under different conditions. A STA-449C thermogravimetric analyzer (Naichi Scientific Instrument Manufacturing Co., Ltd. Germany) was employed for thermogravimetric treatment, in order to compare the anti-carbon deposition performance of different powders.[Results] No color change was observed in the 3S sample, while the solution of the 10S sample was light green. In the XRD patterns, only diffraction peaks of YSZ phase were visible in the 3S sample, while trace of undissolved NiO was detected in the 10S sample, which is consistent with the chemical analysis results. As compared with the 3SR9 sample, the 3SR7 sample had lower content of Ni and relatively smaller particle size. However, compared with the 3SR10 sample, the size of Ni particles did not increase continuously, while the precipitation did not increase with increasing reduction temperature. According to TG analysis results, it was found that the mass gain of samples reduced at 900 ℃ after carbon deposition was generally lower than that of those reduced at 700 ℃ and 1000 ℃. With the same content of Ni, the carbon deposition of the Ni@YSZ catalyst was also significantly lower than that of the mixed powders.[Conclusion] The solid solubility of NiO in YSZ is between 3 mol% and 10 mol%, in the samples prepared by using sol-gel method are calcined at 1650 ℃. Compared with those reduced at 700 ℃ and 1000 ℃, the nano Ni particles reduced at 900 ℃ had larger size, more particles and more uniform distribution. Those (Ni@YSZ) prepared through exsolution method not only exhibited excellent coking resistance, but also possessed effectively alleviate carbon deposition on the surface of traditional Ni particles.

Key words: sol-gel method; anti-coking; precipitation; nano-Ni particles