Density Functional Theory Study of Dopant Effect on Sintering in the Anode of Solid Oxide Fuel Cell

Sintering of Ni nanoparticles in a Ni/YSZ porous anode of a solid oxide fuel cell (SOFC) during the long-term operation take places easily due to the high operation temperature, which leads to the degradation of the Ni/YSZ porous electrode. In previous studies, we developed a multi-nanoparticle modeling methodology that can consider the effects of the properties of the porous structure such as porosity and YSZ nanoparticle framework, etc., for investigating the sintering process in the porous structure and revealed that the porous structure plays a critical role in suppression of the sintering [1,2]. Moreover, the porous structure is determined by the framework consisting of many nanoparticles. Thus, the design of the framework structure that can effectively prevent the sintering during the operation is demanded. For this purpose, the investigation of the YSZ nanoparticle size effect on the framework structure and its effect on the sintering is needed, because the framework structure is determined by the nanoparticle size, nanoparticle ratio and so on. However, the mechanism of different sintering behavior by changing the size of YSZ nanoparticle has not been revealed. In this study, we investigated the effect of YSZ nanoparticle size on the sintering of Ni nanoparticles in the Ni/YSZ porous structure by using our multi-nanoparticle sintering simulation based on the large-scale molecular dynamics simulation method. Our results show that Ni nanoparticles make contact with each other and the sintering proceeds by the growth of the contact area between the Ni nanoparticles. Then, we quantified the degree of sintering and found that the degree of sintering in the Ni/YSZ model with the large YSZ nanoparticles compared to Ni nanoparticles is larger than that with the small YSZ nanoparticles compared to Ni nanoparticles. In the Ni/YSZ model with the large YSZ nanoparticles compared to Ni nanoparticles, the framework of large YSZ nanoparticles generates the large pore. The Ni nanoparticles are easy to move in the framework structure, and the sintering of Ni nanoparticles takes place easily. On the other hand, the framework of small YSZ nanoparticles generates the small pore in the Ni/YSZ model with the small YSZ nanoparticles compared to Ni nanoparticles. The framework of small YSZ nanoparticles restrains the movement of the Ni nanoparticles. Thus, the sintering of Ni nanoparticles is inhibited in the Ni/YSZ model with the small YSZ nanoparticles compared to Ni nanoparticles. 

[1] J. Xu et al., J. Phys. Chem. C 117 (2013) 9663.

[2] J. Xu et al., ECS Trans. 57, (2013) 2459.