(Received: December 21, 2007; Accepted for publication: January 31, 2008; Advance publication: Match 15, 2008)
Irregular porous materials with pore sizes of several tens nm to mm are widely used in industrial applications such as automobile catalysts, gas separation filters, fuel cell electrodes, and lithium ion battery electrodes. Current research and development approaches for irregular porous materials can be classified into the three types shown in Figure 1. Compared to material and interface design approaches, the structure design approach is challenging because no effective method to model realistic porous structures is available presently. To counter this issue, the authors have developed a novel porous structure simulator POCO2, the basic algorithm of which is shown in Figure 2. The POCO2 program is based on an original overlap-allowed particle packing method, where overlaps of particles are allowed up to a certain overlap ratio (Figure 3), and can construct various irregular porous structures as shown in Figure 4. We have also developed tools to quantitatively evaluate microstructures of porous materials, such as cross-sectional area (Figure 5), surface area (Figure 6), pore volume (Figure 7), and triple phase boundary length (Figure 8). In order to investigate the influence of microstructures on the characteristics of irregular porous materials, we have developed a simulator of the overpotential of a solid oxide fuel cell (SOFC) anode (Figure 9). We constructed a model of a Ni-YSZ anode (Figure 10(a)) and confirmed that the overpotential calculated by our simulator agreed well with the experimentally reported value (Figure 10(b)). Finally, we have proposed a scheme for the rational optimization of the microstructure of irregular porous materials (Figure 11(a)) and showed the preliminary results obtained so far (Figure 11(b) and (c)). Based on our preliminary results, we confirmed the potential feasibility of the proposed scheme.
Keywords: Three-dimensional porous structure simulator, Overlap-allowed particle packing method, Irregular porous materials, Microstructure optimization
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