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Shin, Seungho,Kim, Ah-Reum,Um, Sukkee 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol. No.
<P>A two-dimensional material network model has been developed to visualize the nano-structures of fuel-cell catalysts and to search for effective transport paths for the optimal performance of fuel cells in randomly-disordered composite catalysts. Stochastic random modeling based on the Monte Carlo method is developed using random number generation processes over a catalyst layer domain at a 95% confidence level. After the post-determination process of the effective connectivity, particularly for mass transport, the effective catalyst utilization factors are introduced to determine the extent of catalyst utilization in the fuel cells. The results show that the superficial pore volume fractions of 600 trials approximate a normal distribution curve with a mean of 0.5. In contrast, the estimated volume fraction of effectively inter-connected void clusters ranges from 0.097 to 0.420, which is much smaller than the superficial porosity of 0.5 before the percolation process. Furthermore, the effective catalyst utilization factor is determined to be linearly proportional to the effective porosity. More importantly, this study reveals that the average catalyst utilization is less affected by the variations of the catalyst's particle size and the absolute catalyst loading at a fixed volume fraction of void spaces.</P>
Shin, Seungho,Liu, Jiawen,Akbar, Ali,Um, Sukkee Elsevier 2019 Journal of catalysis Vol.377 No.-
<P><B>Abstract</B></P> <P>Nanoscale transport characteristics and catalyst utilization of vertically aligned carbon nanotube (VACNT) catalyst layers (CLs) are evaluated using a fully statistical modeling approach based on the inherent random nature of the catalyst layer structures for fuel cell applications. Composite morphological structures of the catalyst layers are stochastically modeled with a 95% confidence level, and transport phenomena inside the catalyst layers are simulated using the D3Q19 lattice Boltzmann method (LBM). The effective diffusion coefficient of VACNT catalyst layers is predicted to be higher than that of the conventional catalyst layer, despite a relatively small pore diameter and a low-Knudsen diffusion coefficient. Consequently, the VACNT catalyst layers exhibit improved catalyst utilization compared to the conventional catalyst layers. These statistical results obtained from a series of numerical experiments confirm that the PEFC catalyst layers containing the VACNT catalyst supports can provide more efficient reactant transport, resulting in enhanced catalyst utilization for electrochemical reactions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A 3-dimensional Lattice Boltzmann method (LBM) was proposed for catalyst modeling. </LI> <LI> Structure–transport characteristics of catalyst layer were statistically predicted. </LI> <LI> VACNT catalyst layers can form more favorable pore structures for mass transport. </LI> <LI> Nanotube forest effects of VACNT catalyst layers induces lower Knudsen diffusion. </LI> <LI> Improved pore design and low tortuosity yield higher catalyst utilization in VACNT. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>