Effect of morphological properties of ionic liquid-templated mesoporous anatase TiO_2 on performance of PEMFC with Nafion/TiO_2 composite membrane at elevated temperature and low relative humidity

摘要

Three high-purity TiO_2 (anatase) powders (T_(PF6), T_(BF4), and T_(conventional)) were prepared by the sol-gel method with/without ionic liquid as template and calcinations at 450 ℃. These powders were, then, characterized to investigate their differences in morphological properties. Electrochemical performances of the H_2/O_2 PEMFCs employing the Nafion composite membranes with these three TiO_2 powders as fillers were studied over 80-120 ℃ under 50% and 95% relative humidity (RH). The result showed that the order of the fillers effect on the performance at 80 and 90 ℃ was the same as that of the TiO_2 filler's specific surface area (i.e. T_(PF6) ＞ T_(conventional) ＞ T_(BF4) ＞ P25, a commercially available nonporous TiO_2 powder). However, the order between T_(conventional) and T_(BF4) was reversed at 110 and 120 ℃ under 50% RH. This indicates that the size and the amount of mesopores, which better confined the water molecules, were significant contributing factors to the performances at the higher temperatures. The best power density obtained under 50% RH at 120 ℃ and a voltage of 0.4 V was from the PEMFC with the T_(PF6)-containing Nafion composite membrane. It was about 5.7 times higher than the value obtained from that with the recast Nafion membrane.