Functional Design and Structural Control of Meso-and Macro-porous Ceramics

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Design and processing of meso- and macro-porous films and their applications to various electrochemical devices were attempted as below in this research project.1. Some kinds of thermally stable mesoporous (m-) SnO_2 powders with strictly controlled crystallize size and pore distribution were prepared by utilizing self-assembly of general surfactants (e.g. cetylpyridinium chloride) or triblockcopolymers, followed by treatment with phosphoric acid aqueous solution. The m-SnO_2 sensors and conventional (c-) SnO_2 sensors modified with m-SnO_2 showed higher H_2 responses in comparison with general c-SnO_2 sensor. It is also revealed that m-Al_2O_3 powders with surface area were prepared from aluminum isopropoxide in 1-propanol solvent by utilizing behenic acid as a template. The m-Al_2O_3 powders were quite promising as a gas sensing material for absorption/combustion-type sensor for VOC detection. On the other hand, it was confirmed that macroporous (mp-) SnO_2 sensors, which were fabric … More ated by a modified sol-gel technique employing polymethylmethacrylate (PMMA) microspheres, showed high response to H_2 and NOx. In addition, we also showed that a resonant sensor based on quartz crystal microbalance and mp-BaCO_3 was highly sensitive to NO_2.2. Various mp-ceramic films (e.g., CeO_2, BaTiO_3, CaCu_3Ti_4O_<12>, La_<1-x>Sr_xCoO_3) were fabricated even by utilizing typical dry process, such as pulsed laser deposition and r.f. magnetron sputtering, employing PMMA microsphere film templates.3. Mp-noble Pt films were prepared by r.f. magnetron sputtering or electrolytic deposition employing PMMA microsphere film templates. Oxygen reduction activities of their porous films obtained were larger than that of a conventional dense Pt film. In addition, an amperometric glucose sensor coupled with the mp-Pt electrode prepared by electrolytic deposition showed higher sensitivity to glucose, compared with a conventional sensor coupled with Pt black electrode.4. A mp-TiO_2 electrode for a dye-sensitized solar cell was fabricated with fine TiO_2 powder (P25) by using PMMA microspheres as a template. Stacking of the mp-TiO_2 layer on a conventional TiO_2 electrode was effective for improving the conversion efficiency of the solar cell, probably due to the improved diffusivity of electrolyte with a help of macropores in the electrode. Less