Microstructure development of mesoporous silica thin films with pore channels aligned perpendicularly to electrode surfaces and application to proton conducting composite electrolyte membranes

Abstract

We investigated a novel preparation technique of a proton conducting inorganic composite thin membrane consisting of an oxyacid salt proton conductor, CsHSO 4, and a mesoporous SiO 2 thin film that has highly oriented mesopores. The mesoporous SiO 2 thin films were prepared through the removal of the Fe component from Fe–Si–O precursor thin films synthesized by sputter deposition. In this study, we focused on the SEM observation of growth structures of Fe–Si–O precursor thin films and the resultant mesoporous SiO 2 thin films. The relationship between the deposition parameters (working gas pressure and target component) and the growth structures of the thin films is discussed. The obtained mesoporous SiO 2 thin films showed pore channels aligned perpendicularly to electrode surfaces when relevant deposition parameters were applied. A CsHSO 4/SiO 2 composite thin membrane was prepared by the impregnation of a CsHSO 4 aqueous solution into the mesopores of a SiO 2 thin film. The proton conductivity of the CsHSO 4/SiO 2 composite thin membrane was examined with respect to the difference between proton conduction in the composite thin membrane and that in neat CsHSO 4, which suggests that mesopores of a SiO 2 thin film play an important role in the enhancement of proton conductivity, especially in the low-temperature region between 60 and 140 °C.