Development of Coordination Space Controlled Materials and Their Application to Energy Devices

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In this project we aim to develop coordination space controlled materials and apply them to energy devices. We focus on 1) development of perovskite-based new proton conductors, 2) development of new mixed (= ionic and hole (or electronic)) conductors, and 3) their application to energy devices, e.g. fuel cells. We have investigated in detail the conduction properties of LaScO3-based perovskites, (Lal-xSrx)ScO3-δ (x=0.2,0.3), and obtained the "Charge carrier map". The map depicts predominant charge carrier (i.e. oxide-ion, proton, hole, and electron) domains as functions of temperature (T), oxygen partial pressure (P(02)) and hydrogen partial pressure (P(H2)). It is found that at 600℃, those perovskites are expected to work as a proton conductor both under cathode and anode conditions of fuel cells. Also it was revealed that the thin ceramics of those perovskites with 98.2% relative density could be applied for H2 gas sensor and so on.We have studied the electronic states and local structures of metal ions in proton conducting perovskites (Lal-xSrx)ScO3-δ (x=0.1, 0.2, 0.3) and mixed (= proton and hole) conducting perovskites with LaScO3 basic structure, (La0.8Sr0.2) (Scl-xMnx)03-s (x = 0.1, 0.25, 0.5, and 0.75) (LSSM) by powder X-ray diffraction and La. L3-, Sc K-, Mn K-, and Sr K-XAFS analysis. The comparison of Sr K- and Sc K-XANES regions of the proton conducting perovskites revealed that the bonding (i.e. electronic) states of H+ (or D+) ions, which are expected to be coordinated to ScO6 octahedra, could exhibit difference depending on amount of Sr doped. The comparison of Mn K-XANES regions of the LSSM suggested that the Mn ions in the LSSM would have Mn3+/Mn4+ mixed valence. The results of total electrical conductivity measurements of LSSM (x=0.25-0.75) suggested the predominant charge carrier is not proton but hole and (or) oxide ion.