In order to meet strong demands for electronic state analysis for green devices such as ultra-low power consumption LSI, Li ion battery (LIB) and fuel cells, we have developed soft X-ray nano-spectroscopy techniques. In this talk, I will introduce our latest results on electronic structures of non-Pt cathode catalysts for power generation and LIB cathode materials for energy storage revealed by synchrotron radiation analysis.     First of all, we analyzed electronic structures of carbon-related catalysts alternative to Pt for Polymer Electrolyte Fuel Cells (PEFC) in order to elucidate the oxygen reduction reaction (ORR) mechanism. We prepared metal phthalocyanine-based carbon catalysts with 1-2% nitrogen and less than 0.1 % of Fe for PEFC. Photoelectron spectroscopy and first principles calculation revealed that zigzag edge carbons with neighboring graphite-like nitrogen are ORR active sites. Based on these analyses, we fabricated fuel cell stack for PEFC which showed comparable performance to Pt catalysts. Furthermore, we have taken in operando soft X-ray emission spectra of Fe 2p-3d transition during power generation, revealing that Fe impurity may act as an ORR catalyst.     Next, we analyzed the change of Fe 3d states accompanied with the Li intercalation/ deintercalation process by resonant photoemission spectroscopy. The main peak shift and expansion of Fe 3d bands through the Li deintercalation reflect the strong hybridization between Fe 3d states and O 2p state. Since the battery voltage should reflect the energy difference between Li 2s and Fe 3d down-spin state, we measured the change in Fe 3d down-spin states for LiFePO4 (3.4V) and Li2FeP2O7 (3.6V) and found that 0.2 eV shift from PO4 to P2O7 poly-anions directly reflects battery voltage. Furthermore, we investigated the electronic states of Mn 3d during Li intercalation/ deintercalation into LiMn2O4 cathode using in operando soft X-ray emission spectroscopy at different charge/ discharge voltages.

Soft X-ray nanospectroscopy for power generation and energy storage green devices

246th National Meeting (2013)

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