| Summary: | 碩士 === 國立臺灣大學 === 化學研究所 === 104 === Metal oxide of spinel family has performed great potential to replace RuO2 or IrO2 toward oxygen evolution reaction (OER), but the fundamental mechanism of spinel oxides is still far from a complete understanding especially for the role of metal ions. Owing to various coordinated sites of divalent/trivalent metals ions and surface condition (mor-phology and defects), it’s a great challenge to have a fair assessment of electrocatalytic performance of spinel system. Herein, we demonstrated a series of MFe2O4 (M = Mn, Fe, Co, Ni, Zn) family with a well-controlled morphology to achieve comprehensive study of electrocatalytic activity toward OER, in which most of the divalent metals (M2+) of MFe2O4 were located at octahedral sites and well-defined single-crystal nanocubes were synthesized to minimize the influence caused by crystallographic sites/morphology of variables for each samples. The effects of M2+ ion in MFe2O4 can be realized through investigating the OER behaviors of MFe2O4 and that of γ-Fe2O3 as a reference to have in-depth understanding of the roles of divalent/trivalent metal ions. In-situ X-ray diffraction and ex-situ X-ray absorption spec-troscopies were employed to provide direct evidence that the superior OER activities of CoFe2O4 and NiFe2O4 samples could be attributed to a remarkable phase transformation forward metal oxyhydroxide, while the rest of compounds remain unchanged during oxygen evolution reaction.
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