An exsolution constructed FeNi/NiFe2O4 composite: preferential breaking of octahedral metal-oxygen bonds in a spinel
Xiaoyan Guo1, Lu Yao1, Xiangyan Hou1
1State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin Provincial International Cooperation Key Laboratory of Advanced Inorganic Solid Functional Materials, College of Chemistry, Jilin University Qianjin Street 2699 Changchun 130012 China wuxf@jlu.edu.cn kkhuang@jlu.edu.cn.
Abstract:
Exsolution is an ingenious strategy for the in situ construction of metal- or alloy-decorated oxides and, due to its promising energy related catalysis applications, has advanced from use in perovskites to use in spinels. Despite its great importance for designing target composites, the ability to identify whether active metal ions at octahedral or tetrahedral sites will preferentially exsolve in a spinel remains unexplored. Here, an inverse spinel NiFe2O4 (NFO) was employed as a prototype and FeNi/NFO composites were successfully constructed via exsolution. The preferential breaking of octahedral metal-oxygen bonds in the spinel oxide was directly observed using Mössbauer and X-ray absorption spectroscopy. This was further verified from the negative segregation energies calculated based on density-functional theory. One exsolved FeNi/NFO composite exhibits enhanced electrochemical activity with an overpotential of 283 mV at 10 mA cm-2 and a long stability time for the oxygen evolution reaction. This work offers a unique insight into spinel exsolution based on the preferential breaking of chemical bonds and may be an effective guide for the design of new composite catalysts where the desired metal ions are deliberately introduced to octahedral and/or tetrahedral sites.
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