Synthesis of size-controlled CoMn2O4 quantum dots supported on carbon nanotubes for electrocatalytic oxygen reduction/evolution
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A combined hot-injection and heat-up method was developed to synthesize monodisperse and uniform CoMn2O4 quantum dots (CMO QDs). CMO QDs with average size of 2.0, 3.9, and 5.4 nm were selectively obtained at 80, 90, and 105 °C, respectively. The CMO QDs supported on carbon nanotubes (CNTs) were employed as catalysts for the oxygen reduction/evolution reaction (ORR/OER) in alkaline solution to investigate their size-performance relationship. The results revealed that the amount of surface-adsorbed oxygen and the band gap energy, which affect the charge transfer in the oxygen electrocatalysis processes, strongly depend on the size of the CMO QDs. The CMO-3.9/CNT hybrid, consisting of CNT-supported CMO QDs of 3.9 nm size, possesses a moderate amount of surface-adsorbed oxygen, a lower band gap energy, and a larger charge carrier concentration, and exhibits the highest electrocatalytic activity among the hybrid materials investigated. Moreover, the CMO-3.9/CNT hybrid displays ORR and OER performances similar to those of the benchmark Pt/C and RuO2 catalysts, respectively, due to the strong carbon-oxide interactions and the high dispersion of CoMn2O4 QDs on the carbon substrate; this reveals the huge potential of the CMO-3.9/CNT hybrid as a bifunctional OER/ORR electrocatalyst. The present results highlight the importance of controlling the size of metal oxide nanodots in the design of active oxygen electrocatalysts based on spinel-type, nonprecious metal oxides.
Keywordssize effect spinel oxide quantum dots electrocatalysis
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This work was supported by the National Key Research and Development Program of China (Nos. 2016YFA0202500 and 2016YFB0101201), the National Natural Science Foundation of China (Nos. 21322101 and 21231005) and 111 Project (Nos. B12015 and IRT13R30).
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