Alkali metals have been widely used as promoters of metal catalysts in various applications,yet the atomic understanding of the promotional mechanism remains elusive.In this work,we for the first time report the signi...Alkali metals have been widely used as promoters of metal catalysts in various applications,yet the atomic understanding of the promotional mechanism remains elusive.In this work,we for the first time report the significant promotional effect of potassium to the Co-N-C single-atom catalyst for the direct dehydrogenation of ethylbenzene.K cation was introduced by impregnation of Co-N-C with KCl followed by calcination at 600℃,which resulted in the bonding of K to the Co-O moiety of the Co-N-C catalyst as revealed by X-ray absorption spectroscopy in combination with theoretical calculations.The formation of Co-O-K moiety led to the increase of electron density at the O atom due to electron transfer of K to O,and consequently facilitated the heterolytic cleavage of the C-H bond of ethylbenzene across the Co-O moiety.The promotional effect of K was found to be a volcanofunction with the K/Co ratio and became the greatest at the K/Co ratio of 1.36,which resulted in the highest steady-state reaction rate of 9.7 mmolEB·gcat^(−1)·h^(−1)reported thus far.Moreover,the catalyst exhibited excellent stability during 100 h time on stream.展开更多
Transition metal dichalcogenide nanodots （NDs） have received considerable interest. We report a facile bottom-up synthetic route for MoS2 NDs by using molybdenum pentachloride and L-cysteine as precursors in oleylam...Transition metal dichalcogenide nanodots （NDs） have received considerable interest. We report a facile bottom-up synthetic route for MoS2 NDs by using molybdenum pentachloride and L-cysteine as precursors in oleylamine. The synthesis of NDs with a narrow size distribution ranging from 2.2 to 5.3 nm, was tailored by controlling the reaction time. Because of its coating characteristics, oleyalmine leads to uniformity and monodispersity of the NDs. Moreover, the NDs synthesized have large specific surface areas providing active sites. Graphene possesses outstanding conductivity. Combining the advantages of the two materials, the 0D/2D material exhibits superior electrochemical performance because of the 2D permeable channels for ion adsorption, energy storage, and conversion. The as-prepared MoS2/rGO （-2.2 nm） showed a stable capacity of 220 mAh.g-1 after 10,000 cycles at the current density of 20 A.g-1. Furthermore, a reversible capacity -140 mAh·g-1 was obtained at a much higher current density of 40 A.g-L Additionally, this composite exhibited superior catalytic performance evidenced by a small overpotential （222 mV） to afford 10 mA.cm-2, and a small Tafel slope （59.8 mV-decade-1） with good acid-stability. The facile approach may pave the way for the preparation of NDs with these nanostructures for numerous applications.展开更多
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 ...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 ℃,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 surfaceadsorbed 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.展开更多
基金supported by the National Natural Science Foundation of China(Nos.22132006,21878289,and 22172159)CAS Project for Young Scientists in Basic Research(No.YSBR-022)the Youth Innovation Promotion Association CAS(No.2018216).
文摘Alkali metals have been widely used as promoters of metal catalysts in various applications,yet the atomic understanding of the promotional mechanism remains elusive.In this work,we for the first time report the significant promotional effect of potassium to the Co-N-C single-atom catalyst for the direct dehydrogenation of ethylbenzene.K cation was introduced by impregnation of Co-N-C with KCl followed by calcination at 600℃,which resulted in the bonding of K to the Co-O moiety of the Co-N-C catalyst as revealed by X-ray absorption spectroscopy in combination with theoretical calculations.The formation of Co-O-K moiety led to the increase of electron density at the O atom due to electron transfer of K to O,and consequently facilitated the heterolytic cleavage of the C-H bond of ethylbenzene across the Co-O moiety.The promotional effect of K was found to be a volcanofunction with the K/Co ratio and became the greatest at the K/Co ratio of 1.36,which resulted in the highest steady-state reaction rate of 9.7 mmolEB·gcat^(−1)·h^(−1)reported thus far.Moreover,the catalyst exhibited excellent stability during 100 h time on stream.
基金This work was supported by the National Key R＆D Program （No. 2016YFB0901502）, National NaturalScience Foundation of China （Nos. 51231003, 51271094, and 21231005）, Ministry of Education （Nos. B12015 and IRT13R30）, and the Fundamental Research Funds for the Central Universities.
文摘Transition metal dichalcogenide nanodots （NDs） have received considerable interest. We report a facile bottom-up synthetic route for MoS2 NDs by using molybdenum pentachloride and L-cysteine as precursors in oleylamine. The synthesis of NDs with a narrow size distribution ranging from 2.2 to 5.3 nm, was tailored by controlling the reaction time. Because of its coating characteristics, oleyalmine leads to uniformity and monodispersity of the NDs. Moreover, the NDs synthesized have large specific surface areas providing active sites. Graphene possesses outstanding conductivity. Combining the advantages of the two materials, the 0D/2D material exhibits superior electrochemical performance because of the 2D permeable channels for ion adsorption, energy storage, and conversion. The as-prepared MoS2/rGO （-2.2 nm） showed a stable capacity of 220 mAh.g-1 after 10,000 cycles at the current density of 20 A.g-1. Furthermore, a reversible capacity -140 mAh·g-1 was obtained at a much higher current density of 40 A.g-L Additionally, this composite exhibited superior catalytic performance evidenced by a small overpotential （222 mV） to afford 10 mA.cm-2, and a small Tafel slope （59.8 mV-decade-1） with good acid-stability. The facile approach may pave the way for the preparation of NDs with these nanostructures for numerous applications.
基金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）.
文摘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 ℃,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 surfaceadsorbed 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.
