Spinel LiMn2O4 microspheres with durable high rate capability were synthesized by a facile route using spherical MnCO3 precursors as the self-supported templates, combined with the calcinations of LiNO3 at 700 °C...Spinel LiMn2O4 microspheres with durable high rate capability were synthesized by a facile route using spherical MnCO3 precursors as the self-supported templates, combined with the calcinations of LiNO3 at 700 °C for 8 h. The spherical MnCO3 precursors were obtained from the control of the crystallizing process of Mn2＋ ions and NH4HCO3 in aqueous solution. The effects of the mole ratio of the raw materials, reaction time, and reaction temperature on the morphology and yield of the MnCO3 were investigated. The as-synthesized MnCO3 and LiMn2O4 microspheres were characterized by powder X-ray diffractometry （XRD） and scanning electron microscopy （SEM）. Galvanostatic charge/discharge tests indicate that the spinel LiMn2O4 microspheres deliver a discharge capacity of 90 mA-h/g at 10C rate show good capacity retention capability （75% of their initial capacity after 800 cycles at 10C rate）. The durable high rate capability suggests that the as-synthesized LiMn2O4 microspheres are promising cathode materials for high power lithium ion batteries.展开更多
The pore structures and electrochemical performances of mesoporous carbons prepared by silica sol template method as electrode material for supercapacitor were investigated. The mean pore size and mass specific capaci...The pore structures and electrochemical performances of mesoporous carbons prepared by silica sol template method as electrode material for supercapacitor were investigated. The mean pore size and mass specific capacitance of the mesoporous carbons increase with the increase of mass ratio of silica sol to carbon source （glucose）. A modified template method, combining silica sol template method and ZnCl2 chemical activation method, was proposed to improve the mass specific capacitance of the mesoporous carbon with an improved BET surface area. The correlation of rate capability and pore structure was studied by constant current discharge and electrochemical impedance spectroscopy. A commercially available microporous carbon was used for comparison. The result shows that mesoporous carbon with a larger pore size displays a higher rate capability. Mesoporous carbon synthesized by modified template method has both high mass specific capacitance and good rate capability.展开更多
Developing low-cost, high-performance elec- trocatalysts for the oxygen reduction reaction （ORR） is crucial for implementation of fuel cells and metal-air batteries into practical applications. Graphene-based cataly...Developing low-cost, high-performance elec- trocatalysts for the oxygen reduction reaction （ORR） is crucial for implementation of fuel cells and metal-air batteries into practical applications. Graphene-based catalysts have been extensively investigated for ORR in alkaline electrolytes. However, their performance in acidic electrolytes still requires further improvement compared to the Pt/C catalyst. Here we report a self-templating approach to prepare graphene-based sandwich-like porous carbon nanosheets for efficient ORR in both alkaline and acidic electrolytes. Graphene oxides were first used to adsorb m-phenylenediamine molecules which can form a nitrogen-rich polymer network after oxidative poly- merization. Then iron （Fe） salt was introduced into the polymer network and transformed into ORR active Fe-N-C sites along with Fe, FeS, and FEN0.05 nanopartides after pyr- olysis, generating ORR active sandwich-like carbon na- nosheets. Due to the presence of multiple ORR active sites. The as-obtained catalyst exhibited prominent ORR activity with a half-wave potential -30 mV more positive than Pt/C in 0.1 mol L-1 KOH, while the half-wave potential of the catalyst was only -40 mV lower than that of commercial Pt/C in 0.1 mol L-1 HClO4. The unique planar sandwich-like structure could expose abundant active sites for ORR. Meanwhile, the graphene layer and porous structure could simultaneously enhance electrical conductivity and facilitate mass transport. The prominent electrocatalytic activity and durability in both alkaline and acidic electrolytes indicate that these carbon na- nosheets hold great potential as alternatives to precious metal- based catalysts, as demonstrated in zinc-air batteries and proton exchange membrane fuel cells.展开更多
基金Project(2011M501090) upported by the China Postdoctoral Science FoundationProject(SCUT2012ZZ0042) upported by the Fundamental Research Funds for the Central Universities+1 种基金Project supported by the"SPR-2011"of South China University of TechnologyProject(NRC07/08.EG01)supprted by the Fok Ying Tung Foundation
文摘Spinel LiMn2O4 microspheres with durable high rate capability were synthesized by a facile route using spherical MnCO3 precursors as the self-supported templates, combined with the calcinations of LiNO3 at 700 °C for 8 h. The spherical MnCO3 precursors were obtained from the control of the crystallizing process of Mn2＋ ions and NH4HCO3 in aqueous solution. The effects of the mole ratio of the raw materials, reaction time, and reaction temperature on the morphology and yield of the MnCO3 were investigated. The as-synthesized MnCO3 and LiMn2O4 microspheres were characterized by powder X-ray diffractometry （XRD） and scanning electron microscopy （SEM）. Galvanostatic charge/discharge tests indicate that the spinel LiMn2O4 microspheres deliver a discharge capacity of 90 mA-h/g at 10C rate show good capacity retention capability （75% of their initial capacity after 800 cycles at 10C rate）. The durable high rate capability suggests that the as-synthesized LiMn2O4 microspheres are promising cathode materials for high power lithium ion batteries.
文摘The pore structures and electrochemical performances of mesoporous carbons prepared by silica sol template method as electrode material for supercapacitor were investigated. The mean pore size and mass specific capacitance of the mesoporous carbons increase with the increase of mass ratio of silica sol to carbon source （glucose）. A modified template method, combining silica sol template method and ZnCl2 chemical activation method, was proposed to improve the mass specific capacitance of the mesoporous carbon with an improved BET surface area. The correlation of rate capability and pore structure was studied by constant current discharge and electrochemical impedance spectroscopy. A commercially available microporous carbon was used for comparison. The result shows that mesoporous carbon with a larger pore size displays a higher rate capability. Mesoporous carbon synthesized by modified template method has both high mass specific capacitance and good rate capability.
基金supported by the National Basic Research Program of China (973 Program, 2015CB351903)the National Key Research and Development Program (2017YFA0207301)+1 种基金the National Natural Science Foundation of China (51402282, 21474095 and 21476104)CAS Key Research Program of Frontier Sciences (QYZDB-SSW-SLH018)
文摘Developing low-cost, high-performance elec- trocatalysts for the oxygen reduction reaction （ORR） is crucial for implementation of fuel cells and metal-air batteries into practical applications. Graphene-based catalysts have been extensively investigated for ORR in alkaline electrolytes. However, their performance in acidic electrolytes still requires further improvement compared to the Pt/C catalyst. Here we report a self-templating approach to prepare graphene-based sandwich-like porous carbon nanosheets for efficient ORR in both alkaline and acidic electrolytes. Graphene oxides were first used to adsorb m-phenylenediamine molecules which can form a nitrogen-rich polymer network after oxidative poly- merization. Then iron （Fe） salt was introduced into the polymer network and transformed into ORR active Fe-N-C sites along with Fe, FeS, and FEN0.05 nanopartides after pyr- olysis, generating ORR active sandwich-like carbon na- nosheets. Due to the presence of multiple ORR active sites. The as-obtained catalyst exhibited prominent ORR activity with a half-wave potential -30 mV more positive than Pt/C in 0.1 mol L-1 KOH, while the half-wave potential of the catalyst was only -40 mV lower than that of commercial Pt/C in 0.1 mol L-1 HClO4. The unique planar sandwich-like structure could expose abundant active sites for ORR. Meanwhile, the graphene layer and porous structure could simultaneously enhance electrical conductivity and facilitate mass transport. The prominent electrocatalytic activity and durability in both alkaline and acidic electrolytes indicate that these carbon na- nosheets hold great potential as alternatives to precious metal- based catalysts, as demonstrated in zinc-air batteries and proton exchange membrane fuel cells.
