Fabrication Of Helical Carbonaceous Composite Nanomaterials Using Helical Mesoporous Silicas As Hard-template

Helical mesoporous silicas have attracted special interests due to their various morphology,highly ordered pore structure,well thermal stability and high specific surface.Compared to the chiral amphiphilic molecule which can be used to synthesize helical mesoporous silicas via a sol-gel transcription method,using achiral surfactant with the help of organic dopants to form helical structure is much cheaper and more convenient,which is more suitable for wild application.In the first part of this work,mesoporous silicas with different structures have been prepared using cetylpyridinium chloride as the template,amino acid and 1-hexanol as organic dopants.The results indicate that:(1)The amount of amino acid has great impact on the morphology of the materials,especially in the mixture solution of ethanol and water,in which the length of the mesoporous silica nanorods can be changed.(2)When used as additives,1-hexanol can act as a "spacing agent" to optimize the interaction between the OH group of the alcohol and the head group of the ionic surfactant,which can be used to achieve longer silica nanofibers due to the driving of entropy.In the second part,electrochemical performance of anode materials and the oxygen reduction reaction(ORR)electrocatalytic performance were studied.Using helical mesoporous silica nanofibers as hard template,helical C/SiC/Si composite nanofibers and helical SiO2@Fe-N-C nanofibers were fabricated.When applied as anode materials in lithium-ion batteries,they both exhibit outstanding cycling performance.The discharge capacity of helical C/SiC/Si composite nanofibers achieves 724 mA h g-1 after 900 cycles,and the helical SiO2@Fe-N-C nanofibers goes up to 955 mA h g-1 after 500 cycles,which are much better than the capacity of commercial graphite.The helical SiO2@Fe-N-C nanofibers were also tested for ORR catalyst.The results demonstrate that:The SiO2@Fe-N-C nanofibers deliver a positive onset potential of 943 mV(vs RHE)and half-wave potential of 733 mV(vs RHE)as well as a larger diffusion-limited current density of 5.57 mA/cm2,compared to the commercial Pt/C material,which exhibit superior ORR activity.