Novel Carbon-based Materials For Supercapacitor,Lithium Battery And Electrocatalytic Oxygen Reduciton

The rapidly increasing global energy consumption coupled with the critical issue of climate change have attracted tremendous attention and developing the clean,sustainable energy is imperative.Among the diverse energy-related techniques,the three energy storage techniques of supercapacitor,lithium battery and fuel cell have received considerable attention.Despite the huge progess in these areas,many problems still exist,such as low energy density of supercapacitor,poor power density and cycle life of lithium battery,sluggish oxygen reduction reaction?ORR?and high-cost of electrocatalyst in fuel cell and so on.An effective solution towards the problems is developing advanced and novel nanoarchitectured materials.On the other hand,carbon-based nanomateriasl,such as,ordered mesoporous carbon?OMC?,graphene,carbon nanotube and carbon aerogel are of great interest in a wide range of fields from sensors,catalysis,biochemisty to energy storage and conversionhas due to their excellent mechanical,electrical,optical and electrical properties.Through rational consideration of the research frontiers and possible requirements in practical applications of the three above-mentioned energy storage techniques,this thesis mainly focuses on the rational design and controllable synthesis of novel carbon-based nanomaterials for the potentional applications in supercapacitor,lithium battery and fuel cell.1.We demonstrate a doubly enhanced strategy for improving the energy storage performance of graphene through insertion of pristine CNTs between graphene nanosheet and ordered mesoporous carbon coatings.We found that graphene oxide,which typically consists of hydrophobic polyaromatic areas of unoxidized benzene rings and hydrophilic regions containing carboxylic acid?at the periphery?,epoxy,and hydroxyl?in the basal plane?groups could serve as "surfactant" to directly disperse the pristine CNTs without any additives or surfactants,simplifying the process.The inserted pristine CNTs not only impede the aggregation of graphene nanosheets,but also improve the whole conductivity of the nanocomposites.Subsequently,the resulted graphene oxide-CNTs could be used as substrate for triconstituent self-assembly coating of ordered mesoporous carbon and finally the resulting graphene-CNT-ordered mesoporous carbon ternary hybrids?GCMCs?possess an ordered,interconnected mesostructure,a high specific surface area of 1411 m² g^-1,large mesopores of 4.3 nm,and good conductivity.With their tailored architecture,the GCMCs-based supercapacitor and lithium battery show excellent energy storage performance,superior to that of graphene.2.We use graphene oxide-dispersed pristine CNTs?GOCs?as substrate to support electrochemically active MnO2 nanorods and nitrogen heteroatom through redox reaction and hydrothermal deposition,respectively.In contrast to the single graphene,the GOCs-derived hybrid show superior specific capacitance.For example,the specific capacitance of resulted MnO2-CNT-graphene oxide?MCGO?is 4.7-10.5 fold improvement compared to that of free MnO2 under different scan rates.In addition,the specific capacitance of resulted 3D nitrogen-doped graphene-CNT networks?NGCs?is 1.9-5.6 higher than that of nitrogen-doped graphene.3.We synthesize the hollow core,bimodal mesoporous shell carbon nanospheres?HCMSs?with large bimodal mesopores?6.4 and 3.1 nm?and high surface area(1704 m² g^-1)via a surface co-assembly of monodisperse silica nanospheres prepared by the stober method,wherein,the phenolic oligomers were used as organic precursor,TEOS was used as inorganic precursor,triblock copolymer F127 was used as a template.The resulted HCMSs show a high specific capacity of 251 F g^-1 at 50 mV s-1 in 2 M H2SO4 and long cyclic life.4.We propose a green and facile commercially melamine sponge?CMS?-derived stratgegy to prepared nitrogen-doped carbon aerogels?NCAs?.The key difference of this new approach compared to early efforts is that we used CMS,an effective abrasive cleaner,as green N precursor and 3D substrate for self-assembly.The as-prepared NCAs have a low density of 0.01 g cm-3,large opened pores and high specific surface area of 1626 m² g^-1 and moderate nitrogen contents of 2%.Benefiting from these properties,the NCAs-based supercapacitor and ORR electrocatalysts show excellent performance.For example,NCAs-based supercapacitor show high capacitance of 354 F g^-1 at current density of 0.2 A g^-1,the capacitance of 160 F g^-1 can be obtained even the current density increase to 10 A g^-1 and still retain the 90%of the initial capacitance after 3 000 cycles.In addition,the ORR electrocatalysts based on NCAs exhibit the favorable four-electron process and superior stability in terms of a negative shift of only 24 mV after 10 000 cycles.5.We report a unique homogeneous hydrogel-derived bottom-up process to fabricate three dimensional porous carbon-supported nonprecious electrocatalyst.This strategy starts with a facile gelating process followed by freeze-drying and carbonization of a gel matrix containing cobalt acetate,TBE buffer?Tris/Boric acid/EDTA?,and agarose.The TBE buffer not only controls the gel pH but also provides a coordinating interaction with Co2+ to suppress its hydrolysis and alleviate the sintering or agglomeration of Co-based nanoparticles during carbonization.In the meantime,the TBE buffer can act as precursors for the ORR-active N-and B-doping of graphitized carbon,and as salt porogen to achieve high porosity and large specific surface area.The as-obtained hybrid show homogeneous microstructure,moderate heteroatom contents?3.03%Co,4.59%N and 5.96%B?,high specific surface area(432 m² g^-1)and large mesopores?average pore diameter of 6.4 nm?with molecular accessibility,resulting in excellent four-electron ORR performance comparable to commercial Pt/C catalysts.This potentially general hydrogel-based strategy for catalyst preparation is inexpensive,environmentally benign and scalable,opening up a material-oriented new application for hydrogel.It is reasonable to expect that this unique strategy can be extended to synthesize other metal oxide or metal,catalysts supported on N,B co-doped nanocarbons for energy-related applications.