Controllable Construction Of Energy-related Mesoporous Materials Templated By Block Copolymer Assemlies In Solution

Recently,mesoporous materials have attracted tremendous attention for their ultrahigh surface areas,large pore volume,superb mass transfer,tunable mesopore sizes and shapes.Therefore,they exhibit a wide range of potential application in the field of energy storage,energy conversion,catalysis,drug delivery and gas separation.When utilizating as electrode materials,the electrochemical performance of mesoporous materials is governed by their pore size,pore structure and dimensionality.Till now,it still remains a great challenge to fabricate mesoporous materials with well-defined pore size and structure despite that a variety of methods has been developed for the synthesis of mesoporous materials.The solution self-assembly of block copolymers provides a versatile strategy for constructing various ordered nanostructures.It is capable of preparing mesoporous nanomaterials by utilizing suitable precursors for crosslinkage of block copolymers self-assemblies,followed by removal of block copolymers template.The shape and size of mesopores could be conveniently altered by controlling self-assembly behavior of block copolymers.On the other hand,dimensionality of mesoporous materials could also be adjusted with the help of interfacial assembly.On the basis of this conception,we design and prepare a series of multidimensional mesoporous materials with well-defined pore structure and sizes,including two dimensional?2D?and three dimensional?3D?materials.Furthermore,the influence of mesopore size,pore structure and dimensionality on the electrochemical performance has also been systematically investigated.The results are summarized as follows:?1?Pore size is one of key factors for high performance supercapacitor mesoporous carbon electrodes.The second chapter reports the synthesis of nitrogen-doped mesoporous carbon nanospheres?MCNSs?with average diameters of around 300 nm and controlled pore sizes ranging from 8 to 38 nm,by employing polystyrene-b-poly?ethylene oxide?diblocks with different PS block lengths as the soft templates and dopamine as the carbon-rich precursor.For the first time,a linear equation was achieved for the quantitative control of the pore size of MCNSs by simply adjusting a block length of diblock copolymer.The resultant MCNSs possess high surface area of up to 450 m²·g^-1 and nitrogen doping contents of up to?3 wt%.As electrode materials of supercapacitors,the MCNSs exhibited excellent electrochemical performance with high specific capacitances of up to 350 F·g^-1 at 0.1A·g^-1,superior rate capability and cycling stability.The specific capacitance of the MCNSs reduces linearly with increasing pore size,whereas the normalized capacitance by specific surface area remained invariable.This study provides a new spectrum of the relationship between electrochemical capacitance and pore size?>5 nm?for porous carbons,which makes a complement to the existing spectrum focusing on pore diameters of<5 nm.?2?The development of versatile strategies towards 2D porous nanocomposites with tunable pore structures is of immense scientific attention in view of their large amount of accessible active sites and a wide range of promising applications compared with 0D materials.The third chapter describes a self-assembly approach for the directed growth of mesoporous polyaniline?PANi?with tunable pore structures and sizes on ultrathin free-standing MoS₂ nanosheets in solution,which produces2D mesoporous PANi/MoS₂ nanocomposites.The strategy employs spherical and cylindrical micelles,which are formed by controlled solution self-assembly of block copolymers,as the soft templates for the construction of well-defined spherical and cylindrical mesopores in the2D PANi/MoS₂ nanocomposites,respectively.With a potential application as supercapacitor electrode materials,the resultant 2D composites show excellent capacitive performance with a maximum capacitance of 500 F·g^-1 at a current density of 0.5 A·g^-1,good rate performance,as well as outstanding stability for charge-discharge cycling.This superb performance surpasses those of MoS₂-based 2D nanocomposites.Moreover,the 2D mesoporous nanocomposites offer an opportunity for the study on the influence of different pore structures on their capacitive performance,which helps to understand pore structure-property relationship of 2D porous electrode materials and to achieve their electrochemical performance control.?3?2D nitrogen-doped mesoporous carbon materials have been considered as one of the most prominsing electrocatalysts in oxygen reduction reaction?ORR?,which could obtain by directly carbonization of 2D mesoporous PANi.In fourth charpter,nitrogen-doped mesoporous carbon with spherical and cylindrical mesopores were fabricated on graphene nanosheets by employing Pluronic block copolymer micelles as pore-direct agents and m-phenylenediamine as carbon precursor.The resultant posess similar specific surface area(⁴22 m²·g^-1),pore size?⁹nm?and nitrogen content?².5 wt%?.As catalystic materials for oxygen reduction reaction,the resultant materials with cylindrical mesopores exhibit superior electrocatalytic performance compared with spherical mesoporous material when serving as oxygen reduction reaction catalysts,with half-wave-potential?0.74 V?and limiting current density(4.8mA·cm^-2),benefiting from high mass transfer property and large accessible active sites of cylindrical structure.?4?Preferential stacking of 2D nanosheets is unfavorable for the enhancement of ORR performance,which could lead to the decrease of exposed active sites.The construction of holey structure with much exposure of active sites,yet challenging to achieve up till now,is reconginized as one of the most effective methods to overcome the shortcoming of current ORR catalysts.The fifth chapter describes a dual-template method for fabrication of new carbon materials for ORR catalysts,including N-doped carbon nanosheets and nanoflowers with holey mesopores,by employing polystyrene-b-poly?ethylene oxide?block copolymer as the pore-forming agent,layered double hydroxide?LDH?nanosheets or nanoflowers as the sacrificial morphology-directing template,and m-phenylenediamine as the carbon precusor.The resultant carbon materials possess a honeycomb-like mesoporous structure with similar nitrogen content of?4 wt%,average pore size of?14 nm and specific surface area of?260 m²·g^-1.Due to the presence of the holey mesopores that facilitate mass transfer and may shorten the diffusion distance of O₂ molecules to the active sites,the nanosheets and the nanoflowers exhibit excellent electrocatalytic performance when serving as metal-free ORR catalysts in basic media,with high half-wave-potential?0.80 V?and limiting current density(5.5 mA·cm^-2),which surpass those of many reported carbon-based materials with much higher surface areas but without holey pores.Moreover,the porous nanoflowers shows better electrocatalytic activity than that of the nanosheets,profiting from their3D structure that can prevent the blockage of partial holey pores caused by the preferential layer-by-layer stacking of the nanosheets.