Controllable Preparation Of Functional Porous Materials And The Study Of Their Electrochemical Performance

With the advantages of high porosity and specific surface area,porous materials usually exhibit unique physical and chemical properties different from solid structures,which make them have an potential applications in various areas such as electrocatalysts,photocatalysts,battery,supercapacitors and so on.In porous materials,the large mesopores or/and macroporous will serve as high ways for electrolyte to penetrate and evenly cover the electrode material,and contact quickly with the micropores,enhancing the performance of materials.Therefore,the rational combination of interconnected micro-/mesopores in porous materials will be an effective way to improve their performance.Additionally,introducing heteroatoms?such as B,N,O,S,Co and so on?into the framework of materials has been proved to be an efficient method to greatly enhance the chemical and electronic properties of materials.Based on above considerations,hollow structures and hierarchical porous structure materials were constructed and successfully applied in electrolysis,Zn-air battery and supercapacitor area.These systems were constructed by using supramolecular self-assembly complex with specific morphology and structure as template and/or precursor to construct these systems.The following is the main contents and results:Firstly,a facile method was reported to control both the pore dimension and the graphitic nitrogen doping of a net-like carbon material via self-assembly and pyrolysis of nanoparticles and commercial block copolymer poly?ethylene oxide?-block-poly?propyleneoxide?-block-poly?ethyleneoxide?(PEO₂₀-PPO₇₀-PEO₂₀,P123)with the assistance of TiO₂ and DCDA.Only large-area layered carbon formed when TTIP and thus TiO₂ nanoparticles were excluded from the synthetic system.The involvement of TTIP and thus TiO₂ nanoparticles dominated the formation of net-like structure revealing their role as hard-template for directing the assembly of P123.The yield of graphitic nitrogen doped micro/mesoporous carbon net?g-N-MM-Cnet?increased with more P123 added,rather suggesting the role of P123 as carbon source.As an oxygen rich polymer,P123 was usually used as removable ligand to get mesoporous nanomaterials.In order to ensure the carbonization of P123 with high yields,DCDA was used as efficient reductant to reduce the oxygen-containing species for maintaining the nanostructures of P123 assemblies.The enriched graphitic nitrogen dopants,high surface area(1947 m²·g^-1)and microporous-mesoporous bimodal nanopores in the g-N-MM-Cnet make make it an excellent bifunctional electrocatalyst for oxygen evolution and reduction electrocatalysts to construct rechargeable and ultra-stable?cycling lifetime:491 h?two-electrode alkaline zinc-air batteries with an energy density high up to 866.4 Wh·Kg_Zn^-1 at 5 mA·cm^-2.The as-obtained nitrogen doped micro/mesoporous carbon net?N-MM-Cnet?present a large specific surface area(2144 m²·g^-1),high-level nitrogen doping?the content of nitrogen is 8.25%?and hierarchical porous structure containing microporous and mesoporous structures.The N-MM-Cnet materials based supercapacitor exhibited high specific capacitance(537.2 F·g^-1 at 0.5 A·g^-1 in 0.5 M H₂SO₄ electrolyte)and outstanding cycling stability,retaining about 98.8%of their capacitance after 10000 cycles at 5 A·g^-1.The N-MM-Cnet-3 based symmetric supercapacitor could deliver a maximum energy density up to 22.6 Wh·kg^-1.The improved stems from both microporous and mesoporous structures of carbon nets provided accessible pathways for electrolyte transport and high surface area for energy storage.In addition,the incorporation of nitrogen dopants into the carbon was intended to further enhance the capacitance performance.This research provides a facile and effective method to obtain micro-/mesoporous carbon with high surface area and doping level of heteroatoms for high-performance supercapacitor.Secondly,supramolecular assemblies were introduced as concept-new hard templates here for the synthesis of hollow structures?exemplified with TiO₂ hollow structures in this work?.Supramolecular templates with tunable morphology and rich surficial functional groups rather facilitate the tight coating of other materials for the formation of hollow structures.Importantly,the weak interaction between the supramolecules or micromolecules benefits the facile removal of the templates for large-scale synthesis of hollow structure and also affords the supramolecular templates excellent reusability.This method allows for incorporation of various metal dopants into the TiO₂ lattice,as a typical example of nanocatalyst,by introducing the corresponding metal salt as a dopant source.A high-resolution transmission electron microcopy?HRTEM?,the X-ray diffraction?XRD?and absorption spectrum investigation suggested substitution of Ti⁴⁺sites by Co²⁺,which increased the activity of the catalytic sites in the doped materials,further reducing the overpotential of TiO₂ for oxygen evolution reaction.Additionally,cobalt-doped TiO₂ nanoparticles were synthesized via a simple sol-gel method by introducing P123 as surfactant and Co as crystallite growth inhibitor to ensure their small size.The Co dopants were found to be the key component to control the pure anatase phase and elevate the OER/ORR activity and stability.Co-doped TiO₂ nanoparticles as an ultra-stable and cheap electrocatalyst exhibited excellent activity for both ORR and OER in alkaline media.Real air cathode made of Co-doped TiO₂ electrocatalyst further offered superior highly energy density and ultra-high stability in two-electrode Zn-air batteries.