Molecular Design And Preparation Of Covalent Organic Polymers For Clean Energy Applications

Nowadays,the rising global energy demand and environmental impact of traditional energy resources pose serious challenges to human health,energy security,and environmental protection.One promising solution is to introduce clean energy technologies.Clean energy refers to a system of technologies that use energy in a clean,efficient and systematic way,such as fuel cells for clean electricity generation and porous materials that can efficiently absorb gases such as carbon dioxide.Fuel cell technology provides clean and continuous electricity by directly generating electricity through an electrochemical reaction that reduces oxygen and oxidizes fuel into water as the only by-product.This energy conversion technology has high energy conversion efficiency,no pollution,and the potential large-scale application prospect,which has been widely concerned and researched.Whereas there are some disadvantages for platinum(Pt)-based catalysts,researchers need to obtain some new materials with abundant resources,low cost and similar or better performance than Pt in catalyzing oxygen reduction reaction(ORR).In addition,removing carbon dioxide,especially removing carbon dioxide in important gases such as natural gas,are equally important from an energy and environmental perspective.Currently,the methods for removing carbon dioxide from natural gas are mostly expensive and inefficient,which also require the development of new porous materials.It would be ideal if there was a sort of materials which could meet both the needs of fuel cell technology and proper adsorbents for carbon dioxide at the molecular design.Based on first principles and density functional theory(DFT),computational chemistry method and some chemical experiment method have been shown in this paper,which are used to design and prepare a variety of covalent organic polymer(COP)materials.Meanwhile,this paper studied the fuel cell technology application and gas adsorption performance of these COPs for providing reasonable reliable guide to the experiment.The main contents and innovations of this paper are as follows:1.Based on first principles and density functional theory(DFT)calculation,combining with the charge density,the density of states and band structure analysis,the electrochemical catalytic performance for oxygen reduction reaction of six unclosed conjugate COP material models has been carried on the theoretical predictions,and the corresponding unclosed conjugate COPs doped with metal elements was prepared successfully.The results showed that unclosed conjugate COPs without high temperature carbonization generally did not have enough good performance for electrochemically catalyzing oxygen reduction reaction.The doping of metal ions in the molecular structure of polytetraphenyl porphyrin provides catalytic activity sites for COP.In addition,the presence of Metal Organic Framework(MOF)template makes the molecular structure of the corresponding COP more orderly so that the corresponding COP can obtain excellent performance for catalyzing ORR.2.Four undoped closed conjugate COP material models for catalyzing ORR,termed as COP-B3,COP-B4,COP-B5 and COP-B6,were theoretically predicted by using computational chemistry methods based on the first principle and density functional theory(DFT).These COPs were also combined with charge density analysis,state density analysis and energy band structure analysis.The results showed that the closed conjugate COP materials without high temperature carbonization,with the increase of the hexagonal molecular structure size,the electrochemically catalyzing oxygen reduction performance can be improved obviously.This conclusion provides a very important guiding idea for the molecular design and experimental preparation of COP materials without high temperature carbonization.3.The computational chemistry method was applied,which was based on first principles and density functional theory(DFT).Combining with the charge density,the density of states and band structure analysis,undoped closed conjugate COP-B5 material model have been dealt with nitrogen doping,and the molecular structure of the modified model in electrochemically catalyzing performance for oxygen reduction reaction has been carried on the theoretical predictions.The results showed that the catalyzing performance of COP-B5 could not be improved by pure nitrogen atom doping,while could lose its original electrochemically catalyzing performance for oxygen reduction reaction.However,with the introduction of nitro group,the electrochemically catalyzing performance of doping model was significantly improved.Thus,the idea of functional groups being introduced into the molecular structure of COP material may be applied to experimental preparation someday in the future.4.The computational chemistry method was applied,which was based on first principles and density functional theory(DFT).Combining with the charge density,the density of states and band structure analysis,undoped closed conjugate material model COP-B6 has been carried on the nitro doping process,and the molecular structure of the modified model in electrochemically catalyzing performance for oxygen reduction reaction has been carried on the theoretical predictions.The results showed that the catalyzing performance of COP-B6 cannot be improved by single nitro doping,while basically maintained.However,the double nitro doping improved the electrochemically catalyzing performance of the doped model significantly.However,the double nitro doping needs to adopt the appropriate way,the inappropriate way will make the material lose catalytic performance.5.COP-MT,which contains very rich nitrogen,was prepared by chemical synthesis method of melamine and a ligand containing three aldehydes under nitrogen protection and 180? in DMSO for 72 hours.The results showed that COP-MT possessed excellent adsorption performance because of its rich nitrogen content in the process of absorbing carbon dioxide from natural gas,which also possessed excellent adsorption selectivity for methane/carbon dioxide mixture.Moreover,COP-MT only adsorbed a small amount of methane in the process of gas adsorption.This indicated that nitrogen-doped COP material has positive significance not only for electrochemically catalyzing oxygen reduction reaction,but also for the application of gas adsorption.