Control Of Schiff Base Transition Metal Polymer Polymerization Environment And Study Of Its Energy Storage Mechanism

The global energy situation of the world is undergoing tremendous changes and countries around the world vied for the energy transformation path.Compared with the traditional energy sources,new types of clean energy have become the trend along with the booming of clean low-carbon energy revolution.As the world's largest electricity producer and consumer,China has made remarkable achievements in the field of renewable energy in recent years.From "12th Five-Year Plan" to "13th Five-Year Plan",the new energy technology innovation and the industry rising have been witnessed.Supercapacitor drawn strong interest of scientific researchers because of its high power density and long cycle life.However,the energy density as low as 1?10 Wh kg-1 limits its development.This paper takes supercapacitor electrode material Salen-type Schiff-base transition metal polymer as the research object,aims at realizing the high energy density of salen-type Schiff-base transition metal polymer and delving into its energy storage mechanism.The following several works have been carried out:At first,Ni(salen)was in-situ electropolymerized by cyclic voltammetry at various scanning rate.SEM results indicate that polymers prepared at different scanning rate of cyclic voltammetry were grown on multi-walled carbon nanotube,and the polymerization quantity reduces along with the increase of scanning rate.The binding energy peak of element Ni was splited and fitted in the XPS test,the result shows that element Ni of polymers prepared at different scanning rate all have an oxidation number of +2.The electropolymerization of Ni(salen)has two steps:firstly,Ni(salen)monomer is oxidation at the interface of electrolyte and conductive substrate;secondly,monomer molecules form chainlike polymers on multi-walled carbon nanotube surface after oxidation.The polymer prepared at a scanning rate of 20 mV s-1 performs higher charge transfer diffusion coefficient,therefore the capacity is 161.4 F g-1 at 0.1 mA cm-2,which is higher than 135.1 F g-1,capacity of the polymer prepared at 40 mV s-1.Secondly,the electrochemical properties and growth of composite electrode were induced by conductive substrate in the process of preparing the poly[Ni(salen)]via cyclic voltammetry at various scanning rates.Nitrogen doped graphene was prepared via one step solvent heat method and was in-situ composited with Poly[Ni(salen)].SEM results indicate that the oxygen-containing functional groups of graphite oxide fall off in the process of N-doping,which makes the N-doped graphene surface more smooth than graphite oxide.BET results show that when the mass ratio of urea and graphite oxide is 1:60,the prepared NDG-60 presents the largest specific surface area of 553.8 m2 g-1,meanwhile the GO and NDG-30 present 25.7 m2 g-1 and 375.2 m2 g-1 respectively.The specific capacity of P@GO,P@NDG-30 and P@NDG-60 are 1.3,165.6,and 203.7 F g-1 when the current density is 0.1 mA cm-2,which is due to their good kinetics.A moderate amount of nitrogen doping ratio enhanced the specific surface area of nitrogen doped graphene.Take N-doped graphene with high specific surface area as conductive substrate,the composite electrode is provided by REDOX active quinone or aldehyde groups,which promotes the contact of electrode with electrolyte and migration of electrolyte anions.At last,complex monomer Ni(CH3-salen),Ni(CH3O-salen)and Ni(Cl-salen)with corresponding substituent groups were synthesized.The effects of different substituent groups on the specific capacity and energy storage mechanism of the polymer were studied,by taking Ni(salen)without substituent group as a comparison.Nano stripe-like poly[Ni(CH3-salen)]and poly[Ni(CH3O-salen)]with width of 500?800 nm were synthesized for the first time and important progress was made in electropolymerization morphology of salen type Schiff-base ligands.At the same time,redox peaks show up in the cyclic voltammetric polymerization curve of Ni(CH3O-salen),which is caused by the introducing of electronic inductive methyl and methoxyl,and thus the faradaic pseudocapacitance is affected.The specific capacity of Ni(CH3-salen)is 270.1 F g-1 when the current density is 0.1 mA cm-2,which is better than 148.1 Fg-1 of Ni(CH3O-salen)and 106.0 F g-1 of Ni(Cl-salen).In addition,XPS test was adopted to analyze the complex monomer and polymer at different charging status and valence states of Ni at corresponding status were obtained by splitting and fitting the photoelectron energy spectrum peak.Which further illustrates that the energy storage mechanism of polymer.That is,the faradaic pseudocapacitance comes from the reversible change of imino group of the salen type Schiff-base transition metal polymer,instead of proving by the valence change from Ni(?)to Ni(?).