Synthesis And Electrochemical Energy Storage Properties Of Metal Porphyrin Electrode Materials

Lithium-ion batteries as efficient electrochemical energy storage devices,have been widely used in different fields and greatly promoted the development of social economy.Although traditional lithium-ion batteries has been commercialized,great challenges are faced due to the limited theoretical energy density,rare resources,and the enviromental issues for the development of next generation electrochemical energy storage devices.Organic moleculesare considered as potential candidates as electrode active materials for the next generation electrochemical energy storage due to the adjustable structure,low cost and rich elements.Porphyrin molecules withhigh redox activity and multi-electron transfer have been widely studied in solar cells and catalysis,however,it is rarely reported as active materials for electrochemical energy storage.In this paper,we have prepared two types of porphyrin molecules as new cathode materials for organic lithium batteries.The first type of cathode is based on porphyrin monomer[5,15-bis（2,6-dioctyloxyphenyl）-10,20-bis（ethynyl）-Porphyrin]zinc（II）.A series of molecular weight polymerized porphyrin of PPre are obtained through coupling polymerization.The battery performance of different cathodes are compared and the influence of polymerization reaction and degree of polymerization are systematically studied.The second type of cathode is based on tetraethynyl group functionalized porphyrin complex.Metal porphyrins coordinated by different metals as electrode materials are synthesized and the battery performance as well as the charge storage mechanism of the electrode are studied.The main contents are list below:1. A series of polymerized porphyrins（PPre25,PPre15,PPre9）based on porphyrin monomer（Pre）were designed and synthesized and the physical properties were investigated using ultraviolet-visible absorption spectrum and gel permeation chromatography.The electrochemical performance and the charge storage mechanism of these electrode were explored by charge-discharge test,cyclic voltammetry（CV）,electrochemical impedence spectroscopy（EIS）,scaning electron microscopy/energy dispersive X-ray（SEM/EDX）,X-ray photoscpectroscopy（XPS）.The results show that the Pre can be spontaneously stabilized after charging and discharging process.It become insoluble after cycles.The reversible capacity and cycle stability was significantly improved after the polymerization of Pre.The discharge capacities of PPre25,PPre15,PPre9 and Pre at 100m A g^-1were obtained at 110,122,113 and 79m Ah g^-1.PPre15 with low dispersion coefficient showed the best electrochemical performance and excellent cycle performance.The capacity retention was 99.2%after2000 cycles.2. Tetraethynyl porphyrin H₂TEPP and porphyrin coordinated with different metal ions of Mg TEPP,Zn TEPP and Cu TEPP were designed and synthesized.The electrochemcial performance and the charge storage mechanism were studied using charge-discharge test,CV,SEM/EDX,XPS techniques.The charge storage properties of uncoordinated porphyrin H₂TEPP and different metal coordinated porphyrin complex were compared.It was found that the uncoordinated metal porphyrin H₂TEPP showed an excellent capacity retention,and the capacity decaywas basically not observed after thousands of cycles,however the discharge capacity was relatively low.Mg ion coordinated porphyrin（Mg TEPP）delivered a low discharge capacity.Cu TEPP and Zn TEPP demonstrated considerable electrochemical performance,a discharge capacity of more than 200m Ahg^-1was achieved,which is close to the theoretical capacity at a low current density.A discharge capacity of 130m Ahg^-1can still be obtained when the Zn TEPP was cycled for 700 timesat 500m Ag^-1,with a capacity retention of 87%.It was noticed that the oxidation state of copper was reduced during cycling and partial capacity was contributed,however,the oxidation state of Zn ion in Zn TEPP was remained.