Synthesis And Supercapacitive Properties Of Fluorinated Polyindole

The increasing demand for renewable clean energy has promoted the extensive research and application of supercapacitors.As a more important class of electrode materials for supercapacitors,conducting polymers have the advantages of electrochemical reversibility,rapid redox activity,high conductivity,low toxicity,and low cost,making them one of the research hotspots in the field of supercapacitors.Indole combines the structure of benzene ring and pyrrole ring,which makes polyindole and its derivatives have properties similar to polypyrrole and polyparaphenylene,such as good stability,electrochemical reversibility,etc..However,attention and research on polyindole-based conducting polymers as electrode materials for supercapacitors is still scarce.Different substituent groups and positions have different effects on the morphology and electrochemical performance of polyindole.Fluorine has been widely studied as a feature with the largest electronegativity and the smallest atomic radius except hydrogen and fluorinated polymers have been also widely studied and used.In this thesis,polyindoles and a series of fluorinated polyindoles were prepared by electrosynthesis,and the effects of fluorine substitution position and number on the electrosynthetic behavior,morphology,thermogravimetric behavior,and capacitance performance of polyindole were systematically studied.The main contents of the study are as follows:1.Polyindole?PIn?was successfully prepared in an ACN-Bu₄NBF₄?0.1 M?system by electrochemical polymerization.FT-IR confirmed that the polymerization site of indole was the C₂and C₃position on the indole pyrrole ring.The electrochemical test results shown that the specific capacitance of polyindole was 112F g^-1at 18 A g^-1.After 5000 charge and discharge cycle tests,its capacitance retention rate was 68%.The above results proved that polyindole had low specific capacitance and poor stability as an electrode material for supercapacitors,and further improvement is still needed.2.Using one-step electrochemical polymerization method,poly?5-fluoroindole??5-PFIn?nanofibers,poly?6-fluoroindole??6-PFIn?nanofibers and poly?7-fluoroindole??7-PFIn?nanorods were successfully prepared in ACN-Bu₄NBF₄?0.1 M?system.FT-IR showed that their polymerization sites were at positions C₂and C₃on the indole pyrrole ring.It was found through electrochemical tests that the specific capacitances of 5-PFIn,6-PFIn,and 7-PFIn were 432 F g^-1,528 F g^-1,and399 F g^-1at 18 A g^-1,respectively.After 5000 charge-discharge cycle tests,their capacitance retention rates were 84%,78%,and 71%,respectively.Compared with unsubstituted polyindoles,monofluorinated polyindoles have improved thermal stability,capacitive performance,and cycle stability.3.Electrochemical polymerization method was successfully used to prepare poly?4,6-bisfluoroindole??4,6-PDFIn?nanosheets and poly?5,6-bisfluoroindole??5,6-PDFIn?nanowires in ACN-Bu₄NBF₄?0.1 M?system.FT-IR showed that their polymerization sites were at positions 2,3 on the indole pyrrole ring.Electrochemical test results showed that the specific capacitances of 4,6-PDFIn and 5,6-PDFIn were261 F g^-1and 291 F g^-1,respectively.After 5000 charge and discharge tests,their capacitance retention rates were 86%and 82%,respectively.Compared with unsubstituted polyindoles,difluoro-substituted polyindoles have improved thermal stability,capacitance performance,and cycle stability,and difluoro-substituted polyindoles have relatively better cycle stability.4.Poly?5-trifluoromethylindole??5-PFMIn?and poly?6-trifluoromethylindole??6-PFMIn?were successfully prepared in the CH₂Cl₂-Bu₄NBF₄?0.1 M?system by electrochemical deposition.The SEM image showed that?5-PFMIn?presented the comb-like structure with irregularly arranged sawtooth,and 6-PFMIn showed the flower-like structure with numerous cavities.FT-IR showed that their polymerization sites were at positions 2,3 on the indole pyrrole ring.Electrochemical tests revealed that the specific capacitances of 5-PFMIn and 6-PFMIn were 290 F g^-1and 306 F g^-1,respectively.After 5000 charge and discharge tests,their capacitance retention rates were 91%and 89%,respectively.Trifluoro-substituted methyl polyindoles have improved thermal stability,capacitive performance,and cycle stability.