Preparation And Electrochemical Properties Of High-strength Tannic Acid/polypyrrole Hydrogels

Currently,with the rapid development of economy and the drying up of energy,the demand for portable and wearable electronic devices has been increasing.It is very important for the sustainable development of modern society to seek the sustainable,low cost and environment friendly high-performance energy storage devices.Flexible solid-state supercapacitors have attracted much attention due to their excellent flexibility,high power density,fast charging-discharging speed,long cycle life,and high safety and reliability.Polypyrrole(PPy)hydrogel material not only has the advantages of multistage porous structure,continuous conductive network,easy adjustability and easy functionalization of composition and structure,but also has the characteristics of unique mechanical behavior and self-support.Therefore,PPy hydrogel has a broad application prospect in flexible all-solid supercapacitor.Tannic acid(TA),a biomass material possessing reversible redox characteristics,has been widely developed as a more economical and sustainable choice to realize the construction of high-performance supercapacitors due to its abundant sources,low cost,renewable and biodegradable properties.In this work,the TA/PPy-Fe3+composite hydrogels were prepared by the combination of TA and PPy,and applied in supercapacitors.Furthermore,the electrochemical performance and mechanical stability of TA/PPy-Fe3+can be further improved by adding different metal ions during the preparation of TA/PPy composite hydrogels.The research works are summarized as follows:(1)The TA/PPy-Fe3+hydrogel was prepared by in-situ polymerization of Pyrrole with TA as dispersant and Fe3+as initiator.The prepared TA/PPy-Fe3+hydrogel was then used as electrode to assemble into the all-solid-state supercapacitor,and its structure,mechanical properties,electrochemical properties and self-discharge properties were studied.The TA/PPy-Fe3+shows excellent electrochemical performance.The specific capacitance of TA/PPy-Fe3+reaches 545.6 F g-1 at the current density of 1 A g-1.The specific capacitance still maintains 243.4 F g-1 at a high current density of 20 A g-1.After 1000 charge/discharge cycles at a high current density of 10 A g-1,the specific capacitance of TA/PPy-Fe3+can keep 49%.TA/PPy-Fe3+hydrogel also shows excellent mechanical properties with a maximum compression stress as high as about 21 KPa.Meanwhile,the all-solid supercapacitor based on TA/PPy-Fe3+hydrogel exhibits the excellent electrochemical performance.The areal capacitance of this device shows 953 mF cm-2 at a current density of 1 mA cm-2.When the current density increases to 20 mA cm-2,it still exhibits a favorable capacitance of 398.7 mF cm-2.The device can retains 55.6%of its original value after 3000 charge/discharge cycles.Under open circuit potential test,the device shows a high potential of 0.39 V at both ends after 9 h(the potential window is 0～0.8V),and the leakage current is only 36.5 μA after 2 h for the leakage current test.(2)In order to further improve the electrochemical performance of TA/PPy-Fe3+hydrogel,four different metal ions(Ni2+,Co2+,Cu2+and Zn2+)were introduced to preparing TA/PPy composite hydrogels with the same chemical oxidation method with TA/PPy-Fe3+hydrogel.Then the hydrogels were used as electrodes to fabricate supercapacitors and their electrochemical properties were studied.It is found that the hydrogel electrode prepared with Ni2+(TA/PPyNi-Fe3+)shows optimal electrochemical performance.The all-solid supercapacitor based on TA/PPyNi-Fe3+shows an area-specific capacitance of 1325 mF cm-2 at a current density of 1 mA cm-2.It can still remain 562.2 mF cm-2 as the current density increases to 20 mA cm-2.In addition,the potential of the device was 0.41 V at both ends after 10 h(the potential window was 0～0.8 V),and the leakage current was only 23.6 μA after 2 h.