Preparation Of Polypyrrole Composite Hydrogel And Their Capacitive Properties

Supercapacitors（SCs）,a novel kind of electronic devices,have attracted attention in the application of energy storage due to its high power density,fast charge/discharge rate and long cycle stability,which filled the gap between dielectric capacitors and rechargeable batteries.However,the energy density of SCs is rather low when compared to that of batteries.Since the electrode is the most important component of a SC,the key to constructing a well-performed SC is to develop an excellent electrode material.As a new type of electrode material for SCs,conductive polymer hydrogels（CPHs）not only have high conductivity and specific capacitance of conductive polymers,but possess the unique three-dimensional interconnected network structure of hydrogels.Although CPHs overcome the shortcomings of traditional powdery electrode materials,they still have the short cycle life which is the intrinsic disadvantage of conductive polymers.The most used method to solve this problem is to composite with other pseudocapacitive materials for taking full advantages of both components.In this paper,a homogeneous and continuous conductive polypyrrole hydrogel was synthesized.Also,a composite hydrogel that combines polypyrrole and manganese dioxide was prepared to overcome the drawbacks of polypyrrole hydrogel.The main research contents and results are summarized as follows:（1）Polypyrrole hydrogels（PPy Hs）co-doped by Ponceau S（PS）and HCl with different doping levels were synthesized.PPy Hs with continuous three-dimensional network structure could be adhered to the carbon cloth and utilized as electrodes directly.When the total amount of dopants was 1 mmol,the prepared PPy H electrode exhibited the best electrochemical performance.Its specific capacitance was 744.2 F g^-1 at 0.5 A g^-1 which was improved when compared to its counterparts.And the capacitance retention was 52.7%after 2500 cycles at 5A g^-1.In addition,since the lengths of the effective conjugated chain in the PPy H with different doping levels could lead to differences in chemical structures,the doping level of PPy H could be reflected by FT-IR,Raman and XRD spectra.（2）To improve the cycle stability of PPy H,a polypyrrole/manganese dioxide composite hydrogel was synthesized.Pyrrole was in-situ polymerized on the surface ofα-MnO₂ nanotube and the rod-like PPy/MnO₂ composite was obtained.The PPy/MnO₂ hydrogel electrode which was prepared under the optimum condition exhibited a higher specific capacitance(863.0 F g^-1at 0.5 A g^-1)than that of the PPy H.And because of the synergetic effect of PPy andα-MnO₂,the composite hydrogel showed an improved cycle stability(85.9%retention at 5 A g^-1 after2500 cycles).