The Construction Of Layered Manganese Oxides-based Functional Hydrogel And Its Applications On Flexible Energy Storage Devices

In this work,manganese oxide?MnO₂?nanosheets were taken as the research subject.MnO₂ nanobelts were first prepared via a hydrothermal technique,followed by being delaminated into ultrathin nanosheets through a solvent-intercalation process.Meanwhile,the electrochemical properties of MnO₂ nanosheets were studied.A functional hydrogel with three dimensional?3D?networks was then obtained via a facile electrostatic interaction between MnO₂ nanosheets and conductive polymers.The electrochemical performances of the hydrogel and its application in flexible asymmetric supercapacitor were further explored.The main contents and results of this paper are as follows:?1?Study on the preparation of MnO₂ nanosheets and their electrochemical properties.Here,manganese oxide nanobelts with the birnessite-type layered structure were synthesized by a hydrothermal method,which were further delaminated into MnO₂nanosheets suspensions after the acidification and intercalation process.Then,systematic studies were described on the synthesis process and interlayer structure characteristics of the intermediates through physical and chemical characterizations.The results indicated that the as-prepared two dimensional?2D?sheets possessed uniform thickness of about 1 nm and lateral dimensions in the range of 300¹000 nm. ?2?Study on the construction of MnO₂ nanosheets-based functional hydrogel and its electrochemical properties.We demonstrated a facile electrostatic-interaction assisted approach to synthesize 3D porous MnO₂ networks backboned with polyaniline as an efficient supercapacitor electrode.The negatively charged surfaces of the MnO₂ sheets were first grafted with protonated aniline monomers,after which the in-situ polymerization of aniline connected MnO₂ sheets into a 3D interpenetrated porous structure.Thus,the“wiring”of the MnO₂ sheets by the conductive polyaniline chains along with the mesoporous features provided“highways”for both electron and ion transport.Additionally,the sufficient exposure of the active sites in MnO₂ nanosheets would improve the redox reaction efficiently,resulting in improved electrochemical performances.The deliberately designed electrode achieved an excellent capacitance of 762 F g^-1at a current of 1 A g^-1,capacity retention of 77%on increasing the current density from 1 A g^-1to 10 A g^-1,and cycling performance with a capacity retention of 90%over 8000 cycles at a moderate density of 5 A g^-1.?3?The application of the as prepared functional hydrogel in flexible high-performance asymmetric supercapacitor.The functional hydrogel was developed as a flexible positive electrode of an asymmetric supercapacitor,accompanied with a negative electrode of activated carbon and a gel electrolyte of PVA/Na₂SO₄.The so-obtained asymmetric supercapacitor delivered an energy density maximum of 40.2 Wh kg^-1/0.113 Wh cm^-2(at a power density of 340.0 W kg^-1/0.95 W cm^-2)and power density of 6227.0 W kg^-1/17.44 W cm^-2(at an energy density of 19.0 Wh kg^-1/0.053 Wh cm^-2)in an increased operating voltage from 0.7 V to 1.7 V.The3 D network structure showed competitive electrochemical performance when compared with other MnO₂-based asymmetric supercapacitor devices,making it a very attractive electrode candidate for high-performance supercapacitors in future flexible and portable energy storage devices.