The Research Based On Aqueous Hybrid Supercapacitors With Heterostructured NiSe₂/CoSe₂ Hollow Microspheres

Energy resources are important material bases for economic and social development.With the increasingly serious problems of energy shortage and environmental degradation,the demand for the development and research of green and efficient energy storage systems is growing.In recent years,aqueous hybrid supercapacitors(HSCs)as a novel and potential type of energy storage device have recently attracted growing attention,because they can combine the merits of supercapacitor and battery.This paper is directed against the problem of difficult matching between the cathode and anode of HSCs,the cathode with high rate performance and anode with high specific capacitance were first reasonably designed and synthesized,so as to reasonably construct HSCs with high energy density,good power density and long cycle life.The specific research works and results are as follows:(1)Cathode materials.The heterostructured NiSe₂/CoSe₂ hollow microspheres were first reasonably designed and synthesized by a simple hydrothermal reaction.In addition,the electrochemical reaction processes and energy storage mechanisms were studied through the comprehensive ex-situ X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS)analyses.Meanwhile,density functional theory(DFT)calculations were employed to verify a redistribution of interfacial charge when charge transfer occurred during charge/discharge cycles at the heterogeneous interfaces which could further accelerate reaction kinetics of heterostructured NiSe₂/CoSe₂ hollow microspheres.Electrochemical tests reveal that the NiSe₂/CoSe₂ electrode shows substantially improved electrochemical properties with a larger specific capacity(171.5 m Ah g^-1at 1 A g^-1),a more exceptional rate performance(60.8 and 40.9%of capacity retention at 50 and 100 A g^-1,respectively)and a more excellent cycle property(109.8%of initial capacity retention for 5000 cycles at 10A g^-1)compared with pure Ni Se₂ and Co Se₂ electrodes.(2)Anode materials.The nitrogen,sulfur co-doped reduced graphene oxide(N,S-rGO)aerogel was prepared by one-step hydrothermal method.Electrochemical tests indicate that the specific capacitance of the N,S-rGO electrode is 324.1 F g^-1(90.0 m Ah g^-1)at 1 A g^-1,and the capacity retention at 100 A g^-1is up to 51.2%compared with 1A g^-1.On the basis of above,to further enhance the specific capacitance of anode,the novel nitrogen-doped carbon quantum dots/reduced graphene oxide/porous Fe₂O₃(N-CQDs/rGO/Fe₂O₃)was designed and synthesized by one-step hydrothermal method,where the high-capacitance CQDs and high-capacitance Fe₂O₃ were simultaneously introduced into graphene aerogel.Benefiting from the unique 3D network composite aerogel structure with high surface area and hierarchical porous structure as well as the synergistic effect of high-capacity Fe₂O₃and highly conductive and stable N-CQDs/rGO,the N-CQDs/rGO/Fe₂O₃composite aerogels achieve enhanced electrochemical properties with an ultrahigh specific capacity,an admirable rate property and a superior cycling performance.Furthermore,the N-CQDs/rGO/Fe₂O₃-1 electrode(Fe₂O₃,34.9 wt%)exhibits the best rate capability(72.1,58.9 and 46.2%of capacity retention at 5,50 and 100 A g^-1,respectively),while the N-CQDs/rGO/Fe₂O₃-3 electrode(Fe₂O₃,62.3 wt%)displays the highest specific capacity(274.1 m Ah g^-1 at 1 A g^-1).(3)Construction of aqueous HSCs.The NiSe₂/CoSe₂ hollow microspheres are selected as the cathode to combine with the N,S-rGO aerogel or N-CQDs/rGO/Fe₂O₃ composite aerogel anode to build the novel NiSe₂/CoSe₂//N,S-rGO and NiSe₂/CoSe₂//N-CQDs/rGO/Fe₂O₃HSCs,respective.The electrochemical tests exhibit that the NiSe₂/CoSe₂//N,S-rGO HSC device delivers a high energy density(53.7Wh kg^-1)and an ultra-high power density(26.1 k W kg^-1)and the energy density of NiSe₂/CoSe₂//N-CQDs/rGO/Fe₂O₃ HSC device(74.2 Wh kg^-1)is much higher than that of NiSe₂/CoSe₂//N,S-rGO HSC device on the premise of ensuring high power density.This work provides a good reference and guidance for the reasonable construction of HSCs both with high energy density and power density in the future.