Preparation And Properties Of Pseudopotential Materials

In the current and near-future applications,electrochemical devices for energy storage play a vital role in overcoming fossil fuel exhaustion and global warming situation.Supercapacitors have attracted significant interest in both academia and industry,owing to their superior power density,fast charge/discharge rate and long cycle life.Now,the application of supercapacitors related with consumer electronics,transportation,military and aerospace,and power backup by protecting,etc.Supercapacitors include electrochemical double-layer capacitors?EDLCs?and pseudocapacitors.Compared with EDLC,energy storage of pseudocapacitance comes from reversible surface faraday redox reactions happening at the interface between electrolytes and electroactive materials,resulting in a higher capacitance.Electrode materials for pseudocapacitors consist of transition metal oxides/hydroxides/sulfides?RuO₂,MnO₂,Co?OH?₂,MoS₂?and conducting polymers.Among these materials,MnO₂ and Co?OH?₂ have attracted significant interests due to its high theoretical specific capacitance,low-cost,abundance and environmentally friendly property.However,MnO₂ and Co?OH?₂ have their own limitations,limiting the development of electrode materials as supercapacitors.Therefore,it is particularly important to take an effective method to improve its specific capacitance.In this study,we adopt electrodeposition-hydrothermal method to synthesize MnO₂ nanosheets and modify the surface of Co?OH?₂.The performance of MnO₂ nanosheets and functionalized Co?OH?₂nanosheets as pseudopotential electrode materials are studied.Electrochemical workstations were used to test the electrochemical properties of the synthesized materials.This paper has done some research work as follows:In this article,the preparation method of MnO₂ nanosheets and the improved cycle performance of supercapacitor were firstly introduced.The hierarchical MnO₂nanosheets prepared on indium tin oxide?ITO?coated glass substrates via a hybrid two-step protocol,including a cathodic electrodeposition technique and a hydrothermal process.SEM and TEM images show that the as-synthesized MnO₂ nanosheets are hierarchical and porous,which could not only increase the active surface,but also short paths for fast ion diffusion.From the nitrogen adsorption–desorption analysis,we can see that the BET surface area of the MnO₂ nanosheets is 53.031 m² g^-1.The electrochemical results demonstrate that the as-grown MnO₂ nanosheet exhibits an excellent specific capacitance of 335 F g^-1 at 0.5 A g^-1 when it is applied as a potential electrode material for an electrochemical supercapacitor.Additionally,the MnO₂nanosheets electrode also presents high rate capability and excellent cycling stability.It maintains 91.8%capacitance retention after 1000 cycles.This paper also studied the functionalized the surface of Co?OH?₂ nanosheets by immersion method and electrochemical method and their electrochemical properties.The Co?OH?₂ nanosheets are electrodeposited on nickel substrate,followed by immersed in the phosphate ion solution and electrochemical treatment,respectively.The structures,morphologies and electrochemical properties of the functionalized Co?OH?₂nanosheets are investigated.XRD,EDX and FTIR analysis indicate that the phosphate ion has successfully been adsorbed on the surface of the Co?OH?₂ nanosheets.And the electrochemical tests show that through the phosphate ion functionalization by immersion method,the Co?OH?₂ nanosheets exhibit the remarkably enhanced supercapacitive performance with a specific capacitance of 740 F g^-1 at a current density of 1 A g^-1 in 6 M KOH as compared to the bare Co?OH?₂(433 F g^-1).In particular,the functionalized Co?OH?₂ electrode has an excellent long-term cycling stability with 82.7%capacitance retention after 10000 cycles.Through the phosphate ion functionalization by electrochemical method,the specific capacitance can reach 857 F g^-1 at 1 A g^-1 and the capacitance retention can reach 133%after 2000 cycles.In addition,further analysis shows that the enhanced electrochemical performance can be attributed to the functionalized Co?OH?₂ nanosheets providing large reaction surface area,more active sites,and fast ion and electron transfer.