Preparation,Characterization And Electrochemical Properties Of Perovskite-Type Oxide Nanofibers

With the widespread concern of energy and environmental crisis,supercapacitor,as a new type of energy storage equipment,has become one of the research hotspots in the field of energy storage.In particular,it is a great challenge to seek an electrode materials with large capacitance,high power density and energy density,stable rate performance,good cycling performance and safety.The ABO₃ typeperovskite oxide has significant advantages and potential as an electrode materials for supercapacitors due to its excellent charge storage,good conductivity and higher pseudocapacitance from reversible REDOX reaction in a suitable electrolyte.Although ABO₃type perovskite oxides exhibit such outstanding performance,the products produced by traditional methods tend to have poor electron transport and small specific surface area,making them less capacitive as electrode materials.Generally,there are two strategies to improve the electrochemical properties of electrode materials:(?)By improving the synthesis method and controlling the morphology of the product,the specific surface area of the electrode materials can be improved and the reactive sites can be increased;(?)Binary or ternary composites are prepared to improve the electronic conductivity and cycling stability of the electrode materials.First,a series of La_xSr_1-xFeO₃,Gd_xSr_1-xNiO₃ nanofibers and GdNiO₃@c compoud were prepared by using the method of electrostatic spinning and the template method of heteronuclear complex.Then,the Gd_0.7Sr_0.3NiO₃ nanofibers with the best electrochemical propertieswereselectedtofurthersynthesize r GO@Gd_0.7Sr_0.3NiO₃@Poly(p-phenylenediamine)ternary composite.Finally,using LiCoO₂nanofibers prepared by electrostatic spinning method instead of activated carbon as anode material,anasymmetric supercapacitor with excellent performance was obtained.The main research contents are as follows:(1)The electrostatic spinning technology and Sr doping were used in the preparation of La_xSr_1-xFeO₃(LSF-x,x=0.1,0.3,0.5,0.7,1)perovskite oxide nanofibers to control the macro and micro structure,then the structure,morphology and electrochemical properties were systematically discussed.The specific surface area of LSF-0.7 reached 27.96 m²·g^-1,and aperture were mainly distributed around 5.71 nm while discontinuous mesoporous structure appearing in the interior.The specific capacitance and voltage window of LSF-0.7in 1 MNa₂SO₄ electrolyte was 513.0 F·g^-1 and-1-1 V at the scanning rate of 5 mV·S^-1,which was higher than the other electrolyte and the materials reported previously.(2)The same methods with different A,B cations were used to prepare a series of Gd_xSr_1-xNiO₃(GSN-x,x=1,0.9,0.7,0.5,0.3)nanofibers,and comprehensive analysis was undertaken on the crystal structure,morphology and electrochemical properties.When the Sr doping was controlled within a certain proportion(x>0.3),the perovskite configuration of the sample remain stable fibers,and the oxygen holes could be increased as well as the specific surface area of the sample.While x=0.3,the pores disappeared and the fibers diameter shrunken into bramble-like fibers.The Gd_0.7Sr_0.3NiO₃nanofibers had the largest specific surface area,complete and stable morphology and porous structure,especially higher electrochemical properties in the neutral electrolyte.Compared with GSN-0.7//GSN-0.7symmetrical supercapacitor,AC//GSN-0.7 asymmetrical supercapacitor exhibited better capacitance,energy and power density of 96.9 F·g^-1,53.8 Wh·kg^-1 and 1000W·kg^-1 at the current intensity of 1 A·g^-1,possessing-1-1 V voltage window and remaining 62.7%specific capacitance after 5000 cycles.(3)Electrostatic spinning technology was used to prepare LiCoO₂nanofibers with 3D mesoporous structure,and 1 MLi₂SO₄,Na₂SO₄,LiOH,KOH and 6 MKOH were applied as electrolyte to test electrochemical properties in a three-electrode system.LiCoO₂nanofibers with good trigonal,lamellar and mesoporous structure were assembled via aggregation of nanometer crystal particle,and exhibited excellent specific surface area and aperture of 58.13m²·g^-1 and 35.18 nm,respectively.The specific capacitance of this material reached 583.4F·g^-1 and voltage window tended to be-1-1V at the scanning rate of 5 mV·S^-1.Moreover,LiCoO₂was used to prepare symmetrical and asymmetrical supercapacitors.Through a series of characterization,it was proved that electrostatic spinning could be used to regulate the macrostructure and microstructures and improve the electrochemical activity.(4)GdNiO₃@C composite was prepared via imitating a heteronuclear complex with transition metal Ni and rare earth metal Gd,and its morphology presented mesoporous network structure with rough surface lamellar stacking.The specific surface area and aperture reached up to 61.58 m²·g^-1and 26.64 nm,respectively.Electrochemical properties of GdNiO₃@C composite in 1 MNa₂SO₄were superior to that in Li₂SO₄,LiOH,KOH and GdNiO₃nanofiber prepared via electrostatic spinning method.The specific capacitance was817.0 F·g^-1 at the scanning rate of 5 mV·S^-1 and voltage window tended to be-1.1-1.1 V.LiCoO₂//GNO@C asymmetric supercapacitor possessed mix capacitance,energy and power density of 111.7 F·g^-1,52.9 Wh·kg^-1/900 W·kg^-1 at the current intensity of 1 A·g^-1 and 18k W·kg^-1/17.3 Wh·kg^-1 at the current intensity of 20 A·g^-1,remaining 86.7%specific capacitance after 5000 cycles.(5)Firstly,the Gd_0.7Sr_0.7NiO₃ nanofibers prepared by the electrospinning method with the best electrochemical properties in the previous research were selected,and four r GO@Gd_0.7Sr_0.7NiO₃ binary composites(rGO@GSN-0.7)with different mass ratios of 1:2,1:4,1:6 and 1:8 were synthesized by coating the Gd_0.7Sr_0.3NiO₃nanofibers with rGO.Their characterizations showed that BET specific surface areas and average apertures reduced with the quality of GSN-0.7 increasing.Thereinto,GG-4 with porous network structure completely coated by rGO revealed the best electrochemical activity,and its BET specific surface area and average aperture reached 82.34 m²·g^-1 and 27.47 nm,respectively.Afterwards,rGO@GSN-0.7@PpPD ternary compositewas synthesized via compositing PpPD and GG-4.The obtained material retained porous multilayer mesh framework of the compositetemplate and inherited the excellent electrochemical performances of Pp PD and Gd_0.7Sr_0.3NiO₃(specific capacitance at the scanning rate of 5 mV·s^-1:1410.2 F·g^-1).In the end,rGO@GSN-0.7@PpPD//r GO@GSN-0.7@PpPDsymmetricalsupercapacitor,AC//rGO@GSN-0.7@PpPD and LiCoO₂//r GO@GSN-0.7@PpPD hybridsupercapacitors were prepared and the operating voltages of the three capacitors were-1-1 V.The maximum specific capacitances and cyclic stabilities in practical applications increased successively.The mix capacitance,energy and power density of LiCoO₂//r GO@GSN-0.7@PpPD were114.6 F·g^-1 at the current density of 1 A·g^-1,63.6.9 Wh·kg^-1/1 k W·kg^-1(1 A·g^-1)and 20kW·kg^-1/24.2 Wh·kg^-1(20 A·g^-1),remaining 90.1%specific capacitance after 5000 cycles.