Preparation And Electrochemical Properties Of ZnFe₂O₄ Powder And Its Composites

In recent years,the supercapacitor has attracted the attention of researchers as excellent energy storage equipment.In this paper,ZnFe₂O₄ were prepared by a modified molten salt route and many methods were also used to enhance its specific surface area,in which we prepared coral-like Zn Fe₂O₄ particles,Zn Fe₂O₄/rGO composite and ZnFe₂O₄/PPy composite.Meanwhile,the phase,morphology and electrochemical properties of electrode materials were studied,and the main work is as follows:（1）The octahedral ZnFe₂O₄ materials were prepared by a two-step process which contains a hydrothermal process and a molten salt process.The optimum synthesis conditions were determined by controlling the temperature and the proportion of molten salt.It can be seen that the synthesis temperature should be900 ^oC,and the ZnFe₂O₄ particles（mass ratio of molten salt and precursor R=5）displays the largest capacitance(¹64 F g^-1)with the scan rate of 2 mV s^-1 and an excellent stability of cycling performance with 77.5%capacitance retention can be obtained with the current density of 5 A g^-1 after 10000 cycles.（2）In order to improve specific surface area of ZnFe₂O₄ sample,the coral-like ZnFe₂O₄ particles were prepared by an etching process which uses hydrazine hydrate and thioglycolic acid methyl ester as reducing agent and complexing agent,respectively.The ZnFe₂O₄ particles etched for 90 min displays the largest capacitance(⁴71 F g^-1)with the scan rate of 2 mV s^-1 and an excellent stability of cycling performance with 79.6%capacitance retention can be obtained with the current density of 5 A g^-1 after 10000 cycles.The etched Zn Fe₂O₄ particles shows more excellent electrochemical performance,which can be attributed to the fact that high surface area brings about lots of active sites that can augment the de-intercalation and intercalation of electrolyte ions.（3）In order to improve the electrochemical properties of the material,the Zn Fe₂O₄/PPy composite was successfully prepared by polymerizing PPy on the surface of the etched Zn Fe₂O₄.The optimum synthesis conditions were determined by controlling the mass ratio of Zn Fe₂O₄ and Py.The ZnFe₂O₄/PPy particles（the mass ratio of ZnFe₂O₄ and Py R=5）displays the largest capacitance(⁶06 F g^-1)with the scan rate of 2 mV s^-1(The capacitance increased by 135 F g^-1 compared to un-composited ZnFe₂O₄),and an excellent stability of cycling performance with 85.9%capacitance retention can be obtained with the current density of 5 A g^-1 after10000 cycles.It can be attributed to which PPy can act as electron transport channel,and the synergistic effect between the two components in ZnFe₂O₄/PPy could increase the capacitance.The PPy inhibits the collapse of ZnFe₂O₄ structure which causes by the redox reaction,and thereby greatly improves the cycle performance.（4）In order to improve the electrochemical properties of the material,Zn Fe₂O₄/rGO composite was prepared by adding GO into the etching process of Zn Fe₂O₄.The optimum synthesis conditions were determined by controlling the mass ratio of Zn Fe₂O₄ and GO.The ZnFe₂O₄/rGO particles（the mass ratio of Zn Fe₂O₄ and GO=10:2）displays the largest capacitance(⁶29 F g^-1)with the scan rate of 2 mV s^-1(the capacitance increased by 158 F g^-1 compared to uncomplexed ZnFe₂O₄),and an excellent stability of cycling performance with90.6%capacitance retention can be obtained with the current density of 5 A g^-1after 10000 cycles.It can be attributed to the introduction of rGO which can act as electron transport channel,and could lead to the synergistic effect between the two components in Zn Fe₂O₄/rGO increases the capacitance.The rGO inhibits the collapse of ZnFe₂O₄ structure which causes by the redox reaction,and thereby greatly improves the cycle performance.