Preparation And Hybrid Solid-state Supercapacitive Performance Investigation Of Black Fe₂O₃ Thin Film Material

Hybrid solid-state supercapacitors with long cycle life,high power/energy density,stability and high safety have received extensive attention in the field of energy storage.In supercapacitors,electrode materials play an important role.Among,Fe₂O₃ has a relatively negative voltage window(-1-0 V vs Ag/Ag Cl)in aqueous energy storage systems,and is one of the few negative electrode materials.However,the traditional red-brown Fe₂O₃ has some defects such as poor electronic conductivity and insufficient physical/chemical stability,making the development of high-efficiency Fe₂O₃ materials with high energy density for energy storage face with huge challenges.Although capacity can be improved by nanometering and compounding,the specific capacity is still lower due to nonactive materials.Therefore,developing Fe₂O₃ thin film materials grown directly on conductive substrates is a more effective strategy.Unfortunately,due to the limited mass loading of nano-sized Fe₂O₃ film,the low areal capacity still cannot meet the requirements for practical application.Even if Fe(OH)₃ electrode grown on 3D current collector is synthesized in the previous report,its capacity can only reach to 1.5 m Ah cm^-2.Therefore,how to balance the relationship between mass loading and energy density is of great importance.The research contents and conclusions in this work are as follows:(1)Using Fe foam as substrate and KOH solution as electrolyte,black Fe₂O₃(B-Fe₂O₃@Fe F-0)film material is synthesized in situ on Fe foam substrate by one-step hydrothermal method.The results show that black film presents micron-grade polyhedral structure,which increases mass loading of active material.The area capacity of B-Fe₂O₃@Fe F electrode is 1.26 m Ah cm^-2 at current density of 50 m A cm^-2.Solid-state supercapacitor composed of Ni O as the positive electrode and B-Fe₂O₃@Fe F-0 as the negative electrode provides volume energy density of 11.3 k Wh m^-3 when the power density is 1271 k W m^-3.(2)In order to further increase area capacity of B-Fe₂O₃,modified B-Fe₂O₃@Fe F thin film material is successfully synthesized by using a mixed solution of KOH and Na₂S as the electrolyte.The results show that the morphology and structure of the film material have not changed significantly,and present a micron-level polyhedral structure and good electrical conductivity.However,the electrochemical performance has been significantly improved.At a current density of 50 m A cm^-2,the area capacity could reach 3.018 m Ah cm^-2.As anode of solid-state supercapacitors,B-Fe₂O₃@Fe F electrode provides enhanced volume energy density of 14.3 k Wh m^-3 when the power density is 1609 k W m^-3,which is much higher than other supercapacitors(?8 k Wh m^-3).This research may provide greater possibilities for the development of Fe₂O₃ series of high-efficiency iron-based anode materials for solid-state energy storage.