Preparation And Electrochemical Performance Study Of Different Morphology Iron Oxide/Graphene Composites

In this experiment, graphite oxide was used as a composite substrate, which has good hydrophilic and surface easily modified. The positive charged Fe（OH）₃ colloid nanoparticles were easily combined with the negative charged graphene oxide（GO）sheets to form an intermediate Fe（OH）₃/GO because of the strong electrostatic interaction, van der Waals interaction and hydrogen bonding. Then the intermediate product was subjected to different heat treatment, prepared with various morphologies iron oxide/graphene composites. Also, we explored their electrochemical properties as the electrode material.First of all, GO composited with Fe（OH）₃ colloid, after heat treatment at 500 ?C for 2 h in N2 gas flow, target sample hexagonal-Fe₃O₄ sheets/graphene composite（HFGC） was successfully synthesized. During the heat treatment, the carboxylic acid groups on GO sheets were thermally decomposed to produce the reduced graphene oxide（rGO） sheets. At the same time, part of Fe³⁺ ions in Fe（OH）₃ were reduced to Fe²⁺ ions by phenol hydroxyl and epoxide groups on GO sheets. The morphologies of HFGC were characterized by the transmission electron microscope（TEM）. The result showed that graphene and Fe₃O₄ have been successfully compounded, and all hexagonal Fe₃O₄ sheets were tightly attached onto the surface of rGO sheets. The synergy effect and the unique face to face contact make HFGC own the outstanding supercapacitor performance. The cyclic voltammetry（CV） curves of HFGC were ideal rectangular shapes at different scan rates, which indicated the character of double layer capacitance. In 6 M KOH aqueous electrolyte, the specific capacitances were calculated by the relevant galvanostatic charge-discharge（GCD） curves. HFGC exhibited a specific capacitance of 193.4 F g-1 at 0.3 A g-1. In addition, the capacitance remained 83.3% of the initial specific capacitance after 1000 cycles, illustrating the excellent cyclic stability. These results proved that HFGC is an remarkable electrode material for supercapacitor.Secondly, We prepared the flower-like Fe₂O₃/reduced graphene oxide composite（FFGC） for the first time by changing the preparation method of the Fe（OH）₃ colloid and the subsequent heat treatment method. The TEM images showed the flower-like Fe₂O₃ nanoparticles with an average diameter of about 50 nm were loaded uniformly onto the rGO surface and the visible micro-cracks were randomly on its surface. The phenomenon is uncommon, which is probably resulted from the adjacent Fe（OH）₃colloid particles reassembly during the hydrothermal treatment. The presence of graphene improved the electrical conductivity of Fe₂O₃, meanwhile, Fe₂O₃ prevented the reunion of graphene. FFGC was investigated as anode material for lithium-ion battery（LIB） as well as electrode material for supercapacitor（SC）. For instance, the specific charge capacity was of 1366 mAh g-1 at 0.1 A g-1 in LIB case, while the specific capacity of 318.9 F g-1 at 0.1 A g-1 in SC experiment. On the other hand,FFGC exhibited the excellently steady performance in either LIB or SC experiment.Those results suggest its potential application in energy storage device.