Fabrication Of Nanostructed Iron Oxide And Its Pseudocapacitive Property Study

Iron oxide precursor was electrochemically deposited directly on graphite foil by galvanostatic technique in Fe（NH₄）₂（SO₄）₂ solution.Then the obtained iron oxide precursor was heat treated to fabricate nanostructured Fe₂O₃.X-ray photoelectron spectroscopy（XPS）and X-ray diffraction（XRD）were used to study the component of the products,their surface morphologies and structure were observed by scanning electron microscope（SEM）and transmission electron microscope（TEM）.Cyclic voltammetry（CV）was used to test their electrochemical activity,while their pseudocapacitive properties,such as specific capacitance,rate capability and cyclic stability were studied by constant current charge/discharge and AC impedance（EIS）.Through XRD and XPS analyses,it was found that the deposited iron oxide precursor existed in the form of amorphous FeOOH.In:fluences of solution pH on electrochemical deposition of iron oxide precursor were studied.The results showed that the iron oxide precursor existed as nanoparticles in Fe-pH6.2-0.01M prepared at pH 6.2.It displayed a specific capacitance of 248 F/g at 2 A/g,which is higher than those of Fe-pH5.1-0.01 M（224 F/g）and Fe-pH7.5-0.01M（150 F/g）deposited at pH 5.1 and 7.5,respecitively.Influences of Fe²⁺ concentration on electrochemical deposition of iron oxide precursor were also studied.The iron oxide precursor existed as nanorods in Fe-pH6.2-0.05M prepared in the solution containing 0.05 M Fe²⁺.The well separated nanorods distributed uniformly on the graphite foil substrate,effectively increasing the contacting area of the electrode material with the electrolyte and so improving its pseudocapacitive properties.The specific capacitance of Fe-pH6.2-0.05M is 340 F/g at 2 A/g,which is higher than Fe-pH6.2-0.01M（248 F/g）and Fe-pH6.2-0.03M（286 F/g）prepared in the solution containing 0.01 and 0.03 M Fe²⁺,respecitively.Heat treatment was conducted to enhance the pseudocapacitive performance of Fe-pH6.2-0.05M electrode.It was found that the iron oxide precursor on Fe-pH6.2-0.05M converted from amorphous FeOOH to crystalline Fe₂O₃ after heat treated at and above 500 0C.Much interspace between Fe₂O₃ nanorods was formed and 3D network architecture of Fe₂O₃ nanorods constructed due to their gradual dehydration in heat treatment,further enhancing the contact of electrode material and electrolyte.Influences of heat treatment temperature and time on iron oxide precursor conversion were studied.The Fe-550-1.0h electrode prepared through heat treatment of Fe-pH6.2-0.05M at 550 ℃ for 1 h displayed a high specific capacitance of 645 F/g,which increased 305 F/g compared to Fe-pH6.2-0.05M（340 F/g）.Cyclic stability of the electrode was also improved through heat treatment.After 5000 cyclic constant current charge/discharge,87.5%of the capacitance can be maintained for Fe-550-1.0h,while Fe-pH6.2-0.05M electrode can only retain 75%of its capacitance.