Studies On Anodization Of Iron Foils And Supercapacitor Performance Of Iron Oxide Nanomaterials

Supercapacitor is a novel energy storage device which has drawn attention of the researchers in recent years due to its high power density and long cycle life.Theα-Fe₂O₃has been proved to be a promising negative electrode in asymmetric supercapacitor application due to its wide operating potential,high redox activity,low cost and eco-friendliness.Firstly,the iron foil was anodized in oxalic acid solution.This paper innovatively found that the product of anodization in oxalic acid is amorphous ferrous oxalate nanorods with a diameter distribution ranging from 250 to 700 nm.The study focused on the formation mechanism of ferrous oxalate nanorods and the effect of time,anodization voltage and oxalic acid concentration on the morphology of the nanorods,the best anodizing process of the nanorods was researched for 15 min at a constant voltage of 6 V in 0.7 M oxalic acid solution.Amorphous ferrous oxalate nanorods after annealing in air,successfully converted toα-Fe₂O₃ nanosheets,and exhibited enhanced electrochemical properties.Secondly,we studyed the effect of heat treatment temperature,heating rate and annealing atmosphere on the formation ofα-Fe₂O₃ nanosheets,the transformation mechanism of ferrous oxalate nanorods toα-Fe₂O₃nanosheets was analyzed,and the optimal formation condition ofα-Fe₂O₃ nanosheets was determined.Detailed study of the charge storage mechanism and electrochemical performance ofα-Fe₂O₃ nanosheets were also discussed.The results of the charge storage kinetics study ofα-Fe₂O₃ nanosheets show that they are controlled by surface control and diffusion control at the same time.When the material was tested at 5 m V s^-1,the pseudocapacitive current contributes 51.2%of the total current.Then,theα-Fe₂O₃ nanosheets were subjected to ammonia high temperature post-treatment,and the N-dopedα-Fe₂O₃ nanosheets were successfully prepared.The XRD results showed that there were also a small amount of iron nitride impurities,which greatly improved the conductivity ofα-Fe₂O₃ nanosheets.The area specific capacity of this sample at 3 m A cm^-2 is62.08μAh cm^-2,which is 3.92 times that pristine sample.After 5000 cycles of testing,the capacity retention rate of the electrode material is 80%,and it has good electrochemical stability.Theα-Fe₂O₃ nanosheets were subjected to high-temperature sulfur vapor post-treatment.After sulfidation,Fe S₂ nanospheres with enhanced conductivity were prepared.The electrode material had an area specific capacity of 52.78μAh cm^-2 at 2 m A cm^-2.,which was 3.07 times the pristine sample.After 5000 cycles of testing,the capacity retention rate of the electrode material is 83.5%,and the electrochemical stability has been greatly improved.Finally,theα-Fe₂O₃ nanosheets were co-treated with ammonia gas and sulfur vapor to prepare N-doped Fe S₂ nanosphere electrode materials with good conductivity,with a specific capacity of 71.67μAh cm^-2 at 3 m A cm^-2,which is 4.53 times of the original Fe₂O₃.After 5000cycles of testing,the capacity retention rate of the electrode material is 84.3%,which has good electrochemical stability.