?-Fe₂O₃ Nanosheets Structure Modulation And Electrochemical Performance Study Of Stainless Steel By Anodizing

Hematite(?-Fe₂O₃)is characterized by high theoretical capacitance,abundant reserves,and stable negative potential window.The study of combining nanostructured Fe₂O₃ with various conductive substrates has long been explored to improve the performance by combining various Fe₂O₃ nanostructures with different conductive substrates.However,the low specific capacitance of these Fe₂O₃ electrodes(120-300 F g^-1)and the low adhesion stability on conducting substrates make their performance far from practical applications.In addition,the mass loading of nanostructured Fe₂O₃ on conducting substrates is quite low(?1.0 mg cm^-2)and the interfacial interaction between the substrate and the active Fe₂O₃ is not strong enough.These limitations largely hinder the use of Fe₂O₃ as anode for ECs.Against the background of such a demand,anodic oxidation has become a hot topic of current research due to its unique advantages.However,the high voltage and long time required for the preparation process make it difficult to be applied in practical production,and in addition,the additional oxide produced during the subsequent annealing process causes the collapse of some pores,which not only reduces the overall surface area,but also greatly limits its capacitance.In order to improve the above problems,this paper proposes the preparation and optimization scheme of iron oxide nanosheets based on stainless steel(SS)substrates,and the SS substrate templates with nano-layered structure are prepared by pretreating the SS substrates with acid washing.On this basis,the effects of subsequent anodic oxidation voltage,reaction time and temperature rise rate on the nanosheet morphology were investigated in detail by characterization analysis;the subsequent elemental doping of the nanosheet structure by nitriding was further studied to investigate the effects of various factors on the product morphology and properties during the elemental doping process.At the same time,a systematic study on the mechanism of the above research was carried out,and the formation mechanism of nanosheet structure on SS substrate was summarized.The results of the study are as follows(1)A detailed study of the impact of pickling pretreatment on the SS substrate and nanosheets structure formation,it is clear that with the growth of pretreatment time,the SS substrate surface oxide layer is continuously corroded and reached the best at 90min,to remove the oxide layer while retaining the maximum extent of the SS substrate.In the subsequent anodic oxidation process,it was found that the best iron oxide nanoflake structure was obtained at a constant voltage of 30 V and reached the best at20 min,with further increase in voltage due to the lack of oxide layer protection of the substrate is too fragile will lead to burn through phenomenon,but will affect the electrode performance.In addition,a slower heating rate and a higher annealing temperature can further protect the formation of nanosheets structure while ensuring the crystal orientation.In addition,the formation mechanism of iron oxide nanosheets prepared by pickling pretreatment and anodic oxidation process during the experimental process is systematically explained based on the above study.(2)In this work,we present the facile electrochemical preparation and high capacitance characteristics of self-organized?-Fe₂O₃ nanosheets on stainless steel(SS)as flexible anodes for supercapacitors.High-density?-Fe₂O₃ nanosheets were grown vertically on pretreated SS substrates,and nanostructured templates were created by acid etching pretreatment prior to electrochemical anodization.The formation of the pretreated templates greatly reduced the electrochemical voltage and time of the anodic oxidation process.The achieved?-Fe₂O₃ electrode exhibited a high specific capacitance of 271.5m F cm^-2(at a current density of 0.5 m A cm^-2)in a three-electrode system and still had excellent stability performance(63.8%)after 1000 cycles of testing.Subsequently,it was found that the surface products were partially transformed from oxides to nitrides by N-doping,but the surface morphology was basically not destroyed,and the specific capacitance reached up to 479 m F cm^-2.