Preparation Of Metal Single Atom Supported α-Fe₂O₃ By Quenching And Its Application In Electrochemical Supercapacitors

In the past few decades,people have proposed a variety of methods for the preparation of metal hybrids of different sizes,including various material from bulk metals to metal nanomaterials.It plays an important role in various fields such as electrochemistry and photoelectrochemistry.Compared with bulk materials,nanomaterials with unique structures and morphologies generally show better performances.Recently,the high degree of disorder caused by doping,the change of unsaturated coordination environment,and the interaction between single atom and carrier etc,which increases the number of active sites of the material,greatly improving the conductivity and catalytic performance of the material.It has received extensive attention from researchers.The new method proposed in this article,quenching,originally refers to the process of rapid cooling of iron blocks calcined to high temperature in metallurgy,to greatly improve the rigidity,hardness,wear resistance and toughness of iron,so as to meet the different requirements of various mechanical parts and tools.In this paper,using the rapid cooling,metal oxides at high temperature are quickly put into a metal salt solution,so that the lattice that oscillates at high temperature stops vibration and contract instantaneously,and the metal single atom supported metal oxide is obtained.The Fe OOH precursor prepared by hydrothermal method was treated at high temperature in a muffle furnace to generateα-Fe₂O₃,then quickly putting it into different kinds of low-temperature salt solutions to generate different single atoms supportedα-Fe₂O₃,such as Sn-Fe₂O₃（transition metal single atoms supportedα-Fe₂O₃）and Sr-Fe₂O₃（alkaline earth metal single atoms supportedα-Fe₂O₃）.As a comparison,high-temperatureα-Fe₂O₃ also was poured into low-temperature deionized water to obtain quenched DIW-Fe₂O₃.Characterization methods,such as X-ray absorption spectroscopy and spherical aberration corrected transmission electron microscope,proved that the quenching method can synthesize single atom materials,and the method is easy to operate and has high material utilization rate.Under high temperature,the atoms oscillate sharply lead to expansion of the bond length,the metal ions dispersed in the solution are thus easier to dope into the carrier.Through quenching in the transition metal salt solution,various transition metal single atoms are successfully supported onα-Fe₂O₃ nanorods.among them,after the introduction of Sn,the carrier concentration and oxygen vacancies of Sn-Fe₂O₃ are increased,leading to the improved of its conductivity and capacitance.The area capacitance reaches 391.32 m F cm^-2under the current of 0.24 m A cm^-2.The all-solid-state fiber-shaped supercapacitor matched Sn-Fe₂O₃ with Mn O₂ has excellent area capacity and energy density,good stability,and high Faraday reaction reversibility.The wearable device can light up the diode and has good resistance to deformation,which shows broadly application foreground.Area capacity and energy density are 105.68 m F cm^-2 and 6.09 m Wh cm^-3 respectively;the device possesses good cycling stability,with a capacitance of 85.27%of the initial capacitance maintained after2500 charge-discharge cycles.The change and improvement in performance of alkaline-earth metal single atom supportedα-Fe₂O₃ proves that quenching is universal,and it is hopeful that it can be extended to other materials.Different alkaline-earth metal single atoms supportedα-Fe₂O₃ nanorods show different effects due to differences in radius,electronegativity,valence,etc.Among them,Ca²⁺supportedα-Fe₂O₃ has the opposite characteristics to other samples.