Fabrication Of MnO₂/Carbon Nanotubes Composite Electrode On Stainless Steel And Their Capacitance Performance

As an efficient energy storage device,supercapacitors have excellent application prospects.Due to its high specific surface area and good conductivity,carbon nanotubes（CNTs）have become the focus of scientific research in supercapacitors.But the catalyst and binder usually were adopted during its preparation process,which will make electrochemical properties and mechanical properties have serious impact.In this article,carbon nanotube arrays were fabricated by chemical vapor deposition（CVD）on 316L stainless steel substrate without the additional catalyst and binder,and can be used directly for supercapacitor electrode.CNTs grown directly on the stainless steel substrate,integrate with the substrate firmly,and have smaller contact resistance and high specific surface area.By means of controllable oxidation,more edge flat structures were exposed on carbon nanotubes array to promote the electrochemical activity.Then introducing high-reactive transition metal oxides MnO₂,improve the semiconductor MnO₂ conductivity and ratio performance effectively.The main research content is as follows:（1）CNTs was synthesized on 316L stainless steel substrate by chemical vapor deposition,and adopting chemical oxidation treatment to obtain edge flat structures of CNTs,so its hydrophilicity was improved greatly.Loading MnO₂ by the electrodepo-sition process in the mixed solution of 1.0 mol/L Na₂SO₄ and 0.2 mol/L Mn（Ac）₂,it was optimized by adjusting the deposition time（400s,800s,1200s）to achieve the improvement of MnO₂/CNTs composite electrochemical performance.The results show,the composite electrode prepared for 800s has the best capacitance,but MnO₂electrodeposited on unoxidized carbon nanotube array was little and not solid,easy to fall during the cyclic voltammetry test,and after 1000 cycles,finally retained only80.1%of the initial value.Inversely,the carbon nanotubes array with oxidation treatment can facilitate MnO₂ deposite;its specific capacitance can reach 521F/g at1A/g,and the capacitance of the sample still retained 95.7%after 1000 cycles.（2）Using thermochemical method,MnO₂ was obtained by carbon nanotubes array reducted KMnO₄ in 0.03mol/L KMnO₄ solution,and the MnO₂@CNTs nano-shell structure was prepared.the reaction time was 1h,2h,3h,respectively,to explore the better composite structure and capacitance properties.The MnO₂@CNTs-2h sample prepared by a two-step simple reaction exhibited nanoflake MnO₂ and good core-shell structure,with a capacitance of 221 mF cm^-2 at a current density of 1 mA cm^-2.In the cyclic stability test,the capacitance value was retained at 88.7%after 1000 cycles.Herein,the stainless steel was used as a simple current collector for supercapacitors;carbon nanotubes grown on the stainless steel contact MnO₂ and the stainless steel as bonds,and the high specific surface area of carbon nanotubes also facilitates the deposition of MnO₂,not only makes the active material and reduzate integrate firmly,also functions as the conductive channel and the mechanical support.