Fabrication And Performance Analysis Of The Supercapacitor 3D-Mn/MnO_x Electrode

Manganese oxide(MnOx)is regarded as a kind of promising materials for electrochemical capacitors(ECs)owing to its large specific surface area,low cost and environmental friendless.However,manganese oxides suffer poor electronic and ionic conductivity.In this study,the 3D-Mn/MnOx electrode is fabricated through a facile and efficient method based on femtosecond laser structuring combined with chemical oxidation.Firstly,femtosecond laser was used to generate 3D conductive network on metallic manganese surface which also served as the current collector(denoted as 3D-Mn);then,manganese oxides were directly formed on the femtosecond laser-structured surface through chemical oxidation(denoted as 3D-Mn/MnOx).MnOx was composed of Mn2O3 and MnO2.With 0.1 M Na2SO4 electrolyte,the 3D-Mn/MnOx electrode had significantly improved rate capability in both CV and GCPL: the areal capacitances were 81.83 mF/cm2 and 68.77 mF/cm2 at the scan speed of 10 mV/s in CV and the current density of 0.2 mA/cm2 in GCPL respectively.The electrode also exhibited typical pseudocapacitive characteristic and good capacitance retention when the scan rate ranged from 10-200 mV/s and the current density ranged from 0.2-2 mA/cm2.Additionally,the capacitance retention kept 83.58% after 2000 cycles in GCPL at the current density of 0.8 mA/cm2,showing a good cycling stability.With the PVA/KOH solid electrolyte,the symmetric supercapacitor using 3DMn/MnOx as the electrodes achieved an energy density of 11.1 ?Wh/cm2 at a power density of 43.5 ?W/cm3 when the current density was 0.2 mA/cm2,indicating the application in high energy/power density devices.Several factors need be considered in the fabrication of the 3D-Mn/MnOx periodic arrays architecture.First,after femtosecond laser structuring,3D-Mn acted as current collector potentiating its conductivity.Second,after MnOx grown on the surface of 3DMn,the interspaces between the microarrays remained unchanged which was in favor of the electrolyte permeation.Third,the three-dimensional structures provided increased surface area,resulting in more pathway for electron transfer and ions diffusion.Forth,the enhanced contact area between the active materials and electrolyte led to the larger reaction area of MnOx owing to the hydrophilicity of the electrode surface.Fifth,the substrate-grown MnOx improved adherence to the substrate,offering enhanced cycling stability.In summary,3D-Mn/MnOx periodic arrays architecture,which could function as the binder-free electrode for pseudocapacitors,has been successfully fabricated based on femtosecond laser structuring and chemical oxidation.The proposed method is general and might be easily extended to guide the fabrication of other functional metal oxides on metallic substrates.