Fabrication Of Wool Felt-Based Electrode Materials With Electro-capacitive Performance

Nowadays,energy conversion and storage have been the main concerns of the whole society.Supercapacitors,as the most common energy storage devices,have been gaining popularity due to their high power and good cyclability.High energy density is required for advanced energy storage devices,but unfortunately,supercapacitors'energy density still needs to be improved.On the basis,this work aims to improve energy density of supercapacitors through increasing capacitance of electrodes.Wool are widely used in the textile industry but their waste can be surprisingly up to hundreds of thousands of tons,leading to serious waste and environmental pollution.The main solution to this problem is to produce these waste wool into wool felts for applications in some low-value added aspects.Wool felts are featured of 3D fluffy porous structures,and are composed of polar and big-side-group nonpolar amino acids.Such characteristics make them a promising alternative to supports of active materials.However,such a highly potential substrate has not been investigated in this area.Therefore,we herein incorporate carbonated multiwalled carbon nanotubes?CNTs?,polypyrrole?PPy?and CNTs/PPy with wool felts through hydrothermal dipping,in situ polymerization and di-oxidant sandwich-type polymerization methods,respectively,for developing high-capacitance electrodes.?1?Based on physical and chemical characteristics of wool felts,this work employs the hydrothermal dipping route followed by hot press to prepare CNTs@wool felts.Dipping approach has been widely used to prepare CNTs-based electrodes.Differently from previous works,we apply wool felts as 3D supporting frames and conduct hydrothermal dipping to trigger directional friction of wool fibers.The CNTs@3D wool felt shows a high CNTs mass load of 1.88 mg cm^-2 and a high specific capacitance of69.34 mF cm^-2.After that,a“from 3D to 2D”treatment is performed.Consequently,the CNTs@2D wool felt shows a higher specific capacitance of 75.34 mF cm^-2.This is due to the improvement in interconnectedness of CNTs and then the decreases in electrode resistance and charge transfer resistance.?2?The combination of PPy with wool felts is performed through in situ polymerization of PPy to wool felt supports.Herein,the main advantage of using wool felts as supports is that their 3D supporting frame structure provides more deposition sites for PPy and remarkably improves electrolyte accessibility.After that,PPy@3D Wool is hot-pressed to PPy@2D Wool,resulting in superior capacitive properties because of the improvement in interconnectedness of CNTs and the decreases in electrode resistance and charge transfer resistance.The“from 3D to 2D”strategy avoids the problems related to the direct deposition of PPy to 2D substrates,which is the low electrolyte accessibility.The resulting PPy@2D Wool exhibits a high specific capacitance of 6.433 F cm^-2 at 0.25mA cm^-2,which slightly decreases to 4.370 F cm^-2 at 4 mA cm^-2.The capacitance retention is around 80%after 1000 charge-discharge cycles.?3?This work proposes a di-oxidant sandwich-type polymerization strategy to fabricate PPy-and CNTs/PPy-functionalized wool felts while very low concentration?0.08 M?of pyrrole monomer?Py?is used.Most of researches used relatively high concentrations of Py because this is beneficial to get a high mass load of PPy on supports.However,using low concentrations of Py to produce high-performance materials is of high significance to greener and lower-cost production.The main obstacles for this include not only low mass load of PPy but also low performance of PPy under the condition of low Py concentrations.This work designs a di-oxidant sandwich-type polymerization method employing just 0.08 M of Py as raw materials,MnO₂ and FeCl₃6H₂O as di-oxidants.The resulting PPy@Wool gets a high specific capacitance of 0.769F cm^-2 which is increased by?50%than that through the traditional method.After the introduction of CNTs,the specific capacitance can be further increased to 2.333 F cm^-2.