Study On The Electrochemical Performance Of Carbon Fiber Based Flexible Electrodes And Application In Supercapacitors

Faced with increasingly serious environmental pollution and energy crises,the development of sustainable clean energy is an inevitable trend in social development.Electrolytic water for hydrogen production and supercapacitors have received widespread attention in the field of energy conversion and storage.At present,the main challenges that constrain the development of both are the design,performance,and production costs of electrode materials.It not only needs to have good electrochemical activity and conductivity but also needs to meet corrosion resistance and high mechanical properties.Carbon fiber,due to its chemical stability,high conductivity,and flexibility,not only enables rapid electron transfer but also endows electrodes with good mechanical properties,making it an ideal flexible fluid collector.However,its electrochemical inertness and smooth surface will suppress the loading of the active material,resulting in high contact resistance.Therefore,it is necessary to modify the surface of fibers to improve their loading capacity on active materials,thereby improving the electrochemical performance of carbon fiber-based electrodes.This article prepared carbon fiber-based flexible self-supporting electrodes that can be simultaneously applied in flexible supercapacitors and electrocatalytic hydrogen evolution devices through methods such as structural optimization,heteroatom doping,and multi-component combination.By analyzing the phase,morphology,and electrochemical performance of electrode materials,the effects of in-situ growth,structural stability,high conductivity,and multiple active sites on electrochemical performance were elucidated.The main research content of this article is as follows:（1）In response to the problem of inert surface and poor electrochemical activity of carbon fibers,this chapter employed chemical bath and high-temperature calcination methods to in-situ construct B and N atom co-doped porous carbon materials（BNC）on the surface of carbon fiber cloth（CC）.Doping with N atoms can improve the wettability of electrode materials,thereby improving the migration ability of electrolyte ions on their surfaces.The doping of B atoms provides more active sites and additional pseudocapacitance for the electrode.In addition,the effects of BNC morphology and crystallinity on electrochemical performance were investigated by adjusting the calcination temperature.The results indicate that an appropriate calcination temperature can endow BNC with a porous structure,exposing more active sites,and high-temperature calcination effectively reduces the charge transfer resistance of BNC.Based on the above advantages,BNC/CC self-supporting flexible electrodes have good electrochemical performance in the fields of electrocatalytic hydrogen evolution and supercapacitors.At a current density of 10 m A cm^-2,their hydrogen evolution overpotential is only 149 m V,and there is no significant change in overpotential during the 24-hour hydrogen evolution test.In addition,BNC/CC also exhibits excellent performance in the application of flexible supercapacitors,with a specific capacitance of 1630 m F cm^-2when the charging and discharging current is 4 m A cm^-2.The assembled symmetrical flexible all solid-state supercapacitor（FASC）exhibits excellent energy density(65.9 m Wh cm^-2)and power density(1000.2 m W cm^-2)while maintaining good flexibility.Moreover,it can maintain 91%energy output after 5000consecutive charge discharge cycles.（2）Mo S₂has a large specific capacitance and a Gibbs free energy close to Pt,making it an ideal electrochemical active material.This chapter constructs Mo S₂nanosheets（MS）with large interlayer spacing on the surface of BNC/CC using hydrothermal and plasma methods.BNC/CC not only provides good conductivity and flexibility for electrodes,but also effectively inhibits the aggregation of MS nanosheets.In addition,N₂plasma induced the transition of MS from semiconductor phase（2H MS）to metal phase（1T MS）,with a conversion rate of up to 77%,and its interlayer spacing increased from 0.632 nm to 0.728nm,thereby enhancing the migration ability of ions within the electrode.DFT calculations have shown that after plasma bombardment,the bandgap width of MS is significantly reduced,and its conductivity is significantly improved.Thanks to these advantages,the1T-2H MS@BNC/CC electrode has high electrocatalytic hydrogen evolution activity,requiring only 76.2 m V over potential to reach a current density of 10 m A cm^-2.At the same time,the electrode can exhibit a high specific capacitance,which can reach 994.2 F g^-1when the current density is 0.5 A g^-1.In practical energy storage applications,The flexible all solid-state supercapacitors assembled by 1T-2H MS@BNC/CC and AC/CC exhibit excellent energy density(71.6 Wh kg^-1)and power density(700 W kg^-1).Moreover,bending and integration will not have a significant impact on its energy output,and the series connection of the two devices can illuminate LED bulbs for up to 10 minutes.（3）To further improve the electrochemical performance of carbon fiber based flexible electrodes,this chapter uses BNC/CC as a template and constructs a B atom doped Ni Co₂O₄"nanoneedle"array（B-NCO）on its surface through simple hydrothermal and annealing treatment.The three-dimensional structure of BNC/CC not only induces the ordered growth of B-NCO,but also provides more transfer pathways for electrons.The tip effect of B-NCO can form a local electric field at the tip of the"nanoneedle",thereby improving electron utilization.In addition,B atoms are doped inside NCO in the form of gaps and substitutions,respectively.Gap B provides more active sites and additional pseudocapacitance;Replacing B improves the local electronic structure of Co and Ni atoms,enhances the electron delocalization ability of Co and Ni atoms,and effectively enhances the conductivity of NCO.The B-NCO@BNC/CC flexible electrode exhibits a low hydrogen evolution overpotential（69 m V）and Tafel slope(48 m V dec^-1)at 10 m A cm^-2,indicating good electrocatalytic activity.When applied in supercapacitors,The specific capacitance of B-NCO@BNC/CC electrode is as high as 2015.8 F g^-1.Assembled flexible devices B-NCO@BNC/CC//BNC/CC FASCs can provide a voltage of 1.5 V and a high energy output of 87.6 Wh kg^-1for electrical devices,requiring only one device to ensure the normal operation of electronic watches.In addition,the device has good flexibility and can still ensure stable energy output under bending conditions of 90°and 180°.