Construction Of Wood-based Self-supporting Electrodes With Multi Components And Mechanism On Their Energy Storage

The wood with rich sources and renewability has high carbon content and good physical and mechanical properties.After high-temperature heat treatment,a wood-based self-supporting carbon electrode material with good conductivity can be obtained.The cell cavity can be used as a channel for rapid transport of electrolyte and a space for active material loading.Therefore,it is important to improve the electrochemical performance of wood-based self-supporting carbon electrode for the construction of supercapacitors with high specific capacitance,excellent rate capability and long cycle stability under premise of retaining the natural structure of wood.In this study,we aimed to develop a wood-based self-supporting carbon electrode（WC）with intact wood structure and high specific surface area.To achieve this,copper chloride（CuCl₂）was used as a mild chemical activating agent.The results showed that the WC electrode was successfully constructed.To further improve the specific capacitance of the electrode,CuCl₂ was simultaneously used as a donor of pseudocapacitive active material.A wood-based self-supporting electrode（WC/Cu_xO_y）with high specific surface area and Cu-based active material loading was prepared.To enhance the pseudocapacitance of Cu_xO_y in WC/Cu_xO_y,the electrochemical constant potential method was used to regulate the valence state of Cu-related substances.Resultantly,the wood-based self-supporting electrode（WC/Cu₂O）with high-pseudocapacitance Cu₂O loading was further prepared.To overcome the disadvantage of low rate capability and poor cycling stability of WC/Cu₂O,two-dimensional MXene（Ti₃C₂）nanosheets were introduced as the protective layer for Cu₂O to enhance the cycling stability of the electrode（WC/Cu₂O/T）.Simultaneously,this continuous conductive network structure built by Ti₃C₂nanosheets can increase the conductivity of the electrode,thus improving the rate capability of WC/Cu₂O/T.In this work,the activation mechanism of CuCl₂ on wood and the effect on the pore structure and electrochemical performance of the WC electrode were studied.Additionally,the enhancement mechanism of Ti₃C₂ on rate capability and cycling stability of WC/Cu₂O/T-based supercapacitor were analyzed.（1）The WC electrode with high specific surface area and retained wood structure was successfully prepared by using CuCl₂ as the mild activating agent.Pore formation through Cu-related reduction reactions involving C elements in wood components.The high boiling point of Cuavoids structure damage caused by metal shuttle for traditional activating agents.Resultantly,the optimized WC electrode with a high specific surface area(1120 m² g^-1)while maintaining the integrity of the wood structure.The electrode exhibits a high specific capacitance of up to 210F g^-1 at a current density of 200 m A g^-1 and maintains over 80%at 1200 m A g^-1.（2）The WC/Cu_xO_y electrode with developed pore structure and pseudo-capacitive active material loaded was successfully created using CuCl₂ as the donor.Benefiting from the both contribution of pseudo-capacitance and double-layer capacitance,the WC/Cu_xO_y electrode exhibited a high specific capacitance of up to 468 F g^-1,twice that of the WC electrode.To fully utilize Cuand contribute greater pseudo-capacitance,the constant potential method was conducted to control the valence state of Cuin the electrode.Using a potential of-0.15 V,Cu₂O with high theoretical specific capacitance was obtained.The specific capacitance of the WC/Cu₂O composite self-supporting electrode reached 855 F g^-1,about 4 times higher than that of the WC electrode.（3）The WC/Cu₂O/T electrode was constructed by introducing Ti₃C₂ with ultra-high conductivity into WC/Cu₂O electrode.The microstructure,conductivity,and electrochemical properties of the electrode were analyzed to investigate the synergistic enhancement mechanism of Ti₃C₂ on the conductivity and electrochemical performance of the electrode.The two-dimensional Ti₃C₂ nanosheets form a continuous and conductive network by overlapping with each other,greatly improving the overall conductivity of WC/Cu₂O/T electrode(up to 15.38 S cm^-1).The overlapping nanosheet layers also act as a protective layer on the electrode surface,preventing the detachment of Cu₂O due to volume changes during charge and discharge processes,thereby improving the rate capability and cycling stability of the electrode.The assembled supercapacitor exhibits a high specific capacitance(730 F g^-1)and energy density(81.31 Wh kg^-1),and the specific capacitance can still maintain 82%even when the current density is increased to 1800 m A g^-1.The supercapacitor,benefiting from the confined protection effect constructed by Ti₃C₂,maintains 93%capacitance retention after 10,000 cycles.Compared with WC/Cu₂O-based supercapacitor,the rate capability is improved by 22%,and the cycling stability is improved by 50%.