| It is of great significance to develop clean and sustainable energy storage devices in order to meet the increasing energy consumption.Compared with secondary batteries and fuel cells,supercapacitors have the advantages of fast charging and discharging speed,long cycle life and safe operation,so they can be used in the field of power transportation,portable electronic equipment and biomedical equipment.Electrode material,as one of the key components of supercapacitor,has an important influence on the electrochemical performance of supercapacitor.Carbon materials have attracted researchers’attention due to their superiority of extensive sources and good electrical conductivity.The preparation of powdered carbon-based electrodes requires the use of conductive agents and adhesives,which increases the invalid mass,leads to the decrease of energy density of supercapacitors.And its flexibility cannot meet the requirements of commercial flexible devices.The self-supported carbon electrode can avoid the use of any other additives and shows excellent mechanical properties such as excellent bending resistance.In view of the intrinsic double layer adsorption energy storage mechanism of carbon-based electrode,researchers usually adopt activation or surface modification methods,but they only focus on making use of the inner or outer surface of the self-supporting carbon-based electrode,while ignoring the simultaneous utilization of the inner and outer surface,resulting that their specific capacitance is far from commercial requirements.Therefore,how to improve the space utilization rate of carbon based self-supported electrode is of great significance to improve the overall capacitance performance.Based on the above analysis,this paper takes graphene and carbon cloth as substrate materials,small organic molecules are used to modified them.Then,the morphology,structure and electrochemical performance are being characterized.The specific research contents and conclusions are as follows:（1）Tannic acid modified graphene film electrode and its capacitance performance.Interface self-assembly followed by hydrothermal reduction method are proposed to obtain a tannic acid（TA）modified reduced graphene oxide composite film（|TA/RGO|）.TA is inserted between graphene layers,which effectively inhibits the stacking of graphene sheets.The reaction of abundant phenolic hydroxyl groups on TA with protons in the electrolyte provides pseudo-capacitance.The confined thermal reduction method inhibits the excessive volume expansion of graphene sheets,and relatively dense layered structures are achieved.As a result,|TA/RGO|film shows an ultrahigh volumetric performance of 701 F cm-3 in the three-electrode system.When assembled into symmetric supercapacitor,|TA/RGO|film delivers a high volumetric capacitance of 244.8 F cm-3 and a high capacitance retention of 100%after 5000 cycles at the current density of 2 A g-1.（2）Dopamine-modified porous carbon cloth and its zinc-ion capacitance performance.The double utilization of the inner and outer surface of carbon cloth was realized by air activation and hydrothermal dopaminergic polymerization coating method,and the zinc ion storage performance of carbon cloth was improved.Air activation increases the specific surface area of carbon cloth and improves hydrophilicity,which is beneficial to the adsorption of zinc ions.The interaction of the abundant quinone groups on polydopamine（PDA）with zinc ions enhances the pseudo-capacitance contribution.Owing to the dual energy storage mechanism of pseudo-capacitance and electrical double layer adsorption,the area capacity of polydopamine-coated porous carbon cloth（PDA@PCC）is up to 2467 mF cm-2 under the current density of 1 mA cm-2,and the capacity retention rate is 100%after 10000 cycles.In addition,a flexible zinc ion capacitor is assembled using polydopamine-coated PDA@PCC as the cathode,and its capacity reaches 1948 mF cm-2.Meanwhile,its flexibility and operation safety are proved by several extreme conditions such as cutting and sewing tests. |
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