| Due to the advantages of safe,cost-effective and environment friendly,aqueous carbon/carbon supercapacitors attract much attention.The narrow work voltage window greatly hinders the enhancement of energy density.The low work voltage window is limited by the thermodynamic stable potential of solvent water?1.23 V?,which can be surpassed by regulating the physicochemical properties of carbon electrode surface.N/O-enriched carbon cloth with a large surface area and desired pore volume is fabricated by cooperating with Shanghai Lishuo composite material technology co.LTD.An electrochemical oxidation method is introduced to adjust the surface physicochemical properties through incorporation of electrochemical active functional groups to the carbon surface and to further increase the specific surface area and the pore volume of the carbon cloth.The resulting carbon cloth electrode presents excellent electrochemical properties,including wide potential range,ultrahigh areal capacitance,good rate ability and cycling stability.In addition,the fabricated symmetric supercapacitors with a 2 V stable voltage window deliver ultrahigh energy density(9.4 mWh cm-3).The fabric supercapacitors are further tested in various applications,such as a belt-shaped device as a watchband to power an electronic watch for9 hours,a heart-shaped logo to supply power for1 hour and a safety light that functions for1 hour,indicating promising applications of these supercapacitors.The strategy of coating poly-crystallinity ZnSO4·3Zn?OH?2 powder on negative carbon electrode is used to improve the long-term cyclic stability of aqueous carbon-based supercapacitor at 2.1 V.Satisfactory,the capacity retention of 2.1 V ZnSO4·3Zn?OH?2 coated carbon cloth?-?//carbon cloth?+?is up to 100%after 13000cycles at 18 mA cm-2,much higher than that of the pristine device?36%?.The novel strategy avoids the electro-oxidation of positive carbon electrode.By electrodepositing Zn/Zn4SO4?OH?6·4H2O composite?ATDS?on micropore carbon cloth modified with basic functional groups?OCC?as a negative electrode,we develop an aqueous carbon/carbon supercapacitor operated steady at voltage windows as high as 2.1 and 2.5 V.2.1 V beaker-shaped supercapacitor of ATDS@OCC//CC presents almost 100%of capacity retention after 19000 cycles at 18 mA cm-2.The cycled 2.1 V ATDS@OCC//CC supercapacitor exhibits the improved energy density and better retention of energy density.2.5 V ATDS@OCC//CC supercapacitor after4900 cycles exhibits about 100%of capacity retention and the ultrahigh volumetric energy density of 20 mWh cm-3 and the mass energy density of 29 Wh kg-1.2.9 V aqueous carbon-based supercapacitor is proposed to promote the energy density.The positive half of supercapacitor consists of the carbon cloth and the 8 m NaClO4/?H2O?1.5/?AN?2.4.4 electrolyte,demonstrating 1.2 V?vs SCE?of stable potential window.The negative half of supercapacitor composes of Zn/6Zn?OH?2·ZnSO4·4H2O@alkali functional groups modified carbon cloth and the cycled 1 M Na2SO4 aqueous electrolyte,exhibiting-1.7 V?vs SCE?of stable potential window.6Zn?OH?2·ZnSO4·4H2O expands the negative potential window of carbon cloth due to the strong adsorption of Zn2+on?002?plane to the hydrogen confirmed by DFT calculation(?35?GH*=-0.89 eV).The salt bridge in Daniel cell is employed to connect the two electrolytes.Finally,the aqueous carbon-based supercapacitor could operate stably in the voltage window of 2.9 V.After 5000 cycles,90%of the initial capacity is retained and the mass energy density is up to 25 Wh kg-1.The stable work voltage window of aqueous carbon/carbon supercapacitors is expanded to 2.9 V from pristine 1.8 V and exhibit an excellent energy density approaching 30 Wh kg-1,which are comparable to the reported carbon/carbon supercapacitors based on“water-in-salt”(2.5 V,24 Wh kg-1)and organic electrolytes(2.72.9 V,29 Wh kg-1).The strategy proposed in the article may offer the new insights into exploring aqueous high-voltage energy storage devices beyond supercapacitors. |
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