Study On The Optimum Of Activation Strategy And Supercapacitive Performance Of Porous Carbons Derived From Shrimp Shell

With the rapid development of electric vehicles and portable electronic devices,supercapacitors have attracted extensive attention because of its high power density and good cycling stability.Porous carbon materials are the most important active electrode materials for commercial carbon-based supercapacitors.However,porous carbon materials still face with many issues such as high cost,serious equipment corrosion and environmental pollution.The exploration of novel synthsis strategies for porous carbonaceous materials has still been the core problem of carbon-based supercapacitors.In view of above,by using biomass shrimp shell as the carbon and nitrogen sources,a series of nitrogen（N）-doped hierarchical porous carbon was obtained by using minerals in shrimp shell as templates,adopting eutectic complex alkali activation strategy,grafting coupled weak base activation strategy and mixed molten salt activation strategy,respectively.The physicochemical and electrochemical properties of the as-obtained porous carbon are analyzed.The relationship between the microstructure,surface chemical properties and electrochemical properties of the as-prepared porous carbon materials are discussed.In addition,the application of shrimp shell-based porous carbon material in new-style zinc-ion hybrid supercapacitor（ZHS）is explored and its electric storage mechanism is discussed.The main conclusions are summarized as follows:（1）Combining with the phase diagram of Na OH/KOH,N-doped porous carbon（MSHPC）was prepared using single shrimp shell as carbon/nitrogen sources by the eutectic composite alkali activation strategy.The as-prepared MSHPC_1.5-800 possesses a high specific surface area(2465.9 m² g^-1),high micropore volume ratio（52.71%）and high N doping content（1.59 wt.%）.When used as an electrode material of symmetrical supercapacitor,the as-assembled MSHPC_1.5-800-based SC delivered a high specific capacitance(300.3 F g^-1 at 0.05 A g^-1),good rate performance(215.5 F g^-1 at 20 A g^-1),and excellent cycling stability（96.7%capacitance retention after 10000 cycles）.When used as cathode material for ZHS,the as-fabricated ZHSs exhibited high specific capacitance(108.5 m Ah g^-1 at 0.05 A g^-1),outstanding energy density(97.4 Wh kg^-1 at19.6 W kg^-1)and excellent cycling stability（79.82%capacitance retention after 50000charge/discharge cycles）.In addition,the yield of carbon is only 3-6%due to the etching of the alkali.（2）In order to improve carbon yield and alleviate the strong base corrosion,a new method with grafting coupled weak base activation strategy for preparing shrimp shell-based porous carbon materials was proposed.The honeycomb-like/thin carbon nanosheets composites（MSC/HPC）were obtained by using shrimp shell as carbon sources and nitrogen sources,commercial chitin（similar substances to that in shrimp shell）as grafiting carbon sources and weak base K₂CO₃ as activating agent.The as-prepared MSC/HPC₁₀features a high specific surface area(2666.5 m² g^-1),high micropore volume(0.32 cm³ g^-1)and high N content（2.61 at.%）and O content（9.84at.%）.When used as an electrode material of symmetrical supercapacitor,the as-assembled MSC/HPC₁₀-based SC delivered a high specific capacitance(255.8 F g^-1 at0.05 A g^-1),high energy density(8.87 Wh kg^-1 at 6.24 W kg^-1)and superior cycling stability（96.2%capacitance retention after 10000 cycles）.When used as cathode material for ZHS,the as-fabricated ZHSs exhibited high specific capacitance(109.4m Ah g^-1 at 0.05 A g^-1),outstanding energy density(87.25 Wh kg^-1 at 37.11 W kg^-1)and excellent cycling stability（86.64%capacitance retention after 50000 charge/discharge cycles）.In addition,the yield of the composite porous carbon is increased to 19-22%.（3）To validate the universality of the grafting coupled weak base activation strategy and take into account the high value-added utilization of coal chemical by-products,the3D pomegranate-like composites were fabricated by using anthracene oil instead of chitin as grafting carbon sources and weak base K₂CO₃ as the activation agent.When used as an electrode material of symmetrical supercapacitor,the as-assembled MSC/AHPC₈-based SC delivered a high specific capacitance(315 F g^-1 at 0.05 A g^-1),good rate performance(232 F g^-1 at 20 A g^-1),outstanding energy density(10.91 Wh kg^-1 at 6.24 W kg^-1)and superior cycling stability（96.7%capacitance retention after10000 cycles）.When used as cathode material for ZHS,the as-fabricated ZHSs exhibited high specific capacitance(121.2 m Ah g^-1 at 0.05 A g^-1),outstanding energy density(108.8 Wh kg^-1 at 19.52 W kg^-1)and excellent cycling stability（77.76%capacitance retention after 50000 charge/discharge cycles）.Furthermore,the yield of composite porous carbon is increased to approximately 12-15%due to the volatile of anthracene.The anthracene/shrimp shell-based composite porous carbon have optimal electrochemical performance,which fully reflect the advantages of grafting-coupled weak base activation strategy for preparing porous carbon for supercapacitors.（4）To further decrease the corrosion issues which is induced by activation agent,the honeycomb-like porous carbon materials derived from single shrimp shell were obtained by using mixed molten salt（KCl/K₂CO₃）strategy.The mineral Ca CO₃ in shrimp shell is beneficial to produce porous carbon with mesoporous structure.The as-obtained SS-0.7 sample possesses a suitable pore size distribution（42.60%micropore,49.35%mesopore and 8.05%macropore）and small I_D/I_Gvalue（0.9）.When used as an electrode material of symmetrical supercapacitor,the as-assembled symmetrical SC delivered a high specific capacitance(218 F g^-1 at 0.05 A g^-1),good rate performance(171 F g^-1 at 20 A g^-1),and superior cycling stability（94.38%capacitance retention after10000 cycles）.When used as cathode material for ZHS,the as-fabricated ZHSs exhibited high specific capacitance(109.6 m Ah g^-1 at 0.05 A g^-1),outstanding energy density(87.56 Wh kg^-1 at 36.87 W kg^-1)and superior cycling stability（95.81%capacitance retention after 50000 charge/discharge cycles）.In addition,the energy storage mechanism analysis disclosed that the contribution ratio of surface capacitance is 81.91%at 2 m V s^-1 and 97.00%at 1000 m V s^-1,indicating that the capacitive of porous carbon electrodes is the key factor determining the specific capacitance of ZHS devices.