Surface Modification Of Biomass-derived Carbons And Their Electrochemical Properties

The use of biomass for the fabrication of diverse carbon functional nanomaterials is attracting considerable attention due to its sustainability and renewability.As one of the key energy storage devices,supercapacitors（SCs）require the active electrode material to have high specific surface areas（SSA）,interconnected porous structures and excellent conductivity.However,it is difficult to finely tune the pore structures of biomass-derived carbons（BCs）due to the inherent robust microstructures of biomass itself,limiting the wide applications of BCs.How to further optimize the structures of BCs to prepare electrode materials for high-performance supercapacitors is still a large challenge.Inspired by nature that leaves effectively increase the air-accessible surface area of plants to absorb more carbon dioxide for photosynthesis,we increase the surface area of BCs for ion adsorption by grafting leaves-like units onto the surface of BCs.In this work,porous carbon nanosheets（PCNSs）functioned as leaves-like units were grafted onto the surface of BCs for decorating the BCs surface to fabricate PCNS/BC composites.The main conclusions are as follows:（1）PCNS/rice husk-derived carbon（PCNS/RHC）composites were prepared by grafting coal tar pitch-based PCNSs onto the surface of RHCs to boost the functionality of RHCs.The SSA of PCNS/RHC composite reaches 3120 m² g^-1 with a large pore volume up to 3.00 cm³ g^-1.As the electrode materials for SCs,the PCNS/RHC composite exhibits a high specific capacitance of 315 F g^-1 at 0.1 A g^-1,an excellent rate capability of 222 F g^-1 at 20 A g^-1 and a good cycle stability with95.8%capacitance retention after 10000 cycles in 6 M KOH electrolyte.（2）Based on Experiment 1,PCNS/RHC was prepared by grafting coal tar-based PCNSs instead of coal tar pitch-based PCNSs on the surface of RHCs.The as-prepared composite has a larger SSA of 3619 m² g^-1 and a larger pore volume up to 4.17 m³ g^-1.As electrode materials for SCs in 6 M KOH electrolyte,PCNS/RHC exhibits a high specific capacitance of 292 F g^-1 at 0.05 A g^-1,an excellent rate performance of 202 F g^-1 at 20 A g^-1.In the BMIMPF₆ electrolyte,PCNS/RHC exhibits a high energy density of 119 Wh Kg^-1,ca.11.5 times than that of 6 M KOH electrolyte.（3）This strategy is extended to modify the cotton-derived carbon（CC）by grafting coal tar-based PCNSs to prepare PCNS/CC composites.As the electrode materials for SCs in 6 M KOH electrolyte,the composite shows a high specific capacitance of 248 F g^-1 at 0.05 A g^-1,a good rate performance 172 F g^-1 at 20 A g^-1,as well as a good cycle stability with 96.1%capacitance retention after 20000 cycles.In BMIMPF₆ electrolyte,the PCNS/CC SC exhibits a high energy density of 68.3Wh kg^-1.Meanwhile,after cycling 3000 times at a current density of 5 A g^-1,the capacitance still remains 96.7%,showing good cycle stability.