Study On The Synthesis Of Hierarchical Porous Carbons And Their Application In Acid-alkline Eletrochemical Capacitors

As a new type of energy storage devices,supercapacitors（SCs）,also known as electrochemicalcapacitors（ECs）,have drawn tremendous attention from scientific researchers in recent years since they have the advantages of both batteries and traditional capacitors,and display high power density,high efficiency,fast charge/discharge rate,long cycle life,excellent reversibility,wide temperature characteristics,safety and environmental friendly features.However,the relatively low energy density of ECs(usually less than 6 Wh kg^-1)has significantly limited their widespread applications.To overcome this,various strategies have been promoted to design and synthesize new electrode materials to match with the used electrolytes.Nitrogen doped carbon materials have attracted much attention due to their advantages such as low cost,high specific surface area（SSA）,large pore volume,high mechanical strength,good chemical stability and thermal stability,and wide range and non-toxic sources.Usually,aqueous electrolytes are most frequently used since they possess both very high conductivity and easy operability,at the same time they are inexpensive and environmentally friendly.The significant problem for obtaining high energy density of ECs is to develop the new hierarchically porous electrode materials which match with strong acid and strong alkaline electrolytes.The main contents of this paper are as follows:（1）A series of new hierarchically porous nitrogen-doped carbon aerogels（CAs）are synthesized using polyvinyl alcohol（PVA）,aniline（ANI）,boric acid（BA）and ammonium persulfate（APS）as the carbon sources,in-situ nitrogen sources,crosslinking agent and oxidizing agent through the chemical crosslinking polymerization,freezedrying,carbonization and KOH activation processes.The optimal carbon sample with a high BET surface area of 2675 m² g^-1,a wide micropore and mesopores size distribution（0.5-4 nm）,in-situ nitrogen-doping（0.5%）and surface hydrophilicity（contact angle is 12.9^o）exhibits a high specific capacitance(497 F g^-11 and 400 F g^-1),excellent rate capability,high power density(5968 W kg^-1 and 5368 W kg^-1),high energy density(12.6 Wh Kg^-1 and 11.05 Wh Kg^-1),excellent cycling stability（the capacitance retention are 92.8%and 90.71%after 10000 cycles）in strong acid and alkaline electrolytes.（2）Anothertypeofnewnitrogen-dopedhierarchicalporousCAsbased polyacrylamide/polyaniline（PAAM/PANI）are synthesized via in situ self-assembly chemical oxidative dispersion polymerization with acrylamide（AAM）and ANI monomer as precursors,N,N’-Methylenebisacrylamide（MBA）,2-hydroxy-4’-（2-hydroxyethoxy）-2-methylpropiophenone as cross-linking agent and photoinitiator,and polyvinyl pyrrolidone（PVP）as a surface active agent by vacuum drying,carbonized and activation.The sample at 700 ^oC activation possesses a high specific surface area of 3146.2 m² g^-1,a high micropore surface area of 2520.66 m² g^-1（80.1%）,in-situ nitrogen-doping（0.89%）and high hydrophilicity（contact angle is 11.3^o）,and shows high specific capacitance(519.1 F g^-1 and 474.3 F g^-1),outstanding cycling stability（the capacitance retentions are92.72%and 91.43%after 10000 cycles）and high energy density(12.81 Wh Kg^-1 and 10.57 Wh Kg^-1)in strong acid and strong alkaline electrolytes.（3）Nitrogen-doped hierarchical porous carbon materials are prepared utilizing cheap,readily available biomass of canthus and chitosan as precursors.A series of structural analysis methods and electrochemical characterization techniques were used to explore the structure,chemical composition and electrochemical properties of the carbon materials.The results show that the nitrogen doped carbon material with high specific surface area(3239.36 m² g^-1),and abundant micropores specific surface area(2545.07 m² g^-1),hierarchical pore size distribution,certain amount of nitrogen doped（0.7%）,a highly hydrophilic（8.6^o）releases a high specific capacitance(520 F g^-1 at a current density of 1 A g^-1)and outstanding cycle stability（95.07%）,which are better than that of commercial activated carbon,and show the good prospect of application in SCs.