Preparation And Capacitive Performance Of Quinone/Carbon Composite Materials

Supercapacitor(SC) is a novel energy storage component with the merits of high power density,long cycle life,etc,which has become a research hotspot in the field of energy.However,the main problem limiting its practical application is the relatively low energy density.The performance of SC is mainly determined by electrode materials,so the key to improve the energy density of electrode materials is to develop and design advanced electrode materials.Carbon materials are always preferred electrode materials for SC.However,due to the sole electric double layer energy storage mechanism of pure carbon materials,its specific capacitance is lower.Quinones are organic molecules with electrochemical activity,which could undergo redox reaction based on the conversion between phenols and quinones.Therefore,in this paper,quinone molecules were used to modify porous carbon materials,resulting in quinone/carbon composite materials with both electric double layer capacitance and pseudocapacitance.The cooperative enhancement mechanism between quinone and carbon was studied as well.1.Enteromorpha prolifera,a marine pollutant,was used as raw materials and KOH was used as activator,to prepare activated carbons by a two-step strategy.The enteromorpha prolifera based activated carbons(CK carbons)have developed porosity with micro-meso hierarchical pore texture.The influence of alkaline coke ratio on pore structure and electrochemical properties of CK carbons were investigated.The maximum BET surface area of CK carbons is 2405 m² g^-1,the highest specific capacitance of the carbons can reach up to296 F g^-1.And the maximum energy density of SC is 10.76 Wh kg^-1.More importantly,the CK carbons can maintain a high capacitance of up to 152 F g^-1 at a very high current density of 30 A g^-1,showing excellent capacitance performance.In order to further improve the capacitance characteristics of CK carbons,taking CK-3 as an example,HQ modification was performed on this carbon.The effect of different amounts of hydroquinone on the capacitance characteristics of the composite material HQ/CK-3 was investigated.Electrochemical test results show that the best synergistic effect between hydroquinone and CK-3 can be achieved when the hydroquinone loading was 20%.The maximum specific capacitance of the composite material is 447 F g^-1,which is 74%more than that of pure CK-3 carbon.At the current density of 30 A g^-1,the specific capacitance is up to 184 F g^-1.The capacitive performance of hydroquinone modified CK carbon was improved obviously.However,the blockage of partial micropore by HQ molecules results in the deterioration of rate performance.The capacitance retention ratio of the composite maintains 51.1%after 10000 cycles,which should be ascribed to the dissolution of HQ molecules.2.In order to inhibit the blocking of HQ,we took mesoporous carbon nanospheres(MCNS)with larger pore size as carbon carrier and stuied its HQ modification.Herein,we synthesized MCNS with 3D ordered pore symmetry by soft template method.Then,the HQ was used to modify MCNS by hydrothermal method.The results showed that the best synergistic effect can be achieved for the MCNS with 10%HQ loading,and capacitance improvement is most obvious.The specific capacitance of the composite is 285 and 182 F g^-1at the current density of 0.5 and 30 A g^-1,respectively.Compared with hydroquinone modified CK carbon,the rate performance of HQ/MCNS was improved.It was indicated that taking mesoporous materials with larger pore size as carrier can effectively suppress the phenomenon of pore blocking by HQ,and improve the rate performance of materials.3.In order to effectively inhibit the dissolution of HQ,different quinone molecules with various hydrophilicity were introduced onto mesoporous carbon/graphene(MCG).The results showed that the capacitive property of MCG loaded with TBHQ and DBHQ with weak hydrophilicity of alkyl branchchain were significantly improved than that loaded with HQ.By investigating the loading ammount of TBHQ,it can be seen that MCG with 30%loading of TBHQ has the best capacitive property.The maximum specific capacitance is 355 F g^-1 at the current density of 0.5 A g^-1,and 226 F g^-1 at 30 A g^-1with specific capacitance retention ratio of 63.5%.The capacitance retention ratio of the composite maintains 84.2%after 10000cycles,indicating that reducing the hydrophilicity of quinones is helpful to improve the cycling performance of composite material.4.Using hydrophobic anthraquinone(AQ)as modifier,the AQ modified ordered mesoporous carbon(OMC)composite materials(AQ/OMCs)were prepared.The results showed that the composite material prepared at temperature 65?with AQ loading of 40%,has the best capacitive performance.The specific capacitance of 65AQ40/OMC is 346 F g^-1 at current density of 0.5 A g^-1,and 292 F g^-1 at 30 A g^-1 with excellent rate performance.This is mainly because(1)AQ contains three benzene rings with extended electronic system,which helps to reduce the charge transfer resistance of Faraday reactions;(2)after loading AQ,OMC still retained the mesoporous structure,which promoted the rapid diffusion of electrolyte ions.In addition,asymmetric supercapacitor is assembled using OMC and AQ/OMCs as positive and negative electrode,respectively.The effects of electrode matching and electrochemical charge injection(ECI)pretreatment on the capacitance properties of supercapacitors were investigated.The results show that matching the suitable electrode and ECI pretreatment can significantly improve the capacitance performance of supercapacitors.The ASC-ECI can deliver a very high energy density of 14.51 Wh kg^-1 and excellent long-term cycle stability,retaining 96.3%of initial capacitance,after 10,000 cycles.