| Porous carbons with high specific surface area and reasonable pore sizedistribution used for electric double layer capacitor (EDLC) were prepared with resolphenolic resin as raw material by different methods, including chemical activation,sol-gel polymerization, soft-template and polymer blend technique. The influences ofpreparation method and conditions on structure and performance of porous carbonswere thoroughly investigated and the pore-forming mechanisms were discussed. Therelationship between the electrochemical performance of porous carbon and porestructures were clarified. Based on these, the technologic methods and conditions ofcontrolling the pore structures of porous carbon were established, which wouldprovide theoretical basis and experimental supports for further improving theperformance of porous carbon in EDLC.High specific surface area porous carbon with distinct pore structure wasprepared with resol phenolic resin as raw material and KOH as activator by chemicalactivation. The influences of the active agent amount, carbonization temperature andactivation time on yield, pore structure and electrochemical performance of porouscarbon were investigated. The relationship between the pore structure and capacitancewas analyzed and the preparation conditions were established of porous carbonsuitable for different electrolytes.The results show that the active agent amount, carbonization temperature andactivation time have great effect on the pore structure of porous carbon. By controllingcarbonization temperature, the pore structure can be easily adjusted at relative lowcontent of active agent. The pore volume and mesoporosity of porous carbonsincreased with decrease of carbonization temperature, while the BET surface areaincreased firstly and decreased afterwards. The surface area total, pore volume,micropore surface area and mesoporosity of PF-600reach2918.6m~2/g,1.41cm3/g,2628.3m~2/g and19%, respectively. As carbonization temperature decreasing to550℃,the values of PF-550are2983.5m~2/g,1.58cm3/g and2269.4m~2/g and themesoporosity was enhanced to37%. PF-600exhibited the best electrochemicalperformances in30%KOH electrolyte that the specific capacitance value reached310F/g at1mA/cm~2and retained as90%even when the current density was enlarged50times. While the specific capacitance value of PF-550reached the highest value of160F/g in1M Et4NBF4/AN electrolyte and retained82%at50mA/cm~2. It is widelybelieved that to obtain high capacitance and rate performance at the same time especially in organic electrolyte, porous carbon with a high specific surface area and alarge amount of mesopores is effective.Carbon aerogel with high specific surface area and developed mesopore structurewas successfully prepared via a sol-gel process from the polycondensation ofresorcinol and formaldehyde catalyzed by HMTA in alcohol-solvent, followed bydrying at ambient pressure and pyrolysis at900℃under inert atmosphere. The effectsof solvent types, polymerization temperature and carbonization heating rates on thepore structure and capacitance performance were studied systematically. And thetechnologic conditions of preparing carbon aroegels were established.The results show that by employing hexamethylenetetramine (HMTA) as both acatalyst and curing agent and ethanol as solvent, ambient drying of carbon aerogelscan be realized. The network formed in sol-gel polymerization can be ideally keptafter ambient dry and porous carbon with developed mesopores was accordinglyobtained.The pore structure of carbon aerogel could be controlled by changing solventtype, polymerization temperature and carbonization heating rates. The amount andsize of mesopores in carbon aerogel increase with polymerization temperature.Meanwhile, the specific surface area increase first and then decrease with fastercarbonization heating rates, but mesoporesity changed adversely. The best technologicconditions of sol-gel method are the R/F, R/H mole ratio, R/S value, thepolymerization temperature and carbonization heating rates being2.0,50and0.1g/ml,80℃and2℃/min, respectively. The highest specific surface area, mesoporosity andaverage pore diameter of carbon aerogel are739.0m~2/g,51%and2.76nm,respectively, which exhibit the highest capacitance of180F/g at1mA/cm~2and thebest high current charge/discharge performance, retaining86%even at50mA/cm~2.With resorcinol(R), formaldehyde (F) as raw materials, hexamethylenetetramine(HMTA) and hydrochloric acid (HCl) as catalyst, porous carbon material with tailoredpore structure, high specific surface area of701.2m~2/g and developed mesoporosity of67.0%was obtained by self-assembly method of block copolymer F127as the porogenand followed by carbonization. The influence of the content of F127at differentcatalysts on the surface appearance, pore structure and electrochemical performance ofporous carbon were researched. Meanwhile, the pore forming mechanism wasdiscussed.The results show that different catalyst system have great influence on structure ofphenolic resin based composite and further affect pore structure of porous carbon obtained when using block copolymer as thermal decomposable polymer. When weakbasic catalyst HMTA was used, the sol-gel process of resorcinol and formaldehydeproceeded tardily and a single-shaft distortion easily occurred. The ordered porestructure of porous carbon can be hardly guaranteed and the synthesis efficiency wasalso low. The phenolic resin and block copolymer (F127) were partly protonized whenstrong acid (HCl) was used. The reacting system can assemble into a nanometercompound system under both Kulun attraction (I+X-S+mechanism) and the hydrogenbond (the I0S0mechanism). The regularity of composite can be enhanced and thesynthesis speed increased simultaneously. Accordingly, porous carbon with regularpore distribution was obtained.The specific surface area, total pore volume, and average pore size of porouscarbon materials with different F127ratio at HCl catalyst are between640~700m~2/g,0.41~0.55cm3/g and2.46~3.38nm, respectively. When F127/R is1.3, the specificsurface area and mesopore volume of porous carbon is701m~2/g and0.36m3/g,respectively. The mesoporosity achieved67.0%. The capacity maintenance reached ashigh as93%as the current density increases50times and kept94%after cycling5000times.Porous carbons with specific surface area of609m~2/g and mesopore sizecentralized in3~4nm were prepared firstly by chemical blending of phenolic resin(PF) with adipic diacid (hexanedioic acid (HA) and suberic acid (SA)) andepoxy-terminated prepolymer (QS). The influences of the content of pore formationagent to PF on pore structure and capacity performance were investigated. Themechanism of pore formation in chemical blending was also discussed. The methodprovides an ideal experimental carrier for studying pore formation and the correlationwith electrochemical performance.Chemical reaction of PF with diacid is manifested by a shift of carbonylstretching peak of diacid to a higher frequency in FT-IR spectra and a higherdecomposition temperature from150~230℃to400~450℃of diacid in TG curves.Namely, the thermal decomposition didn’t occur until a relative steady skeleton ofphenolic resin has been established. This may be the main reason of the pore-formingability of diacid molecules. The specific surface area and mesopore volume of porouscarbon is550.9m~2/g and0.27m3/g, respectively, as the content of HA is25%. Thespecific capacity of the carbon is145F/g.Porous carbons were prepared by chemical blending of phenolic resin (PF) andepoxy-terminated prepolymer (QS). During the curing reaction, epoxy groups of QS reacts with the phenolic hydroxyl of PF to form ether linkage. The specific surfacearea, total pore volume and micropore volume increase with the ratio of QS to PF atfirst and then decrease, reach the maximum at the value of w(QS)/w(PF)=15%, whichare609.0m~2/g,0.28cm3/g and0.22cm3/g, respectively. When the porous carbon usedfor the electrodes of electrochemical double layer capacitor (EDLC), a satisfiedspecific capacitances of177.5F/g in30wt%KOH aqueous electrolytes is acquiredand the capacitance maintenance achieve76%as the current density enlarged50times.After curing reaction, the microphase separation formed by block or graft chainsin copolymers was restricted and the enlarging of microphase structure was delayedbecause of chemical bonding and molecular interaction between block or graft chainsand carbon precursor. The region of microphase structure was confined in nanometerscale. The pore will come into being after pyrolysis of the block or graft chains andsmaller than the size of the microphase structure existed before. Meanwhile, thethermal decomposition of graft chains didn’t occur until a relative steady skeleton ofphenolic resin has been established, so the pores didn’t disappear with the shrinkageof copolymers. This method has a very good application prospect in preparation ofporous carbon for electric double layer capacitor because of its simple process, porestructure controllable and environmental friendliness. |
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