Synthesis And Performance Of Nano Porous Carbon Electrode Materials Using CaCO₃ Template For Supercapacitors And Oxygen Reduction Reaction

Porous carbon materials have outstanding advantages when used as supercapacitor electrode material,such as high power density,good cycling stability and rate capability.Current researches are focusing on improving their capacity,and enhancing their energy density,to promote their large-scale production and application.Template method is an efficient way to prepared porous carbon materials.Nitrogen-doped and iron/nitrogen co-doped carbon materials are known as effective electrocatalysts toward oxygen reduction reaction（ORR）.A supercapacitor/ORR difunctional electrode material would been obtained by N-doping or Fe/N-co-doping of porous carbon.Considering that the fuel cell vehicles（FCV）usually use a fuel cell as main power source（MPS）and a supercapacitor as peaking power source（PPS）,the MPS and PPS can be integrated into a single electrochemical pool by using the difunctional electrode material.This strategy is expected to simplify the device structure and reduce the cost.In this thesis,we first present preparation of porous carbon materials using in-sute CaCO₃template method.Then,we investigated their electrochemical performances as supercapacitor electrode material and ORR electrocatalyst.Besides,the performance under high power fluctuations which was common in vehicle application have been discussed.The research mainly includes the following aspects:（1）Porous carbon（PC）has been prepared through the carbonization of glucose with the presence of CaCO₃ template which was produced in sute.By controlling the amount of glucose,the carbonization temperature and the species of CaCO₃ precursors,we have achieved the simplification of the preparation process and the increase of specific capacitance.The as-synthisized K-PC has a large specific surface of 1220 m²/g and a high specific capacitance of 311 F/g at 1A/g and 194 F/g at20 A/g.Besides,along cycle stability of 99%capacitance retention was observed after 3000charge-discharge cycles at 20 A/g.（2）Nitrogen-doped porous carbon（NPC）was synthetized via the in-sute CaCO₃ template strategy developed above when 2-methylimidazole was used as a single N-source and C-source.Zn²⁺is indispensable for the successful carbonization of 2-methylimidazole.When tested as supercapacitor electrodes,the NPC delivered a high specific capacitance of 271 F/g at 1 A/g and it still maintained at a value of 196 F/g even at 20 A/g.When used as electrocatalyst toward ORR,the NPC possessed similar catalytic activity to commercial 30 wt.%Pt/C catalyst in 0.1M KOH.The constant potential step test was used to simulate the electricity response during the starting phase of a FCV.A large electricity which was from the capacitor charge current was obtained at a small overpotential.This result indicated that the electrode could keep at a narrow potential range under high power fluctuations which was common in vehicle application.These features help to prolong the life of electrode,improve energy efficiency and simplify the device structure.（3）Iron/Nitrogen co-doped porous carbon（Fe/NPC）was synthetized via the same strategy of NPC when extra FeCl₂ was added.When tested as supercapacitor electrodes,the Fe/NPC delivered a large specific capacitance of 230 F/g at 1 A/g and it still maintained at a value of 170 F/g even at 20A/g.When used as electrocatalyst toward oxygen reduction reaction（ORR）,the Fe/NPC possessed good catalytic activity toward ORR in 0.5 M H₂SO₄.The constant potential step test showed that a large electricity was obtained at a small overpotential.These features help to prolong the life of electrode,improve energy efficiency and simplify the device structure.