Preparation And Electrochemical Capacitance Properties Of Phosphours-doped Nanoporous Carbon Spheres

Porous carbon materials,due to their low cost,good conducity and large specific surface area,have been the most promising commercial electrode materials in supercapacitor.However,pure carbon materials rely on electric double layer capacitors for storage and have poor surface wettability,which limit the high capacitance.By introducing phosphorus atoms into the surface or skeleton of the pure carbon materials through surface modification or doping,the capacitance performance of the pure carbon material can be improved.In this thesis,phosphorus-containing cross-linked polymer spheres were prepared by emulsion polymerization or hydrothermal polymerization,and phosphorus-doped nanoporous carbon spheres with different structure were obtained by high-temperature pyrolysis and KOH activation.Morphology,structure and phosphorous content of phosphorus-doped nanoporous carbon spheres were controlled by changing the experimental conditions.Furthermore,the electrochemical performances were also studied.Firstly,the phosphorus-containing cross-linked polymer spheres were prepared by emulsion polymerization and Friedel-Crafts reaction with divinylbenzene,2-hydroxyethyl diphenylphosphinate(HEDP)and styrene as monomers.Phosphorus-doped porous carbon spheres were subsequently obtained by carbonization and KOH activation.Then,the influence of phosphorus-containing monomer on the morphology,structure and capacitance of the carbon materials was studied.The results showed that the size of polymer spheres increased with the increase of the phosphorus-containing monomer,while homogeneity and smoothness decreased.After carbonizated at 800 ?,carbon materials could still maintain spherical shape,and the disorder degree and specific capacitance increased with the increase of HEDP.When the amount of HEDP reached 60%of the total monomer mass,the phosphorus content of the carbon material was 2.4 at.%,the specific surface area was 398.6 m2 g-1,and the specific capacitance was 98 F g-1 at the current density of 1 A g-1.Furthermore,the effects of KOH activation on the specific surface area,phosphorous content,and capacitance of the carbons were investgated.The results showed that,the specific surface area was widen and surface phosphorus contents was decreased after KOH activation.Besides,the phosphorus element played a more important role in improving the capacitance performance of carbon materials than the surface area in this system.Hollow polymer spheres(HPS)were firstly prepared by hydrothermal method using phenolic precursor and styrene as starting materials.And HPS was treated by phosphorous trichloride as cross-linking agent and phosphorous dopant to obtain phosphorus-containing cross-linked polymer spheres.After carbonization and KOH activation,P-doped hollow porous carbon spheres P-HCS800 and AP-HCS were prepared.Then the effects of KOH activation and activation temperature on the morphology,structure and electrochemical performance of carbon materials were also studied.The results showed that after activated by KOH at 800 ?,the shell thickness and disorder degree of carbons decreased,while the specific surface area increased.And the phosphorus atom content decreased with the increase of the activation temperature.AP-HCS800 exhibited the best capacitance performance of 288 F g-1 at the current density of 1 A g-1,with the specific surface area of 2177 m2 g-1 and the phosphorus content of 0.6 at.%.The capacity retention of AP-HCS800 was as high as 88.9%after charging and discharging for 5000 times at the current density of 5 A g-1 in 1 M H2SO4 electrolyte.