Study On The Electrochemical Performance Of Porous Carbon Prepared From Polymer Materials

Supercapacitors as a kind of green energy storage device, is a new type power energy storage equipment between rechargeable batteries and traditional capacitors that can quickly charge and discharge. In various kinds of components of supercapacitors, electrode material is believed to play a crucial inpact on its electrochemical performance. Herein, porous carbon materials, because of its controable porous structure, high specific surface area, low density, mechanical stability and high thermal conductivity, has attracted great attention. In our work, we first prepared nanoporous carbon materials that own high BET suface area and rational pore distribution. And then, the as prepared nanoporous carbon materials was further processed to enhance its electrochemical behavior. Every parts of our dissertation are summarized as follows:1. Halogen-containing plastic materials in a general manner have been converted into nanoporous carbon by a template carbonization method, using zinc powder as an efficient hard template. The mass ratio between plastics and zinc powder as well as carbonization temperature plays crucial role in determining the carbon structures and resultant electrochemical performances. The PTFE-1:3-700 sample that is obtained by carbonizing polytetrafluoroethene and zinc powder (the mass ratio of 1:3) at 700℃ has a large BET surface area of 800.5 m2 g-1 and a high total pore volume of 1.59 cm3 g-1, also delivering excellent specific capacitance of 313.7 F g-1 at a current density of 0.5 A g-1. Moreover, it exhibits a superior cycling stability with high capacitance retention of 93.10% after cycling for 5000 times. More importantly, it can be readily extended to produce nanoporous carbon derived from other halogen-containing plastic materials such as poly(vinylidene fluoride) and poly(vinyl chloride), revealing the generality of the synthesis method. It is believed that the template carbonization method used can open the door to converting the halogen-containing plastic materials into nanoporous carbon for energy harvesting implementation.2. We herein demonstrate a rational template carbonization approach to convert waste polyvinyl chloride into nanoporous carbon, in which inexpensive Mg(OH)2 serves as hard template. The carbon-blank sample that is obtained by designating the mass ratio of polyvinyl chloride and Mg(OH)2 as 1:2 at the carbonization temperature of 700℃ is amorphous and highly porous in essence. It also exhibits large BET surface area of 958.6 m2g-1, high pore volume of 3.56 cm3 g-1, and hierarchical pore size distribution. To further improve the electrochemical performance, various amounts of MnOx nanoparticles are incorporated into the nanoporous carbon by direct redox reaction between carbon-blank sample and KMnO4 solution at 70℃. Therein, carbon-Mn2 sample (the mass ratio of carbon-blank sample and KMnO4 is 1:1) behaves the optimal electrochemical performance. Though its porosity to some extent decreases, its specific capacitance has greatly elevated up to 751.5F g-1 at 1.0A g-1, compared with that of the carbon-blank sample (-47.8 F g-1). The incremental capacitance of the carbon-Mn2 sample is mostly attributed to the contribution of pseudocapacitance incurred by Faradic reaction of MnOx material. The present synthesis method opens up an avenue to properly dispose waste polyvinyl chloride into nanoporous carbon, especially with the promise in supercapacitor application.3. Nanoporous graphitic carbon materials(NGCM) with hierarchical porosities have been prepared by a synchronous carbonization and graphitization process, using waste polyvinylidene fluoride(PVDF) as carbon precursor and Ni(NO3)2·6H2O as graphitic catalyst. It reveals that the carbonization temperature plays a crucial role in determining the pore structures as well as their electrochemical performances. Increasing the reacting temperature from 800℃ to 1200℃, the corresponding porosity has slightly decreased, accompany with the increase of graphitization degree. Furthermore, the specific capacitances of the samples have decreased to some extent, but the rate capability and long term cycling durability elevated distinctly. Next, to further improve the electrochemical performance of the sample prepared at 800℃, for the first time, a novel redox additive of 4-(4-Nitrophenylazo)-1-naphthol(NPN) with different amounts has been introduced in 2 mol L-1 KOH electrolyte. Therein, the specific capacitance by adding 4 mmol L-1 of NPN can reach up to 430.1 F g-1 at 5.0 A g-1, which is greatly higher than that of 144.5 F g-1 for the case of pristine sample. Apparently, the mixed electrolytes of NPN and KOH have largely enhanced the electrochemical performance by redox reaction, which is expected to be applied in field of high performance supercapacitors.