Study On Synthesis And Capacitance Performance Of Polypyrrole And Its Composites

Nowadays, the problem of energy shortage is getting worse. Supercapacitor has attracted wide attentions from persons in different fields as a kind of energy storage device. It is noteworthy that the electrode material is the most important part in a supercapacitor and it has a big influence on the capacitance performance. So it is significant to study on the electrode material for the development of high performance supercapacitor. Conductive polymer is a kind of electrode materials and polypyrrole (PPy) among that plays an important role in the field of supercapacitors due to its easy preparing, good inoxidizability, high conductivity and excellent environmental stability.In the mixed solvent of acetonitrile and water with FeCl3 as oxidant, PPy products which were named Nl, H1 and M1 separately were synthesized by chemical oxidation method while changing the FeCl3 dosage. On the basis of H1, other H series PPy were prepared which were marked by H0, H2, H3, H4, H5 and H6 through changing the volume ratio of acetonitrile and water (abbr. VRAW). The effects of FeCl3 dosage and the VRAW on the morphology, structure and capacitance performance of PPy were deeply studied. Among PPy products synthesized at different oxidant dosage, the particle size of H1 is obviously smaller than N1 and M1. The electrochemical test results show that the specific capacitances of PPy first increase and then decrease with the increasing of oxidant dosage, and H1 product shows the highest specific capacitance of 143.82 F·g-1 and the best cycling stability. When changing the VRAW, the morphologies of PPy show a transition from particle to film: from HO to H3, the particle size turns smaller and H3 has the smallest particle size; from H4 to H6, the morphologies gradually turn to film. The electrochemical test results show H0, H1, H2 and H3 which are in particle morphology have superior capacitance performances than H4, H5 and H6 which have film morphologies, which is because particles have bigger specific surface area than film to have better capacitance performances. H3 presents to be the superior product which has the highest specific capacitance of 154.61 F·g-1 and the coulomb efficiency of 59.94%. At the same time, H3 product has better cycling stability and faster ion exchange behavior.On the basis of the synthesis condition of H3, MO-1, TSA-1 and SA-1 products were prepared separately with MO, TSA and SA as dopant. And on the basis of SA-1, SA-2-SA-6 products were synthesized at different dopant dosage. The influences of dopant species and dosage on capacitance performance were studied. Among the PPy products synthesized with different dopant, MO-1 is with four-prismatic morphology, and TSA-1 and SA-1 are both in particle morphologies. The particle size of SA-1 is smaller than TSA-1 and the particle packing is looser in SA-1. The electrochemical test results show that SA-1 has the highest specific capacitance of 149.33 F·g-1 among three products. At the same time, SA-1 has better cyclic voltammetry characteristics and holds faster ion exchange behavior than others. SA-1～SA-6 products were synthesized at different dopant dosages. These products are all in particle morphologies. From SA-1 to SA-4, the particle packing becomes looser, and SA-4 holds the fluffiest structure; from SA-5 to SA-6, the particle packing turns denser. The yields of doped PPy grow higher with the increase of dopant dosage, but the increase become unobvious after SA-4 which is due to the almost saturated doping level. The electrochemical test results show the specific capacitance of doped PPy first increases and then decreases with the growth of SA dosage. SA-4 holds the highest specific capacitance of 203.32 F·g-1 and coulomb efficiency of 70.67%. At the same time, SA-4 has better cyclic voltammetry characteristics and faster ion exchange behavior than others.Finally, PA1, PA2 and PA3 composites were prepared at different mass ratio of pyrrole (Py) to active carbon (AC) of 0.5:1,1:1 and 5:1. On the basis of PA3, the PPy/AC/GE composite (PAG) was synthesized while adding the graphene (GE) component. The SEM shows pure AC material presents to be granulum, while PPy material is in large granule morphology. Besides, there are mainly AC granulum in PA1 and PA2 and also some large PPy granule stuck on AC gramulum that stacking together. In the SEM of PA3, there are mainly large granules of PPy. As to PAG composites, we can see large amount of laminar GE, with AC granulum dispersed in the laminar structure, and PPy granule which is in-situ growth on the surface of laminar GE. FT-IR results illustrate that the steric hindrance which is due to the addition of AC has influenced the conjugated structure of PPy which lead to the absorption peak movement towards high wavenumber. Besides, PPy’s addition has little improvement for AC’s capacitance performance in PA1 and PA2 which can be judged by the similar CV curve shapes of PA1 and PA2 to AC. The CV curve area of PA3 becomes larger than AC, PA1 and PA2, but it is deviated from the rectangular. PAG composite has larger CV curve area and better cyclic voltammetry characteristics. The specific capacitance of PA1 and PA2 is a little higher than AC, and that of PA3 is much higher than AC material, while PAG composite has the highest specific capacitance of 155.02 F·g-1 . At the current density of 10 mA·cm-2, PPy, PA3 and PAG materials separately have a capacitance retention of 23.40%, 55.31% and 77.79% after 300 charge-discharge cycles which can be inferred that PAG composites not only increase AC material’s specific capacitance, but also improve the cycling stability of PPy materials.