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Monday, January 18, 2010

Polyaniline Nanoporous Carbon Electrode Materials Yield Most Powerful Supercapacitors to Date Say Max Planck Researchers


 FIG. 3B SEM micrograph of hierarchically porous carbon monolith (HPCM) as used for an electrode developed by Max Planck Society researchers



Researchers at the Max-Planck Society have manufactured an extremely high-performance polyaniline electrode prepared by potentiostatic deposition of aniline on hierarchically porous carbon monolith (HPCM), which is carbonized from mesophase pitch.

According to U.S. Patent Application 20100008021, a capacitance value of 2200 F g-1 of polyaniline was obtained at a power density of 0.47 kW kg.sup.-1 and an energy density of 300 Wh kg-1. This active material deposited on HPCM also has an advantageous high stability.

Up to now the highest specific capacitance reported for a polymer material-application (PANI--polyaniline in a PANI/carbon composite) is a capacitance per mass of PANI of 1221 F g-1. There whisker-like PANI was grown on mesoporous carbon by a chemical polymerization method as described by Y.-G. Wang, H.-Q. Li, Y.-Y. Xia, in Adv. Mater. 2006, 18, 2619.

These superior advantages can be attributed to the backbone role of HPCM. This method also has the advantages of not introducing any binder, thus contributing to the increase of ionic conductivity and power density. High specific capacitance, high power and energy density, high stability, and low cost of active material make it very promising for supercapacitors according to Max-Planck Society researchers Yong-Sheng Hu, Yu-Guo Guo, Lizhen Fan, Joachim Maier, Philipp Adelhelm, Bernd Smarsly and Markus Antonietti

Nanometer-sized electroactive materials with high porosities in contact with liquid electrolytes can exhibit enhanced electrode/electrolyte interface areas, providing highly electroactive regions and decreased diffusion lengths within active materials.

 The use of carbon nanotubes with exceptional conducting and mechanical properties as a support for active materials can not only increase the specific capacitance of active materials, but also relieve the cycle degradation problems caused by mechanical problems.

In such an electrode, a majority of the second pores in the porous carbon material have sizes before coating with the electrically conductive polymer in the range from 50 nm to 3 nm, and particularly from 3 nm to 8 nm. The discovery enhances the capacitive performance of active materials and  provides an improved electrode utilizing such materials.

FIGS. 1A and 1Bshow diagrams illustrating the concept of non-graphitic carbon and the non-graphitic carbon structures used for electrodes.



FIG. 4d SEM of PANI+HPCM-1 at high magnification


The researchers have demonstrated that hierarchically porous carbon monolith is an effective support for the electrodeposition of supercapacitive materials leading to high pseudo-capacitance values. The advantages of this material are: (i) Easy handling compared with powdered carbon; (ii) Binder-free and conductive-agent-free electrode preparation; (iii) Facile and fast synthesis; (iv) Controlled growth of active materials by limited pore spaces; (v) Excellent performance (specific capacitance, power and energy densities, excellent cycling stability).

All these characteristics demonstrate that HPCM can be used as a versatile support for electroactive materials. There is still much room to further improve the electrode performances by tuning porosity and composition of porous carbon monoliths.

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