Supercapacitor is a high-capacity electrochemical capacitor with capacitance values much higher than other capacitors that bridge the gap between electrolytic capacitors and rechargeable batteries.
Professor Chuh-Yung Chen and his student Wei-Min Chang from National Cheng Kung University, Taiwan with Professor Cheng-Chien Wang from Southern Taiwan University of Science and Technology proposed a method for grafting polyaniline PANi onto carbon nanofiber (CNF) which contented carbon nanotube grafted maleic acid (CNT-MA) by plasma to generate a high-performance supercapacitor. The work appeared in the peer-reviewed Journal, Electrochimica Acta.
Conducting polymers are commonly used materials for supercapacitor applications due to it good intrinsic conductivity, light weight and low cost compared to transition metal oxides, explained the primary author, Wei-Min Chang. Conducting polymers can be classified as pseudocapacitors, which store energy by reversible faradic reaction, the pseudocapacitor has higher capacitance than an electric double layer capacitor with the same electrode surface. According to the authors, pseudocapacitor make use of the whole electrode on the molecular level to absorbed and desorbed ions during oxidation and reduction process. The pseudocapacitor has been developed through extensive and intensive research, and conducting polymers have been used as active materials for high energy density applications.
Polyaniline is a representative conducting polymer for supercapacitance research because the entire volume of PANi can conduct the redox reaction and energy storage to obtain high capacitance. The capacitance performance of PANi/carbon materials depends on the interfacial interaction between PANi and the carbon material. Literature shows that, fabricated PANi-grafted CNF by three-step chemical modification of the CNF produces a strong interfacial forces, make charge transfer faster and successfully reduced the interfacial resistance, thereby enhancing the capacitance and improved cyclability. This method was found to be too complex to commercialize. The researchers came up with a one-step, modified plasma technique to graft PANi onto the surface of the CNT-MA/CNF with chemical bonding.
The fabrication of CNF from electrospun polyacrylonitrile nanofiber at low carbonization temperature is suspected to increase the capacitance because more nitrogen groups are retained on the large surface area, explained the research team. The high retain nitrogen groups also can increase the wettability and electrochemical properties in aqueous solution. At this study, the contact angle of the CNF was 33.20 and PANi-P-1.0 was increasing to 62.50 due to the surface of CNT-MA/CNF grafted by PANi which was investigated by the Wilhelmy plate method. Both electrodes are suitable for supercapacitor with aqueous electrolyte.
At low carbonization, the low conductivity limited the performance of CNF as the electrode of the supercapacitor at low carbonization temperature. Therefore, the CNT-MA was added into CNF to improve the conductivity. This high conductivity CNT-MA/CNF was used to graft PANi by plasma modification to fabricate high-performance electrodes.
A one-step method for grafting PANi onto CNT-MA/CNF by plasma was successfully developed and generated a high-performance supercapacitor(606 F/g) with excellent cyclability(100%, 1000 cycles) as proposed by the researchers.
The research team confirmed that the unique structure of the PANiP-1.0 can be employed in equipment with high energy and power applications and that the PANiP-1.0 had good long-term stability.
- Department of Chemical Engineering, National Cheng Kung University, Taiwan.
- Department of Chemical and Materials Engineering, Southern Taiwan University of Science and Technology, Taiwan.
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