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|Title:||Conducting polymer-based electrodes for electrochemical supercapacitors|
|Department:||Materials Science and Engineering|
|Abstract:||The growing interest in the application of polypyrrole (PPy) for electrodes of electrochemical supercapacitors (ES) is attributed to the relatively high specific capacitance (SC), low cost, high electrical conductivity, advanced chemical and mechanical properties of PPy. However, it is found that swelling and shrinkage occurred during charge-discharge, resulting in higher impedance, gradual adhesion loss and poor cycling behavior of PPy electrode. Moreover, mass normalized capacitance decreased significantly with increasing electrode mass, especially at high charge-discharge rates. Therefore, it is challenging to achieve good electrochemical performance, cyclic stability and good capacitance retention at high charge-discharge rates for electrodes with mass loadings above 20 mg/cm2, which is required for many practical applications.To address this problem, PPy-MWCNT (multiwalled carbon nanotube) composites were prepared using polycharged aromatic anionic redox active molecules as dopants for PPy and dispersants for MWCNT. New dopants offer the advantages of their reduced movement during charge-discharge process and reduced PPy swelling because of large molecular size. In addition, polycharged dopants, containing several charged groups, can be linked to different polymer macromolecules, thus increasing interchain mobility of charge carriers and increasing PPy conductivity. Moreover, new dopants exhibit redox active properties and thus contribute to the total electrode capacitance. The reasons for adding MWCNTs are following: first, they can enhance charge storage properties of PPy by increasing the conductivity of composites, which is more obvious when the scan rate is high. Second, the network formed by MWCNTs can restrict the swelling of PPy and improve the cyclic stability.In this research, new promising PPy-MWCNT electrodes were fabricated. 7 different molecules were used as new dopants for chemical synthesis of PPy. The molecular size and functional groups of the anionic dopants and dispersants have great influence on the morphology and capacitive properties of PPy and PPy/MWCNT composites. Moreover, PPy-MWCNT-FeOOH composite was also prepared in order to shift the working voltage window of PPy/CNT composite to more negative direction, which can facilitate the utilization of PPy as negative electrode. The results showed that dopants with large size, multiple charges and high charge to mass ratio can decrease PPy particle size, reduce agglomeration and thus improve PPy capacitive properties. The highest SC of 118.26 F/g was achieved at 2 mV/s by using PMSS-SR31 doped PPy-MWCNT electrodes. The highest SC of 65.09 F/g at 100 mV/s was achieved by using Potassium Benzene-1,2-disofulnate doped PPy-MWCNT electrodes. Adding FeOOH to PPy-MWCNT composite with mass ration between PPy and FeOOH of 7/2 allowed for enhanced performance in a working voltage window of -0.8 - +0.1 V, which facilitated the utilization of PPy as a negative electrode in asymmetrical device.|
|Appears in Collections:||Open Access Dissertations and Theses|
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