Conducting Polymer-based Electrodes for Electrochemical Supercapacitors

Abstract

Electrochemical Supercapacitors (ESs) have been under investigation for decades as advanced energy storage devices. Selection and fabrication of electrode materials are of vital importance for ESs in terms of energy density, power density, cycling stability, specific capacitance, impedance and other capacitive properties. Among various kinds of materials that can be used for electrode fabrication for ES, Polypyrrole (PPy) is found to be promising due to high specific capacitance, high electric conductivity and low cost of fabrication of this material. The addition of advanced anionic dopant enables higher electric conductivity and the combination of PPy and multiwalled carbon nanotubes (MWCNT) enhances cycling stability of polymer backbone during testing process, which improves capacitive behavior of PPy and the composite materials. Since MWCNT has a relatively high aspect ratio making it difficult to be well dispersed, the selection of effective dispersing agents and dispersion of MWCNT consist an important part of this research. In this research, PPy and PPy/MWCNT composite materials were synthesized both in chemical and electrochemical ways. The anionic dopants included 4, 5-Dihydroxy-1, 3-benzenedisulfonic acid disodium salt monohydrate (Tiron) and 4-Formylbenzene-1, i M.A.Sc Thesis Jieming Li McMaster University Materials Science and Engineering 3-disulfonic acid disodium salt hydrate (FDS). And also three kinds of multifunctional dopants were used, that can act as dopant for PPy and dispersing agent for MWCNT at the same time, including Eriochrome Cyanine R (ECR), 4-Amino-5-hydroxy-2, 7-naphthalenedisulfonic acid monosodium salt hydrate (AHN) and 3-Hydroxy-4-nitroso-2, 7-naphthalenedisulfonic acid disodium salt (HNN). 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. Higher specific capacitance and excellent capacitance retention were achieved by chemical synthesis, which also offers advantages for large scale production. The results showed that with dopants possessing larger molecular size and multiple charged groups, smaller particle size of PPy and improved capacitive properties could be obtained. The PPy/MWCNT mass ratio of 7 to 3 and Py monomer to dopant molecule molar ratio of 3 to 1 were found to be optimal. The use of Ni foam current collector enabled high mass loading of active materials, which facilitates the fabrication of advanced electrodes for supercapacitors.