Charge Storage in Organic Electrodes for Energy & Electrochemical Applications

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2014-10-15

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Energy storage has been emerging as an important research topic because of the lack of fossil fuels and growing energy consumption. This thesis focuses on synthesis and characterization of electrode materials such as polyaniline, graphene, and nitrogen-doped porous carbon for use in energy storage applications.

Polyaniline (PANI), a conjugated polymer, has been widely investigated as an electrode material for energy storage. In order to enhance its oxidative stability, polyaniline:poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PANI:PAAMPSA) complex was synthesized using template polymerization. PANI:PAAMPSA possessed significantly increased oxidative stability up to 4.5 V (vs. Li/Li+) due to electrostatic and hydrogen bonding interactions between PANI and PAAMPSA. This polyacid-doped PANI showed a reversible capacity of 230 mAh/gPANI for over 800 cycles.

Three different polyaniline-based layer-by-layer (LbL) electrodes, PANI/PAAMPSA, PANI/PANI:PAAMPSA, and linear poly(ethylenimine)/PANI:PAAMPSA were fabricated and their charge storage natures were assessed in non-aqueous energy storage systems. PANI:PAAMPSA retained its oxidative stability within LbL electrodes. The PANI/PAAMPSA LbL electrode did not show enhanced oxidative stability as compared to PANI:PAAMPSA complexes, which indicates that the interactions between PANI and PAAMPSA are not as strong as in PANI:PAAMPSA complexes.

Porous PANI nanofiber/graphene hybrid electrodes were prepared by electrochemical reduction of PANI nanofiber/graphene oxide (PANI NF/GO) LbL assemblies at 1.5 V (vs. Li/Li+). The limited processibility of reduced graphene oxide was circumvented by using GO to build up PANI NF/GO LbL films followed by electrochemical reduction. PANI NF/electrochemically reduced graphene oxide (ERGO) LbL electrodes show high capacity and enhanced cycling stability. Its performance is strongly dependent on electrode thickness.

Nitrogen-doped porous carbon was synthesized by one-step carbonization of isorecticular metal-organic frameworks (IRMOF-3). Porous IRMOF-3 itself acts as a self-sacrificial template to provide porous structure. Furthermore, additional carbon and nitrogen sources were not required. The nitrogen content can be easily controlled by varying carbonization temperature. Nitrogen-doped porous carbon possessed significantly higher capacitance due to additional pseudocapacitance originating from nitrogen as compared to analogous nitrogen-free porous carbons.

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