Electrochemical and in-situ surface morphology characteristics of radical polymer brushes for thin-film electrodes

• Main Authors: Chia-wei Hsu, 許家瑋
• Other Authors: Jyh-Tsung Lee
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/22926789529737538490

碩士 === 國立中山大學 === 化學系研究所 === 104 === We report a novel approach to study the electrochemical performance of nitroxide radical polymer brushes for thin-film electrodes, in association with the in-situ surface morphology characteristics. In this thesis, we synthesized non-cross-linked nitroxide radical polymer brushes as the positive electrode material for thin-film electrodes via surface-initiated atom transfer radical polymerization (SI-ATRP), which is an effective method to produce smoothly surfaced organic radical polymer brushes with different grafting densities. After SI-ATRP, the covalent bonds between the nitroxide polymers and the conducting substrate are formed, which not only prevent the organic polymer from dissolving into organic electrolyte solution but also improve the cycle life performance of batteries. To understand the correlation between the density of surface-initiator and the amount of polymer chains via calculations of grafting density, we examined the electrochemical performance and the morphology of nitroxide radical polymers by varying their grafting densities. The polymer brushes with different grafting densities are characterized by water contact angle goniometer, atomic force microscope (AFM) and electron spectroscopy for chemical analysis (ESCA), along with electrochemistry techniques such as cyclic voltammetry (CV) and chronopotentiometry (CP). For further study of the mechanism in the polymer layer during electrochemical reactions within designated voltage ranges, in-situ measurements are performed by combining AFM and chronoamperometry (CA). The experimental results show that at 1% initiator composition polymer brushes exhibit better electrochemical performance, and the swelling effect in this electrolyte is also more obvious, implying an enhanced motion of polymer chains. Moreover, the space between ionic channels is enlarged by lowing the grafting density, which leads to a faster ionic diffusion rate. Through in-situ measurements, we found that polymer brushes at 1% initiator composition possess larger variation in thickness than at 100% initiator composition, and the value of apparent diffusion coefficients of polymer brushes reaches its maximum at 1% initiator composition as well, which are both in agreement with the molecular dynamic stimulation results. This study provides direct evidence showing that polymer brushes at 1% initiator composition have larger ionic-channel space, allowing more rapid passage of the anions.