Experimental investigation of cold atmospheric plasma jet for thin film deposition and supercapacitor electrodes

Abstract

Non-equilibrium cold atmospheric plasmas have attracted increasing attention in surface engineering due to the relatively low cost, atmospheric pressure operation, and availability of radical and reactive plasma species. Cold atmosphere plasma technology is a promising alternative to replace some of low-pressure plasma processes in thin film deposition. In this thesis, the major content of investigation is focused on the applications of cold atmospheric plasma jet in thin film deposition and storage energy materials. The research objectives are summarized in the following: (1) to design atmospheric cold plasma jet device and attempt to understand the physics of plasma jet, (2) to deposit macroporous carbon film by cold atmospheric plasma jet and try to investigate the cell compatibility, (3) to synthesize TiO2 coated on carbon fiber paper by cold atmospheric plasma jet and hydrothermal methods for supercapacitor electrodes, and to construct a hierarchical-structure supercapacitor electrode with high electrochemical performance. The atmospheric plasma torch was applied to treat the surface of carbon-fiber-aluminum composite. The plasma produced by atmospheric plasma torch is dusty plasma, which can be attributed to the participation of copper particles in the ejection process of plasma torch. Thus, the dusty plasma copper with copper particles induces the deposition of copper oxide on the surface of substrate. Since the surface treatment of cathode is a major approach to enhance the property of electron beam sources, the surface deposition by plasma torch is a simple method to introduce the heavier particle on the cathode surface. Further, the fluid dynamics of plasma torch is analyzed, and the distributions of velocity, plasma density, and pressure difference are calculated. Microporous nitrogen-doped carbon layers are deposited using an atmospheric-pressure plasma jet at room temperature. The cytocompatibility of the microporous nitrogen-doped carbon layer is investigated by monitoring the proliferation and adhesion of MC3T3-E1 preosteoblasts. The composition and chemical states of the polymer coatings are characterized by Fourier transform infrared spectroscopy (FTIR), Raman scattering, and X-ray photoelectron spectroscopy (XPS). Improved cell proliferation and adhesion are observed from the microporous N-doped carbon layers. The in vitro enhancement can be attributed to the altered surface morphology and new functional groups. The results suggest that the cold atmospheric plasma jet is a simple and practical means to produce good cytocompatibility suitable for biomedical applications. Metal nitride nanoarrays are attractive to electrochemical energy storage and in this work, hierarchical mesoporous manganese oxide (MnOx) nanoflakes and nitrided TiO2 nanorod arrays (NTNA) are prepared on carbon fiber paper (CFP) by hydrothermal synthesis and electro-deposition. The MnOx/NTNA/CFP electrode delivers outstanding electrochemical performance such as high areal capacitance of 327 mF/cm2 at a current density of 0.25 mA/cm2 and good cycling stability with 96% retention after 5000 cycles. Compared to the MnOx/TiO2/CFP and MnOx/CFP electrodes, the MnOx/NTNA/CFP electrode possesses better electrochemical properties such as higher areal capacitance, better electrochemical activity, and cycling life. The enhanced performance can be attributed to the nitrided TiO2 nanorod arrays with higher conductivity offering low electrochemical impedance and fast ion/electron transfer. The MnOx/NTNA/CFP electrode is a promising candidate in high-performance supercapacitor applications.

Date of Award	2 Oct 2015
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Paul Kim Ho CHU (Supervisor)