Year

2014

Degree Name

Doctor of Philosophy

Department

Institute for Superconducting and Electronic Materials

Abstract

This PhD research project is dedicated in developing high performance, non-toxic electrode materials for energy storage devices that can provide power supply for the bio-medical implantable devices. This research direction is of high novelty and very challenging due to the lack of relative studies in the past. However, it is highly demanded by the rapid development of implantable bio-medical devices (IMDs). In chapter 1, a comprehensive review about the current research progress, trends, and challenges in the relevant fields is given.

The goal for this study is to give a systemic discussion on mechanism, optimizing solutions and propose the prospects of the energy devices for IMDs. This thesis contains four studies about various materials applied for both the bio-galvanic cells and solid state supercapacitors. These two types of energy devices has been prospected by authoritative researchers as promising power sources for IMDs.

Firstly, the electrochemical synthesis method was applied for preparing thin layers of p-toluenesulfonic acid sodium doped polypyrrole on the stainless steel mesh substrates. Three types of non-toxic aqueous electrolytes including 0.1M sodium chloride solution, Phosphate buffered saline (PBS) solution, simulated body fluids were used for constructing the zinc/aqueous electrolyte/polypyrrole batteries. The role of polypyrrole as the cathode material for such battery system is discussed based on the electrochemical studies and chemical characterization of polypyrrole before and after discharge.

To further improve the electrochemical property of the cathode material and therefore achieve better battery performances, in the following work, carbon nano tubes were chosen for incorporating with the polypyrrole. A three dimensional nano structure with polypyrrole coated on the carbon nanotube frameworks were produced with large specific surface area and high electric conductivity. Such composites were used as the cathode material for constructing the zinc battery with simulated body fluid as electrolyte. Detailed discussion about the effects of the coating amount of polypyrrole on the battery discharge performance was given to select the optimized cathode material. The battery testing was carried out in both the simulated body fluid with and without bovine serum albumin to test the feasibility of the battery for dry implantation.

In consideration of further improving the bio-compatibility of the cathode material, in chapter 5, reduced graphene oxide (RGO) was selected as the doping material to incorporate with the polypyrrole nano fibers. In addition, adding RGO nano sheets is also aimed to take full advantages of its various predominant properties including low charge carrier resistance and high specific surface area. The RGO/PPy fiber composite was synthesized via a simple one-step chemical polymerization method from the graphene oxide and pyrrole monomer mixture as precursor. Such composite was also utilized as the cathode material for the zinc/bio-fluids/polymer composite battery. The synergism effect of RGO was discussed based on the electrochemical testing data.

In the final work, we focused on developing the high performance flexible solid supercapacitors, which also has the prospects of powering the implantable bio-medical devices. The free standing RGO/PPy paper was produced by vacuum filtration which is a simple and economy method. Flexible solid state capacitors were fabricated by the RGO/PPy paper electrodes and phosphate acid (H3PO4) infused polyvinyl alcohol (PVA) gel electrolyte. Such supercapacitor possess both good cycling stability and high specific capacitance. Its galvanostatic discharge specific capacitance is up to 345 F g-1.

In the conclusion part, the recommendation about the future research directions and the elucidation of key issues is given which can be helpful for researchers who also have interest in the similar fields.

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