One-step synthesis of Graphene/polypyrrole nano fiber composites as cathode material for biocompatible Zinc/polymer battery Sha Li1,2, Kewei Shu2, Chen Zhao2, Caiyun Wang2, Zaiping Guo1, Hua Kun Liu1,2, Gordon.G. Wallace 1, Institute for Superconducting and Electronic Materials, University of Wollongong, 2, ARC Center of Excellence for Electromaterials Science, University of Wollongong, NSW 2522, Australia, Abstract In this work, we choose polypyrrole as the base material in terms of its predominant properties including environmental stability, ease of synthesis and processing. Fibre like polypyrrole is synthesized using micro-micelles templates. The incorporation of graphene nano sheets (GNs) enhances its catalytic activity and thus optimizes its function as the cathode material. The battery is designed for dry implantation and thus simulated body fluid is utilized as electrolyte for battery testing. The discharge performance of such battery suggests its feasibility as a promising power source for micro implantable medical devices (MIMDs).
The discharge curves of batteries composed of pure PPy fiber and PPy/GR electrodes coupled with Zn foil in 0.2M PBS (a) and SBF (b) solution. Batteries with Ppy/GR cathode generally display higher and more stable discharge plateaus. The batteries composed of pure PPy fiber cathodes suffer from almost linearly potential drops. The embedded curves showing the dependence of energy density upon discharge current rates demonstrate that higher energy densities can be driven from the PPy/GR cathode. The batteries with PPy/GR cathode display the highest energy density of up to 264 mWh g-1 in PBS buffer solution and 210 mWh g-1 in SBF, while it is only 139 mWh g-1 and 129 mWh g-1 ,respectively, for the batteries with pure PPy fiber cathodes .
(PPy)n0 AL- Cs+ - e →(PPy)n+ AL- +Cs+ (1) (PPy)n+ AL- Cs+ + e → (PPy)n0 AL- + Cs+ (2)  AL- represents large sized anions (H3PO4- , HPO42-et al) and Cs- means small sized cations (Na+ ,Ket al). in both of the CV curves in PBS and SBF that the redox capacitance of PPy/GR composite is significantly higher than pure PPy fiber as evidenced from their larger current response. This phenomenon can be ascribed to the enhanced electric conductivity of PPy/GR composite. It is notable that the voltage difference between the second reduction/oxidation peak pair is narrower for PPy/GR composite, suggesting better redox reversibility of the material. Therefore, the batteries with PPy/GR cathodes displayed higher and more stable discharge plateaus mainly attributed by its better redox reversibility and higher redox capacitance. It can be concluded that the catalytic efficiency of PPy/GR composite is superior to that of the pure PPy fibers.
Field emission electron scanning microscope (FESEM) image of (a) pure polypyrrole fiber and (b) polypyrrole fiber/ GNs composite; Transmission electron microscope (TEM) images of (c) pure GNs and (d) polypyrrole fiber/ GNs composite
References: 1. Jin, C., F. Yang, et al. (2006). "Electropolymerization and ion exchange properties of a polypyrrole film doped by para‐toluene sulfonate." Journal of applied polymer science 101(4): 2518-2522.
Porous, highly conductive polypyrrole fibre/graphene (Ppy/GR) composite were successfully synthesised using a one step chemical polymerization method. The Ppy/GR composite possess larger redox capacitance and better reversibility , and therefore displayed improved electro-catalytic efficiency than pure Ppy fibre. Batteries with Ppy/GR cathode s have stable discharge performances in both the SBF and PBS electrolyte. The energy density of batteries with Ppy/GR cathode in SBF electrolyte is up to 210mWh g-1, indicating the battery is a promising power scour e for MIMDS.
ACKNOWLEDGEMENTS Financial support provided by the ARC excellent centre for electromaterials are gratefully acknowledged.
Presented by: Sha Li PhD Candidate, ISEM/ACES