Chee O. Too

Buckled, stretchable polypyrrole electrodes for battery applications

Research on stretchable electronics is motivated by the need for electronic systems that can sustain large mechanical strain and still maintain their function. They can be wrapped conformally around complex and unconventional shapes, and have found applications in the biomedical fi elds, electronic paper display devices, sensor skins and photovoltaics. [ 1 ] Within the biomedical fi elds, these electronics need to conform to body shape for use as wearables with a match in mechanical properties to minimise discomfort. [ 2–5 ] As an indispensable component of stretchable electronics, a stretchable power-source device should also be able to accommodate large strain while retaining its function. Recently, there has been an emerging interest in stretchable power sources including energy storage [ 6–8 ] and energy harvesting. [ 9 , 10 ] Energy storage devices, including batteries and supercapacitors, play an important role in powering systems of portable electronic devices or implantable medical devices. Stretchable supercapacitor electrodes using single-walled carbon nanotubes (SWNT) integrated into poly(dimethylsiloxane) (PDMS) or textile substrates have been developed. [ 6 , 7 ] Ultracompliant electrochemical dry gel cells have been reported, comprising a cathode (MnO 2 ) and anode (Zn) paste plotted on a carbon black with structured elastomer as substrate. [ 8 ] To date, however, the application of inherently conducting polymers (ICPs) as stretchable supercapacitor or battery electrodes has not been reported. In particular, ICPs have been shown to be biocompatible with potential applications in biomedical implants, devices and tissue engineering. [ 11 , 12 ] This class of materials has attracted widespread attention in the applications in energy storage devices such as batteries or supercapacitors. [ 13 , 14 ] Here we report a stretchable battery electrode material based on buckled polypyrrole (PPy) and its application in a biocompatible battery system with a bioadsorbable Mg alloy (AZ61) in phosphate buffered saline (PBS). Remarkably, this PPy electrode demonstrates excellent stretchability. It can endure 2000 stretching cycles with 30% tensile strain applied at a 5% s − 1

Parameters influencing transport across conducting electroactive polymer-membranes

Abstract The parameters which influence electrochemically facilitated transport of electroinactive ions across conducting electroactive polymer membranes have been investigated. The design of membranes and the materials used as well as transport cells and systems have been addressed to improve selectivity and flux. Polypyrrole- para -toluenesulfonate (PPy-pTS) was compared with the copolymer of pyrrole with 3-carboxy-4-methylpyrrole (PPy/PCMP-pTS) and their different chemistries resulted in different membrane selectivities for ions. Platinum mesh was found to be the most suitable auxiliary electrode material and its placement in the cell chamber(s) facilitated ion incorporation/expulsion at the membrane working electrode. This enhanced the flux of ion transport. The flux can also further enhanced by narrowing the distance between the membrane working electrode and the platinum mesh auxiliary electrode(s), and/or by stirring to improve the hydrodynamics. An alternative cell design, namely a dual membrane flow through cell, also proved to be more efficient for ion transport. Good connection geometry to the membrane as well as the application of a square wave pulsed potential waveform to the membrane was found to be essential for achieving high and sustainable flux in ion transport.

Conducting Polmers as a Basis for Responsive Materials Systems

Conducting polymers such as polypyrrole and polyaniline are being extensively studied for their use in a wide range of new products. These materials are unique in that they have switchable properties due to their 2 or more mechanically stable oxidation states. Thus, films or coatings can be easily switched by the application of small voltages and currents to change the mechanical and electrical properties, the density, light absorbance and even to emit light in a diode arrangement. This paper reviews the factors that influence the performance of conducting polymers in four applications being developed at the Intelligent Polymer Research Institute: actuators, membranes, sensors and corrosion resistant coatings.

Redox-active conducting polymers incorporating ferrocenes. Preparation, characterization and bio-sensing properties of ferrocenylpropyl and -butyl polypyrroles

The multi-step synthesis of the novel ferrocene-substituted pyrrole monomers, N-(3-ferrocenylpropyl)pyrrole (1), and 3-(4-ferrocenylbutyl)pyrrole (2), have been studied and optimized. A single crystal X-ray structure analysis has been performed on the synthetic intermediate 3-(4-ferrocenylbutyl)-N-(triisopropylsilyl)pyrrole. Monomers 1 and 2 can be electropolymerized to form the homopolymer, poly-2, and the copolymers, pyrrole-co-1 and pyrrole-co-2. The polymers have been characterized using cyclic voltammetry, UV–visible spectroscopy, scanning electron microscopy (SEM) and four-point probe conductivity measurements. The use of pyrrole-co-1 coatings for quantitative sensing and determination of the redox-active enzyme cytochrome C in solution has been demonstrated.

Electrochemically controlled transport of metal ions across polypyrrole membranes using a flow-through cell

Electrochemically facilitated transport of an aqueous mixture containing Na+, K+, Ca2+ and Mg2+ across two different conducting polymer composite membranes has been examined. The two membranes consisted of polypyrrole (PPy) doped with either polystyrenesulfonate/dodecylbenzenesulfonate (1%) (PPy/PSS/DBS) or polyvinylphosphate/dodecylbenzenesulfonate (1%) (PPy/PVP/DBS). In both cases the conducting polymer was deposited onto a platinum sputter-coated polyvinylidene fluoride filter. For both membranes, transport experiments were conducted using a flow-through cell with both pulsed potential and constant potential techniques. In addition, facilitated transport in a stirred solution cell with pulsed potential method was also investigated. The flux of Na+, K+ and Ca2+ ions was significantly higher when transport was examined using the flow-through cell and driven by application of a constant potential. In all the systems examined, the flux of metal ions followed the sequence Na+>K+>Ca2+>Mg2+. Transport of each metal ion was more facile under all conditions examined across composite membranes containing PPy/PSS/DBS. Atomic force microscopic examination of the surface of this membrane showed it to have a significantly smoother surface morphology compared to PPy/PVP/DBS.

Novel ACNT arrays based MEA structure-nano-Pt loaded ACNT/Nafion/ACNT for fuel cell applications.

A novel designed free-standing, sandwich-structured membrane electrode assembly (MEA), nano-Pt loaded (0.142 mg cm(-2)) ACNT/Nafion/ACNT via the attachment of two sets of aligned CNT array electrode structures to opposite sides of a Nafion PEM membrane exhibits significantly improved performance compared to commercially available Pt/CB catalysts used in PEM fuel cell applications.

A readily-prepared electrocatalytic coating that is more active than platinum for hydrogen generation in 1 M strong acid

Coating of a platinum electrode with conducting polypyrrole containing ferrocene sulfonate as counter-ion induces a 0.27 V anodic shift for hydrogen gas evolution in 1 M strong acids and a 7-fold amplification in hydrogen production when poised at −0.44 V.

Nanofiber mats from DNA, SWNTs, and poly(ethylene oxide) and their application in glucose biosensors

Ultrafine fibers with diameters ranging from 50 to 300 nm were prepared from DNA/single-walled carbon nanotubes (SWNTs)/ poly(ethylene oxide) blended dispersion. Well-defined electrospun fibers were obtained by good control of key dispersion properties related to electrospinning, such as ionic conductivity, surface tension, and viscosity. Raman spectroscopy confirmed the presence of SWNT in the resulting fibers, indicating good interaction between DNA and SWNT. The resulting fibers also exhibited electroactive behavior and could be used as an immobilization matrix for a glucose oxidase enzyme biosensor. The sensor response was linear up to 20 mM glucose with a sensitivity of 2.4 mA cm -2 M -1 .

Dynamic Polymeric Membrane Structures for Separation of Proteins

Novel dynamic polymeric membrane structures have been successfully prepared. These membranes have the necessary strength and pore size for use in electrochemically facilitated transport and separation of proteins. The transport of proteins can be electrochemically initiated and sustained or hindered when required. A high purity of human serum albumin (HSA) can be separated from a mixture containing equimolar concentrations of HSA and Myoglobin. Quartz crystal microbalance studies show that, in these cases of transport and separation, the overriding controlling factor was electrochemical control, although polymer/protein interactions do affect the transport fluxes.

Electropolymerization of 4-(3-pyrrolyl)-4-oxobutyric acid by in situ potentiodynamic pre-reduction/oxidation

Abstract Electrochemical polymerization of 4-(3-pyrrolyl)-4-oxobutyric acid and its copolymerization with pyrrole produces electroactive polymers and copolymers, respectively. This study highlights the advantages to be gained by using transient potential waveforms for production of polymer materials.