Template Synthesis Of Polypyrrole Nano-materials And Devices And Their Electrochemical Properties

The fabrication of ordered array nano structures are particularly important for obtaining scaled-up functional devices such as probes, sensors and micromechanical devices. One of strategies is to use Nanoporous alumina membranes with highly ordered nanochannel as template to prepare such structures on a large scale.Conducting polymers could be extensively used in the field of energy (photoelectrochemical cells, battery), photoelectronic device, electromagnetism materials, shield technique, sensors, corrosion-resistance of metal, molecular devices and biology science for their excellent physical properties. As one of the most important conducting polymers, PPy is reversible in electrochemical behavior and stable to environment and it can be used in many fields.Preparation of uniform and ordered nano-sized material make the use of the new material possible, which attracts the attention of the chemical, physical and material science. In the paper, anodic aluminum oxide (AAO) films were used as the templates. The PPy nano-sized materials were prepared in the pores of the template through ac and dc electrochemical methods. Nano devices such as diode, supercapacitor, biosensor based on PPy nanofibers were fabricated and their electronic and electrochemical properties were studied via electrochemical methods. The main results and conclusion can be summarized as following:1. The anodic aluminum oxide (AAO) template with the ordered straight nano-channel has been prepared by two-step anodizing process. The length and the pore diameter ranging from 60 to 80 nm of the AAO membrane can be adjusted in oxalic acid solutions by controlling the anodizing time and dipping time in acid solution.2. This work demonstrates the preparation of polypyrrole nano-tubules using AAO membranes as the template by electrochemical ac method which is an easy route to proceed. The presence of hollow tubules suggests that PPy initially deposits on the surface of the inner pore walls. The relative surface coverage of the filled pores is not uniform. The diameters of some nano-pores reduced to 10nm. Some nano-poreswere not filled completely and PPy did not stick out of membrane even by increasing the synthesis time and voltage.3. Polypyrrole nanofibers have been prepared by electrochemical dc method in AAO templates. The cyclic voltammgrams of a PPy nano-fiber arrays electrode at different scan rate were tested. The linear relationship between cathodic current peak and the potential sweeping rate reflects the electrochemical characteristic of thin film electrode. In the potential region higher than 0.2V the anodic current curves are paralleled with the cathodic current curves with relative high margins between. The behavior indicates that the charge and discharge of double layer capacity are the main processes in this region. The AC impedance spectrums of PPy nanofibers at different potential were also tested. The AC impedance spectrum at more positive potential accorded with the Ho model. The diffusion coefficient D of PPy nanofiber was calculated to be 2.38 × 10^-9cm²s^-1 much higher than 1.13 × 10^-11cm²s^-1 of PPy film.4. PPy nanofiber devices have been fabricated within two-step oxidized AAO membrane. Their electrical properties were measured using a simple way, in which an external power source and a very sharp Pt tip was used for measuring the I—V curves. The ITO/PPy nanofiber device presents a common resistance behavior. But after an alkaline treatment the ITO/ inactive PPy nanofiber device shows unusual behavior, at high voltage its conductivity becomes high. It might be used for nano-fiber switching diode. The Au/PPy or Au/ inactive PPy nanofiber devices demonstrate a rectifying behavior and might be used as nano-fiber rectifiers.5. The nano-supercapacitor consisted of electropolymerized PPy electrode / porous TiO₂ separator / chemical polymerized PPy electrode was fabricated in the array pores of two-step anodizing aluminum oxide (AAO) membrane, based upon layer-by-layer synthetic strategy. It performs typical electrochemical supercapacitor behavior with good charge-discharge ability, and presents the smallest capacity of 3.5nF right now. The nano devices could be useful for the development of nano electronic devices and microelectromechanical systems (MEMS).6. Photoelectrochemical behavior of PPy nanofiber array electrode has been studied. The cathodic photocurrent response of PPy nanofiber array electrode hasbeen observed due to the semiconductor properties of PPy nanofiber. It was found that the thickness of PPy nanofiber array electrode was very important factor. There was an optimism thickness for photocurrent response. When the length of PPy fibers was more than 1.4 μ m, no photocurrent appeared. It could be explained that for thick PPy film the photoinduced electrons and holes were easy to recombine. No anodic photocurrent was observed.7. Novel glucose oxidase (GOx) sensor arrays with nanoelectrode population densities of up to 1×10¹⁰ / cm² nanoelectrodes was reported. The nanoelectrode sensors, were fabricated by first electroadsorping GOD followed by electrochemical codepositing PPy and GOx within the nanopores of anodic aluminum oxide (AAO) membrane electrodes. FTIR spectrum and TEM images show that GOx enzyme clusters were intercalated in PPy nanofiber, mainly in the region close to nanofiber surface. Due to the small size of the nanofiber sensor, the sensor gave very fast response (<15 s). With the increase in glucose concentration, the response curve tends to be level off, featuring Michaelis-Menten characteristics. These features make the nanofiber sensor potentially useful for in vivo detection of glucose. The biosensor arrays also showed good stability. Amperometric measurements of lmM glucose were conducted over two monthes still with 80% of original sensitivity.