Yu-Chen Tsai

Dye-sensitized solar cells based on multiwalled carbon nanotube-titania/titania bilayer structure photoelectrode.

Dye-sensitized solar cells (DSSCs) were fabricated using multiwalled carbon nanotube (MWCNT)-TiO(2) nanocomposite as a light scattering layer. Morphology of the MWCNT-TiO(2) film was investigated by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). FESEM and TEM images demonstrate that MWCNTs and TiO(2) nanoparticles can be dispersed with chitosan. Internal resistance in the DSSC was characterized by electrochemical impedance spectroscopy (EIS). EIS results reveal a decrease in the charge resistance of electrolyte/dye/MWCNT-TiO(2)/TiO(2) interface with increasing MWCNT content up to 3 wt% which leads to an improvement in the photovoltaic performance. Compare with a nanocrystalline TiO(2) single-layer cell, the DSSC based on the MWCNT (3 wt%)-TiO(2)/TiO(2) bilayer structure photoelectrode shows ~100% increase in solar-to-electric energy conversion efficiency, which is attributed to the inclusion of MWCNTs in TiO(2) matrix.

Sensitive electrochemical thrombin aptasensor based on gold disk microelectrode arrays

The construction of a sensitive electrochemical aptamer sensor (aptasensor) for thrombin detection is described. Among the advantages of using microelectrode-based devices are the possibility to work with small sample volumes and enjoying faster mass transport rates and lower interfacial capacitance than at macroelectrodes. Therefore, gold disk microelectrode arrays are an attractive transducer option for aptasensors. The morphology of the gold disk microelectrode arrays was inspected by scanning electron microscope. The interaction between a thrombin aptamer and thrombin on gold disk microelectrode arrays was demonstrated by differential pulse voltammetry using methylene blue (MB) as an electrochemical indicator. MB adsorbed to aptamers via their guanine base. When thrombin was introduced, it displaced the MB adsorbed to the aptamers and bound to them. This resulted in a decrease of MB peak current which correlated to the concentration of thrombin over a dynamic range spanning from 10⁻⁵ to 10⁻¹² M. This method was able to linearly and selectively detect thrombin with a detection limit of 0.143 pM.

Microwave activation of electrochemical processes: convection, thermal gradients and hot spot formation at the electrode|solution interface

Microwave activation of electrochemical processes is possible by self-focussing of intense microwave radiation at the electrode|solution (electrolyte) interface of an electrode immersed in a solution and placed in a microwave cavity. Considerable changes in voltammetric current responses are observed experimentally for the one-electron reduction of Ru(NH3)63+ in aqueous 0.1 M KCl and for the stepwise two-electron reduction of the methylviologen dication (MV2+) in aqueous 0.1 M NaCl. The formation and interconversion of two distinct forms of solid deposits, MVam0 and MVcryst0, on a mercury electrode surface is investigated, both in the presence of microwave activation and with conventional heating. It is shown that microwave activation achieves (i) high temperatures in the vicinity of the electrode, (ii) thermal desorption of deposits from the electrode surface and (iii) limiting currents an order of magnitude higher compared to those induced by conventional isothermal heating to the same electrode temperature.A simple physical model based on Joule heating of the aqueous solution phase is employed in a finite element simulation (FIDAPTM) procedure to explain the differences observed experimentally between conventional heating and microwave activation. Based on the comparison of simulation and experimental data, a considerable thermal gradient and ‘hot spot ’ region in the diffusion layer of the electrode, together with convective mass transport are proposed.

Nanostructured Ag surface fabricated by femtosecond laser for surface-enhanced Raman scattering

Femtosecond laser was employed to fabricate nanostructured Ag surface for surface-enhanced Raman scattering (SERS) application. The prepared nanostructured Ag surface was characterized by field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The FESEM images demonstrate the formation of nanostructure-covered femtosecond laser-induced periodic surface structure, also termed as ripples, on the Ag surface. The AFM images indicate that the surface roughness of the produced nanostructured Ag substrate is larger than the untreated Ag substrate. The XRD and XPS of the nanostructured Ag surface fabricated by femtosecond laser show a face centered cubic phase of metallic Ag and no impurities of Ag oxide species. The application of the produced nanostructured Ag surface in SERS was investigated by using rhodamine 6G (R6G) as a reference chemical. The SERS intensity of R6G in aqueous solution at the prepared nanostructured Ag surface is 15 times greater than that of an untreated Ag substrate. The Raman intensities vary linearly with the concentrations of R6G in the range of 10(-8)-10(-4)M. The present methodology demonstrates that the nanostructured Ag surface fabricated by femtosecond laser is potential for qualification and quantification of low concentration molecules.

Determination of the Critical Temperature for Forming a Chromium‐Rich Oxide on AISI 430 Stainless Steel and Its Corrosion Resistance

The early oxidation (t {le} 120 min) of AISI 430 stainless steel has been investigated by thermal gravimetric analysis and Auger electron spectroscopy. It is found that the oxidation can be divided into two regions: one is a rapid growth rate for t {le} 5 min and the other is a parabolic or slower growth rate for t {ge} 5 min. Through analysis of the components of the oxide film and mathematical modeling, a critical temperature, T{sub c}, above which a chromium-rich oxide film is formed is determined to be 947 K. The corrosion resistance of the oxidized metal is enhanced at T {ge} T{sub c} but is worse at T < T{sub c}. Formation of a protective chromium-rich oxide film on this metal is considered to be a dominant factor in improving corrosion resistance.

Preparation and Electrochemical Performance of Externally Doped Sulfonated Polyaniline/Multiwalled Carbon Nanotube Composites

The externally doped sulfonated polyaniline (ED-SPANI) has emerged as a potential candidate for electrochemical sensors because of its unique electroactive property and water solubility. However, the lower conductivity is the major drawback for the application of ED-SPANI. Thus, this study describes a simple procedure for the fabrication of water-soluble and high conductivity composites containing ED-SPANI and multiwalled carbon nanotubes with attached carboxylic groups (c-MWCNTs) by electrostatic adsorption in aqueous colloids. The results of Fourier transform IR and Raman spectroscopy demonstrate the electrostatic interaction between the C―N + species of the ED-SPANI structures and the COO- species of the c-MWCNTs. The incorporation of the c-MWCNTs into ED-SPANI can significantly enhance the electrical conductivity and electrochemical activity of ED-SPANI/c-MWCNT composites. Furthermore, the morphology of ED-SPANI/c-MWCNT composites measured by scanning electron microscopy and atomic force microscopy indicates the presence of well-distributed tubular structures that are individually coated with ED-SPANI on the surface of the composite, in accordance with the high electrical conductivity and electrochemical properties of the composites.

Improved performance of dye-sensitized solar cells using gallium nitride-titanium dioxide composite photoelectrodes.

Dye-sensitized solar cells (DSSCs) are fabricated with gallium nitride-titanium dioxide (GaN-TiO2) composite photoelectrodes to enhance the power conversion efficiency. The value of power conversion efficiency increases with the incorporation of GaN in TiO2 matrix and reaches a maximum at 0.05 wt% GaN. Internal resistance in the DSSC is characterized by electrochemical impedance spectroscopy (EIS). From the EIS of electrolyte/dye/GaN-TiO2 interface resistances under illumination and in the dark, a decrease in the charge transfer resistance and an increase in the charge recombination resistance of the DSSCs are obtained after the inclusion of GaN (0.01-0.05 wt%) in the TiO2 matrix. The power conversion efficiency of the DSSC based on the GaN (0.05 wt%)-TiO2 composite photoelectrode is enhanced by ∼61% in comparison with a pristine TiO2 photoelectrode.

Ag/Carbon Nanotubes for Surface-Enhanced Raman Scattering

The surface-enhanced Raman scattering (SERS)-active substrates were prepared by electrodeposition of Ag nanoparticles in multiwalled carbon nanotubes (MWCNTs)-based nanocomposites for SERS sensor application.

Scanning electrochemical microscopy for study of aptamer-thrombin interfacial interactions on gold disk microelectrodes.

A feasibility for the determination of thrombin on gold disk microelectrodes (GDMs) using scanning electrochemical microscopy (SECM) is reported. The assembly process step-by-step of thrombin aptasensor on GDMs is monitored by SECM. SECM analysis reveals the immobilization of thrombin aptamers on GDMs. The interaction between thrombin aptamers and thrombin on GDMs is imaged by SECM with feedback mode using ferrocenemethanol as an electrochemical mediator. The formation of thrombin/thrombin aptamer complex on GDMs results in a decrease in the tip peak current on spatial SECM images. This method is able to linearly and selectively detect thrombin over a linear range from 10(-12) to 10(-5)M with a detection limit of 6.07 fM.

Electrochemical sensors based on multi-walled carbon nanotube-Nafion/spl trade/ nanocomposite film for determination of heavy metals and hydrogen peroxide

A nanocomposite film of multi-walled carbon nanotubes (MWNTs) with Nafion/spl trade/ is prepared by cast deposition on glassy carbon electrodes (GCE). The morphologies of the MWNTs and MWNTs/Nafion/spl trade/ modified electrode are characterized by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The MWNTs are cylindrically shaped and uniform with a diameter in the range of 40 - 60 nm. The MWNTs/Nafion/spl trade/ composite film is cast homogeneously onto GCE. Well-defined voltammetric responses are observed for the Fe(CN)/sub 6//sup 4-//Fe(CN)/sub 6//sup 3-/ redox system in aqueous 0.1 M KCl on the MWNTs/Nafion/spl trade/ modified electrode. The anodic stripping response for Cd metal from a solution of 1 to 4 /spl mu/M in aqueous 0.1 M acetate buffer solution is demonstrated. The amounts of hydrogen peroxide and the heights of amperometric response of this sensor vary proportionately. The results indicate that the electroanalytical nanocomposite film composed of MWNTs and Nafion/spl trade/ is highly sensitive and suitable for potential electrochemical sensor applications.