A nonmonotonic dependence of standard rate constant on reorganization energy for heterogeneous electron transfer processes on electrode surface

In the present work a nonmonotonic dependence of standard rate constant (k(0)) on reorganization energy (lambda) was discovered qualitatively from electron transfer (Marcus-Hush-Levich) theory for heterogeneous electron transfer processes on electrode surface. It was found that the nonmonotonic dependence of k(0) on lambda is another result, besides the disappearance of the famous Marcus inverted region, coming from the continuum of electronic states in electrode: with the increase of lambda, the states for both Process I and Process II ET processes all vary from nonadiabatic to adiabatic state continuously, and the lambda dependence of k(0) for Process I is monotonic thoroughly, while for Process II on electrode surface the lambda dependence of k(0) could show a nonmonotonicity.

Analysis of strychnos alkaloids using electrospray ionization Fourier transform ion cyclotron resonance multi-stage tandem mass spectrometry

The fragmentations of four strychnos alkaloids have been investigated by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) in the positive ion mode. Experiments using multi-stage tandem mass spectrometry (ESI-FT-ICR-MSn) allowed us to obtain precise elemental compositions of product ions at high mass resolution. The experimental data demonstrated that the nitrogen bridge and the coordinated oxygen atom on the nitrogen bridge in the alkaloid compounds were the active sites in the MS2 fragmentations. The loss of CH3 or the OCH3 group in those alkaloids, which have an OCH3 substituent, was the dominant fragmentation mode in the MS3 fragmentations. Logical fragmentation schemes for strychnos alkaloids have been proposed and these should be useful for the identification of these compounds.

The preparation of high activity DMFC Pt/C electrocatalysts using a pre-precipitation method

It is suggested that a Pt/C cathodic catalyst for the direct methanol fuel cell (DMFC) can be prepared with a pre-precipitation method, in which, H2PtCl6 is precipitated onto the carbon black as (NH4)(2)PtCl6 before H2PtCl6 is reduced to Pt. The electrocatalytic activity of this Pt/C-A catalyst for oxygen reduction is excellent because the Pt/C catalyst prepared with this pre-precipitation method possesses a small average particle size, low relative crystalinity and a large electrochemically active surface area. In addition, the pre-precipitation method is simple and economical and it can be used to prepare a Pt/C catalyst on a large scale.

A new flow field and its two-dimension model for polymer electrolyte membrane fuel cells (PEMFCs)

A new flow field was designed to search flow fields fitting polymer electrolyte membrane fuel cells (PEMFCs) better due its extensible. There are many independent inlets and outlets in the new flow field. The new flow field we named NINO can extend to be more general when pressures at the inlet and outlet vary and some usual flow fields will be obtained. A new mathematical model whose view angle is obverse is used to describe the flow field.

Room temperature preparation of carbon supported Pt-Ru catalysts

A carbon supported Pt-Ru (Pt-Ru/C-T) catalyst can be prepared by a chemical reduction method in an aqueous solution with tetrahydrofuran (THF) at room temperature. The Pt-Ru particles possess high alloying, small average size and a low relative crystallinity. The electrocatalytic activity of the prepared Pt-Ru/C catalyst for methanol oxidation is much higher than that of commercial Pt-Ru/C (Pt-Ru/C-E) catalysts which have a similar average size and relative crystallinity, but the alloying extent is much lower than that in our Pt-Ru/C-T catalyst. The results illustrate that the alloying extent of Pt and Ru in the Pt-Ru/C catalyst plays an important role in the electrocatalytic activity of the Pt-Ru/C catalyst for methanol oxidation.

Preparation of a carbon supported Pt catalyst using an improved organic sol method and its electrocatalytic activity for methanol oxidation

The organic sol method for preparing ultrafine transition metal colloid particles reported for the first time by Bonnemann et al. [H. Bonnemann, W Brijoux, R. Brinkmann, E. Dinjus, T. Jou beta en, B. Korall, Angew. Chem. Int. Ed. Engl., 30 (1991) 1312] has been improved in this paper. The improved organic sol method uses SnCl2 as the reductant and methanol as the organic solvent. Thus, this method is very simple and inexpensive. It was found that the average size of the Pt particles in the Pt/C catalysts can be controlled by adjusting the evaporating temperature of the solvent. Therefore, the Pt/C catalysts prepared by the same method are suitable for evaluating the size effect of the Pt particles on electrocatalytic performance for methanol oxidation. The results of the X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that when the evaporating temperatures of the solvent are 65, 60, 50, 40, and 30 degrees C, the average sizes of the Pt particles in the Pt/C catalysts prepared are: 2.2, 3.2, 3.8, 4.3, and 4.8 nm, respectively. The X-ray photoelectron spectroscopic (XPS) results demonstrated that the small Pt particles are easily oxidized and the decomposition/adsorption of methanol cannot proceed on the surfaces of Pt oxides.

Preparation and properties of sulfonated poly(ether ether ketone)s (SPEEK)/polypyrrole composite membranes for direct methanol fuel cells

Polypyrrole (Ppy) was successfully introduced into methyl substituted sulfonated poly(ether ether ketone) (SPEEK) membranes by polymerization in SPEEK solutions to improve their methanol resistance. Uniform polypyrrole (Ppy) distributed composite membranes were formed by this method by the interaction between SPEEK and Ppy. The properties of the composite membranes were characterized in detail. The composite membranes show very good proton conductive capability (25 degrees C: 0.05-0.06s cm(-1)) and good methanol resistance (25 degrees C: 5.3 x 10(-7) 1.1 x 10(-6) cm(2) s(-1)). The methanol diffusion coefficients of composite membranes are much lower than that of pure SPEEK membranes (1.5 x 10(-6) cm(2) s(-1)). The composite membranes show very good potential usage in direct methanol fuel cells (DMFCs).

Structure-activity relationship of surfactant for preparing DMFC anodic catalyst

Three kinds of surfactants as stabilizer were applied to the preparation of electrocatalysts for direct methanol fuel cell (DMFC). The catalysts have been characterized by examining their catalytic activities, morphologies and particle sizes by means of cyclic voltammetry, chronoamperometry, X-ray diffraction and transmission electron microscopy (TEM). It is found that the surfactants with different structures have a significantly influence on the catalyst shape and activity. The catalysts prepared with non-ionic surfactants as the stabilizer show higher activity for direct oxidation of methanol. The structure-activity relationship (SAR) analysis has been explored and the effect of hydrophile-lipophile balance (HLB value) has also been discussed.

Effect of cations in solution on the oxidation of methanol on the surface of platinum electrode

The effect of metal cations in solution on the oxidation of methanol on the electrode surface of platinum is a neglected aspect to direct methanol fuel cell (DMFC). In this paper, a smooth platinum electrode absorbing metal cations as the working electrode was applied to investigate the methanol oxidation with the cyclic voltammetry (CV) in 1.0 mol L-1 H2SO4. From the analysis of experiment, it is found that the cations, Li+, Ce4+, Mn2+, Ni2+, Cu2+, have some negative effect on the catalytic oxidation of methanol on the surface of platinum. The degree of the effect from different cations was analyzed.

Study on mechanism of interaction between Eu3+ and microperoxidase-11

The interaction mechanism between Eu3+ and microperoxidase-II (MP-11) in the aqueous solution was investigated using the UV-vis absorption spectroscopy, cyclic voltammetry and electrospray ionization mass spectrometry. It was found that one Eu3+ ion can coordinate with two carboxyl oxygen of two propionic acid groups of the heme group in the MP-11 molecule, leading the increase in the nonplanarity of the porphyrin ring and exposure degree of Fe(III) in the heme group. Therefore, the reversibility of the electrochemical reaction and the electrocatalytic activity of MP-11 for the reduction of oxygen are increased.

Preparation and simulation of an additional catalyst layer for direct methanol fuel cell

An additional anode catalyst layer with PtRu/C was hot pressed between two Nafion (R) 112 membranes and a conventional direct methanol fuel cell (DMFC) cathode/membrane/anode assembly with the above membranes as separator was fabricated. The additional catalyst layer formed an assistant cell with the cathode to prevent methanol crossover. A simple one-dimensional mathematical model was presented to describe the performance of this new type of membrane electrode assembly system. As seen from both experimental result and model analysis, the additional catalyst layer can not only effectively prevent the methanol crossover, but also generate electrical power with the crossover methanol. The percentage of output power of the assistant cell to the total power analyzed by the model is about 40% under usual condition, which is much higher than that from experimental result, indicating the potential of the development in the DMFC designing. It was also discovered that the electrical power generated from the assistant cell with crossover methanol could take higher percentage in total electrical power when the main DMFC current density became lower.

Physical and electrochemical characterizations of PtRu/C catalysts by spray pyrolysis for electrocatalytic oxidation of methanol

In this paper, it was reported that the carbon-supported Pt-Ru(Pt-Ru/C) catalyst used as the anodic catalyst in the direct methanol fuel cell (DMFC) was synthesized with a two-step spray pyrolysis (SP) method using the Pt and Ru metal salt as the precursors and polyethylene glycol (PEG) with the different molecular weights (Mw= 200,600,and 1000 analytical reagent) as cosolvent. PEG as a cosolvent plays a crucial role in producing PtRu/C catalysts. It was found that the Mw of PEG could affect the electrocatalytic activity of Pt-Ru and the morphology of the Pt-Ru particles in the Pt-Ru/C catalysts prepared with this method. When the Mw of PEG is 600, the Pt-Ru particles in the Pt-Ru/C catalyst prepared with this method possess the small average size, narrow size distribution, uniform dispersion, and high electrochemically active specific surface area. The electrocatalytic activity of the Pt-Ru/C catalyst prepared with this method using the cosolvent PEG with Mw = 600 for the methanol oxidation is much higher than that of the commercial E-TEK Pt-Ru/C catalyst. Therefore, the two-step SP method is an excellent method for the preparation of the Pt-Ru/C catalyst used in DMFCs.

Enhanced thermal stability of zinc-based titanate (dielectric) ceramics prepared by the modified sol-gel route

A multi-component substitution of Co and Ni was incorporated into ZnTiO3 to form pure hexagonal Zn1-x(Co1/2Ni1/2)xTiO(3) (x = 0,0.8,0.9,1.0) dielectric ceramic powders by a modified sol-gel route, following heat treatments at 600 degrees C for 3 h and at 800 degrees C for 6 h. Differential scanning calorimetry measurements revealed that the order of increasing thermal stability of solid solution compound Zn1-x(Co1/2Ni1/2)(x)TiO3 was ZnTiO3 (945 degrees C), Zn0.1Ni0.9TiO3 (1346 degrees C), Zn-0.1(Co1/2Ni1/2)(0.9)TiO3 (1390 degrees C), and Zn0.1Co0.9TiO3 (> 1400 degrees C). Both the dielectric constant and loss tangent reached a maximum at x = 0.8 and then decreased with solubility, x, and measurement frequency.

Facile preparation of ZnTiO3 ceramic powders in sodium/potassium chloride melts

A facile molten salt synthesis route was developed to prepare ZnTiO3 ceramic powders with simple oxides ZnO and TiO2 using sodium and potassium chloride eutectic salts as flux. The role of calcination temperature and time and the amount of salt addition to ZnTiO3 formation was investigated by thermogravimetry-differential thermal analysis, X-ray diffraction and Fourier transformation-infrared spectroscopy measurements. Pure hexagonal phase of ZnTiO3 could be obtained from the mixture of the simple oxides and the chlorides (50 mol% KCl, 20 times to oxides in molar ratio) heating at 800 degrees C for 6 h. The scanning electron microscopy images revealed the products were hexagonal sheets of about 1-3 mu m size. Increasing the amount of salt aids in reducing the crystal sizes of final ceramic powders because of diluting the solution.

Complex aggregates of spherical colloids via modified micromolding in capillaries

This paper describes a simple approach to fabricate aggregates composed of monodispersed silica microspheres by modified micromolding in capillaries (MIMIC). Two different kinds of contact modes, namely, conformal contact and non-conformal contact, between the poly(dimethylsiloxane) (PDMS) mold and the underlying prepatterned substrate, can be controlled during the micromolding, which result in the formation of different aggregates under the influence of template confinement and capillary forces. These aggregates, including woodpile structure, discoid, conoid and rectangular clusters, possess well-controlled sizes and orientation. The possible mechanisms for the formation of different aggregates are discussed in detail.