Bing-liang Wu

Electro-oxidation of glucose on platinum in alkaline solution and selective oxidation in the presence of additives

Abstract The electrochemical behavior of glucose at Pt electrodes was investigated in alkaline solutions using cyclic voltammetry and the modulated potential-time waveform (MPTW) technique. It was found that suitable MPTWs can produce reproducible results after the elimination of the absorbed “poison” formed during glucose oxidation, leaving a clean electrode surface. The effects of the experimental conditions on the voltammetric characteristics of glucose oxidation were studied systematically. These results were explained by an oxidation mechanism via the rate-determining decomposition of adsorbed glucose with the release of a hydrogen atom. The applicability of MPTW amperometry and coulometry to the measurement of glucose concentration was demonstrated. Glucose can penetrate the Nafion ® membrane which modifies the Pt electrode surface. By making use of Nafion ® -modified Pt electrodes, it was found that the interference of several biologically active small organic molecules, such as ascorbic acid, cysteine and uric acid, with the oxidation of glucose was suppressed effectively, forming the basis for studies of practical electrochemical sensors.

Study of the powder/membrane interface by using the powder microelectrode technique I. The Pt-black/Nafion® interfaces

The polarization behavior of a Pt microdisk electrode, a platinized Pt microdisk electrode and a Pt-black powder microelectrode immersed in sulfuric acid solution, in contact with a moist Nafion® membrane were studied by cyclic voltammetry. The experimental results reveal that the surface diffusion of the adsorbed species plays an important role in determining the kinetics of interfacial reactions taking place at the powder/Nafion® membrane interface. The weakly adsorbed hydrogen atoms diffuse significantly faster than the strongly adsorbed hydrogen and the oxygen-containing surface species. Surface active sites in the range of tens of microns from the powder/Nafion® interface can be involved in interfacial reactions. The apparent coefficients of diffusion of various surface species were estimated from the variation of peak current with scan rate of potential. The apparently higher irreversibility of electrode reaction observed at the powder/membrane composite electrode is explained by considering mechanism of current generation of this type of electrode.

Application of time-resolved EQCM to the study of the mechanism of silver(I) oxide formation on a polycrystalline silver electrode in alkaline solution

Abstract The time-resolved EQCM was used to investigate the mechanism of the electrochemical formation of silver(I) oxide on a polycrystalline silver electrode in 0.1 M NaOH. The mass change was monitored in a series of potentiodynamic experiments. The first stage of the oxidation can be unambiguously attributed to the formation of a monolayer of Ag 2 O. In the second stage of the oxidation, a very small amount of Ag or its oxide dissolves into the solution and the Ag 2 O layer thickens gradually. No species other than Ag 2 O was detected during the whole oxidation process. The structure of the Ag 2 O layers formed is different at different stages of the oxidation. Compact Ag 2 O layers are formed in the first two stages, while Ag 2 O formed at more positive potentials is porous. The roughening of the electrode during the formation and reduction of the oxide is also discussed on the basis of the mass changes.

Investigation of the mechanism of the electrochemical oxidation of formic acid at a gold electrode in sulfuric acid solution

Abstract The oxidation of formic acid at the Au electrode in sulfuric acid solution was investigated using a programmed potential step procedure. The j – t curve of the direct reactive oxidation of formic acid suggested a two-stage mechanism of the electrode reaction. The oxidation current density peak on the chronoamperometric plot corresponded to the formation of a steady adsorptive layer of COOH ads through adsorption of HCOOH and the first electron transfer, while the steady current density corresponded to the further oxidation of the adsorptive layer of COOH ads formed. A data fitting program was developed for extracting kinetic parameters from the j to t transient experimental data. The adsorption rate constants ( k a ) for formic acid, the reaction rate constants ( k 2 ) and the transfer coefficient ( β ) for the further oxidation of COOH ads were obtained at various potentials. These results confirmed that the further oxidation of COOH ads was the rate-limiting step after the adsorption balance of COOH ads was achieved, and before that, the adsorption of formic acid was the rate-limiting step.

Electrochemical recognition of alkali metal ions at the micro-water 1,2-dichloroethane interface using a calix[4]arene derivative

In this paper, a calix[4]arene derivative, 5,11,17,23-butyl-25,26,27,28-tetra-(ethanoxycarbonyl)-methoxy-calix[4]arene (L), is investigated as a host to recognize alkali metal ions (Li+, Na+, K+, Rb+ and Cs+) at the interface between two immiscible electrolyte solutions (ITIES). Well-defined cyclic voltammograms are obtained at the micro- and nano-water \ 1,2-dichloroethane (W \ DCE) interfaces supported at micro- and nano-pipets.

Alkali metal ions transfer across a water/1,2-dichloroethane interface facilitated by a novel monoaza-B15C5 derivative

In this paper, a novel monoaza-B15C5 derivative, N-(2-tosylamino)-isopentyl-monoaza-15-crown-5 (L), is used as an ionophore to facilitate alkali metal cations transfer across a water/1,2-dichloroethane (W/DCE) interface. Well-defined voltammetric behaviors are observed at the polarized W/DCE interfaces supported at micro- and nano-pipets except Cs+. The diffusion coefficient of this ionophore in the DCE phase is calculated to be equal to (3.3+/-0.2) x 10(-6) cm(2) s(-1). The experimental results indicate that a 1:1 (metal: ionophore) complex is formed at the interface with a TIC/TID mechanism. The selectivity of this ionophore towards alkali ions follows the sequence Na+ > Li+ > K+ > Rb+ > Cs+. The logarithm of the association constants (log beta(1)(0)) of the LiL+, NaL+, KL+ and RbL+ complexes in the DCE phase are calculated to be 10.6, 11.6, 9.0 and 7.1, respectively. The kinetic parameters are determined by steady-state voltammograms using nanopipets. The standard rate constants (k(0)) for Li+, Na+, K+ and Rb+ transfers facilitated by L are 0.54+/-0.05, 0.63+/-0.09, 0.51+/-0.04 and 0.46+/-0.06 cm s(-1), respectively. The pH values of aqueous solution have little effect on the electrochemical behaviors of these facilitated processes. The results predicate that this new type of ionophore might be useful to fabricate electrochemical sensor of sodium ion.

An EQCM investigation of oxidation of formic acid at gold electrode in sulfuric acid solution

The oxidation of HCOOH at Au electrode in sulfuric acid solution was investigated using the electrochemical quartz crystal microbalance (EQCM). The potentiodynamic mass responses in HCOOH-containing solution were compared to that in the background solution. This comparison provided valuable information on the mechanism of HCOOH oxidation. The effect of the potential scan rate on the current peak corresponding to oxide reduction was also discussed.

The time-resolved EQCM and study of the kinetics of silver(I) oxide formation on a polycrystalline silver electrode in alkaline solution

The time-resolved EQCM method is described and a theoretical analysis of the relation between the frequency resolution and the sampling rate (time resolution) is presented. It is shown that the time-resolved EQCM can fulfil simultaneously good frequency resolution and time resolution. The kinetics of the oxidation of Ag to Ag2O are studied using this method combined with the potentiostatic technique. The monolayer Ag2O formed at the first stage shows a potential dependent coverage. In the first two stages, the Ag2O layer thickens layer by layer with a rate-determining step of diffusion of Ag+ to the surface, where it forms an Ag2O base layer. The frequency transients associated with the formation of the bulk phase Ag2O are well consistent with the current transients, and both indicate an instantaneous nucleation and 3D growth mechanism. A relatively accurate method to estimate the mean height h of the cavities at the rough surface is also presented based on the frequency transient and charge density, and a linear increase of h with anodic charge is observed during the potentiostatic process. It has been demonstrated that the time-resolved EQCM can provide valuable information on the transient change of the morphology at the electrode|electrolyte interface.

SPE composite microdisk electrodes used in organic electrosynthesis

Abstract An SPE composite microdisk electrode is made by pressing a microdisk electrode on a piece of SPE membrane. It has a small ohmic drop and shows good reproducibility and some well-developed cyclic voltammograms and steady-state polarization curves are obtained. The electrochemical behavior of nitrobenzene and ferrocene at different microelectrode¦SPE membrane interfaces is investigated. It is found that electroactive compounds in the vicinity of the interface diffuse from the bulk solution to the electrode surface through the SPE membrane. This technique is suitable for investigating the electrochemical behavior of gases at the metal¦SPE interface or organic electroactive compounds poorly soluble in aqueous solution without addition of supporting electrolyte.

The adsorbed intermediate of the hydrogen evolution reaction at Pt in acid solution

Abstract The rotating-disc electrode-potential-step coulometry (RDE-PSC) method was extended to the study of those cases in which the surface concentration cs* of soluble intermediate or product depends only on the rate of electron transfer. In the potential range where the steady-state current does not vary with the rotation speed, the quantity of electricity Qs involved in the reaction of soluble intermediate or product is proportional to the inverse of the angular velocity of rotation ω−1. When this method was applied to the study of the adsorbed intermediate of the hydrogen evolution reaction (HER) at Pt in acid solution, it was found that the charge QHad of hydrogen electrosorption increases continuously from the underpotential deposition (UDP) region to the HER region. It seems to indicate that the reactive intermediate in the HER is different from the underpotential deposited hydrogen.