Peifang Liu

Nitrite reduction at powder microelectrodes

The limiting current of nitrite reduction in acid media is usually controlled by a preceding chemical reaction occurring in a very thin reaction zone. We propose that the apparent current density of this kind of reaction can be effectively enhanced by using a porous electrode and, for analytical purposes, the powder microelectrode (PME) is a convenient version. The apparent limiting current densities of nitrite reduction at the PMEs made from Au and carbon powders are found to be 50 and 100 times larger, respectively, than those obtained with smooth electrodes. For the carbon PME, the current is linear with nitrite concentration spanning five orders of magnitude with a lower detection limit of 4.4 μmol l−1.

Improvement of the output characteristics of amperometric enzyme electrode by using the powder microelectrode technique

Application of the powder microelectrode technique to the fabrication of enzyme electrodes can result in significant improvement of the output behaviours of an amperometric enzyme electrode. The theoretical kinetic equation of the powder enzyme electrode is derived and compared with that of the planar enzyme electrode, together with a simple method for the estimation of apparent Michaelis constant Km′ from the response of the powder enzyme electrode. The glucose oxidase (GOD) electrode is used as the model to verify the theoretical equations. Values of Km′ estimated from experimental data obtained with powder electrodes are closer to the intrinsic values of the same enzyme system in bulk phase. The working life of the enzyme electrode was found to improve and the interfering effects of various bioactive molecules were found to be less in the case of powder enzyme electrodes.

Improvement of the adhesion of a Nafion® modifying layer on electrodes

In recent years, solution-cast Nafion @ layers have been gaining increasing popularity in the fabrication of redox-polymer-modified electrodes. The main merits of using Nafion as the matrix of surface modifying layer include easy fabrication, high ionic conductivity, the high partition coefficients of many redox mediators in Nafion, high chemical stability, low interference from anions and biological macromolecules, and fairly good biocompatibility. There is already a large amount of literature covering many aspects of Nafion-based redox-polymermodified electrodes [1,2]. However, there are still problems hampering the practical application of this interesting type of chemically modified electrode. One of these is the frequently poor adhesion of the Nafion layer on a number of commonly used electrodes, especially smooth Pt and Au electrodes. Solution-cast Nafion layers are often easily detached from surfaces of clean smooth metals, glass, glazed ceramics and many other surfaces which are hydrophilic to some extent. The well-known experimental fact that after immersion of a Nafion-coated Pt electrode in an aqueous solution its cyclic voltammogram (CV) soon becomes similar to that of the bare Pt electrode clearly indicates that most of the Pt surface is in direct contact with the aqueous phase, rather than the C-F backbone of the Nafion matrix. In other words, the Nafion layer is already detached from the surface of the electrode. Since the main reason for the poor adhesion of the Nafion layer on many smooth hydrophilic surfaces seems to be the predominantly hydrophobic nature of its cross-section, an intermediate layer of oriented bifunctional molecules may be helpful. The intermediate layer of oriented molecules should be able both to adhere firmly to the electrode surface and to provide a highly hydrophobic outer surface to facilitate the adhesion of the Nafion layer. We have found that the self-assembled alkyl-thiol monolayer meets these basic requirements fairly successfully. Self-assembled alkyl-thiol monolayers are very popular nowadays in surface

A novel application of gas-diffusion electrodes as electrochemical gas sensors

Abstract Gas-diffusion electrodes of the hydrophobic type were employed as thin-layer gas electrode (TLGE) sensors for monitoring the concentrations of gas components either in the gas phase or dissolved in solution. The sampling and flushing manipulations of such thin-layer devices were designed to be exceedingly simple, and the temperature coefficient of the calibration curves is significantly lower than that of gas sensors based on the limiting current concept. Multi-component determination could also be achieved comparatively easily with the TLGE sensor, as illustrated by the case of analysis of O 2 +N 2 O mixtures.