I. Iliev

Investigations of catalysts from the pyrolyzates of cobalt-containing and metal-free dibenzotetraazaannulenes on active carbon for oxygen electrodes in an acid medium

Abstract Gas-diffusion electrodes for the reduction of oxygen in an acid medium were investigated. The catalyst is based on an active carbon, pyrolysed with a N 4 -chelate percentage of 20%. The optimum pyrolysis temperature for the electrochemically most active catalyst is shifted towards higher temperatures compared with a cobalt-containing dibenzotetraazaannulene for the metal-free compound. This effect is also observed as far as the catalytic activity is concerned. The BET surface areas of the active materials obtained are compared with each other. The two N 4 -chelates are investigated by infrared and X-ray spectroscopy. The role of the metallic central atom is explained in terms of its catalytic influence on the pyrolysis.

Optimization of the pyrolysis temperature of active carbon-CoTMPP catalysts for air electrodes in alkaline media

Abstract Catalysts prepared from active carbon impregnated with CoTMPP, and then heat treated in argon at temperatures between 200 and 1200 °C were investigat It was found that heating the catalyst at temperatures between 460 and 810 °C improved the initial polarization characteristics of air electrodes. Th

A contribution to the characterization of heat-treated electrocatalytically active tetramethoxy-phenylporphyrinato-cobalt-II

Abstract The physico-chemical properties of activated material for electrodes for the electrochemical reduction of oxygen are discussed. These electrodes contai

Influence of mass transport on the performance of carbon gas-diffusion air electrodes in alkaline solution

The effect of mass transport on the electrochemical behaviour of carbon gas-diffusion air electrodes in alkaline solution was investigated on the basis of ΔE(i) curves. These curves are obtained by subtraction of potential values for an electrode operating with airEair(i) from potential values for the same electrode operating with pure oxygenEoxygen(i) at the same current densityi. Three different regions on these curves connected with different modes of mass transport are recognized. A model of the gas-diffusion air electrode which takes into account the diffusion of the gas, diffusion of the dissolved gas, electrochemical reaction and IR drop is used to explain the experimental results.

Bifunctional hydrogen peroxide electrode as an amperometric transducer for biosensors

Abstract This work presents a novel approach to design an amperometric transducer capable to detect hydrogen peroxide in anodic (oxidation) and cathodic (reduction) mode of operation. The basic transducer employs non-platinum electrocatalyst—pyrolyzed cobalt–tetramethoxy–phenylporphyrin (CoTMPP)—for H 2 O 2 electrooxidation, and bio-electrocatalyst—horseradish peroxidase (HRP)—for H 2 O 2 electroreduction. The bifunctional hydrogen peroxide electrode was used as an amperometric transducer in designing a glucose biosensor utilizing glucose oxidase (GOD) as second enzyme. A technique for preparation of the transducer electrode with the catalyst and adsorbed enzymes (bienzyme electrode) from a pressed matrix (tablet) of Teflonized carbon black is described. This technique allows manufacturing of numerous sensors from the same pressed tablet, all of which demonstrate good reproducibility of their parameters (sensitivity, linear range, lifetime). Bifunctional glucose sensors were operated in H 2 O 2 oxidation mode at applied potentials from +0.2 to +0.6 V versus Ag/AgCl, and in H 2 O 2 reduction mode at 0.0 V versus the same reference electrode. Linearity of the sensor response to glucose concentrations up to 25 mM in H 2 O 2 reduction mode is reported. Electro-interference from some substances commonly present in physiological fluids was investigated in both reduction and oxidation modes. Sensors can be used for continuous glucose monitoring in vitro for at least 1 month with constant parameters of the signal output. Sensor demonstrated satisfactory performances in undiluted blood plasma in vitro.

Investigations of a large-capacity medium-power saline aluminium-air battery

This paper describes the development and operation of a medium-power (24 W) aluminium-air battery with saline electrolyte or sea water. The battery consisted of two packs of 10 cells, each connected in series with a projected aluminium anode capacity of 2590 Ah. The anodes were made of a Ga−Sn−Mg alloy capable of giving 89% material efficiency, with an open circuit voltage of 13.4V. The specific energy based on aluminium was calculated at 577 Wh kg−1.

Electrochemical gas biosensor for phenol

A gas biosensor for vapors of phenolic compounds, comprising an enzyme/gas-diffusion electrode with tyrosinase enzyme is investigated. The transient amperometric signal and the calibration curves of this gas biosensor are studied in the presence of phenol, p-cresol and 4-chlorphenol vapors. It is shown that phenol vapor concentrations in the ppb range are detectable with this type of gas biosensor. The stable steady-state performance of the biosensor allow the measurement of the electrochemical impedance of the system in a broad frequency range (50 kHz to 1 mHz).

Transient response of electrochemical biosensors with asymmetrical sandwich membranes

Abstract A mathematical model of a sandwich membrane biosensor operating in the diffusion-limited regime is proposed. The enzyme (oxidase) is immobilized between two diffusion membranes with different thicknesses. The electrochemically active product of the enzymatic reaction (H2O2) is detected on a catalytic electrode. The exact transient solution of the model is obtained under the assumptions of diffusion-limited enzymatic and electrochemical reactions, a stepwise increase of the substrate concentration (from 0 to CG°) and zero concentration of the electrochemically active product (H2O2) in the bulk solution. The thickness of the enzyme layer in the sandwich is assumed to be negligibly small in comparison with that of the diffusionn membranes. The numerical values of the transient concentration distribution C(x, t), of the transient current i(t) and its time derivative di(t)/dt are computed and presented in dimensionless form for different sets of parameters of the model. The influence of the enzyme layer position in the sandwich membrane and of the ratio of the effective diffusion coefficients of the substrate and the electrochemically active product on the transient behaviour of the sensor is discussed. The model gives some hints for the design of amperometric biosensors.

Enzyme/gas-diffusion electrodes for determination of phenol

Abstract An enzyme/gas diffusion electrode for the determination of phenol concentration is investigated comprising a new type of porous hydrophobic carbon electrode (made from acetylene black treated with PTFE by a special technology) on which enzyme tyrosinase is immobilized. In the enzyme/gas-diffusion electrode the oxygen needed for the enzymatic reaction can be transported in gas phase from the air through the porous hydrophobic carbon electrode to the immobilized enzyme. It is shown that the fast O 2 supply in the gas phase results in an increase of the amperometric signal of the phenol electrode and an enlargement of the linear part of its calibration curve. The described phenol enzyme/gas-diffusion electrode is applied also for monitoring of phenol vapour.

Comparative methods for the estimation of the activity and the transport hindrances of air gas-diffusion electrodes

Abstract Comparative methods are developed for the estimation of the activity and the transport hindrances of air gas-diffusion electrodes. The value of the int These methods are successfully employed for the investigation of air electrodes in alkaline solution. Different porous hydrophobic materials are invest