S. Gamburzev

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.

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.

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

On the effect of various active carbon catalysts on the behaviour of carbon gas-diffusion air electrodes: 2. Acid solutions

The electrochemical performance of carbon gas-diffusion air electrodes was studied in acid solutions. Electrodes with defined structure prepared from 11 different active carbon samples were investigated when working with air and oxygen. The catalytic activity of these samples both in acid and in alkaline solutions was compared. The extent of mass transport hindrances was estimated in terms of ΔE(i) curves. The effect of platinum and polymeric phthalocyanines as promoters on the overall electrochemical characteristics of oxygen and air electrodes was studied. In the case of oxygen electrodes at E = 700 mV (vs. RHE) 120 mA/c2 were obtained with NORIT NK active carbon promoted with 2.36 mg platinum/cm2 and 30 mA/cm2 with P-33-active carbon promoted with 13 mg iron phthalocyanine/cm2 . At low current loads the ΔE(i) curves and the slopes of the linear portion of the E vs. log i curves of oxygen electrodes reflect a different electrochemical mechanism and a different rate of mass transport for pure active carbon and active carbon promoted with the above-mentioned catalysts.

Heat-treated Co-tetramethoxyphenylporphyrin on different carbon carriers as catalysts for the electrochemical reduction of oxygen in acid electrolytes

Abstract In this paper it is shown that the type of carbon support used in pyrolyzed TMeOPPCo catalysts modifies their properties in sulphuric acid. The type of carbon support influences both the catalytic activity for oxygen reduction and their long-term stability. The observed effects are probably

Metallocene-mediated amperometric biosensors for one-shot glucose determination

Abstract Amperometric biosensors for the determination of glucose based on carbon black screen-printed on ceramics are described. The mediators, nickelocene, ferrocene and their derivatives, are used for the conjunction of glucose oxidase-catalysed oxidation of glucose and electrochemical reaction at the applied potential. It is shown that the nickelocene-mediated glucose oxidase electrode exhibits a similar behaviour to that mediated with ferrocene. However, the quasi-redox potential of nickelocene/nickelocenium cation, which is by 0.3 V more negative than that of any of the investigated ferrocene derivatives, significantly lowers the operating potential of the biosensor to ≈0.00 V versus an Ag/AgCl electrode.

Partially immersed gas-diffusion electrodes

A new type of partially immersed carbon gas-diffusion electrode with a sandwich-like structure consisting of two active layers each side of the gas-supplying layer is described. The current collector grid is embedded into the electrically conductive gas-supplying layer. A theoretical model of the partially immersed electrodes is proposed and experimentally confirmed. The model can be used for the theoretical prediction of the steady state behaviour of partially immersed electrodes from experimental data obtained with non-immersed gas-diffusion electrodes. An experimental zinc-air battery of 1900 A h capacity with the new type of partially immersed carbon air gas-diffusion electrodes has shown a specific energy density of 250 W h kg−1 and 420 W h 1−1 at a current density of 0·5 mA cm−2.