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Glucose was selectively oxidized to gluconic acid in a membraneless, flow-through electroenzymatic reactor operated in the mode of co-generating chemicals and electrical energy. At the anode the enzyme glucose oxidase (GOx) in combination with the redox mediator tetrathiafulvalene (TTF) was used as catalyst, while the cathode was equipped with an enzyme cascade consisting of GOx and horseradish peroxidase (HRP). The influence of the electrode preparation procedure, the structural and the operating parameters on the reactor performance was investigated in detail. Under optimized conditions, an open circuit potential of 0.75 V, a current density of 0.6 mA cm −2 and a power density of 100 μA cm −2 were measured. The space time yield of gluconic acid achieved at a glucose conversion of 47% was 18.2 g h −1 cm −2 . [ABSTRACT FROM AUTHOR]

Abstract: The application of electrochemical impedance spectroscopy (EIS) in theory and experiment for investigation of redox enzyme kinetics has been described. As a model system an enzyme horseradish peroxidase adsorbed on graphite electrode has been chosen. Three different mathematical models based on generalized mechanism of horseradish peroxidase catalyzed hydrogen peroxide reduction have been formulated and used for derivation of theoretical electrochemical impedances. In this way, mechanistic details related to bioelectrochemical reaction including all relevant kinetic parameters are obtained. The presented approach overcomes limitations of classical equivalent circuit approach, since it does not rely on phenomenological elements, but on particular reaction mechanism. We have shown that the EIS is more sensitive for parameter estimation and model discrimination than a steady state response. [Copyright &y& Elsevier]

Fuel cells convert chemically stored energy directly into electrical energy at high thermodynamic efficiencies. But, despite significant progress in research and development during the last two decades, further improvement of performance and reduction of costs are required in order to translate fuel cell technologies into commercial products. The present mini-review sheds some light on four particular fields of fuel cell research where chemical reaction engineers can bring in their expertise: (1) understanding the nonlinear dynamic behavior of fuel cells as electrochemical reactors, (2) development of new concepts for efficient mass and heat integration of fuel cell systems, (3) use of biomass as renewable primary energy source for feeding fuel cells, (4) use of enzymes for catalyzing the electrode reactions in fuel cells. [Copyright &y& Elsevier]

Understanding the kinetics of the oxygen reduction reaction on silver in highly concentrated alkaline solutions (e.g., 11 M NaOH) and elevated temperature is of great interest both in terms of technical applications of this reaction (e.g., in chloralkali electrolysis) and in fundamental terms. To gain a better understanding of this process, a nonlinear frequency response analysis was performed in combination with a rotating ring disk analysis. Firstly, the ORR was analyzed under steady-state conditions. The number of exchanged electrons was determined based on rotating ring disk experiments. Secondly, two different dynamic ORR kinetic models have been formulated. These models were used to derive the theoretical first- and second-order frequency response functions (FRFs). Furthermore, the first and second-order FRFs were determined experimentally for both 0.1 M NaOH and 11 M NaOH at different temperatures. In the next step, the kinetic model parameters were numerically estimated from the experimental frequency-domain data. Despite its simplicity, the so-called 1-step model was able to reproduce experimental first- and second-order FRFs in 0.1 M NaOH under different conditions (steady-state potentials and rotation rates). At the same time, this model was able to reproduce the first-order FRF in 11 M NaOH at 60 °C, but not the features observed in the second-order FRF spectra. The more complex 4-step model has shown a better capability in explaining experimental findings, like the first and second-order FRFs, but also experimentally observed change of the Tafel slope as well as the influence of mass transport on the number of exchanged electrons. However, it was also not able to reproduce all experimental features. Possible reasons for these discrepancies are discussed. [Display omitted] [ABSTRACT FROM AUTHOR]

1-D model of a porous enzymatic electrode with direct electron transfer mechanism has been developed. As a model reaction, hydrogen peroxide reduction catalyzed by Horseradish Peroxidase has been chosen. The model description includes material and charge balances in different phases as well as detailed kinetics of bioelectrochemical hydrogen peroxide reduction. The model has been solved numerically and validated experimentally under steady state conditions. To investigate the influence of the electrode structure and the immobilization procedure, two types of enzymatic electrodes have been developed. In one procedure (Vulcan-PVDF) enzymes were entrapped into a porous conductive matrix, while in the second one (Vulcan-Gelatin) gelatin was used as a binder and enzymes were cross-linked. The performances of Vulcan-PVDF electrodes were significantly better than of Vulcan-Gelatin electrodes under all studied conditions. According to the model, the main reasons for this observation are higher number of active enzymes and higher diffusivity of hydrogen peroxide in the catalyst layer (CL) in case of Vulcan-PVDF procedure. The model pointed out that the major limitation in both studied systems is mass transfer limitation. Enzyme utilization in both systems is very low. [ABSTRACT FROM AUTHOR]