Mathematical Modeling of a Porous Enzymatic Electrode with Direct Electron Transfer Mechanism

• Detailed 1-D model of a porous enzymatic electrode with direct electron transfer mechanism
• Model based understanding of structure/activity relationship
• Cross-linking decreases enzyme utilization, stabilizers like gelatin slows down the diffusion through the electrode structure
• Low electrode performance due to high mass transfer limitations and low enzyme utilization

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.

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