Mathematical modeling of direct electron transfer and mediated electron transfer mechanisms in enzymatic glucose fuel cells under substrate inhibition

Abstract

Kinetic and transport factors are of crucial importance for the performance of enzymatic glucose fuel cells, EGFCs, particularly under conditions of substrate inhibition. This study focuses on the development, implementation, and comparison of Direct Electron Transfer (DET) and Mediated Electron Transfer(MET) mechanisms, with the aim of investigating substrate inhibition effects. Explicitly, it accounts for substrate inhibition, enzyme concentration, mediator dynamics, and electrochemical reactions to determine optimal working conditions. In the MET model, the Nernst Ping-pong model is used to account for mediator-dependent electron transfer and overpotential effects. Simulation results show that the DET current peaks at 1.2 mol m⁻³ substrate with 1.05 mA, whereas the MET current peaks at 1.25 mA for a lower concentration of 0.94 mol m⁻³. Furthermore, a 50% and 45% degradation of the catalytic current is observed at a 5 mol m⁻³ substrate concentration for both. The model identifies an optimal mediator concentration of 77 mM and shows that increasing mediator loading from 50 to 100 mM enhances the catalytic current by ~ 30–35%, whereas increasing the overpotential from 0.05 to 0.2 V results in a comparatively smaller improvement of ~ 10–15%. This indicates that EGFC performance is significantly more sensitive to mediator loading than to overpotential within the investigated range. Validation against experimental data demonstrates excellent agreement, with an R² value of 0.92. The models developed in this work provide guidelines for optimizing enzyme and mediator loading to mitigate substrate inhibition and enhance the efficiency of EGFC.