Temporal dynamics of the biofilm-mediated open circuit potentials: Understanding the fundamentals via a combined thermodynamic and kinetic modeling approach.

This study provides in-depth insights into the thermodynamics of electrochemical processes that govern the generation and temporal modulation of open-circuit potentials in biofilms and presents the foundation and applications of open-circuit potential methods to study the bioelectrochemical behaviors of biofilms. This investigation was guided by an overarching hypothesis that models should adequately explain the open-circuit potential patterns generated by biofilms when environmental conditions change; and from this work, a generalized model of electrochemical processes endemic to the biofilm electrode was developed and validated. The proposed model accounts for open system thermodynamics and the kinetics of bioelectrochemical transformations, and the model is simplified to enable applicability to a wide range of processes that are possible within biofilms. As such, the model can account for different parameters associated with various biofilm systems and is extendable to include numerous other experimental conditions. The model predictions were compared to the experimental data generated by 48 equidistantly located microbial potentiometric sensor electrodes in a chamber capable of simulating naturally occurring water matrix, which was exposed to environmental conditions. By combining electrochemical-cell thermodynamics and kinetics approaches, the model explained the temporal dependences of the open circuit potentials in aerobic and anaerobic conditions and the interconversion of two regimes commonly observed in natural systems. At the same time, it enables extraction of the relevant kinetic parameters from experimentally measured time evolution of the open circuit potentials.