(586b) Electrode Surface Kinetics of Methyl Viologen for Biological Processes

Electrons are essential for biological processes and are often supplied by reduced species (e.g. glucose, H₂, CO, etc.).  However, a recent focus has also been the use of electrodes to supply electrons for biological processes.  For electrodes, electrons are either transferred by an extracellular electron mediator or directly transferred to immobilized bacteria on the electrode.

External chemical electron mediators, such as methyl viologen (MV), NADH and neutral red, can support metabolic functions of various bacteria. There is great potential in using electrodes but a more rigorous engineering analysis is needed to assess constraints such as electron efficiency, toxicity, thermodynamics, reaction rates, and availability of species. This work focuses on characterizing the kinetics of methyl viologen (MV) at the surface of an electrode. MV was chosen as a model compound as a result of its reported beneficial effects on various biological processes.

MV has three redox states (MV²⁺, MV⁺ and MV⁰).  MV²⁺ undergoes a two-step reduction to acquire 2 electrons, forming MV⁰. MV⁰ is capable of delivering electrons to cells. The reduction by an electrode is an electrochemical reaction and the reaction rate is a function of the applied potential. The relationship can be expressed by the Bulter-Volmer equation. The MV²⁺ reduction is also a surface reaction with three steps of absorption, surface reaction and desorption. The MV²⁺ reduction is demonstrated to be surface reaction limiting. This study combined the surface reaction with the electro-chemical expression which provides a more detailed engineering analysis to improve future design and control for electrode-mediated biological processes.  Results of the kinetic study will be presented, along with thermodynamic constraints of utilizing MV.  A key component of the presentation will be a discussion of the importance of engineering analysis when applying electrode systems to biological processes.