Recent advances in nano/bio technology are eliminating the past well-known power output limitations that bio-fuel cells (~microW/cm2) faced with respect to chemical fuel cells (W to MW/cm2). Enzymatic fuel cells are currently being used to make electricity to power any number of electrical devices, such as pumps, valves and pacemakers, or electronic devices including but not limited to radios, sensors, controllers, and processors.[1] Currently a biocatalytic fuel cell that uses bacterial Methanol Dehydrogenase (MDH) enzyme as the anodic catalyst immobilized on N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD)-functionalized carbon paste electrode, produces a continuous power output of 0.25 mW/cm2 for 30 days of continuous operation,[2] although the expected (theoretical) output is 100 mW/cm2.[3] It is believed that the TMPD mediator, responsible for electron transfer resulting from the fuel oxidation by the enzyme to the electrode, is the major factor limiting the power output, and deteriorating the fuel cell performance. The active site of the enzyme is buried deep within the structure making the use of a mediator necessary to draw out the electron. The naturally occurring electron acceptor is cytochrome cL but the use of a variety of mediators has been proposed to more appropriately facilitate electron transfer. [2, 4] In this work interaction between the active site of the enzyme and a variety of mediators is investigated using diverse molecular modeling techniques. Insight to how these molecules network to facilitate electron transport is achieved using molecular simulations. Calculations of ionization potentials and electron affinities are presented for a range of mediators varying in size and composition to determine the ideal properties of the most effective mediator for electron transfer in a methanol dehydrogenase enzymatic fuel cell.
1. Karyakin, A.A., S.V. Morozov, E.E. Karyakina, V. S.D., N.A. Zorin, and S. Cosnier, Hydrogen Fuel Electrode Based on Bioelectrocatalysis by the Enzyme Hydrogenase. Electrochem. Comm., 2002. 4: p. 417-420.
2. Zhang, X.-C., A. Ranta, and A. Halme, Direct methanol biocatalytic fuel cell-Considerations of restraints on electron transfer. Biosensors and Bioelectronics, 2006(21): p. 2052-2057.
3. Zhang, X.C., A. Ranta, and A. Halme. Effect of Different Catalytic Oxidants on the Performance of a Biocatalytic Methanol Fuel Cell. in Proceedings 204th Meeting of The Electrochemical Society. 2003.
4. Patel,R.N., and A. Felix, Microbial Oxidation of Methane and Methanol: Crystallization and Properties of Methanol Dehydrogenase from Methylsinus Sporium. Journal of Bacteriology, 1976(128): p. 413-424