(12a) Factors Limiting the Electron Transfer in Methanol Dehydrogenase Enzymatic Fuel Cells

Recent advances in nano/bio technology are eliminating the past well-known power output limitations that bio-fuel cells (micro-Watts/cm2) faced with respect to chemical fuel cells (Watts to milli-Watts/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 (TPMD)-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 TPMD 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. In this work interaction between the MDH enzyme and the mediator TPMD is investigated using diverse molecular modeling techniques. Insight into how these molecules network to facilitate electron transport is achieved using quantum mechanical Density Functional Theory (DFT) and Molecular Dynamics simulations to obtain geometry, electronic configurations, and binding energies. The structure and stability of MDH enzymes and MDH/mediator complexes immobilized on electrode surfaces is investigated to further understand their behavior upon methanol oxidation. Moreover, studies of the enzyme conformational changes upon immobilization on electrode supports will be conducted and their effects on the enzyme activity and effectiveness for methanol oxidation elucidated.

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.