(452g) Modified-Methanol Dehydrogenase Enzymatic Catalysts for Fuel Cell Applications

Promising novel catalysts for small fuel cell applications (in the order of milliwatts) include enzymes, which might be able to improve the performance characteristics of chemical fuel cells where platinum is used as catalyst. These enzymatic catalysts may eliminate the use of expensive materials allowing miniaturization, normal conditions of operation, and promising fuel cell power outputs for some consumer electronic devices. For instance, fuel cells using bacterial Methanol Dehydrogenase (MDH) enzyme as anode catalyst are potential attractive power sources producing continuous power output of about 100 mW. MDH is an enzyme that speeds up the oxidation of methanol, a considerable cheap fuel for fuel cell devices, and other primary alcohols to their corresponding aldehydes. The active site of MDH contains a Ca2+ ion, which is linked to pyrroloquinoline quinone (PQQ) and amino acids. The role of Ca2+ ion is not well understood. It has been suggested that apart from holding the PQQ molecule in place in the active site, the calcium ion might have an important role in the oxidation reaction mechanism. Moreover, it has been suggested that the replacement of the Ca2+ in the MDH active site by other ion, such as Ba2+, might modify the activation energy of the enzyme, facilitating the methanol oxidation reaction and contributing to enlarge the overall fuel cell power output. Understanding the role of the ion in the active site of MDH, as well as the fuel oxidation mechanism will help to contribute to the design of novel catalysts for fuel cell applications. In this work Ca2+-MDH and Ba2+-MDH enzymes are being investigated to fully understand the methanol oxidation reaction produced by these enzymes using state-of-the-art molecular simulations. Quantum mechanical Density Functional Theory (DFT) simulations are used to obtain geometry, energetic, electronic configurations, and binding energies of small portions of the active site of the enzyme. Moreover, the activation energies for the dissociation of methanol in the presence of Ca2+- and Ba2+-containing MDH active sites are calculated using Transition State Theory. Our findings suggest that the nature of the ion modifies the binding and orientation of methanol with respect to the active site of the enzyme, facilitating the methanol oxidation reaction as the hydrogen-oxygen distance highlighted in the figure decreases. In addition, molecular modeling on the MDH immobilization on silica in the presence of a mediator will be discussed, and transport properties as well as water solvent effects will be presented.