Chemical and Biological Engineering ETDs

Publication Date

2-9-2011

Abstract

Enzymatic biofuel cells are a very attractive young technology based on utilization of natural, renewable and plentiful resources that offer an alternative energy source. Most fuel cells run on hydrogen; but it is extremely expensive and difficult to obtain, which is why research has moved to target fuels that are already available in nature, avoiding high costs of production, both economically and environmentally. Several biofuels with very high energy densities are available to us in abundance, but the challenges to make use of them are plenty. These biofuels contain several carbon-to-carbon bonds which make their oxidation processes significantly more complex than those of hydrogen. Examples of these biofuels are sugars and alcohols. If we refer back to nature, we have learned that enzymes play a very important role in oxidizing these types of fuels to obtain energy. If we could mimic such processes in a fuel cell, we would be able to harvest the energy of the fuels and convert it into electrical power. There are several advantages to using enzymes as catalysts for biofuel cells including their availability, easiness to produce in large quantities and selectivity. The main pitfall when mimicking natures pathways to oxidize biofuels by enzymatic action is that they usually require multiple oxidation steps. The full energy potential of biofuels can only be attained if all of the reaction steps are completed achieving the complete oxidation to CO2. This must be achieved by including all individual enzymes that catalyze each step of the oxidation of biofuels. Several of the necessary enzymes for those oxidation steps depend on the diffusive cofactor NAD+/NADH which by itself presents a great challenge. The optimal performance of a biofuel cell requires continuous operation and oxidation of the fuel which can only be achieved if the enzymes' cofactors are constantly regenerated. NADH oxidation has been a practical challenge in biotechnology over decades, since it requires very large overpotentials. In this work, we evaluated the utilization of standardized fuel cell apparatus built for cross-lab analysis by preparing poly-(MG) electrocatalysts for NADH oxidation onto different electrode materials. These electrocatalysts have been studied and characterized both electrochemically and structurally in order to develop NAD+-dependent enzyme anodes. Immobilization of enzymes also represents an important design aspect. One immobilization technique is chosen in this research; based on the combination of porous chitosan scaffolds and multi-walled carbon nanotubes that stabilizes enzymes while enabling mass transport of fuels and providing electrical conductivity. This research ultimately introduces a common technology platform for NADH re-oxidation in a flow through electrode format that can sustain single- or multi-enzyme anodes into biofuel cell technology. Future directions and optimization of the design are discussed.'

Keywords

Biofuel cell, alternative energy, enzymes, anode, NAD-dependent, poly-(methylene green), 3-D, flow-through, chitosan, carbon nanotubes

Document Type

Dissertation

Language

English

Degree Name

Chemical Engineering

Level of Degree

Doctoral

Department Name

Chemical and Biological Engineering

First Committee Member (Chair)

Petsev, Dimiter

Second Committee Member

Artyushkova, Kateryna

Third Committee Member

Grey, John

Fourth Committee Member

Minteer, Shelley

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