Switchable Electrode Assemblies Employing Nano-Bio Hybrid Structures in Cascaded Enzymatic Fuel Cells
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2018
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Doctoral Thesis
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Abstract
Enzymatic biofuel cells may become more accessible for applications powering portable or implantable electronic devices by extending the range and conversion efficiency of the fuels and oxidizers used. One of the major challenges of enzyme-modified electrodes is their susceptibility to time-dependent degradation of the active biocatalysts, which typically leads to limited operational lifetimes.
Within this thesis, we introduce concepts and methodologies that promote enzymatic biofuel cells as alternative power sources. These concepts are exemplified and validated through a series of saccharide/oxygen-based enzymatic biofuel cells.
To broaden the spectrum of usable biofuels and operational conditions, we describe integrated assemblies consisting of multi-substrate electrodes composed of enzymatic cascades immobilized to mesoporous carbon nanoparticle supports. In this design, entrapped electron relay molecules facilitate the electrical communication between the linked redox enzymes and the conductive carbon supports, thus efficiently mediating the oxidation of multiple fuels and reduction of oxidizers for the generation of electrical power. By using a cascade consisting of the enzymes invertase, mutarotase, glucose oxidase and fructose dehydrogenase, and by employing tetrathiafulvalen mediator units, we are able to effectively oxidize, separately and simultaneously, the fuels glucose, fructose and sucrose. A cathode consisting of the enzymes catalase and bilirubin oxidase, employing the mediator 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), is successfully shown to operate in environments of varied oxygen availability. Whereas bilirubin oxidase reduces oxygen to water under aerobic conditions, catalase catalyzes the disproportionation reaction of hydrogen peroxide to water and oxygen, allowing hydrogen peroxide to act as an internal source of oxygen under anaerobic operation conditions. A combined assembly of these cascaded electrode architectures yields a non-compartmentalized biofuel cell based on mediated electron transfer bioelectrocatalysis, operating with multiple fuels and oxidizer re-sources. This cell can be repeatedly switched between aerobic and anaerobic operating conditions without any significant decrease in discharge performance.
To overcome limitations imposed by the time-dependent degradation of the biological components in enzymatic biofuel cells, we propose a magnetically assisted methodology to reenergize the cells. In this case, carbon coated magnetic nanoparticles are modified with fructose dehydrogenase or bilirubin oxidase. These can be channeled towards and away from designated current collectors by externally applied magnetic field gradients. The magneto-assisted loading of the current collectors results in direct electron transfer currents. Similarly, by applying appropriate magnetic field gradients, bioelectrocatalysis can be switched ON and OFF to generate power on demand, and the active components of the cell can be exchanged entirely to regenerate power. By repeatedly refreshing the particles at a deep stage of the discharge, the biofuel cell operation is considerably extended beyond a single full discharge. Taken individually and even more so when combined together, these concepts open new possibilities to exploit a broad range of fuels and oxidizers, and to harvest electrical energy from alternative biomass resources.
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Examiner : Stemmer, Andreas
Examiner : Frasconi, Marco
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ETH Zurich
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03444 - Stemmer, Andreas (emeritus) / Stemmer, Andreas (emeritus)