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Development of Metalloenzyme Dioxygen Reduction Cathodes

Citation

Agbo, Peter Chukwudi Ifeanychukwu (2015) Development of Metalloenzyme Dioxygen Reduction Cathodes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9MK69TD. http://resolver.caltech.edu/CaltechTHESIS:09192014-121956600

Abstract

The prime thrust of this dissertation is to advance the development of fuel cell dioxygen reduction cathodes that employ some variant of multicopper oxidase enzymes as the catalyst. The low earth-abundance of platinum metal and its correspondingly high market cost has prompted a general search amongst chemists and materials scientists for reasonable alternatives to this metal for facilitating catalytic dioxygen reduction chemistry. The multicopper oxidases (MCOs), which constitute a class of enzyme that naturally catalyze the reaction O2 + 4H+ + 4e- → 2H2O, provide a promising set of biochemical contenders for fuel cell cathode catalysts. In MCOs, a substrate reduces a copper atom at the type 1 site, where charge is then transferred to a trinuclear copper cluster consisting of a mononuclear type 2 or “normal copper” site and a binuclear type 3 copper site. Following the reduction of all four copper atoms in the enzyme, dioxygen is then reduced to water in two two-electron steps, upon binding to the trinuclear copper cluster. We identified an MCO, a laccase from the hyperthermophilic bacterium Thermus thermophilus strain HB27, as a promising candidate for cathodic fuel cell catalysis. This protein demonstrates resilience at high temperatures, exhibiting no denaturing transition at temperatures high as 95°C, conditions relevant to typical polymer electrolyte fuel cell operation.

In Chapter I of this thesis, we discuss initial efforts to physically characterize the enzyme when operating as a heterogeneous cathode catalyst. Following this, in Chapter II we then outline the development of a model capable of describing the observed electrochemical behavior of this enzyme when operating on porous carbon electrodes. Developing a rigorous mathematical framework with which to describe this system had the potential to improve our understanding of MCO electrokinetics, while also providing a level of predictive power that might guide any future efforts to fabricate MCO cathodes with optimized electrochemical performance. In Chapter III we detail efforts to reduce electrode overpotentials through site-directed mutagenesis of the inner and outer-sphere ligands of the Cu sites in laccase, using electrochemical methods and electronic spectroscopy to try and understand the resultant behavior of our mutant constructs. Finally, in Chapter IV, we examine future work concerning the fabrication of enhanced MCO cathodes, exploring the possibility of new cathode materials and advanced enzyme deposition techniques.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Laccase, MCO, multicopper oxidase, cathode, fuel cell
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Gray, Harry B. (advisor)
  • Heath, James R. (co-advisor)
Thesis Committee:
  • Richards, John H. (chair)
  • Gray, Harry B.
  • Heath, James R.
  • Arnold, Frances Hamilton
Defense Date:1 August 2014
Funders:
Funding AgencyGrant Number
GCEP (Stanford)UNSPECIFIED
CSER (The Gordon and Betty Moore Foundation)UNSPECIFIED
Institute for Collaborative BiotechnologiesW911NF-09-0001
Department of Energy, Basic Energy SciencesDE-FG03-01ER46175
NSF CCI Solar Fuels ProgramCHE-1305124
Perkins GrantJRH.PERKINS3-1- GRANT.PERKINS3
Record Number:CaltechTHESIS:09192014-121956600
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:09192014-121956600
DOI:10.7907/Z9MK69TD
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1021/jp309759gDOIArticle adapted for ch. 1: Catalysis of dioxygen reduction by Thermus thermophilus strain HB27 laccase on ketjen black electrodes.
http://dx.doi.org/10.1021/ja5077519DOIArticle adapted for ch. 2: Modelling Dioxygen Reduction at Multicopper Oxidase Cathodes
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8662
Collection:CaltechTHESIS
Deposited By: Peter Agbo
Deposited On:25 Sep 2014 17:11
Last Modified:03 Feb 2016 22:43

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