Investigation of electrochemical interfaces for the development of novel electrodes for biomimetic energy conversion and hydrogen fuel cells

Abstract

Heightened awareness in global warming and an increasing demand in energy consumption have generated a surging interest in creating sustainable alternative energy sources. One of the major challenges of incorporating existing technologies into societal infrastructure is the cost of alternative energies, such as solar and fuel cells. In order to reduce the cost of these technologies, either existing technologies need to be made more efficient or a fundamental rethink of current designs is necessary. An essential component of these energy conversion technologies is the interfacial charge transfer from the cells to an external circuit. The research presented in this thesis focuses on the engineering of electrode interfaces for biomimetic energy conversion and the “triple-interface” of the cathode in proton exchange membrane fuel cells (PEM-FCs). The first part of this thesis describes the incorporation of Photosystem I, a 500 kDa protein macromolecule involved in the light reactions of photosynthesis, onto electrodes that enable the conversion of photons into chemical and ultimately electrical energy. Self-assembled monolayers (SAMs) were used to directly wire the protein complexes to gold electrode surfaces in a simple, fast manner. The vacuum-assisted deposition technique developed to assemble PSI enabled the formation of active PSI films ~80 times faster than previous methods. Additionally, this deposition technique allows for the formation of thick, ~ 1 micron, PSI films that produce an order of magnitude more photocurrent than monolayer films. The second part of this thesis describes the synthesis and surface-initiated polymerization of a new class of partially fluorinated polymers for use in PEM-FCs. The 5-(perfluoro-n-alkyl)norbornenes (where n = 4, 6, 8, 10) were synthesized using a Diels-Alder reaction between a perfluorinated alkene and cyclopentadiene. Utilizing surface-initiated ring-opening metathesis (SI-ROMP) and appropriate surface-bound initiators, polymer films were grown from 2-D planar gold, 3-D nanoporous gold leaf, and 3-D carbon fiber electrodes. Upon sulfonation, the barrier properties of these films change dramatically. The transport properties of aqueous species through these systems were measured using electrochemical impedance spectroscopy and are discussed.