Advisor(s)

Elizabeth J. Podlaha-Murphy

Contributor(s)

Shashi Krishna Murthy, Michael C. Murphy, Akram N. Alshawabkeh

Date of Award

2010

Date Accepted

12-2010

Degree Grantor

Northeastern University

Degree Level

Ph.D.

Degree Name

Doctor of Philosophy

Department or Academic Unit

College of Engineering. Department of Chemical Engineering.

Keywords

Au/FeAu multilayer nanowires, Photocatalysis, Titania

Subject Categories

Semiconductors, Nanowires, Titanium dioxide - Stability

Disciplines

Catalysis and Reaction Engineering | Nanoscience and Nanotechnology

Abstract

Environmentally clean hydrogen fuel represents a number of advantages over popularly utilized petroleum-based derivatives. Among alternative technologies, hydrogen can be generated by direct electrolysis of water upon irradiating a semiconductor material with light of energy greater than its energy band gap. A strategy to improve the photocatalytic efficacy of bare semiconductors and promote the sluggish kinetics of the oxidation reaction has been the incorporation of noble metals onto their surface. In particular, the Au-TiO2 system has been effective at enhancing and shifting the photoactivity to irradiation of longer wavelengths through relatively more efficient electron transfer processes involved in redox reactions. Main drawbacks that limit the applicability of Au-TiO2 composites are aging and/or deactivation effects arising from prolonged exposure to irradiating light. A novel approach to circumvent such effects, improve the stability of the composite towards atmospheric conditions and achieve long-lasting activity is presented in this study. The design involved incorporation of solid-state Fe in galvanic contact with Au(s), which theoretically induces a deactivation resistance on Au(s), owing to differences in nobility and electromotive potential (emf) of the electrochemical reactions involved. A preferential natural corrosion of the sacrificial less noble Fe serves as protection by oxidizing first at the expense of protecting the nobler Au from corrosion. In the present study, Fe(s) was tailored in galvanic contact to Au(s) in the form of Au/AuFe multilayered nanowires, which were fabricated electrochemically by means of a square-wave pulsed current scheme from a cyanide-free electrolyte. Variations in porosity and Fe content of the alloy layer were controlled via the deposition conditions and the type of complexant species present in the electrolyte. The fabricated Au/FeAu multilayer nanowires were subsequently integrated on electrosynthesized TiO2 to form the composite and its photocatalytic potential for the water splitting reaction assessed by means of a step in illumination, cyclic voltammetry and impedance modulated photocurrent spectroscopy (IMPS). The efficacy of Fe at preventing catalyst deactivation, as well as the effect of variations in porosity and Fe content of nanowires integrated onto TiO2, on the catalytic performance, were assessed.

Document Type

Dissertation

Rights Holder

Savidra Chavez Lucatero


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