Generating Small Molecule Fuels: (Photo)Electrochemical Catalysts

The work contained in this thesis focuses on the synthesis and electrochemistry of certain metal complexes that are involved in either catalysing production of a renewable fuel, hydrogen, or are capable of mediating the reduction of molecular nitrogen to ammonia, nitrogen fixation. Electrochemical analysis is used to measure the kinetic and mechanistic properties of the molecular catalysts used in this work. Semiconducting silicon electrodes have been explored as a means of coupling these hydrogen evolving and nitrogen fixation systems to the harvesting of visible light – solar fuels and solar synthesis respectively. Chapter 1 gives a general overview of the world demand for energy and how it is currently produced. The current methods of renewable energy conversion are discussed with solar energy capture offering the greatest potential. Conversion of solar to chemical energy is described to be best attained by a solar producer cell which employs metal catalysts. Chapter 2 outlines the major techniques used throughout the course of the work with light harvesting solar cells and electrocatalysts as described in this thesis, including the theory behind them. Chapter 3 expands the study of hydrogen evolution by cationic hydrido- complexes of molybdenum and tungsten. The understanding of the basic electrochemistry of the systems is extended and electrocatalytic hydrogen evolution is optimised. Chapter 4 is concerned with an enzyme related to the formate dehydrogenases which has been shown to exhibit hydrogen metabolising chemistry (Sawers et al.). Molybdenum and tungsten dithiolene complexes are analysed for catalysis of hydrogen evolution and/or oxidation by (spectro)electrochemical methods as potential models for this pterin enzyme. Chapter 5 extends the studies of electrochemical nitrogen fixation by a tungsten hydrazido- complex at the synthetic and mechanistic levels. Photofixation of dinitrogen at a p-type silicon electrode via this hydrazide system is explored and limitations discussed.

Name dc:type.qualificationname

dphil

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2014

Author dc:creator

• Webster, Lee

Language dc:language

en