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Dr Andrew P. Doherty
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Dr A.P. Doherty Examinations Officer |
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Research KeywordsElectrochemistry in organised mediaStructural evolution of mesophase liquids Electrocatalysis Electrosynthesis Nano-particle electrochemistry |
Publications |
Research
Electrochemistry
Due to diversity of application, electrochemistry is a cornerstone discipline within the physical sciences. For example, electrochemistry may be used to synthesis molecules, analyse diverse trace species such as heavy metals or neuro-transmitters in vivo, as well as for technological applications including fuel cells, batteries and photovoltaic devices. Electrochemical events are also important biologically e.g. photosynthesis and respiration involve concerted electron transfer reactions via redox enzymes. Electrochemical research has contributed profoundly to both the development of our understanding of such complex reactions and the design of synthetic redox materials to mimic such processes. Our interest lies in a number of areas; primarily in electrochemistry in organised self-assembled nanofluids, electrosynthesis of small organic molecules and redox catalysis.
Nanofluids
These technologically important liquids contain discrete structurally dynamic nano-scale particles (micelles and microemulsions) formed by the molecular self-assembly of a small number of molecules (usually 100-1000s) into hydrophobic and hydrophilic domains. Since these structures are dynamic, small perturbations of the system results in structural evolution; because they exhibit structure-function relationships, determination of particle structure is of fundamental importance. We have been developing electrochemical techniques to study the structure of such particles and observe structural evolution. In addition, because of the relatively large size of such structures, inter-nanoparticle interactions (attractive, repulsive, excluded volume etc.) occur strongly we have observed and quantified various inter-nanoparticle interaction processes electrochemically. For micellar systems, we have, for the first time, located the micellar shear plane and observed the shear plane collapse due to coulombic screening as well as spherical micellar expansion and structural transitions. We have also correlated the inter-micellar interaction parameters with the calculated interaction energies. In true reverse micellar systems, we have simultaneously observed and quantified attractive interactions, depletion forces and "sticky" interactions using microelectrode electrochemistry. This is the first example of electrochemistry in such media. We are currently developing these techniques for time-resolved investigation of structural evolution and evolution of interaction processes in order to elucidate the kinetic, mechanistic and thermodynamic aspects of such processes. Shown below is a simple schematic of some of the structural evolution processes which may be observed voltammetrically where T is temperature and I is the ionic strength of the supporting medium.
Organic electrosynthesis and redox catalysis in Ionic Liquids
Electrosynthesis is considered a key enabling technology for the future development of clean industrial processes because electrosynthesis provides the opportunity to use the inherently clean reagent, the electron, as well as providing a very powerful and controllable form of oxidation/reduction power. One significant drawback of electrosynthesis is the frequent requirement for organic solvents and extraneous electrolytes as support media. Recent work in our laboratory has concentrated on the use of room temperature ionic liquids (RTILs) as support media for organic electrosynthesis reactions. RTILs are conducting molten salts comprised of an organic cation (typically an n-alkylimidazolium species) and an inorganic anions such a nitrate or tetrafluoroborate. The diagram below shows a cyclic voltammogram for the reduction of benzaldehyde in pyrrolidinium bis-triflimide ionic liquid recorded at 5000 V s-1; the voltammogram shows the initial reversible reduction to the radical anion species followed by the reversible reduction of the radical anion to the dianion species. This work has evolved into a new field, namely, "redox catalytic ionic liquids" (C. Brooks, PhD Thesis, QUB, 2003; patent applied for). In this paradigm, one of the ions is a specific molecular redox catalysts. In this way, we can perform redox catalysis using a molten salt that acts as, 1) support medium for reaction, 2) electrolyte for electrical conduction and 3) as the redox catalyst. Because ionic liquids are inherently clean solvents which act as both solvent and electrolyte, and have tuneable solvent and redox catalytic properties, this research aims to develop new electrosynthetic processes which may be of technological importance.
