The use of photoelectrochemical processes for the production of chemical fuels is an attractive form to store solar energy. These processes require the use of a photoactive material, usually a semiconductor in which electron-hole pairs are created when light of energy equal or larger than the band gap excites an electron from the valence into the conduction band. The reactivity of these electron and holes, as compared with their tendency to recombine, determines the quantum yield of the photoelectrochemical reaction, and is obviously affected by the applied bias voltage. The transport properties of electrons and holes play an important role, and are strongly affected by the presence of trap states in the semiconductor. Similarly, the photoelectrochemical reaction often involves the formation of radicals, and the identification of these radicals and their fate is essential in order to understand the product distribution of the reaction. EPR has a high sensitivity for the detection of unpaired electrons, and is hence perfectly suited to study trap states and radicals. However, it involves immersing the sample in an oscillating magnetic field, which prevents its application at the electrode electrolyte interface.
In the approach proposed, semiconductor nanoparticles will be assembled at the polarisable interface between two immiscible liquids. This will allow the detection of radicals generated upon illumination of the interface, and to monitor their evolution with time. This will allow us to throw some light into the reaction mechanism of some reactions relevant to the photosynthesis of fuels, and to understand the product distribution in these reactions.
The objectives of this work are: (i) to develop a system for EPR measurements at polarisable liquid-liquid interfaces: (ii) to demonstrate the ability of the setup to detect radicals formed as intermediates during target photoelectrochemical reactions; (iii) to develop kinetic models of those reactions.