Photo-oxidation of water on oxidic semi-conductor surfaces

Dr. Francesca Costanzo
Photo-oxidation of water on oxidic semi-conductor surfaces

Photoelectrochemical water splitting has attracted substantial interest in the recent years as a key process in hydrogen production from sunlight and other sources of electricity. The conversion of solar radiation into fuels can take place directly by photons that excite electrons in a semiconductor in which the energy level of the valence band is sufficiently low. This process results in oxygen evolution at the photoanode, providing hydrogen as a clean sustainable carrier of solar energy. However, several challenging issues have to be solved for the process to become sufficiently efficient. One of them is associated with the substantial overpotential and thereby energy losses at the anode, where the oxygen is evolved.

To minimize the overpotential and increase the reaction rate, a water oxidation catalyst is required.  Among them, metal oxides, due to their band position, band gap and chemical stability in water, are attractive materials for photo-catalytic water oxidation. In particular, nickel oxide NiOx electrodes have been widely used in alkaline batteries.

Our aim is to describe the thermochemistry of the electrochemical reactions involved in the process through the reaction free energy diagram through electronic structure calculations, which involves the calculation of the adsorption energies of all the intermediates in the water oxidation process.

The method we use concerns an extension made by the Leiden Theoretical Chemistry group of the thermodynamic computationak method developed by Nørskov and co-workers. To correctly describe the electronic structure and the high electron correlation of the system we investigate,  we currently use the DFT + U approach. 

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