Hybrid Photocatalytic Systems for Solar Energy Applications
Developments over the last three decades have led to an exponential growth in research concerning semiconductor photocatalysis and the related applications [1] which include water and waste water treatment [2,3,4], air remediation, CO2 reduction to fuels, and photo-splitting of water to yield H2 and O2. Titanium dioxide ( TiO2) is the most suitable metal oxide semiconductor for use as a photocatalyst as it is photo-stable, inexpensive, and non-soluble. However, TiO2 is a wide band gap semiconductor ( 3.2 eV for anatase corresponding to light of >=387 nm) and therefore solar powered applications are limited as only 5 % of the solar spectrum may be utilised. Although it is possible to shift the absorption spectrum of the TiO2 into the visible portion of the electromagnetic spectrum by doping with other metals[5] this approach has thus far been unsuccessful. An alternative approach is to use two narrow band (visible absorbing) semiconductor materials. The materials are selected so that the band edge potentials are in a suitable position for the relay of photogenerated electrons. (See fig 1.) Two photons of visible light are therefore required to promote one electron from the valence band of the n-type material to the conduction band of the p-type material. However, the voltage window achievable is very large. If successful, this approach would find application in fields such as solar powered water splitting for O2 and H2, solar powered CO2 reduction to fuels, and solar powered photoelectrochemical chemical synthesis. Nanometer-scale control of the surface structure of the semiconductor electrode is critical to the photoelectrode behaviour. The photocatalysis group in NIBEC has shown that by preparing nano-crystalline microporous TiO2 electrodes, the quantum efficiency for photogenerated electrons was increased from less than 5% up to 40% under UV irradiation[6,7]. The use of advanced methods of thin film deposition techniques supported by advanced surface chararacterisation and analytical techniques will give insight into the reasons for the differences in the photoelectrochemical response of the electrodes. Particle size, crystal phase, dopant density, stoichiometry, etc. all have an effect on the photocatalytic and photoelectrochemical properties of the semiconductor material. Electrolyte conditions, more specifically pH, have a significant effect on photocurrent response, and possibly may determine stability of doped materials as leaching of the dopant metal may occur under certain conditions. Work Plan: Year I: Carry out detail literature survey of publications in the field. Undertake training in photoelectrochemical techniques and advanced surface analytical techniques including Auger Electron Spectroscopy (AES), X-ray Photoelectron Spectroscopy (XPS), Scanning Probe Microscopy e.g. Atomic Force Microscopy (AFM), Scanning Electron Microscopy with Energy Dispersive Analysis of X-rays (EDAX), and X-ray Diffraction. Prepare a protocol for the preparation of photo-anode materials based on the knowledge of physicochemical properties of the materials required. Year II: Prepare photo-anode materials using both sol-gel and vacuum deposition techniques and characterise the materials using photoelectrochemical, surface characterisation and analytical techniques. Year III: Based on the results of the characterisation define the most suitable application for the materials e.g. photo-oxidation of water, photocatalytic treatment of polluted water, or photo-voltaics. Design, construct, and test a bench scale prototype utilising the selected photo-anode material for the appropriate application. Write up and submit Ph.D. thesis. 1. D A Tryk, A Fujishima, K Honda, \"Recent topics in photoelectrochemistry: achievements and future prospects.\" Electrochimica Acta, 2000, 45, 2363-2376. 2. H M Coleman, B R Eggins, J A Byrne, F L Palmer and E King, \"Photocatalytic degradation of oestrogens in water\" Applied Catalysis B: Environmental, 2000, 24, L1 - L5 3. J A Byrne, B R Eggins, N M D Brown, and W Byers, \"Photoelectrochemical cell for the combined photocatalytic oxidation of organic pollutants and the recovery of metals from waste waters\". Applied Catal. B Environment, 1999, 20, L85 - L89. 4. J A Byrne, B R Eggins, N M D Brown, B McKinney, M Rouse and H Coleman, \"Immobilisation of titanium dioxide for the treatment of polluted water\", Applied Catalysis B: Environmental, 1998, 17, 25 - 36 5. M A Malati, W K Wong, Surface Technol. 1984, 22, 305 6. J A Byrne, B R Eggins, S Linquette-Mailley, and P S Dunlop, \"The effect of hole acceptors on the photocurrent response of particulate titanium dioxide\", Analyst, 1998, 123, 2007-2012. 7. J A Byrne, B R Eggins, Photoelectrochemistry of oxalate on particulate titanium dioxide\", J Electroanal Chem, 1998, 457, 61 - 72.
Personnel Involved
First Supervisor: Byrne, J Dr
Second Supervisor: Mariotti, D Dr
Collaboration: This project does not involve collaboration with another establishment
Synopsis:
Developments over the last three decades have led to an exponential growth in research concerning semiconductor photocatalysis and the related applications which include water and waste water treatment, air remediation, CO2 reduction to fuels, and photo-splitting of water to yield H2 and O2. Current research is focused on the development of narrow band semiconductor systems which can utilise solar energy efficienty. This research will involve the preparation, characterisation and testing of novel hybrid photocatalytic seminductors for solar energy harvesting.