With increasing concerns over rising global energy demand and environmental sustainability, development of new energy solutions with minimal impact on the environment is critical to the continuation of socio-economic development. The concept of using hydrogen to replace fossil fuels is an exciting one and full of opportunities. The term ‘hydrogen economy’ born out of this concept brings to mind a sustainable energy system for society. One way of producing hydrogen from renewal sources is by the photoelectrochemical (PEC) method in which suitable electrodes immersed in an aqueous solution split water molecules to oxygen and hydrogen with the aid of sunlight.

GaN and InGaN have the desirable properties that are required as the electrodes, such as the correct band alignment with redox potential of H2/H2O and O2/H2O, excellent carrier transport and charge transfer properties, strong optical absorption at wavelengths within the solar spectrum and good corrosion resistance in aqueous solutions. The aims and scope of this project cover the following:

• Study the photoelectrochemical properties of various GaN-based semiconductors and quantum wells
• Engineer the band bending at the semiconductor-electrolyte interface to improve device efficiency
• Investigate the effect of a very thin layer of passivation material
• Understand charge carrier generation, recombination, trapping and transfer processes in a photoelectrochemical cell

Depending of the interests of the student and the length of the course, any combination of the aspects listed above can be chosen to suit the student.

Physics, Material Science, Engineering

The quest for abundant, renewable energy is currently one of the world’s greatest technological challenges. One solution to this problem is the conversion of solar energy to storable chemical fuels, such as H2. Hydrogen generated from solar-driven electrolysis of water has the potential to provide clean, sustainable, abundant and transportable energy. Towards realizing this goal, artificial photosynthetic approaches such as photoelectrochemical (PEC) cells are being extensively investigated. A PEC cell requires a semiconductor electrode that fulfills several essential prerequisites: a small semiconductor bandgap for efficiently harvesting a large proportion of the solar spectrum, appropriate band edges for water oxidation and reduction, high conversion efficiency of photogenerated carriers to hydrogen, durability in aqueous environments, and low cost. 

Hematite (α-Fe2O3), often referred to as “rust”, is a promising electrode material for photoelectrochemical hydrogen generation from water – it has low cost, good long-term stability and absorbs light efficiently. However, its use is limited by its poor electrical conductivity. In this project, a novel host-guest nanostructure will be developed that exploits the beneficial light-absorption properties of hematite (the guest) but shifts the charge transport function to a nanostructured transparent conductive oxide (TCO) host. The specific objectives of this project are:

• Develop a novel hematite electrode based on a porous 3D nanostructured TCO film as a host for an
extremely thin hematite layer
• Understand the mechanism of charge separation and transport in these photoanodes based on the host-guest nanostructure approach through systematic investigations employing time-resolved absorption spectroscopy and electrochemical impedance measurements.

Depending on the interests of the student and the length of the course, various aspects of the project can be tailored to suit the student.