Atomic layer deposition of mixed oxides for solar hydrogen production

Group: CoCooN

Promotors: Jolien Dendooven and Christophe Detavernier

Supervisor: Ranjith Ramachandran

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Reliable supply of clean and renewable energy is one of the most significant concerns in the 21st century. Hydrogen is a very promising candidate as a future energy carrier. Splitting water using solar energy (photocatalytic water splitting) is the most efficient way to produce hydrogen. Transition metal oxides are commonly used as the materials for photocatalytic water splitting, but their higher band-gaps make them less efficient under visible light irradiation. Tuning the band gap by mixing two different metal oxides (ternary oxides) found to be a potential way to improve the efficiency. Among the ternary oxides, Bi containing oxides such as BiVO4, BiFeO3 are extensively used as electrode materials in photoelectrochemical cell for water splitting. However, an advanced synthesis method to effectively control the morphology and composition of the electrode material is still a bottleneck for the development of more effective solar hydrogen cells.

During this master thesis, we aim to synthesis bismuth vanadate (BiVO4) system using atomic layer deposition (ALD). ALD is a chemical vapor deposition technique, which enables conformal deposition of uniform thin films, even on complex 3D structures. Even though the deposition of binary oxides is comparatively straightforward, the ALD of mixed oxides represents severe challenges. Here, we propose the combination of ALD with solid-state reactions of the deposited layers to achieve conformal deposition of complex oxides. First, Bi and V oxides will be deposited as alternate layers on to a silicon substrate. In the second step, these mixed layers will be subjected to a high temperature treatment. After finding a reliable strategy to synthesize BiVO4, this method can be extended to the deposition of the BiFeO3 system. VO2 and Fe2O3 can be deposited using the standard ALD processes available in the CoCooN Lab, but for Bi2O3, a new ALD process will be developed, as a part of this thesis work. The deposited films will be characterized by x-ray reflection, diffraction and fluorescence techniques. This project is ideally suited to gain a broad knowledge in the fields of thin film deposition, x-ray based characterization techniques, materials science and water splitting technology.