Nanoporous Gallium Zinc Oxynitride Photocatalyst for Visible Light Hydrogen Generation

Oral, Babak Adeli, presentation 016
Publication date: 16th April 2014

Among the various clean and renewable energy sources, sunlight by far is the largest. Solar hydrogen makes solar energy as storable and transportable as fossil fuels without their negative environmental impacts. The conversion of sunlight into chemical fuels, through water splitting, is one of the promising approaches to harvest solar energy to store energy in the form of H-H bond.
Gallium-zinc oxynitride solid solution (GaN:ZnO; where x is the fraction of ZnO in GaN:ZnO solid solutions crystal structure) is one of the few photocatalysts which is capable of splitting water to hydrogen and oxygen under visible light with high and stable photocatalytic activity . The GaN:ZnO solid solution photocatalyst is typically synthesized by nitridation of a mixture of Ga2O3 and ZnO at high temperatures for 5–15 h [1] via the solid-state reaction. Although the photocatalyst prepared through the traditional method demonstrates high activity for overall water splitting, the long synthesis time at high temperature is considered a drawback of this synthesis technique [2].
We have synthesised nanoporous gallium-zinc oxynitride solid solution through a fast and cost effective synthesis technique. Pre-treatment of the synthesis precursor improved the homogeneity of the prepared photocatalyst. We have examined the effect of microwave irradiation and heat convection as the heat source of the facile solid state reaction.
The composition and surface structure of the solid solution have been controlled by adjusting the ratio of starting materials in the precursor and the synthesis conditions. The crystalline structure of the photocatalyst has been improved through post-heat treatment. Various characterization techniques confirmed the formation of visible-light activated nano-porous solid solution with higher surface area, comparing to the one prepared via traditional technique. Various hydrogen and oxygen evolution co-catalysts have been loaded on the surface of the photocatalyst through impregnation and in-situ photodeposition techniques and their effect on the activity of the photocatalyst has been investigated. Hydrogen and oxygen half reaction analysis indicated the high performance of this newly synthesized photocatalyst. The overall rate of water splitting of the synthesized photocatalyst demonstrated promising trend for improving not only the cost of preparation, but also the efficiency of solar hydrogen generation.
References:      
[1] K. Maeda, T. Takata, M. Hara, N. Saito, Y. Inoue, H. Kobayashi, and K. Domen, J. Am. Chem. Soc., 127, 8286 (2005).      
[2] B. Adeli and F. Taghipour, ECS Journal of Solid State Science and Technology, 2 (7) Q118-Q126 (2013).

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