Hocking, Rosalie K., King, Hannah J., Hesson, Aimee, Bonke, Shannon A., Johannessen, Bernt, Fekete, Monika, Spiccia, Leone, and Chang, Shery L.Y. (2015) Engineering disorder at a nanoscale: a combined TEM and XAS investigation of amorphous versus nanocrystalline sodium birnessite. Australian Journal of Chemistry, 68. pp. 1715-1722.

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Abstract

The term amorphous metal oxide is becoming widely used in the catalysis community. The term is generally used when there are no apparent peaks in an X-ray diffraction pattern. However, the absence of such features in X-ray diffraction can mean that the material is either truly amorphous or that it is better described as nanocrystalline. By coprecipitating a sodium birnessite-like phase with and without phosphate (1.5 %), we are able to engineer two very similar but distinct materials – one that is nanocrystalline and the other that is amorphous. The two closely related phases were characterized with both Mn K-edge X-ray absorption spectroscopy and high-resolution transmission electron microscopy. These structural results were then correlated with catalytic and electrocatalytic activities for water oxidation catalysis. In this case, the amorphous phosphate-doped material was less catalytically active than the nanocrystalline material.

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