Mikkel Juelsholt1 Troels Christiansen1 Kirsten Jensen1

1, University of Copenhagen, Copenhagen, , Denmark

Nanoparticles of tungsten oxides have a range of important applications in e.g. gas-sensing, catalysis and in supercapacitors[1]. Tungsten oxides show rich structural chemistry due to rich redox chemistry and a range of stable crystal structures. The properties are highly dependent on the size and structure of the material, and in order to obtain a ‘tailor-made’ material, it is crucial to understand the mechanisms that dictate the formation of the material during synthesis. X-ray total scattering with Pair Distribution Function (PDF) analysis allows following the structural changes that take place all the way from precursor cluster over nucleation clusters to the final crystalline particles[2].
We here present a study of WOx nanostructures formed in a solvothermal synthesis by thermal decomposition of ammonium metatungstate hydrate under different experimental conditions. Using Ex Situ and In Situ X-ray Total Scattering and Pair Distribution Function analysis, we study how different experimental conditions induces changes in the final size and crystal structure of the nanomaterials. We also observe how different reaction conditions influence the precursor and induce two distinct crystallisation pathways. We determine the changes in molecular geometries as the system moves from polyanion clusters to crystalline nanoparticles. Using small box modelling we determine the structure of the ionic clusters present at all stages of the reaction, revealing complex equilibria between different polyoxometalate structures. Furthermore we determine the atomic structuture of crystalline nanoparticles.

1. Zheng, H., et al., Nanostructured Tungsten Oxide – Properties, Synthesis, and Applications. Advanced Functional Materials, 2011. 21(12): p. 2175-2196.
2. Jensen, K.M.Ø., et al., In Situ Studies of Solvothermal Synthesis of Energy Materials, ChemSusChem, 2014. 7(6): p. 1594-1611.