Researchers using the XSD 11-ID-B beamline at the APS are performing High Energy X-ray Scattering (HEXS) to explore Cobalt Polyoxometalates (Co-POMs) for a wide range of potential applications.
The team is targeting Co-POMs for their rich redox and colorimetric behavior, acid-base chemistry, ligating properties, high anionic charge and discrete and water-soluble nature.
Polyoxometalate (POM) chemistry has been explored since the late 19th century, but it is only since the early 1950s that more characterization techniques have greatly aided the research in this field, enabling the relation between solid-state and solution speciation and the link between structure and reactivity.
In the last five years several Cobalt Polyoxometalates (Co-POMs) have been reported as all-inorganic water oxidation catalysts (WOCs) with enhanced stability, because oxidative ligand decomposition is not possible. However, while they are promising homogeneous WOCs, they have been highly debated with regard to their stability under turnover conditions. For this reason, these systems are interesting subjects for speciation and stability studies using X-ray scattering techniques – not broadly used in the WOC field. Here we rigorously characterize the speciation of Co-POMs under catalytically relevant conditions.
Our studies reveal that:
- the clusters remain largely intact during reaction with a chemical oxidant, especially in the absence of phosphate buffer; and
- common phosphate buffers have the greatest effect on the degradation of the Co-POMs under these conditions.
This study of the structure in the aqueous state under various conditions provides invaluable information in the understanding of the solution behaviour of Co-POMs and in the development of the next generation of WOCs.
Sara Goberna-Ferron, Joaquín Soriano-Lopez, Jose Ramon Galan-Mascaros and May Nyman, “Solution Speciation and Stability of Cobalt-Polyoxometalate Water Oxidation Catalysts by X-ray Scattering,” European Journal of Inorganic Chemistry, DOI: 10.1002/ejic.201500404, Published Online May 27, 2015.