Polyoxometalate-based homogeneous catalysis of electrode reactions: Recent achievements

Polyoxometalates (POMs) constitute a broad family of molecular oxides showing promise in several efficient and clean electrocatalytic processes, when they are handled in appropriate conditions. Reduction and oxidation possibilities exist as well. The present short focused review shows the usefulness of POMs in selected electrocatalytic processes. Quantitative transformations were demonstrated in several examples, including hydrogen production, NO, reduction, dioxygen reduction, coenzyme oxidation... This selection leaves room for a wealth of other possibilities. It appears clearly that several parameters must be taken into account in the design and study of these processes. Among them, the stability in aqueous or non aqueous solutions is an absolute prerequisite, which excludes the use of several newly synthesised fragments solely stable in the solid state. New parameters, in addition of those highlighted here, might emerge because POMs with new atomic compositions, new structures and new reactivities, continue to be synthesised and characterised. The challenge, however, is to find new POMs or new POM-based systems to decrease overpotentials which remain high for most reactions and improve the overall kinetics. Finally, an optimistic prediction is that POMs, owing to their versatility and possibility to accommodate nearly all the atoms of the periodic classification, will become popular to drive selected electrocatalytic processes. (c) 2006 Elsevier B.V. All rights reserved.